Hamstrings training and injury prevention

Hamstrings

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ABSTRACT

The hamstrings are a group of four muscles on the back of the thigh. Three ofthem are two-joint muscles (performing both knee flexion and hip extension)while the fourth performs only knee flexion. As a group, the hamstrings cantherefore be trained by exercises that involve either hip extension or kneeflexion.

The four hamstrings muscles are: the biceps femoris (long head), the bicepsfemoris (short head), the semitendinosus, and the semimembranosus. Thetwo biceps femoris muscles are located on the lateral part of the thigh.The semitendinosus and the semimembranosus are located on the medialpart of the thigh.

The total volume of the medial hamstrings is greater than that of the lateralhamstrings, the lateral hamstrings are more often injured, but the medialhamstrings are more highly activated during high-speed running. Differentexercises may be required to develop the medial and lateral hamstrings, andboth groups should be trained for improving sprint running ability.

There are at least two separate regions within the hamstringmusculature (upper and lower) that appear to respond differently to the sameresistance training exercises. Optimal programming maytherefore require multiple exercises to target both regions.

The hamstrings have a large moment arm for hip extension, making them akey hip extensor. They also have a large knee flexion moment arm, makingthem a key knee flexor. This moment arm increases with increasing kneeflexion, making the hamstrings better knee flexors when the knee is bentthan when it is extended. This may imply that exercises involving peakcontractions when the knee is bent (like leg curls) are more effective atdeveloping the hamstrings.

Despite the popular belief that the hamstrings are a fast-twitch muscle

http://www.strengthandconditioningresearch.com/muscles/hamstrings/ 5/22/16, 6:40 AMPágina 1 de 54

group, they in fact display a balanced fiber type, with a slight trend towardsmore slow-twitch fibers. Using a range of high and low repetitions, and bothslow and fast speeds may be beneficial.

The hamstrings display no clear tendency to greater EMG amplitude at anyone joint angle. However, there are differences between individualhamstrings muscles. In contrast to the moment arm findings, this suggeststhat exercises involving peak contractions at a range of joint angles may beoptimal.

Research is limited regarding the best resistance training exercises for thehamstrings. Leg curls are a reliable option, while good mornings, Romaniandeadlifts, and Nordic hamstring curls (glute-ham raises) are goodalternatives.

Some exercises appear to target the medial hamstrings to a greater extent(kettlebell swings and deadlifts) while other exercises target the lateralhamstrings more (leg curls and back extensions). Optimal programs maytherefore include a range of exercises that target both medial and lateralhamstrings.

The hamstrings are essential for sprint running performance. Hamstringstrains are common in team sports, accounting for around 12 – 16% ofinjuries. As expected, most strains occur during high-speed running, with thelargest proportion affecting the biceps femoris.

The acute mechanisms producing hamstring strains are unclear. Either fastchanges in length in the terminal swing phase or high loading during the earlystance phase could be responsible. The mechanisms of recurrent hamstringstrain could include alterations in biomechanics, including muscle activation.

Previous hamstring strain increases the risk of an athlete incurring a similarsubsequent injury substantially. Strength and conditioning programsshould aim to prevent hamstring strains happening in the firstplace. Eccentric hamstring training, particularly the Nordic hamstring curlexercise, reduces the incidence of both novel and recurrent hamstring straininjury. Compliance is essential in order to prevent recurrent injury.


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CONTENTS

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ANATOMY

PURPOSE

This section provides a summary of the anatomy of the hamstrings.

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BACKGROUND

Introduction

The hamstrings are important for sporting performance, particularly during high-speed running and sprinting (Higashihara et al. 2010b; Kyröläinen et al. 2005;Morin et al. 2015). The hamstrings also often require rehabilitation from injury,with hamstring strains accounting for around 12 – 16% of injuries in popular teamsports (Woods et al. 2004; Orchard & Seward, 2002). Most such strains seem tooccur during high-speed running (Brooks et al. 2006). Therefore, much of theanatomical research into the hamstrings has focused on their role during runningand the potential for strain injury.

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GROSS ANATOMY

Introduction

There are four hamstrings muscles: the biceps femoris (long head), the bicepsfemoris (short head), the semitendinosus, and the semimembranosus. They areusually divided into two groups, the lateral hamstrings (biceps femoris long and


short heads) and the medial hamstrings (semitendinosus and thesemimembranosus) on the basis of their locations on the rear part of the thigh.The biceps femoris (long head), the semitendinosus, and the semimembranosusare all bi-articular (two-joint) muscles. These bi-articular muscles cross the hip,being attached to the ischiac tuberosity of the pelvis (Batterman et al. 2011), andalso cross the knee, being attached to the tibia and fibula, although otherinsertion points have also been reported (Tubbs et al. 2006). These bi-articularmuscles therefore cause both hip extension and knee flexion. The biceps femoris(short head) is a single-joint muscle and causes only knee flexion. Thehamstrings as a group can therefore be trained by exercises that involve eitherhip extension or knee flexion.

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Common tendons

Although the hamstrings are generally discussed separately, the semitendinosusand biceps femoris (long head) almost certainly share a proximal origin by way ofa conjoined tendon in most people. Additionally, some studies have found thatthe semimembranosus also shares this same tendon (Neuschwander et al.2015). When it does have a separate tendon, the proximal tendon ofthe semimembranosus is located anteriorly and laterally to the shared tendon ofthe semitendinosus and biceps femoris (long head) (Miller et al. 2007; Philipponet al. 2014; Feucht et al. 2014). In addition, the combined semitendinosus andbiceps femoris (long head) footprint on the ischial tuberosity is smaller in length(3.9 ± 0.4 vs. 4.5 ± 0.5cm) and may also be smaller in height (1.4 ± 0.5 vs. 1.2 ±0.3cm) than the semimembranosus footprint (Feucht et al. 2014).

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Origins and insertions

Overall, the origins and insertions of each of the hamstrings are as follows:

Semitendinosus (medial) – originates on the ischiac tuberosity of the pelvis andinserts on the upper anterior medial surface of the tibia.

Semimembranosus (medial) – originates on the ischiac tuberosity of the pelvisand inserts on the postero-medial surface of the medial tibial condyle.


Biceps femoris long head (lateral) – originates on the ischiac tuberosity of thepelvis and inserts on the lateral condyle of the tibia and head of the fibula.

Biceps femoris short head (lateral) – originates on the lower half of the lineaaspera and the lateral condyloid ridge of the femur and inserts on the lateralcondyle of the tibia and head of the fibula.

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Muscle weight

From the limited literature, it is apparent that the biceps femoris (long head) andthe semimembranosus are the heaviest muscles, while the biceps femoris (shorthead) and semitendinosus are usually the lightest when comparing withinstudies, although there are discrepancies (Wickiewicz et al. 1983; Ito et al. 2003;Horsman et al. 2007; Ward et al. 2009; Kellis et al. 2012). The weight of thebiceps femoris (long head) has been recorded at between 55.8 – 245.0g, theweight of the semimembranosus has been recorded at between 109.3 – 146.0g,the weight of the biceps femoris (short head) has been recorded at between 57.1– 114.0g, and the weight of the semitendinosus has been measured at between84.7 – 220g (Wickiewicz et al. 1983; Ito et al. 2003; Horsman et al. 2007; Wardet al. 2009; Kellis et al. 2012).

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Muscle cross-sectional area

From the limited literature, it is generally apparent that the biceps femoris (longhead) and the semimembranosus have the greatest muscle cross-sectional area,while the biceps femoris (short head) and semitendinosus generally have thesmallest muscle cross-sectional area (Pohtilla et al. 1969; Ito et al. 2003;Woodley and Mercer, 2005). This is in accordance with the data on muscleweight, which gives some confidence that the relative weights and sizes of thesemuscles is largely correct.

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Muscle thickness

Very little research has examined the muscle thickness of the hamstrings (Ikezoe


et al. 2011a; 2011b) and no studies have yet compared the muscle thickness ofthe different hamstrings muscles to one another. The literature is thereforecurrently too limited to ascertain whether the muscle thickness of any of thehamstrings muscles is substantially different from the others.

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Muscle volume

From the limited literature, it is generally apparent that the biceps femoris (longhead) and the semimembranosus have the greatest muscle volume, while thebiceps femoris (short head) and semitendinosus generally have thesmallest muscle volume (Friederich and Brand, 1990; Miokovic et al. 2011;Nakase et al. 2013). This is in accordance with the data on muscle cross-sectional area and muscle weight, which gives some confidence that the relativeweights, sizes and volumes of these muscles are largely correct.

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Medial and lateral differences

The medial and lateral hamstrings muscles are different from one another inseveral respects. They are different in weight (Ito et al. 2003; Horsman et al.2007; Ward et al. 2009; Kellis et al. 2012), cross-sectional area (Pohtilla et al.1969; Ito et al. 2003), volume (Friederich and Brand, 1990; Miokovic et al. 2011;Nakase et al. 2013), function, and risk of injury, with the lateral hamstrings beingmore commonly injured (De Smet et al. 2000; Garrett et al. 1989; Slavotinek etal. 2002). Several studies have found that the medial and lateral hamstringsdisplay differences in EMG amplitude in response to common resistance trainingexercises (Fiebert et al. 2001; Escamilla et al. 2002; Lynn & Costigan, 2009;Simenz et al. 2012; Jakobsen et al. 2012; Zebis et al. 2013; McAllister et al.2014). In addition, the medial hamstrings are more strongly activated normalizedto maximum voluntary isometric contraction (MVIC) than the lateral hamstringsduring running (Jönhagen et al. 1996; Higashihara et al. 2010b). Thesefindings suggest that different exercises may be required to develop the medialand lateral hamstrings, and that both groups should be trained for improvingsprint running ability.

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Regional differences

The existence of regions within hamstring muscles have been assessed both byanatomical investigation and by using electromyography (EMG). The anatomy ofthe semitendinosus has been observed to differ substantially from the otherhamstrings in several reports. Specifically, it has been noted that thesemitendinosus is the only hamstring to display a tendinous inscription that runsproximally to distally through the middle of it, which may be responsible for theproduction of separate regions within this muscle (Garrett et al. 1989; Woodleyand Mercer, 2005; Van de Made et al. 2013). In addition, some studies haveexplored differences in EMG amplitude between individual regions of the samehamstring muscle using EMG. Schoenfeld et al. (2015) explored the EMGamplitude of the proximal (upper) and distal (lower) regions of the medial andlateral hamstrings during the stiff-legged deadlift and the lying leg curl exercisesin resistance-trained males. They found that the lying leg curl produced greatermedial and lateral EMG amplitude in the lower region compared with the stiff-legged deadlift. In contrast, there was no difference between exercises inrespect of the upper region. This indicates that different exercises do lead todifferences in EMG amplitude in different parts of the individual hamstringsmuscles. This in turn provides further evidence that there may be separateregions within each hamstring muscle that may require training with differentexercises.

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SECTION CONCLUSIONS

The hamstrings are a group of four muscles on the back of the thigh. Three ofthem are two-joint muscles (performing both knee flexion and hip extension)while the fourth performs only knee flexion. As a group, the hamstrings cantherefore be trained by exercises that involve either hip extension or kneeflexion.

The four hamstrings muscles are: the biceps femoris (long head), the bicepsfemoris (short head), the semitendinosus, and the semimembranosus. Thetwo biceps femoris muscles are located on the lateral part of the thigh.The semitendinosus and the semimembranosus are located on the medialpart of the thigh.


There are at least two separate regions within the hamstring muscles (upperand lower) that appear to respond differently to the same resistance trainingexercises. Optimal programming may therefore require multiple exercises totarget both regions.

The total volume of the medial hamstrings is greater than that of the lateralhamstrings, the lateral hamstrings are more often injured, but the medialhamstrings are more highly activated during high-speed running. Differentexercises may be required to develop the medial and lateral hamstrings, andboth groups should be trained for improving sprint running ability.


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MUSCLE MOMENT ARMS

[Read more about: moments]

PURPOSE

This section provides a summary of the studies into the muscle momentarms of the hamstrings.

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MUSCLE MOMENT ARMS

Introduction

Muscle moment arms are often overlooked when determining the precisefunction of a muscle. However, they are essential for establishing how effective amuscle can be at producing torque at a given joint, at any given joint angle. Sincethe hamstrings act as both hip extensors and knee flexors, they have musclemoment arms at both joints.

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Hip extension


Very few studies have reported on the moment arms for the hamstrings in hipextension. Dostal et al. (1986) reported that the moment arms were 5.6cm forthe semitendinosus, 4.6cm for the semimembranosus, and 5.4cm for the bicepsfemoris (long head). Németh et al. (1985) reported a moment arm for allhamstrings combined of 6.1cm. These figures indicate that the hamstrings arean effective hip extension in the anatomical position. However, exactly how thehip extension muscle moment arms of the hamstrings compare with the gluteusmaximus is unclear. Dostal et al. (1986) reported a figure for the gluteusmaximus of 4.5cm, which is lower than that seen in the hamstrings. On the otherhand, Németh and Ohlsén (1985) reported a figure for the gluteus maximus of8cm, which is much greater. It seems likely that the hamstrings and gluteusmaximus therefore have similar muscle moment arms to one another for hipextension and are therefore expected to be involved in this joint action to asimilar extent.

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Hip adduction

Very few studies have reported on the moment arms for the hamstrings in hipadduction. Dostal et al. (1986) reported that the moment arms were 0.9cm forthe semitendinosus, 0.4cm for the semimembranosus, and 1.9cm for the bicepsfemoris (long head). These figures indicate that the hamstrings are notparticularly active in hip adduction in the anatomical position.

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Hip internal rotation

Very few studies have reported on the moment arms for the hamstrings in hipinternal rotation. Dostal et al. (1986) reported that the moment arms were 0.5cmfor the semitendinosus, 0.3cm for the semimembranosus, and -0.6cm for thebiceps femoris (long head). These figures indicate that the hamstrings are notparticularly active in hip internal or external rotation (negative numbers) in theanatomical position. However, the presence of small differences between themedial (semitendinosus and semimembranosus) and lateral (biceps femoris)hamstrings in respect of their hip internal and external rotation muscle momentarms may imply a slight difference in function. This slight difference in function


might be discerned when the feet are internally or externally rotated duringcertain hip extension exercises like the back extension in order to place moreemphasis upon one set of hamstrings or the other (Fiebert et al. 1992; Fiebert etal. 1997).

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Knee flexion: effect of angle

Many studies that have reported muscle moment arms for the varioushamstrings muscles for knee flexion with changing knee angle (Spoor et al.1992; Herzog & Read, 1993; Wretenberg et al. 1996; Lu et al. 1996; Buford et al.1997; Kellis et al. 1999). In general, there is a trend for hamstrings musclemoment arms to increase with increasing knee flexion angle.

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SECTION CONCLUSIONS

The hamstrings have a large moment arm for hip extension, making them akey hip extensor. They also have a large knee flexion moment arm, makingthem a key knee flexor. This moment arm increases with increasing kneeflexion, making the hamstrings better knee flexors when the knee is bentthan when it is extended. This may imply that exercises involving peakcontractions when the knee is bent (like leg curls) are more effective atdeveloping the hamstrings.


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MUSCLE ARCHITECTURE

[Read more about: muscle architecture]

PURPOSE

This section provides a summary of the studies into the musclearchitecture of the hamstrings.


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MUSCLE ARCHITECTURE

Introduction

Muscle architecture describes the arrangement of muscle fibers within theoverall framework of the muscle itself, which is surrounded by fascia. It has beendescribed as “the macroscopic arrangement of muscle fibers” (see review byLieber and Fridén, 2000). Since muscles are roughly cylindrical structurescomprising fascicle bundles that run at an angle to the axis of force generation,there are three main measurements of the structure of a muscle: normalizedfiber length, physiological cross-sectional area, and pennation angle. Musclearchitecture of the hamstrings is of particular interest for the prevention andrehabilitation of hamstring strain injury, as studies have reported differences inmuscle architecture between previously strained and healthy muscles in thesame individual (e.g. Timmins et al. 2014). Unlike the quadriceps (Blazevich et al.2006), the hamstrings are a group of muscles that display very different musclearchitecture to one another.

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Pennation angle

Only a small number of studies have assessed the pennation angle of thehamstrings (Friederich & Brand, 1990; Horsman et al. 2007; Ward et al. 2009;Kellis et al. 2012). The pennation angle of the hamstrings varies slightly betweenmuscle. In general, the bigger, heavier semimembranosus seems to be morepennated than the semitendinosus. Exactly how the biceps femoris (long head)and biceps femoris (short head) compare is less clear. While early studiesindicated that they were different from one another (Friederich & Brand, 1990;Horsman et al. 2007), later studies found no differences (Ward et al. 2009; Kelliset al. 2012).

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Fascicle length

Only a small number of studies have assessed the fascicle lengths of the


hamstrings (Friederich & Brand, 1990; Horsman et al. 2007; Ward et al. 2009;Kellis et al. 2012; Kumazaki et al. 2012). The fascicle lengths of the hamstringsvaries slightly between muscles. The bigger, heavier semimembranosus seemsto be shorter than the semitendinosus. Similarly, the biceps femoris (long head)is longer than the biceps femoris (short head), although this is likely a function ofdifferences in the placements of the origins.

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Physiological cross-sectional area

Only a small number of studies have assessed the physiological cross-sectionalarea of the hamstrings (Friederich & Brand, 1990; Horsman et al. 2007; Ward etal. 2009; Kellis et al. 2012). The physiological cross-sectional area ofthe hamstrings varies slightly between muscle. The bigger, heaviersemimembranosus seems to be greater in size than the semitendinosus.Similarly, the biceps femoris (long head) is usually found to be greater in sizethan the biceps femoris (short head).

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Medial and lateral hamstrings

From the above analysis, it is interesting to note that across the medial andlateral hamstrings, there is one muscle that has a high normalized fiber lengthand a low physiological cross-sectional area and another muscle that has a lownormalized fiber length and a high physiological cross-sectional area (Friederich& Brand, 1990; Horsman et al. 2007; Ward et al. 2009; Kellis et al. 2012). Sincethe moment arm lengths for hip extension appear to be similar between thesemitendinosus, semimembranosus and biceps femoris (long head) (Dostal et al.1986), this may imply that one muscle in each subgroup is better suited forproducing large excursions with high joint angular velocities while the other maybe better suited for performing very forceful muscular contractions over shortexcursions (see review by Lieber and Fridén, 2000). Additionally, the differencein normalized fiber lengths between the two muscles in each group implies thateach of the hamstrings will produce their individual maximum forces at differentjoint angles and muscle lengths. Training the hamstrings with a range of differentloads and speeds may therefore be necessary for maximum development.


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SECTION CONCLUSIONS

The hamstrings have very different muscle architecture from one another,with a range of fiber lengths, pennation angles and physiological cross-sectional areas. Training the hamstrings with a range of different loads andspeeds may therefore be necessary.


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MUSCLE FIBER TYPE

[Read more about: muscle fiber type]

PURPOSE

This section provides a summary of the studies into the muscle fiber type ofthe hamstrings.

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BACKGROUND

Many strength and conditioning coaches believe that the prevailing hamstringstend to display a prevailing type II muscle fiber type (fast twitch). Thisassumption has been rarely challenged by other coaches. However, it is notsupported by all of the available studies (Johnson et al. 1973; Garrett et al.1984; Pierrynowski& Morrison, 1985; Dahmane et al. 2005; 2006).Rather, most studies indicate that the hamstrings display a fairly balancedmuscle fiber type. If anything, there is a slight trend for hamstrings to display apredominance of type I muscle fibers (slow twitch), with type I fiber proportionsranging from around 49% – 67%.

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SECTION CONCLUSIONS


Despite the popular belief that the hamstrings are a fast-twitch musclegroup, they in fact display a balanced fiber type, with a slight trend towardsmore slow-twitch fibers. Using a range of high and low repetitions, and bothslow and fast speeds may be beneficial.


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ELECTROMYOGRAPHY

[Read more about: electromyography]

PURPOSE

This section provides a summary of the electromyography (EMG) studies intothe hamstrings.

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BACKGROUND

Introduction

Both strength and conditioning coaches and rehabilitation specialists often haveneed to find suitable exercises to develop the hamstrings in their athletes andclients. The hamstrings are considered to be important players in sprint running,which is a key attribute of many team sports athletes, and are often injured,meaning that they need to be rehabilitated and trained in order to return to sport.Therefore, it is important to identify the best hamstrings exercises, which can beused both in standard training and during rehabilitation and in the post-injuryperiod prior to return-to-sport.

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RESISTANCE TRAINING EXERCISES

Introduction

Since 3 of the 4 hamstrings muscles are biarticular, hamstrings exercises can


involve either hip or knee movement, or both. When both hip and kneemovements are involved, exercises involving the hamstrings can cause a widerange of muscle length changes, from very small to very large, through a rangeof different combinations of joint movements. Hamstrings exercises can usuallybe placed into one of the following categories:

Hip extension and knee extension (e.g. squat)

Hip extension with partial knee extension (e.g. deadlift)

Hip extension without knee movement (e.g. back extension)

Knee flexion without hip movement (e.g. leg curl)

Hip extension and knee flexion (e.g. glute-ham raise)

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Comparing hamstrings exercises

Only a small number of studies have directly compared hamstringsEMG amplitude across a range of common resistance-training exercises (Wrightet al. 1999; Andersen et al. 2006; Ebben, 2009; McCurdy et al. 2010; Zebis et al.2013; McAllister et al. 2014; Schoenfeld et al. 2015). Very few of these (Ebben,2009; Zebis et al. 2013) included exercises from all joint movement categoriesand yet did not identify consistent results. In general, it seems that exercisesfrom the knee flexion category (i.e. leg curls) almost always feature as one of thebest exercises, while exercises from the hip extension and kneeextension category (i.e. squats) never feature as one of the best exercises. It isunclear how the other categories should be viewed, with exercises from the hipextension with partial knee extension, hip extension without knee movement, andhip extension and knee flexion categories all appearing in the best exercisescategory in some but not all studies.

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Back squat

Some strength coaches continue to refer to the back squat as a useful exercisefor the hamstrings. However, the literature does not provide support for this


view. Indeed, studies have reported that the hamstrings are not activated to thesame extent as the quadriceps during squats (Isear et al. 1997; McCaw& Melrose, 1999; Escamilla et al. 2001; Manabe et al. 2007; Paoli et al. 2009; Li &Chen, 2013; Aspe & Swinton, 2014; Yavuz et al. 2015; Contreras et al. 2015) andit is also apparent that hamstrings EMG amplitude does not always increase withincreasing external load (Savelberg et al. 2007; Li & Chen, 2013).

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Effect of load and speed

Some research has reported that hamstrings EMG amplitude does not increaseto the same extent as the EMG amplitude of other lower body muscles duringback squats with increasing load. Savelberg et al. (2007) found that as the loadincreased in a sit-to-stand movement, the EMG amplitude of most of the lowerbody muscles increased accordingly, although the increase in theEMG amplitude of the biceps femoris was less marked than that of the othermuscles and only significantly increased with the largest load increment. Li& Chen (2013) investigated the differences in EMG amplitude of the lower bodymuscles during back squats with increasing load and found that although theEMG amplitudes of the soleus, vastus medialis, gluteus maximus, and upperlumbar erector spinae all increased as the load was increased, there was nosignificant increase in the EMG amplitude of the biceps femoris with increasingload. However, Manabe et al. (2007) reported that the hamstrings weresignificantly more active during squats performed with a fast repetition velocitythan during normal and slow squats.

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Effect of back squat techniques

Different squat techniques, including foot position, depth, lumbar posture, andtype of load (i.e. conventional loading or accommodating resistance) appear tohave little effect on hamstrings EMG amplitude, although load position appearsto have a significant effect. In respect of foot position, Escamilla et al. (2001),Paoli et al. (2009) and McCaw and Melrose (1999) all reported that wide stancesquats do not lead to greater hamstrings EMG amplitude than narrow stancesquats. Similarly, Ninos et al. (1997) reported that there was no difference in


hamstrings EMG amplitude when using either a self-selected stance or a stancethat was 30 degrees of external rotation from the self-selected position. Inrespect of depth, Gorsuch et al. (2013) reported that the biceps femoris did notdisplay different EMG amplitude between partial and parallel squats with thesame relative load. Caterisano et al. (2002) also reported that the biceps femorisdid not display different EMG amplitude between partial and parallel squats withthe same absolute load (the relative loads used were therefore different).Similarly, Ninos et al. (1997) found no changes in EMG amplitude with kneeflexion angles during the squat, while changes in quadriceps EMG amplitudewere noted. Using the same relative loads for each squat depth, Contreras et al.(2015) found that there was no difference in biceps femoris EMG amplitudebetween parallel and full squats. In respect of lumbar posture, Vakos et al. (1994)compared the hamstrings EMG amplitude during squats with kyphotic andlordotic postures and found no differences between the two variations.

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Effect of back squat load type

In respect of load type, Ebben & Jensen (2002) compared hamstringsEMG amplitude in squats with conventional barbell loading and using barbells incombination with either bands or chains. No differences were observed betweenthe conditions. In respect of load position, Lynn & Noffal (2012) used dumbbellsin two different positions (on the shoulders and with arms outstretched) tocompare the effect of squatting by “sitting back” with squatting normally. Theyfound that “sitting back” led to much reduced rectus femoris EMG amplitudeand slightly greater gluteus maximus and hamstrings EMG amplitudes. However,whether the same effect would be achieved by simply performing a squat usinga different technique with the load in the same position is unclear and furtherresearch is needed in this area. In a related study performed not in free-weightsquats but with a leg press, Da Silva et al. (2008) explored the differencesbetween high and low foot positions in a horizontal leg press and found thatthere were no significant differences in hamstrings EMG amplitude, althoughthere were differences in respect of quadriceps EMG amplitude.

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Why is the squat a poor hamstrings exercise?


Exactly why the squat is a poor exercise for the hamstrings is not entirely clear. Itmay relate to the bi-articular nature of the hamstrings musculature. While thesquat exercise involves hip extension, for which the hamstrings are a primemover, it also involves knee extension, for which the hamstrings are anantagonist. Yamashita (1988) compared hamstrings EMG amplitude duringisolated hip extension and isolated knee extension movements performed with20% of the MVIC moment to hamstrings EMG amplitude with a combined hip andknee extension movement using the same hip and knee extension moments. Itwas found that hamstrings EMG amplitude in combined hip and knee extensionwas only 42% of the level in the isolated hip extension movement, despite the hipextension moment being identical in both cases. It was concluded thathamstrings EMG amplitude is depressed when combined hip and knee extensionare performed compared to during isolated hip extension. This may occurbecause the hamstrings change length to a greater extent when performingisolated hip extension compared to when performing combined hip and kneeextension, where they remain largely the same length. Alternatively, it is plausible(but as yet unexplored in the literature) that the motor strategy during combinedhip and knee extension takes into account the need for the quadriceps tocounteract the knee flexion moment that would be generated when thehamstrings are activated and consequently hamstrings EMG amplitude isactively suppressed.

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The deadlift

Introduction

The conventional deadlift and its variations (sumo deadlift, RDL, stiff-leggeddeadlift, and unilateral stiff-legged deadlift) all appear to lead to relatively highlevels of hamstrings EMG amplitude (Wright et al. 1999, Escamilla et al. 2002;Ebben, 2009; Zebis et al. 2013; McAllister et al. 2014; Schoenfeld et al. 2015).

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Effect of deadlift techniques

Few studies have been performed comparing hamstrings EMG amplitude duringthe deadlift and its variations while varying load, speed, depth, stance width or


variation. Escamilla et al. (2002) compared conventional and sumo deadlifts andfound no differences between the two variations. In addition, Bezerra et al.(2013) compared the hamstrings EMG amplitude during the deadlift and stiff-legged deadlift and also reported no differences between the two variations.Nemeth et al. (1984) compared four types of deadlift with a 12.8 kg load,including lifts with straight knees and lifts with flexed knees. While the load waslow and therefore only led to small-to-moderate levels of hamstringsEMG amplitude, the researchers did find that there was a time difference in thehamstrings EMG amplitude in that in the straight-leg lift the peak EMG amplitudeoccurred early in the lift but in the bent-leg lift the peak occurred later on. Ono etal. (2011) assessed hamstrings EMG amplitude during a stiff-legged deadlift andreported that the EMG amplitudes of the biceps femoris and of thesemimembranosus were significantly higher than that of the semitendinosus.

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The good morning

The good morning appears to lead to relatively high hamstrings EMG amplitude(Ebben, 2009; McAllister et al. 2014; Vigotsky et al. 2015). In addition,Vigotsky etal. (2015) tested lateral and medial hamstrings EMG amplitude with 50%, 60%,70%, 80%, and 90% of 1RM and reported steadily increasing levels ofEMG amplitude with increasing load. This confirms previous assumptions thatthe hamstrings are a prime mover in this exercise.

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Unconventional exercises

Some researchers have investigated hamstrings EMG amplitude during lesscommonly performed exercises. Zebis et al. (2013) measured hamstringsEMG amplitude separately between the medial and lateral hamstrings during 1-leg glute bridges, two-hand kettlebell swings, Nordic curls, supine slide-boardcurls, horizontal back extensions, weighted horizontal back extensions, RDLs,seated leg curls, and lying leg curls. It was found that all of the exercisesdisplayed >60% and >50% of peak EMG amplitude in the medial and lateralhamstring, respectively. McGill and Marshall (2012) compared different kettlebellexercises and found that the snatch and swing activated the biceps femoris to a


similar extent. McGill et al. (2009) compared a variety of strongman exercisesand found that the tire flip led to greater biceps femoris EMG amplitude thanother strongman movements, including the Atlas stone lift and log lift. Oliver andDougherty (2009a) investigated hamstrings EMG amplitude in the Razor curl, avariant of the Nordic curl, and found that it produced significant hamstringsEMG amplitude. Oliver and Dougherty (2009b) compared the hamstringsEMG amplitude produced by the Razor curl and the leg curl. They found that theRazor curl produced similar levels of hamstring EMG amplitude to the leg curl.

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REHABILITATION EXERCISES

Introduction

As with resistance training exercises, hamstrings rehabilitation exercises caninvolve either hip or knee movement, or both. When both hip and kneemovements are involved, exercises involving the hamstrings can cause a widerange of muscle length changes, from very small to very large, through a rangeof different combinations of joint movements. As with resistance trainingexercises hamstrings rehabilitation exercises can be placed into one ofthe following categories:

Hip extension and knee extension (e.g. single-leg squat)

Hip extension with partial knee extension (e.g. single-legdeadlift)

Hip extension without knee movement (e.g. back extension)

Knee flexion without hip movement (e.g. sliding leg curl)

Hip extension and knee flexion (e.g. glute-ham raise)

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Few studies have directly compared hamstrings EMG amplitude across a rangeof common rehabilitation exercises (Cook et al. 1992; Graham et al. 1993; Ayotteet al. 2007; Begalle et al. 2012; Orishimo et al. 2015; Youdas et al. 2015; Tsakliset al. 2015). Few (if any) have compared exercises from more than one jointmovement category. Those studies that have only compared exercises within a


single joint movement category (e.g. Beutler et al. 2002) or in exercises thatinvolve joint movements not covered by the above system (e.g. Andersen et al.2006) have been excluded. From a review of the literature, it is immediatelyapparent that very few studies have included any rehabilitation exercises in thehip extension and knee flexion, and hip extension without kneemovement categories. This may reflect a lack of variation in exercises for thehamstrings being commonly programmed among rehabilitation professionals. Itis noteworthy that in the studies that included exercises involving knee flexionwithout hip movement (Graham et al. 1993; Orishimo & McHugh, 2015; Tsaklis2015), these exercises produced the greatest hamstrings EMG amplitude. This isthe same finding as for resistance training exercises, where isolated knee flexionexercises (such as leg curls) produced the best results with the greatestregularity.

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Unilateral exercises

Studies investigating hamstrings EMG amplitude during common unilateralexercises have generally found that hamstrings EMG amplitude is low,particularly when compared to quadriceps EMG amplitude. For example, Zeller etal. (2003) investigated leg muscle EMG amplitude during the 1-leg squat andfound that hamstrings EMG amplitude was low, particularly in comparison withquadriceps EMG amplitude. They noted that the quadriceps-to-hamstrings ratioof EMG amplitude ranged from 1.2 for females to 3.6 for males. Similarly, Shieldset al. (2005) also reported that although hamstrings EMG amplitude increasedwith increasing load during 1-leg squats, the quadriceps displayed much greaterEMG amplitude than the hamstrings at all loads, with the quadriceps-to-hamstrings ratio of EMG amplitude ranging from 2.3 – 3.0. In addition, genderdifferences may exist in terms of the quadriceps-to-hamstrings ratio ofEMG amplitude during 1-leg exercises. For example, Youdas et al. (2007) foundthat males but not females displayed greater hamstrings EMG amplitude thanquadriceps EMG amplitude during the split squat. Similarly, Zeller et al. (2003)found that females displayed a much smaller quadriceps-to-hamstrings ratio ofEMG amplitude in the 1-leg squat (1.2) compared to males (3.6).

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Stability and instability

Different support surfaces appear to have some effect on hamstringsEMG amplitude. Eom et al. (2013) compared the effects of different supportsurfaces on hamstrings EMG amplitude during a glute bridge exercise. Theyfound that using a sling to create instability led to twice the hamstringsEMG amplitude as compared with the stable, ground surface. In contrast,Youdas et al. (2007) did not find any significant differences in hamstringsEMG amplitude during 1-leg squats performed on stable and labile surfaces.Similarly, Li and Chen (2013) investigated the differences in hamstringsEMG amplitude when squatting either on the ground or on the Reebok coreboard with three different loads. They found that the unstable surface had noeffect on the EMG amplitude of the hamstrings.

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Pelvic restriction

Pelvic restriction seems to have little effect on hamstrings EMG amplitude duringback extensions. Da Silva et al. (2009a) investigated the effects of pelvicstabilization and degree of hip flexion on hamstring EMG amplitude duringhorizontal back extensions. They found a non-significant trend for hamstringsEMG amplitude to be increased during horizontal back extensions with pelvicrestriction. Udermann et al. reported a similar non-significant trend. On the otherhand, Da Silva et al. (2009b) found a non-significant trend for decreasinghamstrings EMG amplitude in the order of: unrestrained, partially restrained, andfully restrained pelvis.

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EXERCISES FOR THE MEDIAL AND LATERAL HAMSTRINGS

Introduction

Many studies have compared the medial and lateral hamstrings EMG amplitudeduring different exercises with varying results (Fiebert et al. 2001; Escamilla et al.2002; Lynn & Costigan, 2009; Simenz et al. 2012; Jakobsen et al. 2012; Zebis etal. 2013; McAllister et al. 2014). In general, it appears that leg curls of varyingkinds (prone leg curl and supine slide-board curl), back extensions and lunges


may be useful for targeting the lateral hamstrings (Fiebert et al. 2001; Lynn &Costigan, 2009; Jakobsen et al. 2012; Zebis et al. 2013), while kettlebell swings,deadlifts of varying kinds (Romanian and 1-leg), good mornings and glute-hamraises may be superior for targeting the medial hamstrings (Lynn & Costigan,2009; Zebis et al. 2013; McAllister et al. 2014). Programs aimed at improving thestrength and size of the hamstrings muscle group may therefore benefit fromincluding exercises from both of these groups in each training session. Careshould be taken in the interpretation of these findings, as differences may alsoexist between individual medial and lateral hamstrings muscles. Ono et al. (2010)found that EMG amplitude of the semitendinosus was significantly higher thanthat of the semimembranosus during eccentric leg curls and Kubota et al. (2007)found that muscular soreness and signal intensity was greatest in the ordersemitendinosus > biceps femoris (long head) > semimembranosus followingeccentric leg curls. The exact ratio of medial-to-lateral hamstringsEMG amplitude may therefore depend upon the precise muscles measured. Forexample, it may be the case that preferential stimulation of the semitendinosus incertain exercises occurs because the muscle is fusiform and is therefore moreeasily damaged during lengthening exercises than the other more pennatehamstring muscles.

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Foot position

Directing athletes to use internal tibial rotation during certain movementsappears to cause greater medial hamstrings EMG amplitude during a range ofdifferent hip extension exercises and movements (Fiebert et al. 1992;1997; Mohamed et al. 2003; Lynn & Costigan, 2009; Jónasson et al. 2015).

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Ankle position

Since the gastrocnemius is both a knee flexor and a plantar flexor, it is possiblethat ankle position may affect either the hamstrings EMG amplitude or kneeflexion peak torque during knee flexion movements. However, this remains to bedemonstrated in the literature (Croce et al. 2000).

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Internal and external cues

Although external cues are widely used, as they appear to enhance performance(see review by Wulf, 2007), the use of internal cues may be useful in order toalter the degree to which the medial and lateral hamstrings are activated duringcertain movements. Oh et al. (2007) reported that using the Abdominal drawing-in maneuver (ADIM) led to increased medial hamstring EMG amplitude, whileLewis & Sahrmann (2009) found that using a hamstrings cue led to increasedlateral hamstrings EMG amplitude.

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Hamstrings EMG amplitude, ADIM and anterior pelvic tilt

The increasing medial hamstrings EMG amplitude reported by Oh et al. (2007)might not be medial-hamstring-specific, as the EMG amplitude of the lateralhamstrings was not reported. It is interesting that Oh et al. (2007) noted that theuse of the abdominal drawing-in maneuver also led to reduced anterior pelvic tiltduring the prone hip extension exercise. Tateuchi et al. (2012) found that duringprone hip extension, increased EMG amplitude of the hip flexor (tensor fasciaelatae) relative to that of hip extensors (gluteus maximus and semitendinosus)was significantly associated with increased anterior pelvic tilt. Thus, increasedEMG amplitude of the hip extensors and abdominals both seem to lead toreduced anterior pelvic tilt during hip extension movements.

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EFFECTS OF HIP JOINT ANGLE ON HAMSTRINGS EMG AMPLITUDE

Several dynamometry studies have been performed to explore the way in whichhamstrings EMG amplitude changes in various hip angles and have generallyreported that changing joint angle has little or no effect (Lunnen et al. 1981;Worrell et al. 2001; Mohamed et al. 2002; Guex et al. 2012). However, there arekey differences between the study protocols used in the literature. For example,Lunnen et al. (1981) studied a much greater hip flexion angle (135 degrees) thanmany of the other researchers (e.g. Mohamed et al. 2002; Guex et al. 2012) andit is possible that the large stretch in this position moved the muscle up thepassive arm of the length-tension curve, thereby reducing neural drive.Additionally, Lunnen et al. (1981) made use of surface electrodes while Guex et


al. (2012) used fine wire electrodes, which may have also led to differences inthe results observed.

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EFFECTS OF KNEE JOINT ANGLE ON HAMSTRINGS EMG AMPLITUDE

Several dynamometry studies have been performed to explore the way in whichhamstrings EMG amplitude changes with knee angle and have reportedconflicting results (Andriacchi et al. 1983; Fiebert et al. 1996; Worrell et al. 2001;Onishi et al. 2002; Croce et al. 2006; Higashihara et al. 2010a; Kwon & Lee,2013; Kumazaki et al. 2013). On the one hand, some trials have reported that thehamstrings EMG amplitude is greatest in the middle of the overall knee joint ROM(Worrell et al. 2001; Higashihara et al. 2010a). In contrast, other studies havereported that either medial, lateral or both groups of hamstrings display theirgreatest EMG amplitude at one end of the overall joint ROM. The effect of kneejoint angle on hamstrings EMG amplitude is therefore currently unclear.

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EFFECTS OF HIP JOINT ANGLE ON HAMSTRINGS EMGAMPLITUDE DURING RESISTANCE TRAINING EXERCISES

Several studies have been performed to explore the way in which hamstringsEMG amplitude changes with hip angle during resistance training exercises (DaSilva et al. 2009a; Zebis et al. 2013). Of note is that Zebis et al. (2012) foundthat hamstrings EMG amplitude was greater with increasing hip angle in theRomanian deadlift, 2-hand kettlebell swing and seated leg curl. In contrast, theyalso found that EMG amplitude was greater at with reduced hip angle in thesupine slide-board curl, prone leg curl, Nordic curl, 1-leg glute bridge, horizontalback extension, and back extension.

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EFFECTS OF KNEE JOINT ANGLE ON HAMSTRINGS EMGAMPLITUDE DURING RESISTANCE TRAINING EXERCISES

Several studies have been performed to explore the way in which hamstringsEMG amplitude changes with knee angle during resistance training exercises (Iga


et al. 2012; Zebis et al. 2013). It has been found that during Nordic curls,hamstrings EMG amplitude is greater when the torso is closer to the ground thanwhen the torso is more upright.

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Implications for hypertrophy

Where exercises display peak hamstrings EMG amplitude at different degrees ofknee flexion, this may imply that they could lead to increases in strength andhypertrophy in different parts of the hamstring muscles. Using magneticresonance imaging (MRI) scans, Mendiguchia et al. (2013b) reported that thesignal intensity in various regions of three different hamstring muscles differeddepending on the exercise selected. Similar results have been observed in othermuscle groups, which have confirmed the association between acuteobservations of signal intensity (Mendiguchia et al. 2013b) with long-termhypertrophic effects (e.g. Wakahara et al. 2013; Bloomquist et al. 2014).

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SECTION CONCLUSIONS

The hamstrings display no clear tendency to greater EMG amplitude at anyone joint angle. However, there are differences between individualhamstrings muscles. In contrast to the moment arm findings, this suggeststhat exercises involving peak contractions at a range of joint angles may beoptimal.

Research is limited regarding the best exercises for the hamstrings. Leg curlsare a reliable option, while good mornings, Romanian deadlifts, and Nordichamstring curls (glute-ham raises) are good alternatives.

Some exercises appear to target the medial hamstrings to a greater extent(e.g. kettlebell swings and deadlifts) while other exercises target the lateralhamstrings more (e.g. leg curls and back extensions). Optimal programs maytherefore include exercises that target both sub-groups.



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ECCENTRIC TRAINING

PURPOSE

This section provides a summary of the long-term studies performedusing eccentric training exercises for the hamstrings, either for injuryprevention or for injury rehabilitation.

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BACKGROUND

Introduction

Hamstring strain injury is a particularly prevalent form of non-contact injury inmany sports involving high-speed running or sprinting. Hamstring strainsaccount for around 12 – 16% of injuries in popular team sports (Woods et al.2004; Orchard & Seward, 2002). Most such strains seem to occur during high-speed running (Brooks et al. 2006) in diverse locations throughout the muscle(De Smet et al. 2000; Koulouris & Connell, 2003) and the largest proportionoccur in the biceps femoris (De Smet et al. 2000; Garrett et al. 1989; Slavotineket al. 2002; Ekstrand et al. 2012). This is likely because of the very central rolethat the hamstrings play in sprinting and the development of the horizontal forcethat is needed to accelerate and maintain maximal speed (Morin et al. 2015).Hamstring strain injury can be a serious problem for team sports because of thetime lost to training and match play for key athletes. Although the mean time toreturn-to-sport is often reported as only around a week (Cross et al. 2015), theseverity of the injury can differ very widely (Cross et al. 2015). Ekstrand et al.(2012) found that the grade of the hamstring strain was a key determinant of thetime to return-to-sport, with grades from 1 – 4 requiring an average of 8 ± 3days, 17 ± 10 days, 22 ± 11 days, and 73 ± 60 days, respectively.

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HAMSTRING STRAIN INJURY BIOMECHANICS

Novel hamstring strain injuries


The point at which a hamstring strain injury occurs in the gait cycle remainsunclear. It was originally suggested that hamstring strain injury occurred mostcommonly during the early stance phase, as this is where both knee flexion andhip extension moments are highest (Mann and Sprague, 1980). However, laterresearchers proposed that hamstring strains most likely occur in the terminalswing phase (just prior to ground contact), as this is where the hamstringsmuscles are lengthening quickly and reach peak length (Thelen et al. 2005;Chumanov et al. 2007; Chumanov et al. 2011; Schache et al. 2012; Higashihara etal. 2014) and is also where the biceps femoris (long head) displays a peak inEMG amplitude (Higashihara et al. 2014). The hamstrings lengthen quickly whilethe hip is flexing and while the knee is extending because the hamstrings areboth hip extensors and knee flexors. Since Lieber and Fridén (1993) haveexplained that muscle damage is not a function of force but rather of mechanicaldeformation (i.e. relative change in length), this may suggest that this is the pointin the gait cycle that is most dangerous for the hamstrings. While someresearchers still argue in favour of either one of these explanations, recentresearch by Sun et al. (2015) indicates that both may in fact be similarly likely.Sun et al. (2015) noted that their analysis of intersegmental dynamics suggeststhat the hamstrings experience very high loads in both early stance and lateswing phases.

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Recurrent hamstring strain injuries

The risk factors for recurrent hamstring strain are likely multifactorial, with manyfactors influencing others (see review by Mendiguchia et al. 2011). Someresearch has identified that athletes who have previously incurred a hamstringstrain injury tend to display altered biomechanics in comparison with athleteswho have never experienced such an injury. In particular, injured athletes tend todisplay reduced biceps femoris EMG amplitude both during eccentric isokinetictesting (Sole et al. 2011; Opar et al. 2013b) and during the Nordic hamstring curlexercise (Bourne et al. 2015) and may also display lower biceps femorisEMG amplitude during running in comparison with other muscles in the trunk andthigh than uninjured athletes (Daly et al. 2015), although there are conflictingfindings in this respect (Silder et al. 2011). There are also indications thatinjured athletes tend to display greater peak anterior pelvic tilt and peak hip


flexion on the injured side than on the uninjured side during running, whileuninjured athletes do not (Daly et al. 2015). The greater anterior pelvic tilt andpeak hip flexion on the injured side may lead to a greater maximum length of thishamstring muscle during running, which may predispose them to greater risk ofrecurrent hamstring strain injury. However, other investigations have found nodifferences in the length of the biceps femoris muscle during sprint runningbetween injured and uninjured athletes (Silder et al. 2011).–

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HAMSTRING STRAIN INJURY EPIDEMIOLOGY

Incidence

The incidence of hamstring strain injury has been explored in rugby union andAmerican football and ranges between 0.27 – 5.6 injuries per 1,000 exposurehours, depending upon the sport and on the exact definition of exposure (Brookset al. 2006; Elliott et al. 2011).

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Proportion of injuries comprising hamstring strains

The proportion of total injuries comprised of hamstring strains in common teamsports varies between 12 – 15% in Australian Rules Football, track and field, andsoccer (Seward et al. 1993; Bennell et al. 1996; Orchard & Seward, 2002; Woods et al. 2004).

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RISK FACTORS FOR HAMSTRING STRAINS

Introduction

Overall, the factors that drive hamstring strains and the optimal strategies forrehabilitation remain largely unclear (Mendiguchia et al. 2011; Brukner, 2015).Indeed, previous reviews have identified that there are many different individualrisk factors for hamstring strain injury, which include previous hamstring straininjury, hamstrings weakness and various other factors (Mendiguchia et al. 2011).This links into the common strategies for rehabilitation which frequently take


multiple factors into account (Valle et al. 2015). Mendiguchia et al. (2011)proposed that hamstring strains are not only multifactorial but that each of theindividual factors can have an influence on the others, as shown in the diagrambelow:

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Previous hamstring strain injury

In reviewing the literature relating to previous hamstring strain injury,Mendiguchia et al. (2011) concluded that previous hamstring strain injuryincreases the risk of re-injury substantially and suggested that previoushamstring strain injury is likely the greatest individual risk factor for future injury.However, whether this increased risk arises because of some feature of the initialinjury or because of a failure to perform sufficient rehabilitation is currentlyunclear. The odds ratio associated with previous hamstring strain injury rangesbetween 1.4 – 16.5 times (Orchard et al. 1997; Bennell et al. 1998; Arnason et al.2004; Hägglund et al. 2006; Gabbe et al. 2006a; Engebretsen et al. 2010), whilethe relative risk ranges between 2.1 – 2.4 times (Orchard, 2001; Opar et al. 2014).

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Hamstring weakness


Studies exploring the retrospective relationships between hamstring strengthand the risk of hamstring strain injury have historically reported conflictingresults (Worrell et al. 1991; Brockett et al. 2004; Opar et al. 2013a; Opar et al.2013b; Timmins et al. 2014). Strength measures were traditionally recordedusing isokinetic methods (Worrell et al. 1991; Brockett et al. 2004; Opar et al.2013b) but some more recent assessments have used isoinertial (eccentric) andisometric tests instead (Opar et al. 2013a; Timmins et al. 2014). Similarly, studiesexploring the prospective relationships between hamstring strength and the riskof hamstring strain injury have also reported conflicting results (Orchard et a l.1997; Bennell et al. 1998; Sugiura et al. 2008; Croisier et al. 2008; Yeung et al.2009; Opar et al. 2014; Goossens et al. 2014). Again, strength measures weretraditionally recorded using isokinetic methods (Orchard et a l. 1997; Bennell etal. 1998; Sugiura et al. 2008; Croisier et al. 2008; Yeung et al. 2009) but morerecent assessments have used isoinertial (eccentric) and isometric tests instead(Opar et al. 2014; Goossens et al. 2014). Overall, the literature indicates thathamstrings weakness, when measured both retrospectively and prospectively,can indicate a greater risk of strain injury.

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ECCENTRIC TRAINING FOR HAMSTRING STRAIN PREVENTION ANDREHABILITATION

Introduction

Eccentric training has been proposed as a method of training for the hamstringsthat may be useful both for preventing hamstring strains from occurring and forrehabilitation of hamstring strain injury after is has occurred. There are at leasttwo possible reasons why this type of training may be effective for this purpose.Firstly, eccentric training of any muscle has been found to shift the optimumlength at which torque is developed in the hamstrings (Brockett et al. 2001). Thischange in the optimal length at which torque is developed appears to occurbecause of an increase in length of the individual muscle fibers(sarcomerogenesis). Increasing muscle length may help reduce the risk of straininjury because it allows the muscle fibers to change length more quickly and withless resistance. Secondly, since several studies have found that eccentricstrength of the hamstrings is a risk factor for hamstring strain injury, eccentrichamstring training may be useful for addressing this problem. Indeed, eccentric


hamstring training has been found to be more effective than concentrichamstring training for improving eccentric hamstring strength (Mjølsnes et al.2004) as well as hamstring strength overall (Kaminski et al. 1998).

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Nordic hamstring curl

INTRODUCTION

The Nordic hamstring curl is the primary exercise used for performing eccentrictraining of the hamstring musculature during long-term trialsinvestigating hamstring strain injury prevention (Gabbe et al. 2006b;Engebretsen et al. 2008; Arnason et al. 2010; Petersen et al. 2011; Van der Horstet al. 2015) although a range of others have also been developed that may alsobe suitable (Askling et al. 2013; Orishimo & McHugh, 2015). Consequently, anumber of investigations have explored this exercise (Small et al. 2009; Iga et al.2012; Zebis et al. 2013; Mendiguchia et al. 2013a; 2013b; Ditroilo et al. 2013;Bourne et al. 2015; Marshall et al. 2015). Additionally, it iscommonly recommended as the primary exercise to perform in order to preventand rehabilitate hamstring strain injury (Schmitt & McHugh, 2012; Bahr et al.2015). This is important, as few other conservative treatments have any support(Reurink et al. 2011). Despite this common advice, the majority of elite soccerteams fail to use the Nordic hamstring curl in either prevention or rehabilitationprograms, which may explain the continued high incidence of both novel andrecurrent hamstring strain injury (Bahr et al. 2015).

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EMG AMPLITUDE

Exploring the EMG amplitude of the hamstrings during the Nordic hamstring curl,Iga et al. (2012) found that EMG amplitude of the hamstrings was higher whenthe knee was extended than when the knee was flexed, indicating that theexercise trains the hamstrings at long muscle lengths. However, Zebis et al.(2013) did not find any effect of joint angle on EMG amplitude during the Nordichamstring curl. Bourne et al. (2015) found that the Nordic hamstring curlproduced preferentially higher semitendinosus EMG amplitude; but again, Zebiset al. (2013) did not report any preferential activation; Mendiguchia et al. (2013a)


reported preferential biceps (short head) activation; and Ditroilo et al. (2013)reported that biceps femoris EMG amplitude exceeded maximum voluntaryeccentric contraction levels by some margin. Therefore, whether there isany difference between medial and lateral hamstrings EMG amplitudes in theNordic hamstring curl (and whether it in fact matters) remains unclear.

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EFFECTS OF FATIGUE

Exploring multiple sets of the Nordic hamstring curl exercise, Marshall et al.(2015) noted that a single set of 5 repetitions led to substantial reductions inpeak eccentric knee flexion moments during the exercise, with even furtherreductions in subsequent sets, implying that performing the Nordic hamstringcurl prior to practice or other exercise might not be advisable. Nevertheless,training under fatigued conditions may have benefits if carefully managed. Smallet al. (2009) found that long-term training using the Nordic hamstring curl eitherbefore or after practice had different effects. Training before practice led togreater strength gains being displayed when measured before a simulated gamebut training after practice led to greater strength gains being displayed whenmeasured after the simulated game. This indicates that performing hamstringstraining under conditions of fatigue may benefit the demonstration of hamstringsstrength under fatigued conditions.

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Meta-analysis

The effects of eccentric hamstring training on the incidence of hamstring straininjury was recently subjected to a review and meta-analysis by Goode et al.(2014). The review included 4 of the following trials in order to determine theeffect of eccentric hamstring strengthening on the risk of hamstring injury andspecifically investigated the effect of intervention non-compliance on outcomes.It was found that while the trials involving eccentric hamstring training did notsignificantly reduce the risk of hamstring injury (risk ratio of 0.59 times), this wasbecause of significant heterogeneity. Importantly, most of this heterogeneitycame from compliance. When considering only those subjects compliant withthe eccentric strengthening, the reviewers found an overall significant reduction


in hamstring injury risk (risk ratio of 0.35 times) and this effect had littleheterogeneity. This finding is supported by more recent investigations (Tyler etal. 2015), where athletes who were compliant with an eccentric trainingrehabilitation program did not incur any recurrent hamstring strain injury after amean follow-up period of 24 ± 12 months, whereas 4 of 8 non-compliantathletes (50%) incurred a recurrent hamstring strain (Tyler et al. 2015).

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Effect of eccentric hamstring training on hamstring strain injury incidence

A small number of studies have explored the effects of eccentric trainingon novel hamstring strain injury (Askling et al. 2003; Gabbe et al.2006b; Engebretsen et al. 2008; Arnason et al. 2008; Petersen et al. 2011;Van Van der Horst et al. 2015). In these studies, the most commonly-used eccentric hamstring exercise is the Nordic hamstring curl (Gabbe et al.2006b; Engebretsen et al. 2008; Arnason et al. 2008; Petersen et al. 2011; VanVan der Horst et al. 2015). However, there are several other similar exercises,which have been reviewed in detail by Brughelli and Cronin (2008), and whichmay also be valuable. The odds ratio for hamstring strain injury between playerstaking part in the injury prevention program and those not taking parts rangedbetween 0.13 – 0.28 times as likely, while the relative risks ranged between 0.30– 1.55). Overall, there is a strong indication that eccentric training for thehamstrings is beneficial for reducing the risk of novel hamstring strain injury.

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Effect of eccentric hamstring training on recurrent hamstring strain injuryincidence

A very small number of studies have explored the effects of eccentric training onrecurrent hamstring strain injury (Petersen et al. 2011; Askling et al. 2013; Tyleret al. 2015). There is an extremely strong indication that eccentric training for thehamstrings is beneficial for reducing the risk of recurrent hamstring strain injury.The relative risk is 0.14 (Petersen et al. 2011), the period of time to return tosport was shorter (28 ± 15 days vs. 51 ± 21 days), and there is no recurrence inathletes who are compliant to the program, while there is a 50% re-injury rate innon-compliant athletes (Tyler et al. 2015). Therefore, eccentric training for the


hamstrings is strongly recommended for the rehabilitation of injured athletes.

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SECTION CONCLUSIONS

The hamstrings are essential for sprint running performance. Hamstringstrains are common in team sports, accounting for around 12 – 16% ofinjuries. As expected, most strains occur during high-speed running, with thelargest proportion affecting the biceps femoris.

The acute mechanisms producing hamstring strains are unclear. Either fastchanges in length in the terminal swing phase or high loading during the earlystance phase could be responsible. The mechanisms of recurrent hamstringstrain could include alterations in biomechanics, including muscle activation.

Previous hamstring strain increases the risk of an athlete incurring a similarsubsequent injury substantially. Strength and conditioning programs shouldaim to prevent hamstring strains happening in the first place.

Eccentric hamstring training, particularly the Nordic hamstring curl exercise,reduces the incidence of both novel and recurrent hamstring strain injury.Compliance with eccentric hamstring training is essential to preventhamstring strain injury.


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REFERENCES

1. Andersen, L. L., Magnusson, S. P., Nielsen, M., Haleem, J., Poulsen, K., &Aagaard, P. (2006). Neuromuscular activation in conventional therapeuticexercises and heavy resistance exercises: implications for rehabilitation.Physical Therapy, 86(5), 683-697.[PubMed]

2. Andriacchi, T. P., Andersson, G. B. J., Örtengren, R., & Mikosz, R. P. (1983).A study of factors influencing muscle activity about the knee joint. Journalof Orthopaedic Research, 1(3), 266-275.[PubMed]

3. Arnason, A., Sigurdsson, S. B., Gudmundsson, A., Holme, I., Engebretsen,L., & Bahr, R. (2004). Risk factors for injuries in football. The American


Journal of Sports Medicine, 32(1 suppl), 5S-16S.[PubMed]4. Arnason, A., Andersen, T. E., Holme, I., Engebretsen, L., & Bahr, R. (2008).

Prevention of hamstring strains in elite soccer: an intervention study.Scandinavian journal of medicine & science in sports, 18(1), 40-48.[PubMed]

5. Askling, C., Karlsson, J., & Thorstensson, A. (2003). Hamstring injuryoccurrence in elite soccer players after preseason strength training witheccentric overload. Scandinavian journal of medicine & science in sports,13(4), 244-250.[PubMed]

6. Askling, C. M., Tengvar, M., & Thorstensson, A. (2013). Acute hamstringinjuries in Swedish elite football: a prospective randomised controlledclinical trial comparing two rehabilitation protocols. British Journal ofSports Medicine, 47(15):953-9.[PubMed]

7. Aspe, R. R., & Swinton, P. A. (2014). Electromyographic and kineticcomparison of the back squat and overhead squat. The Journal of Strength& Conditioning Research, 28(10), 2827-2836.[PubMed]

8. Ayotte, N. W., Stetts, D. M., Keenan, G., & Greenway, E. H. (2007).Electromyographical analysis of selected lower extremity muscles during 5unilateral weight-bearing exercises. Journal of Orthopaedic and SportsPhysical Therapy, 37(2), 48.[PubMed]

9. Bahr, R., Thorborg, K., & Ekstrand, J. (2015). Evidence-based hamstringinjury prevention is not adopted by the majority of Champions League orNorwegian Premier League football teams: the Nordic Hamstring survey.British journal of sports medicine, bjsports-2015.[PubMed]

10. Battermann, N., Appell, H. J., Dargel, J., & Koebke, J. (2011). An anatomicalstudy of the proximal hamstring muscle complex to elucidate musclestrains in this region. International Journal of Sports Medicine, 32(03), 211-215.[PubMed]

11. Begalle, R. L., DiStefano, L. J., Blackburn, T., & Padua, D. A. (2012).Quadriceps and Hamstrings Coactivation During Common TherapeuticExercises. Journal of Athletic Training, 47(4), 396-405.[PubMed]

12. Bennell, K. L., & Crossley, K. (1996). Musculoskeletal injuries in track andfield: incidence, distribution and risk factors. Australian journal of scienceand medicine in sport, 28(3), 69-75.[PubMed]

13. Bennell, K., Wajswelner, H., Lew, P., Schall-Riaucour, A., Leslie, S., Plant, D.,& Cirone, J. (1998). Isokinetic strength testing does not predict hamstring


injury in Australian Rules footballers. British Journal of Sports Medicine,32(4), 309-314.[PubMed]

14. Beutler, A. I., Cooper, L. W., Kirkendall, D. T., & Garrett Jr, W. E. (2002).Electromyographic analysis of single-leg, closed chain exercises:implications for rehabilitation after anterior cruciate ligamentreconstruction. Journal of Athletic Training, 37(1), 13.[PubMed]

15. Bezerra, E. S., Simão, R., Fleck, S. J., Paz, G., Maia, M., Costa, P. B., &Serrão, J. C. (2013). Electromyographic Activity of Lower Body Musclesduring the Deadlift and Still-Legged Deadlift. Journal of ExercisePhysiology Online, 16(3).[Citation]

16. Blazevich, A. J., Gill, N. D., & Zhou, S. (2006). Intra‐and intermuscularvariation in human quadriceps femoris architecture assessed in vivo.Journal of Anatomy, 209(3), 289-310.[PubMed]

17. Bloomquist, K., Langberg, H., Karlsen, S., Madsgaard, S., Boesen, M., &Raastad, T. (2013). Effect of range of motion in heavy load squatting onmuscle and tendon adaptations. European Journal of Applied Physiology,1-10.[PubMed]

18. Bourne, M. N., Opar, D. A., Williams, M. D., Al Najjar, A., & Shield, A. J.(2015). Muscle activation patterns in the Nordic hamstring exercise: Impactof prior strain injury. Scandinavian journal of medicine & science in sports.[PubMed]

19. Brask, B., Lueke, R. H., & Soderberg, G. L. (1984). Electromyographicanalysis of selected muscles during the lateral step-up exercise. PhysicalTherapy, 64(3), 324-329.[PubMed]

20. Brockett, C. L., Morgan, D. L., & Proske, U. W. E. (2001). Human hamstringmuscles adapt to eccentric exercise by changing optimum length. Medicineand Science in Sports and Exercise, 33(5), 783-790.[PubMed]

21. Brockett, C. L., Morgan, D. L., & Proske, U. (2004). Predicting hamstringstrain injury in elite athletes. Medicine & Science in Sports & Exercise, (36),379-87.[PubMed]

22. Brooks, J. H., Fuller, C. W., Kemp, S. P., & Reddin, D. B. (2006). Incidence,risk, and prevention of hamstring muscle injuries in professional rugbyunion. The American journal of sports medicine, 34(8), 1297.[PubMed]

23. Brukner, P. (2015). Hamstring injuries: prevention and treatment—anupdate. British journal of sports medicine, bjsports-2014.[PubMed]

24. Brughelli, M., & Cronin, J. (2008). Preventing hamstring injuries in sport.


Strength & Conditioning Journal, 30(1), 55-64.[Citation]25. Buford, W. L., Ivey Jr, F. M., Malone, J. D., Patterson, R. M., Pearce, G. L.,

Nguyen, D. K., & Stewart, A. A. (1997). Muscle balance at the knee-momentarms for the normal knee and the ACL-minus knee. RehabilitationEngineering, IEEE Transactions on, 5(4), 367-379.[PubMed]

26. Caterisano, A., Moss, R. F., Pellinger, T. K., Woodruff, K., Lewis, V. C., Booth,W., & Khadra, T. (2002). The effect of back squat depth on the EMGactivity of 4 superficial hip and thigh muscles. The Journal of Strength andConditioning Research, 16(3), 428.[PubMed]

27. Chumanov, E. S., Heiderscheit, B. C., & Thelen, D. G. (2007). The effect ofspeed and influence of individual muscles on hamstring mechanics duringthe swing phase of sprinting. Journal of biomechanics, 40(16), 3555-3562.[PubMed]

28. Chumanov, E. S., Heiderscheit, B. C., & Thelen, D. G. (2011). Hamstringmusculotendon dynamics during stance and swing phases of high speedrunning. Medicine and science in sports and exercise, 43(3), 525.[PubMed]

29. Cook, T. M., Zimmermann, C. L., Lux, K. M., Neubrand, C. M., & Nicholson,T. D. (1992). EMG Comparison of Lateral Step-up and Stepping MachineExercise. The Journal of Orthopaedic and Sports Physical Therapy, 16(3),108.[PubMed]

30. Contreras, B. M., Cronin, J. B., Schoenfeld, B. J., Nates, R. J., & Sonmez, G.T. (2013). Are All Hip Extension Exercises Created Equal? Strength &Conditioning Journal, 35(2), 17-22.[Citation]

31. Contreras, B., Vigotsky, A. D., Schoenfeld, B. J., Beardsley, C., & Cronin, J.(2015). A Comparison of Gluteus Maximus, Biceps Femoris, and VastusLateralis EMG Amplitude in the Parallel, Full, and Front Squat Variations inResistance Trained Females. Journal of applied biomechanics.[PubMed]

32. Croce, R. V., Miller, J. P., & St Pierre, P. (2000). Effect of ankle positionfixation on peak torque and electromyographic activity of the knee flexorsand extensors. Electromyography and clinical neurophysiology, 40(6), 365-373.[PubMed]

33. Croce, R. V., & Miller, J. P. (2005). Angle-and velocity-specific alterations intorque and semg activity of the quadriceps and hamstrings duringisokinetic extension-flexion movements. Electromyography and clinicalneurophysiology, 46(2), 83-100.[PubMed]

34. Croisier, J. L., Ganteaume, S., Binet, J., Genty, M., & Ferret, J. M. (2008).


Strength Imbalances and Prevention of Hamstring Injury in ProfessionalSoccer Players A Prospective Study. The American journal of sportsmedicine, 36(8), 1469-1475.[PubMed]

35. Cross, K. M., Saliba, S. A., Conaway, M., Gurka, K. K., & Hertel, J. (2015).Days to Return to Participation After a Hamstrings Strain Among AmericanCollegiate Soccer Players. Journal of athletic training.[PubMed]

36. Dahmane, R., Djordjevič, S., Šimunič, B., & Valenčič, V. (2005). Spatial fibertype distribution in normal human muscle: histochemical andtensiomyographical evaluation. Journal of Biomechanics, 38(12), 2451-2459.[PubMed]

37. Dahmane, R., Djordjevič, S., & Smerdu, V. (2006). Adaptive potential ofhuman biceps femoris muscle demonstrated by histochemical,immunohistochemical and mechanomyographical methods. Medical andBiological Engineering and Computing, 44(11), 999-1006.[PubMed]

38. Daly, C., McCarthy Persson, U., Twycross‐Lewis, R., Woledge, R. C., &Morrissey, D. (2015). The biomechanics of running in athletes with previoushamstring injury: A case‐control study. Scandinavian journal of medicine &science in sports.[PubMed]

39. Da Silva, E. M., Brentano, M. A., Cadore, E. L., De Almeida, A. P. V., & Kruel,L. F. M. (2008). Analysis of muscle activation during different leg pressexercises at submaximum effort levels. The Journal of Strength &Conditioning Research, 22(4), 1059-1065.[PubMed]

40. Da Silva, R. A., Larivière, C., Arsenault, A. B., Nadeau, S., & Plamondon, A.(2009a). Effect of pelvic stabilization and hip position on trunk extensoractivity during back extension exercises on a Roman chair. Journal ofRehabilitation Medicine, 41(3), 136-142.[PubMed]

41. Da Silva, R., Larivière, C., Arsenault, A. B., Nadeau, S., & Plamondon, A.(2009b). Pelvic stabilization and semisitting position increase thespecificity of back exercises. Medicine & Science in Sports & Exercise,41(2), 435.[PubMed]

42. De Smet, A. A., & Best, T. M. (2000). MR imaging of the distribution andlocation of acute hamstring injuries in athletes. American Journal ofRoentgenology, 174(2), 393-399.[PubMed]

43. Ditroilo, M., De Vito, G., & Delahunt, E. (2013). Kinematic andelectromyographic analysis of the Nordic Hamstring Exercise. Journal ofElectromyography and Kinesiology, 23(5), 1111-1118.[PubMed]


44. Dostal, W. F., Soderberg, G. L., & Andrews, J. G. (1986). Actions of hipmuscles. Physical Therapy, 66(3), 351-359.[PubMed]

45. Ebben, W. P. (2009). Hamstring activation during lower body resistancetraining exercises. International journal of Sports Physiology andPerformance, 4(1), 84.[PubMed]

46. Ebben, W. P., & Jensen, R. L. (2002). Electromyographic and kineticanalysis of traditional, chain, and elastic band squats. The Journal ofStrength & Conditioning research, 16(4), 547.[PubMed]

47. Elliott, M. C., Zarins, B., Powell, J. W., & Kenyon, C. D. (2011). Hamstringmuscle strains in professional football players a 10-year review. TheAmerican journal of sports medicine, 39(4), 843-850.[PubMed]

48. Ekstrand, J., Healy, J. C., Waldén, M., Lee, J. C., English, B., & Hägglund, M.(2012). Hamstring muscle injuries in professional football: the correlation ofMRI findings with return to play.[PubMed]

49. Engebretsen, A. H., Myklebust, G., Holme, I., Engebretsen, L., & Bahr, R.(2008). Prevention of Injuries Among Male Soccer Players A Prospective,Randomized Intervention Study Targeting Players With Previous Injuries orReduced Function. The American journal of sports medicine, 36(6), 1052-1060.[PubMed]

50. Engebretsen, A. H., Myklebust, G., Holme, I., Engebretsen, L., & Bahr, R.(2010). Intrinsic Risk Factors for Hamstring Injuries Among Male SoccerPlayers A Prospective Cohort Study. The American Journal of SportsMedicine, 38(6), 1147-1153.[PubMed]

51. Eom, M. Y., Chung, S. H., & Ko, T. S. (2013). Effects of Bridging Exercise onDifferent Support Surfaces on the Transverse Abdominis. Journal ofPhysical Therapy Science, 25(10), 1343.[PubMed]

52. Escamilla, R. F., Fleisig, G. S., Zheng, N., Lander, J. E., Barrentine, S. W.,Andrews, J. R., & Moorman, C. T. (2001). Effects of technique variations onknee biomechanics during the squat and leg press. Medicine & Science inSports & Exercise, 33(9), 1552-1566.[PubMed]

53. Escamilla, R. F., Francisco, A. C., Kayes, A. V., Speer, K. P., & Moorman, C.T. (2002). An electromyographic analysis of sumo and conventional styledeadlifts. Medicine & Science in Sports & Exercise, 34(4), 682-688.[PubMed]

54. Farrokhi, S., Pollard, C. D., Souza, R. B., Chen, Y., Reischl, S., & Powers, C.M. (2008). Trunk position influences the kinematics, kinetics, and muscle


activity of the lead lower extremity during the forward lunge exercise.Journal of Orthopaedic and Sports Physical Therapy, 38(7), 403.[PubMed]

55. Feucht, M. J., Plath, J. E., Seppel, G., Hinterwimmer, S., Imhoff, A. B., &Brucker, P. U. (2014). Gross anatomical and dimensional characteristics ofthe proximal hamstring origin. Knee Surgery, Sports Traumatology,Arthroscopy, 1-7.[PubMed]

56. Fiebert, I. M., Haas, J. M., Dworkin, K. J., & LeBlanc, W. G. (1992). Acomparison of medial versus lateral hamstring electromyographic activityand force output during isometric contractions. Isokinetics and ExerciseScience, 2(2), 47-55.[Citation]

57. Fiebert, I. M., Pahl, C. H., Applegate, E. B., Spielholz, N. I., & Beernik, K.(1996). Medial-lateral hamstring electromyographic activity duringmaximum isometric knee flexion at different angles. Isokinetics andExercise Science, 6(2), 157-162.[Citation]

58. Fiebert, I. M., Roach, K. E., Fingerhut, B., Levy, J., & Schumacher, A. (1997).EMG activity of medial and lateral hamstrings at three positions of tibialrotation during low-force isometric knee flexion contractions. Journal ofBack and Musculoskeletal Rehabilitation, 8(3), 215-222.[PubMed]

59. Fiebert, I. M., Spielholz, N. I., Applegate, E. B., Fox, C., Jaro, J., Joel, L., &Raper, L. (2001). Comparison of EMG activity of medial and lateralhamstrings during isometric contractions at various cuff weight loads. TheKnee, 8(2), 145-150.[PubMed]

60. Friederich, J. A., & Brand, R. A. (1990). Muscle fiber architecture in thehuman lower limb. Journal of Biomechanics, 23(1), 91-95.[PubMed]

61. Gabbe, B. J., Bennell, K. L., Finch, C. F., Wajswelner, H., & Orchard, J. W.(2006a). Predictors of hamstring injury at the elite level of Australianfootball. Scandinavian journal of medicine & science in sports, 16(1), 7-13.[PubMed]

62. Gabbe, B. J., Branson, R., & Bennell, K. L. (2006b). A pilot randomisedcontrolled trial of eccentric exercise to prevent hamstring injuries incommunity-level Australian Football. Journal of science and medicine insport, 9(1), 103-109.[PubMed]

63. Garrett, W. E., Califf, J. C., & Bassett, F. H. (1984). Histochemical correlatesof hamstring injuries. The American Journal of Sports Medicine, 12(2), 98-103.[PubMed]

64. Garrett Jr, W. E., Rich, F. R., Nikolaou, P. K., & Vogler 3rd, J. B. (1989).


Computed tomography of hamstring muscle strains. Medicine & Science inSports & Exercise, 21(5), 506.[PubMed]

65. Goode, A. P., Reiman, M. P., Harris, L., DeLisa, L., Kauffman, A., Beltramo,D., & Taylor, A. B. (2014). Eccentric training for prevention of hamstringinjuries may depend on intervention compliance: a systematic review andmeta-analysis. British journal of sports medicine.[PubMed]

66. Goossens, L., Witvrouw, E., Vanden, B. L., & De Clercq, D. (2014). Lowereccentric hamstring strength and single leg hop for distance predicthamstring injury in PETE students. European journal of sport science, 1.[PubMed]

67. Graham, V. L., Gehlsen, G. M., & Edwards, J. A. (1993). Electromyographicevaluation of closed and open kinetic chain knee rehabilitation exercises.Journal of Athletic Training, 28(1), 23.[PubMed]

68. Gorsuch, J., Long, J., Miller, K., Primeau, K., Rutledge, S., Sossong, A., &Durocher, J. J. (2013). The effect of squat depth on multiarticular muscleactivation in collegiate cross-country runners. The Journal of Strength &Conditioning Research, 27(9):2619-25.[PubMed]

69. Guex, K., Gojanovic, B., & Millet, G. P. (2012). Influence of hip-flexion angleon hamstrings isokinetic activity in sprinters. Journal of Athletic Training,47(4), 390-395.[PubMed]

70. Hägglund, M., Waldén, M., & Ekstrand, J. (2006). Previous injury as a riskfactor for injury in elite football: a prospective study over two consecutiveseasons. British journal of sports medicine, 40(9), 767-772.[PubMed]

71. Hägglund, M., Waldén, M., & Ekstrand, J. (2013). Risk factors for lowerextremity muscle injury in professional soccer the UEFA injury study. TheAmerican journal of sports medicine, 41(2), 327-335.[PubMed]

72. Herzog, W., & Read, L. J. (1993). Lines of action and moment arms of themajor force-carrying structures crossing the human knee joint. Journal ofanatomy, 182(Pt 2), 213.[PubMed]

73. Higashihara, A., Ono, T., Kubota, J., & Fukubayashi, T. (2010a). Differencesin the electromyographic activity of the hamstring muscles during maximaleccentric knee flexion. European Journal of Applied Physiology, 108(2),355-362.[PubMed]

74. Higashihara, A., Ono, T., Kubota, J., Okuwaki, T., & Fukubayashi, T. (2010b).Functional differences in the activity of the hamstring muscles withincreasing running speed. Journal of Sports Sciences, 28(10), 1085-1092.


[PubMed]75. Higashihara, A., Nagano, Y., Ono, T., & Fukubayashi, T. (2014). Relationship

between the peak time of hamstring stretch and activation during sprinting.European journal of sport science, (ahead-of-print), 1-6.[PubMed]

76. Iga, J., Fruer, C. S., Deighan, M., Croix, M. D. S., & James, D. V. B. (2012).‘Nordic’ Hamstrings Exercise-Engagement Characteristics and TrainingResponses. International Journal of Sports Medicine, (EFirst).[PubMed]

77. Ikezoe, T., Mori, N., Nakamura, M., & Ichihashi, N. (2011a). Age-relatedmuscle atrophy in the lower extremities and daily physical activity in elderlywomen. Archives of gerontology and geriatrics, 53(2), e153-e157.[PubMed]

78. Ikezoe, T., Mori, N., Nakamura, M., & Ichihashi, N. (2011b). Atrophy of thelower limbs in elderly women: is it related to walking ability?. Europeanjournal of applied physiology, 111(6), 989-995.[PubMed]

79. Imran, A., Huss, R. A., Holstein, H., & O’Connor, J. J. (2000). The variationin the orientations and moment arms of the knee extensor and flexormuscle tendons with increasing muscle force: a mathematical analysis.Proceedings of the Institution of Mechanical Engineers, Part H: Journal ofEngineering in Medicine, 214(3), 277-286.[PubMed]

80. Isear Jr, J. A., Erickson, J. C., & Worrell, T. W. (1997). EMG analysis of lowerextremity muscle recruitment patterns during an unloaded squat. Medicine& Science in Sports & Exercise, 29(4), 532.[PubMed]

81. Ito, J. (1996). Morphological analysis of the human lower extremity basedon the relative muscle weight. Okajimas Folia Anatomica Japonica, 73(5),247.[PubMed]

82. Ito, J., Moriyama, H., Inokuchi, S., & Goto, N. (2003). Human lower limbmuscles: an evaluation of weight and fiber size. Okajimas folia anatomicaJaponica, 80(2-3), 47.[PubMed]

83. Jakobsen, M. D., Sundstrup, E., Andersen, C. H., Aagaard, P., & Andersen,L. L. (2012). Muscle activity during leg strengthening exercise using freeweights and elastic resistance: Effects of ballistic vs controlledcontractions. Human Movement Science, 32(1):65-78.[PubMed]

84. Jönhagen, S., Ericson, M. O., Nemeth, G., & Eriksson, E. (1996). Amplitudeand timing of electromyographic activity during sprinting. ScandinavianJournal of Medicine & Science in Sports, 6(1), 15-21.[PubMed]

85. Johnson, M., Polgar, J., Weightman, D., & Appleton, D. (1973). Data on thedistribution of fibre types in thirty-six human muscles: an autopsy study.


Journal of the Neurological Sciences, 18(1), 111-129.[PubMed]86. Jónasson, G., Helgason, A., Ingvarsson, Þ., Kristjánsson, A. M., & Briem, K.

(2015). The Effect of Tibial Rotation on the Contribution of Medial andLateral Hamstrings During Isometric Knee Flexion. Sports Health: AMultidisciplinary Approach.[PubMed]

87. Kellis, E., & Baltzopoulos, V. (1999). In vivo determination of the patellatendon and hamstrings moment arms in adult males usingvideofluoroscopy during submaximal knee extension and flexion. ClinicalBiomechanics, 14(2), 118-124.[PubMed]

88. Kellis, E., Galanis, N., Kapetanos, G., & Natsis, K. (2012). Architecturaldifferences between the hamstring muscles. Journal of Electromyographyand Kinesiology, 22(4), 520-526.[PubMed]

89. Kaminski, T. W., Wabbersen, C. V., & Murphy, R. M. (1998). Concentricversus enhanced eccentric hamstring strength training: clinicalimplications. Journal of athletic training, 33(3), 216.[PubMed]

90. Koulouris, G., & Connell, D. (2003). Evaluation of the hamstring musclecomplex following acute injury. Skeletal radiology, 32(10), 582-589.[PubMed]

91. Kubota, J., Ono, T., Araki, M., Torii, S., Okuwaki, T., & Fukubayashi, T.(2007). Non-uniform changes in magnetic resonance measurements of thesemitendinosus muscle following intensive eccentric exercise. EuropeanJournal of Applied Physiology, 101(6), 713-720.[PubMed]

92. Kumazaki, T., Ehara, Y., & Sakai, T. (2012). Anatomy and physiology ofhamstring injury. International Journal of Sports Medicine, (EFirst).[PubMed]

93. Kwon, Y. J., & Lee, H. O. (2013). How Different Knee Flexion AnglesInfluence the Hip Extensor in the Prone Position. Journal of PhysicalTherapy Science, 25(10), 1295.[PubMed]

94. Kyröläinen, H., Avela, J., & Komi, P. V. (2005). Changes in muscle activitywith increasing running speed. Journal of Sports Sciences, 23(10), 1101-1109.[PubMed]

95. Lewis, C. L., & Sahrmann, S. A. (2009). Muscle activation and movementpatterns during prone hip extension exercise in women. Journal of AthleticTraining, 44(3), 238.[PubMed]

96. Lieber, R. L., & Fridén, J. (2000). Functional and clinical significance ofskeletal muscle architecture. Muscle & Nerve, 23(11), 1647-1666.[PubMed]


97. Li, Y., Cao, C., & Chen, X. (2013). Similar Electromyographic Activities ofLower Limbs Between Squatting on a Reebok Core Board and Ground. TheJournal of Strength & Conditioning Research, 27(5), 1349-1353.[PubMed]

98. Lu, T. W., & O’Connor, J. J. (1996). Lines of action and moment arms of themajor force-bearing structures crossing the human knee joint: comparisonbetween theory and experiment. Journal of anatomy, 189(Pt 3), 575.[PubMed]

99. Lunnen, J. D., Yack, J., & LeVeau, B. F. (1981). Relationship between musclelength, muscle activity, and torque of the hamstring muscles. PhysicalTherapy, 61(2), 190-195.[PubMed]

100. Lynn, S. K., & Costigan, P. A. (2009). Changes in the medial–lateralhamstring activation ratio with foot rotation during lower limb exercise.Journal of Electromyography and Kinesiology, 19(3), e197-e205.[PubMed]

101. Lynn, S. K., & Noffal, G. J. (2012). Lower Extremity Biomechanics During aRegular and Counterbalanced Squat. The Journal of Strength &Conditioning Research, 26(9), 2417-2425.[PubMed]

102. Manabe, Y., Shimada, K., & Ogata, M. (2007). Effect of slow movement andstretch-shortening cycle on lower extremity muscle activity and jointmoments during squat. Journal of Sports Medicine and Physical Fitness,47(1), 1-12.[PubMed]

103. Mann, R., & Sprague, P. (1980). A kinetic analysis of the ground leg duringsprint running. Research Quarterly for exercise and sport, 51(2), 334-348.[Citation]

104. Marshall, P. W., Lovell, R., Knox, M. F., Brennan, S. L., Siegler, J. C., & South,P. (2015). Hamstring fatigue and muscle activation changes during six setsof Nordic hamstring exercise in amateur soccer players. Journal of strengthand conditioning research.[PubMed]

105. McAllister, M. J., Hammond, K. G., Schilling, B. K., Ferreria, L. C., Reed, J.P., & Weiss, L. W. (2014). Muscle activation during various hamstringexercises. Journal of Strength & Conditioning Research.[PubMed].

106. McCaw, S. T., & Melrose, D. R. (1999). Stance width and bar load effects onleg muscle activity during the parallel squat. Medicine & Science in Sports& Exercise, 31(3), 428.[PubMed]

107. McCurdy, K., O’Kelley, E., Kutz, M., Langford, G., Ernest, J., & Torres, M.(2010). Comparison of lower extremity EMG between the 2-leg squat andmodified single-leg squat in female athletes. Journal of Sport


Rehabilitation, 19(1), 57.[PubMed]108. McGill, S. M., McDermott, A., & Fenwick, C. M. (2009). Comparison of

different strongman events: trunk muscle activation and lumbar spinemotion, load, and stiffness. The Journal of Strength & ConditioningResearch, 23(4), 1148-1161.[PubMed]

109. McGill, S. M., & Marshall, L. W. (2012). Kettlebell swing, snatch, andbottoms-up carry: back and hip muscle activation, motion, and low backloads. The Journal of Strength & Conditioning Research, 26(1), 16-27.[PubMed]

110. Mendiguchia, J., Alentorn-Geli, E., & Brughelli, M. (2011). Hamstring straininjuries: are we heading in the right direction?. British journal of sportsmedicine, bjsports81695.[PubMed]

111. Mendiguchia, J., Arcos, A. L., Garrues, M. A., Myer, G. D., Yanci, J., &Idoate, F. (2013a). The use of MRI to evaluate posterior thigh muscleactivity and damage during nordic hamstring exercise. The Journal ofStrength & Conditioning Research, 27(12), 3426-3435.[PubMed]

112. Mendiguchia, J., Garrues, M. A., Cronin, J. B., Contreras, B., Los Arcos, A.,Malliaropoulos, N., & Idoate, F. (2013b). Nonuniform Changes in MRIMeasurements of the Thigh Muscles After Two Hamstring StrengtheningExercises. The Journal of Strength & Conditioning Research, 27(3), 574-581.[PubMed]

113. Miller, S. L., Gill, J., & Webb, G. R. (2007). The proximal origin of thehamstrings and surrounding anatomy encountered during repair. Acadaveric study. The Journal of bone and joint surgery. American volume,89(1), 44.[PubMed]

114. Miokovic, T., Armbrecht, G., Felsenberg, D., & Belavý, D. L. (2011).Differential atrophy of the postero-lateral hip musculature during prolongedbedrest and the influence of exercise countermeasures. Journal of AppliedPhysiology, 110(4), 926-934.[PubMed]

115. Mjølsnes, R., Arnason, A., Raastad, T., & Bahr, R. (2004). A 10‐weekrandomized trial comparing eccentric vs. concentric hamstring strengthtraining in well‐trained soccer players. Scandinavian journal of medicine &science in sports, 14(5), 311-317.[PubMed]

116. Mohamed, O., Perry, J., & Hislop, H. (2002). Relationship between wireEMG activity, muscle length, and torque of the hamstrings. ClinicalBiomechanics, 17(8), 569-579.[PubMed]


117. Mohamed, O., Perry, J., & Hislop, H. (2003). Synergy of medial and lateralhamstrings at three positions of tibial rotation during maximum isometricknee flexion. The Knee, 10(3), 277-281.[PubMed]

118. Morin, J. B., Gimenez, P., Edouard, P., Arnal, P., Jiménez-Reyes, P.,Samozino, P., & Mendiguchia, J. (2015). Sprint Acceleration Mechanics:The Major Role of Hamstrings in Horizontal Force Production. Frontiers inPhysiology, 6, 404.[PubMed]

119. Nemeth, G., Ekholm, J., & Arborelius, U. P. (1984). Hip load moments andmuscular activity during lifting. Scandinavian Journal of RehabilitationMedicine, 16(3), 103.[PubMed]

120. Németh, G., & Ohlsén, H. (1985). In vivo moment arm lengths for hipextensor muscles at different angles of hip flexion. Journal ofbiomechanics, 18(2), 129-140.[PubMed]

121. Neuschwander, T. B., Benke, M. T., & Gerhardt, M. B. (2015). AnatomicDescription of the Origin of the Proximal Hamstring. Arthroscopy: TheJournal of Arthroscopic & Related Surgery.[PubMed]

122. Nichols, A. W. (2013). Does eccentric training of hamstring muscles reduceacute injuries in soccer?. Clinical Journal of Sport Medicine, 23(1), 85-86.[PubMed]

123. Ninos, J. C., Irrgang, J. J., Burdett, R., & Weiss, J. R. (1997).Electromyographic analysis of the squat performed in self-selected lowerextremity neutral rotation and 30 degrees of lower extremity turn-out fromthe self-selected neutral position. The Journal of Orthopaedic and SportsPhysical Therapy, 25(5), 307.[PubMed]

124. Oliver, G. D., & Dougherty, C. P. (2009a). The RAZOR curl: a functionalapproach to hamstring training. The Journal of Strength & ConditioningResearch, 23(2), 401-405.[PubMed]

125. Oliver, G. D., & Dougherty, C. P. (2009b). Comparison of hamstring andgluteus muscles electromyographic activity while performing the razor curlvs. the traditional prone hamstring curl. The Journal of Strength &Conditioning Research, 23(8), 2250-2255.[PubMed]

126. Oh, J. S., Cynn, H. S., Won, J. H., Kwon, O. Y., & Yi, C. H. (2007). Effects ofperforming an abdominal drawing-in maneuver during prone hip extensionexercises on hip and back extensor muscle activity and amount of anteriorpelvic tilt. The Journal of Orthopaedic and Sports Physical Therapy, 37(6),320.[PubMed]


127. Opar, D. A., Piatkowski, T., Williams, M. D., & Shield, A. J. (2013a). A noveldevice using the Nordic hamstring exercise to assess eccentric knee flexorstrength: a reliability and retrospective injury study. journal of orthopaedic& sports physical therapy, 43(9), 636-640.[PubMed]

128. Opar, D. A., Williams, M. D., Timmins, R. G., Dear, N. M., & Shield, A. J.(2013b). Knee flexor strength and bicep femoris electromyographicalactivity is lower in previously strained hamstrings. Journal ofElectromyography and Kinesiology, 23(3), 696-703.[PubMed]

129. Opar, D. A., Williams, M. D., Timmins, R. G., Hickey, J., Duhig, S. J., &Shield, A. J. (2014). Eccentric hamstring strength and hamstring injury riskin Australian footballers. Medicine & Science in Sports & Exercise.[PubMed]

130. Onishi, H., Yagi, R., Oyama, M., Akasaka, K., Ihashi, K., & Handa, Y. (2002).EMG-angle relationship of the hamstring muscles during maximum kneeflexion. Journal of Electromyography and Kinesiology, 12(5), 399-406.[PubMed]

131. Ono, T., Higashihara, A., & Fukubayashi, T. (2010). Hamstring functionsduring hip-extension exercise assessed with electromyography andmagnetic resonance imaging. Research in Sports Medicine, 19(1), 42-52.[PubMed]

132. Orchard, J., Marsden, J., Lord, S., & Garlick, D. (1997). Preseasonhamstring muscle weakness associated with hamstring muscle injury inAustralian footballers. The American Journal of Sports Medicine, 25(1), 81-85.[PubMed]

133. Orchard, J. W. (2001). Intrinsic and Extrinsic Risk Factors for Muscle Strainsin Australian Football. The American Journal of Sports Medicine, 29(3),300-303.[PubMed]

134. Orchard, J., & Seward, H. (2002). Epidemiology of injuries in the AustralianFootball League, seasons 1997–2000. British Journal of Sports Medicine,36(1), 39-44.[PubMed]

135. Orishimo, K. F., & McHugh, M. P. (2015). Effect of an Eccentrically BiasedHamstring Strengthening Home Program on Knee Flexor Strength and theLength-Tension Relationship. The Journal of Strength & ConditioningResearch, 29(3), 772-778.[PubMed]

136. Paoli, A., Marcolin, G., & Petrone, N. (2009). The effect of stance width onthe electromyographical activity of eight superficial thigh muscles during


back squat with different bar loads. The Journal of Strength & ConditioningResearch, 23(1), 246-250.[PubMed]

137. Petersen, J., Thorborg, K., Nielsen, M. B., Budtz-Jørgensen, E., & Hölmich,P. (2011). Preventive effect of eccentric training on acute hamstring injuriesin men’s soccer a cluster-randomized controlled trial. The American journalof sports medicine, 39(11), 2296-2303.[PubMed]

138. Philippon, M. J., Ferro, F. P., Campbell, K. J., Michalski, M. P., Goldsmith, M.T., Devitt, B. M., & LaPrade, R. F. (2014). A qualitative and quantitativeanalysis of the attachment sites of the proximal hamstrings. Knee Surgery,Sports Traumatology, Arthroscopy, 1-8.[PubMed]

139. Pierrynowski, M. R., & Morrison, J. B. (1985). A physiological model for theevaluation of muscular forces in human locomotion: theoretical aspects.Mathematical Biosciences, 75(1), 69-101.[Citation]

140. Pohtilla, J. F. (1969). Kinesiology of hip extension at selected angles ofpelvifemoral extension. Archives of physical medicine and rehabilitation,50(5), 241-250.[PubMed]

141. Reurink, G., Goudswaard, G. J., Tol, J. L., Verhaar, J. A., Weir, A., & Moen,M. H. (2011). Therapeutic interventions for acute hamstring injuries: asystematic review. British journal of sports medicine, bjsports-2011.[PubMed]

142. Sakamoto, A. C. L., Teixeira-Salmela, L. F., de Paula-Goulart, F. R., deMorais Faria, C. D. C., & Guimarães, C. Q. (2009). Muscular activationpatterns during active prone hip extension exercises. Journal ofElectromyography and Kinesiology, 19(1), 105-112.[PubMed]

143. Savelberg, H. H. C. M., Fastenau, A., Willems, P. J. B., & Meijer, K. (2007).The load/capacity ratio affects the sit-to-stand movement strategy. ClinicalBiomechanics, 22(7), 805-812.[PubMed]

144. Schache, A. G., Dorn, T. W., Blanch, P. D., Brown, N. A., & Pandy, M. G.(2012). Mechanics of the human hamstring muscles during sprinting.Medicine & Science in Sports & Exercise, 44(4), 647-658.[PubMed]

145. Schache, A. (2012). Eccentric hamstring muscle training can preventhamstring injuries in soccer players. Journal of physiotherapy, 58(1), 58.[PubMed]

146. Schmitt, B., Tim, T., & McHugh, M. (2012). Hamstring injury rehabilitationand prevention of reinjury using lengthened state eccentric training: a newconcept. International journal of sports physical therapy, 7(3), 333.


[PubMed]147. Schoenfeld, B. J., Contreras, B., Tiryaki-Sonmez, G., Wilson, J. M., Kolber,

M. J., & Peterson, M. D. (2015). Regional differences in muscle activationduring hamstrings exercise. Journal of strength and conditioning research,29(1), 159-164.[PubMed]

148. Seward, H., Orchard, J., Hazard, H., & Collinson, D. (1993). Football injuriesin Australia at the elite level. The Medical Journal of Australia, 159(5), 298-301.[PubMed]

149. Shields, R. K., Madhavan, S., Gregg, E., Leitch, J., Petersen, B., Salata, S., &Wallerich, S. (2005). Neuromuscular control of the knee during a resistedsingle-limb squat exercise. The American Journal of Sports Medicine,33(10), 1520-1526.[PubMed]

150. Silder, A., Thelen, D. G., & Heiderscheit, B. C. (2010). Effects of priorhamstring strain injury on strength, flexibility, and running mechanics.Clinical Biomechanics, 25(7), 681-686.[PubMed]

151. Simenz, C. J., Garceau, L. R., Lutsch, B. N., Suchomel, T. J., & Ebben, W. P.(2012). Electromyographical Analysis of Lower Extremity Muscle ActivationDuring Variations of the Loaded Step-Up Exercise. The Journal of Strength& Conditioning Research, 26(12), 3398-3405.[PubMed]

152. Slavotinek, J. P., Verrall, G. M., & Fon, G. T. (2002). Hamstring injury inathletes: using MR imaging measurements to compare extent of muscleinjury with amount of time lost from competition. American Journal ofRoentgenology, 179(6), 1621-1628.[PubMed]

153. Small, K., McNaughton, L., Greig, M., & Lovell, R. (2009). Effect of timing ofeccentric hamstring strengthening exercises during soccer training:implications for muscle fatigability. The Journal of Strength & ConditioningResearch, 23(4), 1077-1083.[PubMed]

154. Sole, G., Milosavljevic, S., Nicholson, H., & Sullivan, S. J. (2011). Selectivestrength loss and decreased muscle activity in hamstring injury. journal oforthopaedic & sports physical therapy, 41(5), 354-363.[PubMed]

155. Spoor, C. W., & van Leeuwen, J. L. (1992). Knee muscle moment arms fromMRI and from tendon travel. Journal of biomechanics, 25(2), 201.[PubMed]

156. Sugiura, Y., Saito, T., Sakuraba, K., Sakuma, K., & Suzuki, E. (2008).Strength deficits identified with concentric action of the hip extensors andeccentric action of the hamstrings predispose to hamstring injury in elitesprinters. journal of orthopaedic & sports physical therapy, 38(8), 457-


464.[PubMed]157. Sun, Y., Wei, S., Liu, Y., Zhong, Y., Fu, W., & Li, L. (2015). How Joint Torques

Affect Hamstring Injury Risk in Sprinting Swing–Stance Transition. Medicineand science in sports and exercise.[PubMed]

158. Tateuchi, H., Taniguchi, M., Mori, N., & Ichihashi, N. (2012). Balance of hipand trunk muscle activity is associated with increased anterior pelvic tiltduring prone hip extension. Journal of Electromyography and Kinesiology,22(3), 391-397.[PubMed]

159. Thelen, D. G., Chumanov, E. S., Hoerth, D. M., Best, T. M., Swanson, S. C.,Li, L., & Heiderscheit, B. C. (2005). Hamstring muscle kinematics duringtreadmill sprinting. Med Sci Sports Exerc, 37(1), 108-114.[PubMed]

160. Timmins, R. G., Shield, A. J., Williams, M. D., Lorenzen, C., & Opar, D. A.(2014). Biceps Femoris Long-Head Architecture: A Reliability andRetrospective Injury Study. Medicine and science in sports and exercise.[PubMed]

161. Tsaklis, P., Malliaropoulos, N., Mendiguchia, J., Korakakis, V., Tsapralis, K.,Pyne, D., & Malliaras, P. (2015). Muscle and intensity based hamstringexercise classification in elite female track and field athletes: implicationsfor exercise selection during rehabilitation. Open access journal of sportsmedicine, 6, 209.[PubMed]

162. Tubbs, R. S., Caycedo, F. J., Oakes, W. J., & Salter, E. G. (2006). Descriptiveanatomy of the insertion of the biceps femoris muscle. Clinical Anatomy,19(6), 517-521.[PubMed]

163. Tyler, T. F., Schmitt, B. M., Nicholas, S. J., & McHugh, M. (2015).Rehabilitation After Hamstring Strain Injury Emphasizing EccentricStrengthening at Long Muscle Lengths: Results of Long Term Follow-up.Journal of sport rehabilitation.[PubMed]

164. Udermann, B. E., Graves, J. E., Donelson, R. G., Ploutz-Snyder, L., Boucher,J. P., & Iriso, J. H. (1999). Pelvic restraint effect on lumbar gluteal andhamstring muscle electromyographic activation. Archives of PhysicalMedicine and Rehabilitation, 80(4), 428-431.[PubMed]

165. Vakos, J. P., Nitz, A. J., Threlkeld, A. J., Shapiro, R., & Horn, T. (1994).Electromyographic Activity of Selected Trunk adn Hip Muscles During aSquat Left: Effect of varying the Lumbar Posture. Spine, 19(6), 687-695.[PubMed]

166. Valle, X., Tol, J. L., Hamilton, B., Rodas, G., Malliaras, P., Malliaropoulos, N.,


& Jardi, J. (2015). Hamstring Muscle Injuries, a Rehabilitation ProtocolPurpose. Asian Journal of Sports Medicine, 6(4).[PubMed]

167. Van der Horst, N., Smits, D. W., Petersen, J., Goedhart, E. A., & Backx, F. J.(2015). The Preventive Effect of the Nordic Hamstring Exercise onHamstring Injuries in Amateur Soccer Players A Randomized ControlledTrial. The American journal of sports medicine.[PubMed]

168. Van der Made, A. D., Wieldraaijer, T., Kerkhoffs, G. M., Kleipool, R. P.,Engebretsen, L., van Dijk, C. N., & Golanó, P. (2013). The hamstring musclecomplex. Knee Surgery, Sports Traumatology, Arthroscopy, 1-8.[PubMed]

169. Vigotsky, A. D., Harper, E. N., Ryan, D. R., & Contreras, B. (2015). Effects ofload on good morning kinematics and EMG activity. PeerJ, 2, e708.[PubMed]

170. Wakahara, T., Miyamoto, N., Sugisaki, N., Murata, K., Kanehisa, H.,Kawakami, Y., Fukunaga, T. & Yanai, T. (2012). Association betweenregional differences in muscle activation in one session of resistanceexercise and in muscle hypertrophy after resistance training. EuropeanJournal of Applied Physiology, 112(4), 1569-1576.[PubMed]

171. Ward, S. R., Eng, C. M., & Smallwood, L. H. (2009). Are currentmeasurements of lower extremity muscle architecture accurate?. Clinicalorthopaedics and related research, 467(4), 1074-1082.[PubMed]

172. Wickiewicz, T. L., Roy, R. R., Powell, P. L., & Edgerton, V. R. (1983). Musclearchitecture of the human lower limb. Clinical orthopaedics and relatedresearch, 179, 275-283.[PubMed]

173. Woodley, S. J., & Mercer, S. R. (2005). Hamstring muscles: architecture andinnervation. Cells tissues organs, 179(3), 125-141.[PubMed]

174. Woods, C., Hawkins, R. D., Maltby, S., Hulse, M., Thomas, A., & Hodson, A.(2004). The Football Association Medical Research Programme: an audit ofinjuries in professional football—analysis of hamstring injuries. BritishJournal of Sports Medicine, 38(1), 36-41.[PubMed]

175. Worrell, T. W., Perrin, D. H., Gansneder, B. M., & Gieck, J. H. (1991).Comparison of lsokinetic Strength and Flexibility Measures BetweenHamstring Injured and Noninjured Athletes. Journal of Orthopaedic &Sports Physical Therapy, 13(3), 118-125.[PubMed]

176. Worrell, T. W., Crisp, E., & LaRosa, C. (1998). Electromyographic reliabilityand analysis of selected lower extremity muscles during lateral step-upconditions. Journal of Athletic Training, 33(2), 156.[PubMed]


177. Worrell, T. W., Karst, G., Adamczyk, D., Moore, R., Stanley, C., Steimel, B., &Steimel, S. (2001). Influence of joint position on electromyographic andtorque generation during maximal voluntary isometric contractions of thehamstrings and gluteus maximus muscles. The Journal of Orthopaedic andSports Physical Therapy, 31(12), 730.[PubMed]

178. Wretenberg, P., Németh, G., Lamontagne, M., & Lundin, B. (1996). Passiveknee muscle moment arms measured in vivo with MRI. ClinicalBiomechanics, 11(8), 439-446.[PubMed]

179. Wright, G. A., Delong, T. H., & Gehlsen, G. (1999). ElectromyographicActivity of the Hamstrings During Performance of the Leg Curl, Stiff-LegDeadlift, and Back Squat Movements. Journal of Strength and ConditioningResearch, 13(2), 168-174.[Citation]

180. Wulf, G. (2007). Attentional focus and motor learning: A review of 10 yearsof research. E-Journal Bewegung und Training, 1(2-3), 1-11.[Citation]

181. Yamashita, N. (1988). EMG activities in mono-and bi-articular thighmuscles in combined hip and knee extension. European Journal of AppliedPhysiology and Occupational Physiology, 58(3), 274-277.[PubMed]

182. Yavuz, H. U., Erdağ, D., Amca, A. M., & Aritan, S. (2015). Kinematic andEMG activities during front and back squat variations in maximum loads.Journal of sports sciences, (ahead-of-print), 1-9.[Citation]

183. Yeung, S. S., Suen, A. M., & Yeung, E. W. (2009). A prospective cohortstudy of hamstring injuries in competitive sprinters: preseason muscleimbalance as a possible risk factor. British journal of sports medicine,43(8), 589-594.[PubMed]

184. Youdas, J. W., Hollman, J. H., Hitchcock, J. R., Hoyme, G. J., & Johnsen, J.J. (2007). Comparison of hamstring and quadriceps femoriselectromyographic activity between men and women during a single-limbsquat on both a stable and labile surface. The Journal of Strength &Conditioning Research, 21(1), 105-111.[PubMed]

185. Youdas, J. W., Hartman, J. P., Murphy, B. A., Rundle, A. M., Ugorowski, J.M., & Hollman, J. H. (2015). Magnitudes of muscle activation of spinestabilizers, gluteals, and hamstrings during supine bridge to neutralposition. Physiotherapy theory and practice, (0), 1-10.[PubMed]

186. Zebis, M. K., Skotte, J., Andersen, C. H., Mortensen, P., Petersen, M. H.,Viskær, T. C., & Andersen, L. L. (2013). Kettlebell swing targetssemitendinosus and supine leg curl targets biceps femoris: an EMG study


with rehabilitation implications. British Journal of Sports Medicine,47(18):1192-8.[PubMed]

187. Zeller, B. L., McCrory, J. L., Kibler, W. B., & Uhl, T. L. (2003). Differences inKinematics and Electromyographic Activity Between Men and Womenduring the Single-Legged Squat. The American Journal of Sports Medicine,31(3), 449-456.[PubMed]

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