Core Training: Evidence Translating to Better …...Core Training: Evidence Translating to Better Performance and Injury Prevention Stuart McGill, PhD Spine Biomechanics, Department

Core Training: EvidenceTranslating to BetterPerformance and InjuryPreventionStuart McGill, PhDSpine Biomechanics, Department of Kinesiology, Faculty of Applied Health Sciences, University of Waterloo,Waterloo, Ontario, Canada

S U M M A R Y

THIS REVIEW ARTICLE RECOG-

NIZES THE UNIQUE FUNCTION OF

THE CORE MUSCULATURE. IN

MANY REAL LIFE ACTIVITIES,

THESE MUSCLES ACT TO STIFFEN

THE TORSO AND FUNCTION

PRIMARILY TO PREVENT MOTION.

THIS IS A FUNDAMENTALLY DIF-

FERENT FUNCTION FROM THOSE

MUSCLES OF THE LIMBS, WHICH

CREATE MOTION. BY STIFFENING

THE TORSO, POWER GENERATED

AT THE HIPS IS TRANSMITTED

MORE EFFECTIVELY BY THE CORE.

RECOGNIZING THIS UNIQUENESS,

IMPLICATIONS FOR EXERCISE

PROGRAM DESIGN ARE DIS-

CUSSED USING PROGRESSIONS

BEGINNING WITH CORRECTIVE

AND THERAPEUTIC EXERCISES

THROUGH STABILITY/MOBILITY,

ENDURANCE, STRENGTH AND

POWER STAGES, TO ASSIST THE

PERSONAL TRAINER WITH A

BROAD SPECTRUM OF CLIENTS.

INTRODUCTION

The well-trained core is essentialfor optimal performance andinjury prevention. This article

introduces several elements related tothe core to assist personal trainers indesigning the most appropriate

progressions for their clients. The coreis composed of the lumbar spine, themuscles of the abdominal wall, theback extensors, and quadratus lumbo-rum. Also included are the multijointmuscles, namely, latissimus dorsi andpsoas that pass through the core,linking it to the pelvis, legs, shoulders,and arms. Given the anatomic andbiomechanical synergy with the pelvis,the gluteal muscles may also be con-sidered to be essential components asprimary power generators (the synergyof these components is outlined else-where (36)).

The core musculature functions differ-ently than the limb musculature in thatcore muscles often cocontract, stiffeningthe torso such that all muscles becomesynergists—examples in a wide variety oftraining and athletic activities are pro-vided in Refs. (2,3,5,13,14,15,19,20,53,55).Thus, training the core effectively meanstraining it differently than the limbmuscles.

Evidence and common practice are notalways consistent in the training com-munity. For example, some believe thatrepeated spine flexion is a good methodto train the flexors (the rectus abdom-inis and the abdominal wall). Interest-ingly, these muscles are rarely used inthis way because they are more oftenused to brace while stopping motion.Thus, they more often act as stabilizersthan flexors. Furthermore, repeated

bending of the spinal discs is a potentinjury mechanism (10,61). Anotherexample of misdirected practice com-monly occurs when some trainers havetheir clients pull in their abdominals to‘‘activate their transverse abdominis’’ toenhance stability. First, this does nottarget the major stabilizers of the spinebecause studies that measure stabilityshow that the most important stabil-izers are task specific.

For example, sometimes the quadratuslumborum is most important, yet manytrainers neglect this muscle (19). Sec-ond, drawing the abdominals inwardreduces stability (57). Third, evidenceon transverse abdominis shows thatactivation disturbances may occur insome people with specific types of backdisorders, but that these same distur-bances are not unique to transverseabdominis because they occur in manymuscles (11,59). People are unable toactivate this muscle in isolation beyondvery low levels of contraction becauseit is designed to activate with internaloblique muscle for athletic tasks (18). Itwould appear that trainers who focuson this muscle are misdirected.

Other evidence shows how the coremakes the rest of the body morecapable. For example, in our work

KEY WORDS :

core; exercise; back pain

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quantifying the tasks of strongmantraining, we documented how the coreassisted hip function to allow thecompetitors to accomplish tasks thatthey did not have the hip strength toperform (53). Specifically, the quad-ratus lumborum assisted in pelviselevation to allow the swing leg tomake a step. This was the first evidencesuggesting that a strong core allowsstrength to radiate out peripherally tomore distant regions of the body.Similarly, in training, our recent work(58) demonstrated how an individualcan only bench press half of their bodyweight when standing—otherwise theywould push themselves over. Whilelaying, bench press performance wasprimarily governed by the chest andshoulder musculature, whereas stand-ing press performance was governedby core strength, particularly one-armpresses. Thus, the limiting factor instanding press ability was core strength.

The core, more often than not, func-tions to prevent motion rather thaninitiating it, which is contrary to theapproaches that many trainers employin designing exercise for their clients.Good technique in most sporting, anddaily living tasks demands that powerbe generated at the hips and trans-mitted through a stiffened core (37).Pushing, pulling, lifting, carrying, andtorsional exertions are enhanced usingthis basic technique of hip powergeneration but are compromised whenthe spine bends causing what is oftenreferred to as ‘‘energy leaks.’’ Interest-ingly, these task classifications greatlyassist the organization of programdesign (think of building exercises tofulfill a push, pull, lift, carry, and atorsional buttressing task rather thanspecific isolationist exercises for theabdominals, back extensors, latissimusdorsi, and the like).

As a contribution to this special issue,I thought about how best to assistincreasing the competency of trainers.But after writing 2 textbooks (25,35)based on our hundreds of scientificpublications, I feel as though I havealready said what is necessary andimportant in a cohesive story.

Thoughts are provided here for exer-cise professionals who deal with issuesrelated to the assessment and design oftherapeutic exercise for the core. Coretraining is of interest given the preva-lence of back pain among clients. Coretraining is associated with spine stabil-ity and instability that results from backdisorders. Evidence from the backdisorders’ literature shows that poormovement patterns can lead to backdisorders. In this way, trainers shouldconsider the quality of movementpatterns in all clients and by defaultshould consider beginning any exerciseprogram with corrective exercises.

Many trainers follow a ‘‘recipe’’ forassessment, corrective exercise, or per-formance training. Using this genericapproach ensures ‘‘average’’ results—some clients will improve and getbetter, but many will fail simplybecause the approach was above orbelow the optimum level necessary toaddress the deficit. The program andapproach principles introduced hereare based on principles intended toassist development of elite correctiveexercise and training specialists.

CONSIDER THE CAUSES OFBACK DISORDERS

Here is a disturbing fact: many of theback pain patients I see have beenexacerbated by poor training programsbecause the mechanism of injury wasunknowingly incorporated. The firststep in any exercise progression is toremove the cause of pain or potentialpain, namely, the perturbed motionand motor patterns. For example, theflexion intolerant back is very commonin today’s society (i.e., pain is producedafter repeated or prolonged back flex-ion). Giving this type of client stretchessuch as pulling the knees to the chestmay give the perception of relief(through the stimulation of erectorspinae muscle stretch receptors), butthis approach only guarantees morepain and stiffness the following daybecause the underlying tissues sustainmore cumulative damage.

Eliminating spine flexion, particularlyin the morning when the discs are

swollen from the osmotic superhydra-tion of the disc that occurs with bedrest, has been proven very effectivewith this type of client (60). Further-more, typically, when this client bendsto pick up a weight, they flex the spineadding to the cumulative trauma. Thisoften continues without correctionfrom the trainer. This is a missed oppor-tunity. Realize that the spine discs onlyhave so many numbers of bends beforethey damage (10). Keep the bends foressential tasks such as tying shoesrather than using them up in training.Many lifestyle and occupational exam-ples have been provided elsewhere (28)to guide the elimination of the cause ofa client’s back troubles; the trainer willfind that half of their initial effective-ness will be because of preventing thecause (i.e., a flawed movement pattern).This need not be so complicated. Con-sider the client who stands slouchedwhere the back muscles are chronicallycontracted to the point of chronicmuscle pain. The family doctor typicallyprescribes muscle relaxants, which fail torelax the muscle. The trainer addressesthe postural cause and corrects standingto effectively silence the muscles andremove the associated crushing loadfrom the spine (Figure 1) (32).

BUILDING THE SCIENTIFICFOUNDATION

Myths and controversies regardingspine function and injury mechanismsare common. Consider ‘‘the cause’’ ofback troubles, specifically the commonperception regarding common injurypathways in which the back is injuredfrom an ‘‘event.’’ Generally, statisticsare compiled from epidemiologicalapproaches, which ignore the largerole of cumulative trauma. Compensa-tion board data are often used, how-ever, and they ask clinicians to fill outreports and name the ‘‘event’’ thatcaused the ‘‘injury.’’ For example, ‘‘MrX lifted and twisted at the time that theinjury occurred.’’ Kinesiologists andtrainers know that twisting is differentfrom generating twisting torque, butvery few of the individuals filling outthe reports will know. So, was ittwisting torque that caused the injury?

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Core Training for Better Performance

Or, was it being twisted that caused theinjury? Furthermore, despite the injury/incident reporting system geared to thereporting of the ‘‘event’’ associatedwith the ‘‘injury,’’ very few back injuriesoccur this way.

Evidence of the process of disc herni-ation provides a proof of principle. Forexample, the damaging mechanismleading to herniation, or prolapse, isrepeated lumbar flexion requiring onlyvery modest concomitant compressiveloads (10). This trauma accumulateswith little indication to the futurepatient. With repeated flexion cycles,the annulus breaches layer by layerwith progressive delamination of thelayers (61). This allows gradual accu-mulation of nucleus material betweenthe delaminated layers. The location ofthe annulus breaches can be predictedby the direction of the bend. Specifi-cally, a left posterior lateral disc bulgewill more likely result if the spine isflexed with some additional rightlateral bend (1). Subsequent twistingleads circumferential rents in theannulus that tends to make McKenzieextension approaches for these clientsuseless or even exacerbating (23). Thisis critical information for the trainer,both in terms of prevention and in

treatment. Avoiding this specific direc-tional cause will lead to optimal thera-peutic exercise design together withelimination of activities in the patient’sdaily routine identified as replicatingthe cause.

Many training programs have theobjectives of strengthening muscleand increasing spine range of motion.This is problematic for some becausethose who have more motion in theirbacks have a greater risk of havingfuture back troubles (56). Strengthmay, or may not, help a particularindividual because strength withoutcontrol and endurance to repeatedlyexecute perfect form increases risk.Interestingly, the differences betweenmany ‘‘troubled backs’’ (the chronicback with recurrent episodes) andmatched asymptomatic controls per-forming the same jobs have beenshown to be variables other than backstrength or mobility. Rather deficits inmotion and motor patterns have beendocumented as being more critical andthus should be targets for therapeuticexercise.

For example, people with troubledbacks use their backs more. Generally,they walk, sit, stand, and lift using

mechanics that increase back loads.Many of them have stronger backsbut are less endurable than matchedasymptomatic controls (47). They tendto have more motion in their backs andless motion and load in their hips. Acommon aberrant motor pattern isknown as ‘‘gluteal amnesia’’ (27), whichmay be both a common consequenceof back troubles and possibly a cause ofthem as well. The general principlethat joint pain causes inhibition of theextensors and chronic facilitation of theflexors to the point of ‘‘tightness’’appears to be true with hip or backpain. Obviously, for this category ofclient, exercises to enhance the in-tegration of the gluteal muscles willenhance back function while alsosparing knees. Hip flexor mobility isalso needed (but special technique isneeded to separately target psoas fromiliacus) (Figure 2) (38). Optimal backexercise therapy results from theidentification of these clients withperturbed patterns followed by specificcorrective exercise—this precedes allother exercise progressions.

THE SCIENCE OF CORE STABILITY

Effective core/spine stabilizationapproaches must begin with a solid

Figure 1. (a) Poor standing posture causes constant spine load and chronic contracture of the erector spinae muscles causingmuscular pain. (b) One approach for correction is to externally rotate the arms about the shoulders (steering the thumbsout). (c) Correcting the posture with chin and shoulder retraction reduces the chronic muscle contraction reducing painand building training capacity.

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understanding of what stability is.From a spine perspective, it has littleto do with the ability to balance ona gym ball. This is simply the abilityto maintain the body in balance, whichis important but does not address theunstable spine. In fact, in many in-stances, the unstable spine is alsoflexion intolerant and with associatedintolerance to compression. Sitting onan exercise ball and performing move-ment exercises increases spine com-pression to a flexed spine (52). Thisretards progress—it is generally a poorchoice of back exercise until quite latein a therapeutic progression. Truespine stability is achieved with ‘‘bal-anced’’ stiffening from the entiremusculature, including the rectus ab-dominis and the abdominal wall;quadratus lumborum; latissimus dorsi;and the back extensors of longissimus,iliocostalis, and multifidus. Focusing on

a single muscle generally does notenhance stability but creates patternsthat when quantified result in lessstability (20). It is impossible to trainmuscles such as transverse abdominisor multifidus in isolation—people can-not activate just these muscles. Do notperform abdominal hollowing techni-ques because it reduces the potentialenergy of the column causing it to failat lower applied loads (39). Interest-ingly, a recent clinical trial (22) com-pared the efficacy of many of theexercises quantified and published inPhysical Therapy (24), with the sameexercises combined with specific trans-verse abdominis isolation (hollowingand the like). Adding the specifictransverse abdominis training reducedefficacy. Instead, the abdominal brace(contracting all abdominal muscles)enhances stability. Target contractionlevels for bracing and training

techniques are described (38). Finally,some provocative tests, such as a sheartest, will help reveal which classifica-tion of client is best suited for a stabi-lization approach (17).

It is also interesting to consider thestudies that have quantified trainingdevices, which claim to enhancespine/core stability. For example,Moreside et al. (54) quantified stabilitywhen using the ‘‘Bodyblade’’ (MadDogg Athletics, Venice, CA), which is aflexible foil that is shaken at a resonantfrequency. As with virtually all othertools, the technique determines theactual stability achieved. Poor bodyblade technique can actually reducestability, whereas good technique,where the core is locked into anisometric contraction to control mo-tion, enhances core stability. The roleof the trainer is to be aware of thisscience, its implication on technique,and devote their attention to exerciseform in the client.

TOLERANCE AND CAPACITY

Suppose a trainer wants to includea lifting pattern to challenge theposterior components of the core.They are wondering if a squat witha weighted bar would be better thanthe birddog exercise. The choice isassisted by determining the toleranceand capacity of the individual to ensurethat a given exercise dosage is matchedto the client. Each individual hasa loading tolerance which, when ex-ceeded, will cause pain and ultimatelytissue damage. For example, a clientmay tolerate a ‘‘birddog’’ extensionposture but not a ‘‘superman’’ exten-sion over a gym ball, which imposestwice the compressive load on thelumbar spine. For a more highlytrained person with a higher tolerancemay find ‘‘supermans’’ very appropri-ate. A person’s capacity is the cumula-tive work that he or she can performbefore pain or troubles begin.

For example, someone who can onlywalk 20 m before pain sets in has a lowcapacity. This kind of person will notbenefit from therapeutic exercise that isperformed 3 times per week; instead,

Figure 2. Lunging with the arm directed overhead helps to differentiate and targetpsoas from iliacus during hip flexor stretching. Hip extensor patterns aresimultaneously trained on the opposite side of the body. When this exerciseis performed as walking steps, holding the posture for 2 seconds andpulsing the arm upward through the core, then taking a step andrepeating, it becomes a facilitator and a good ‘‘warm-up’’ exercise.



he or she has a better chance with 3short sessions per day. Correctedwalking in 3 short sessions per day,never exceeding the current toleranceand capacity, is an alternate approachto building capacity. Typically, clientswill progress to 1 session per day astheir pain-free capacity grows and thenbe tolerant of a session with theirtrainers.

INTERPRETING CLIENTPRESENTATION

Our approach to client assessmentincorporates a strong biomechanicalfoundation and blends expertise fromvarious disciplines. First, an impressionis formed from the first meeting of theclient, their sitting posture, how theyrise from the chair, their initial gaitpattern, and so on. Then, a history istaken looking for possible candidateinjury mechanisms and perceived painexacerbators and relievers. Observationcontinues during some basic motionpatterns as the evaluation processproceeds delving further into themechanics and nature of the symp-toms. Then, provocative tests areperformed to identify motion andmotor patterns that are tolerated.Specifically, we include a range of

motions, postures, and loads. All in-formation is used to formulate theexercise progression plan starting withcorrective exercise and the startingdosage of tolerable therapeutic exer-cise. This process concludes withfunctional screens and tests that werechosen based on information obtainedin the preceding process—the assess-ment process is well documented (29).These results are used to substantiatesome speculation as to the existence ofperturbed motion and motor patternsand for considering exercise choice andrates of subsequent exercise progression.

Interpreting client presentationSpecific exercise programs for a clientwith back pain are derived from thefollowing process (it is assumed thatappropriate medical screening hastranspired):

1. Observe everything, starting withthe client rising from a chair.

2. History—link injury mechanisms,pain mechanisms with specific ac-tivities, and past exercise regimens.Of course, if ‘‘red flags’’ appear,make the appropriate referral.

3. Perform provocative tests—whatloads, postures, and motions exac-erbate, what relieve?

4. Perform movement screens andtests—Are there perturbed postural,motion, and motor patterns? Dothey move well in daily activitiessuch as getting out of a chair or upoff the floor? If not, the trainershould recognize corrective squat,and lunge training is needed beforeany loaded resistance progressions.

5. If the clinical picture is complex andbeyond your comfort zone, developa referral relationship with a compe-tent corrective exercise specialist.This is reciprocal and will serve youwell with more clients in the future.

AN EXAMPLE OF A PROVOCATIVETEST THAT IS HELPFUL

Provocative testing is a potent tool inthe assessment of back problems andis easily performed. A wide variety ofprovocation tests together with somecorrective techniques are in a DVD(see Ref. (34)) because the expertisegained by viewing the technique can-not be obtained from written text.Figure 3 (31) illustrates an example ofprovocative testing for compressive loadtolerance. This posture-modulated tol-erance test provides powerful informa-tion and can serve as a guide to avoiddamaging/exacerbating activity, and italso helps to design appropriate therapy.

More practical information can begleaned from simply asking whethera client has better and worse days inrelation to pain. Even though it seemsstraightforward, it cannot be stressedenough that if there are indeed betterand worse days, it means that someactivities help and others hurt. Findout what they are and eliminate theexacerbating elements. For example, ifprolonged sitting is not tolerated,avoidance of flexion by using a lumbarsupport will help, together with orga-nizing tasks to eliminate prolongedsitting. This is known as ‘‘spine hy-giene’’ and will build more capacity forthe client to work with you. Specificexercises designed to combat thecumulative stresses of sitting shouldthen be prescribed.

REDUCING THE RISK OF INJURY

No exercise professional can befully successful without removing the

Figure 3. An example of provocative testing. The patient compresses the spine bygrabbing the side edges of the seat and pulling up. When doing this withan upright back (a), the torso is stiffened with muscle activity. The test isthen repeated in a slouched posture (b); discomfort in this position ascompared with an upright back shows a lower tolerance when the spine isflexed (and a flexion intolerant patient). This reveals where the spinetolerance is highest, and therefore, a posture to begin therapeutic exercise(i.e., no spine flexion).


movement flaws that are the cause ofback troubles in clients throughout theday. Recommendations such as ‘‘whenlifting, bend the knees and keep theback straight’’ rarely address the realissue, despite their popularity. Fewpatients are able to use this strategyin their jobs; furthermore, this is oftennot the best strategy. For example, the‘‘golfers lift’’ is much more joint con-serving for repeated lifting of light loadsfrom the floor. Here, one leg is raisedbehind, the torso tilts forward about aflexed hip of the stance leg forming afulcrum. No spine or knee bendingoccurs. Another example illustrates thepoor choice of movement strategies fora particular task. For example, observethe client who transitions to laying onthe floor by using a deep squat—thisoverloads their back. Squatting may beappropriate for getting off a toilet orchair but not necessarily for droppingto the floor. Instead a lunge that doesnot bend the spinal discs may be amuch more appropriate choice. Again,this builds capacity for them to ac-complish more in their training sessionwith you (see Ref. (30) for full explana-tion and evidence for spine sparingguidelines). Although it is not theexpertise of this author, ‘‘core stability’’training has been shown to be effectivefor both preventing and rehabilitatingshoulders (21) and knees (16,55).

LINKING ANATOMY WITHFUNCTION

Consider the usual and popular ap-proach to train the abdominal wallmuscles by performing sit-ups or curl-ups over a gym ball for example. Butconsider the rectus abdominis wherethe contractile components are inter-rupted with transverse tendons givingthe ‘‘6 pack’’ look. The muscle is notdesigned for optimal length change butrather to function as a spring. Whyhave these transverse tendons in rectusabdominis? The reason is that whenthe abdominals contract, ‘‘hoopstresses’’ are formed by the obliquemuscles that would split the rectusapart (26). In addition to the spring-likearchitecture of the muscle, considerhow it is used. People rarely flex the ribcage to the pelvis shortening the rectusin sport or everyday activity. Ratherthey stiffen the wall and load the hipsor shoulders—if this is performedrapidly such as in a throw or move-ment direction change, the rectusfunctions as an elastic storage andrecovery device. When lifting weights,it stiffens to efficiently transmit thepower generated at the hips throughthe torso. Those individuals who doactively flex the torso (think of cricketbowlers and gymnasts) are the oneswho suffer with high rates of spinejoint damage and pain. Now, revisit the

common training approach of curlingthe torso over a gym ball that replicatesthe injury mechanics while not creat-ing the athleticism that enhancesperformance. This is a rather poorchoice of exercise for most situations.Yet many clients will expect that a gymball be used. Disguise your intentionswith these clients and retain the gymball, but change the exercise from aspine compromising curl-up to a plankwhere the elbows are placed on the ball.Now, perform a ‘‘stir the pot’’ motionto enhance the torso/abdominal springand spare the spine—this is often a muchsuperior exercise for most people (seeFigure 4) (41).

DESIGNING STAGED COREEXERCISE—BIOMECHANICS ANDCLINICAL PRACTICE

Exercise progression is a staged pro-cess. Several sources are available(30,40) that expand on the manyconsiderations and techniques to honeclinical skills at each stage some ofwhich are listed below.:

Stages of progressive exercise design:

1. Corrective and therapeutic exercise2. Groove appropriate and perfect

motion and motor patterns3. Build whole-body and joint stability

(mobility at some joints such as thehips and stability through the lum-bar/core region)

Figure 4. (a) Curl-up over a gym ball motions stresses the discs, mimics a potent disc injury mechanism, and unwisely uses pain-freetraining capacity. (b) The ‘‘stir the pot’’ exercise spares the painful discs of motion and builds abdominal athleticism.



4. Increase enduranceFor occupational/athletic clients:5. Build strength6. Develop speed, power, and agilityThe first stage of designing the appro-priate corrective exercise emanatesfrom the identification of any per-turbed motion and motor patterns.Every exercise is considered withinthe working diagnostic hypothesissuch that the first time the exercise isperformed, it is considered a provoca-tion test. If it is tolerated, the clientproceeds. If it is not tolerated, thetechnique is reexamined and adjustedand/or a more tolerable variation istried—see Ref. (51) for some exampleswhere technique adjustments withstabilization exercise make them toler-ate much more challenge but withoutpain. Examples of corrective exerciseare introduced here, although manyare provided in Ref. (33).

For example, gluteal muscle activationretraining based primarily on theoriginal work of Janda has been honedin our laboratory (Figure 5). Thiscannot be accomplished with tradi-tional squat training (37). Chronic backpain tends to inhibit the glutealmuscles as hip extensors, and as a result,clients create hip extension using thehamstrings as a substituting pattern.Subsequent back extension overacti-vating the spine extensors creates un-necessary crushing loads. Gluteal

muscle reintegration helps to unloadthe back. Another critical concept forthis stage of exercise design is thattechnique ‘‘details’’ are important. It isnot a matter of client performing anexercise, but it is a matter of the clientperforming the exercise with perfec-tion. Exercise form, subtle maneuversto eliminate pain, pacing, duration, andother coconsiderations are all ex-tremely important (51). The next stagein the progressive algorithm is toencode movement and motor patternsto ensure stability. Stability is consid-ered at 2 levels—both joint stability (inthis case spine/core stability) andwhole-body stability. Quantificationof stability proves that these 2 objec-tives are fundamentally different andneed 2 different exercise approaches.

Our observation is that the 2 types ofstability are often confused in theclinic/gym. Variations of our ‘‘Big 3’’stabilization exercises (modified curl-up, side bridge, and quadruped bird-dog) have been quantified and selectedfor their ability to ensure sufficientspine stability and optimal motorpatterns; they spare the spine of manyinjury mechanisms and pain exacerba-tors and are designed to build muscleendurance (see Figures 6–9) (49).Then, specific muscle group enduranceis enhanced. Spine stability requiresthat the musculature be cocontractedfor substantial durations but at

relatively low levels of contraction.This is an endurance and motorcontrol challenge—not a strength chal-lenge. For many clients wanting toaccomplish tasks of daily living painfree, this is sufficient. In the precedingprogressions, of course, strength isenhanced as are specific patterns, suchas the ability to squat, push/pull, lunge,and so on. But strength is not specif-ically trained because this requiresoverload and elevated risk—this isreserved for performance training.Many people, whether they haveathletic objectives (such as wanting toplay golf ) or have demanding occupa-tions will fall into this category.

On the other hand, many clientsconfuse health objectives (minimizingpain, developing joint sparing strate-gies) with performance objectives(which require risk) and compromisetheir progress with specific strengthtraining too early in the progression.Many exercises typically prescribed topatients with low back pain are done sowithout the trainer having knowledgeof the spine load and associated muscleactivation levels. For this reason, wehave quantified exercises in this way(see Ref. (2,9,19,20)) to allow evidence-based decisions when planning optimalexercise progressions. Consider devel-oping progressions with some exer-cises shown in Figures 10 and 11(14,43).

Figure 5. Chronic back pain tends to cause people to use their hamstring muscles, instead of their gluteals to extend the hip. Thischanges patterns that increase spine load when squatting. Performing the back bridge, squeezing the gluteal muscles,and eliminating hamstrings helps to establish gluteal dominance during hip extension. Clinical cues are presented inMcGill (37)—one is shown here as the trainer palpates the hamstrings, and if they are active, the client is cued to push thefeet with knee extension and externally rotate the hips to ensure gluteal dominance.


CAVEATS FOR THERAPEUTIC/CORRECTIVE EXERCISE

1. Keep the duration of isometricexercises under 10 seconds andbuild endurance with repetitions(reps), not by increasing the dura-tion of the holds. Near infraredspectroscopy of the muscles showedthat this was the way to buildendurance without the musclescramping from oxygen starvationand acid buildup (48).

2. Use the Russian descending pyra-mid to design sets and reps to make

bigger initial gains in progress to-ward a pain-free back (see Ref. (42)).

3. Maintain impeccable form to en-hance available strength and main-tain the spine in its strongest (mosttolerable) posture.

CORE EXERCISE AS AN INJURYPREVENTION PROGRAM

The exercises that form the ‘‘Big 3’’noted in the previous section havebeen used by many occupational andsporting groups as part of an injuryprevention program.

For example Durall et al. (12) docu-mented how training the flexors, lateralmusculature, and extensors of the corewith the Big 3 in the preseason for10 weeks prevented any new back painincidents and controlled the pain inthose with a history of pain in apopulation of competitive collegiategymnasts. Gymnasts form a high-riskgroup for back pain/disorders. In-terestingly, similar exercises havebeen shown to prevent knee injuriesin female intercollegiate basketballplayers (16).

Figure 6. The ‘‘Big 3’’ stabilization exercises selected to create muscle patterns that ensure stability in a spine sparing way include thecurl-up (poor formwith too much spine flexion resulting in disc stress is shown in (a)) (better form shown in (b)). Althoughwe have quantified many variations and progressions, there are several cues for correct form. For example, during thecurl-up, try and remove any motion from the lumbar spine and the cervical spine. Progression included prebracing of theabdominal wall, elevating the elbows off the floor, and breathing, to name a few.

Figure 7. The beginner’s side bridge (a) is held for sets of 10-second contractions before more challenging progressions areattempted (b–d). Challenge is added by bridging from the feet and adding more mass to the bridge with arm placement.



TRAINING FOR PERFORMANCE

Training the back for performance (foreither athletic or occupational applica-tion) requires different approaches andobjectives than training to fulfill re-habilitation objectives. Some of thetechniques developed in our work withworld-class athletes are beyond thescope of this article and have beendetailed extensively elsewhere (35).These include the progressions fromestablishing motor control patternsonce the appropriate corrective exer-cise was performed, through stability,endurance, strength, speed, power, andagility. A note is needed here: power

(force 3 velocity) development in thespine is usually very risky. Instead,power is developed about the should-ers and hips to both increase perfor-mance and to minimize risk to thespine and related tissues. Specifically, ifthe force in the spine/core is high (e.g.,deadlifting), then the spine velocity(i.e., bending to create muscle lengthchange) must be low. If the spinevelocity is high (e.g., golf ), then themuscle force must be low (particularlywhen the spine is deviated). This iswhy the great golfers ‘‘pulse’’ when thespine is traveling through the neutralrange just before ball contact.

An interesting example is providedwith speed training. Many train speedby using resistance exercise forstrength gain. But speed technique,when measured, also usually requiressuperior rates of relaxation. This ap-parent paradox can be exemplified thisway. Consider the golf swing. Theinitiation of the downswing involvessome muscle contraction but too muchactually slows the swing. Speed comesfrom compliance and relaxation. Atthe instant just before ball contact, thefarthest ball hitters in the world thenundergo a full-body contraction thatcreates superstiffness throughout theentire linkage (45). Then, just asquickly the stiffening contraction isreleased to allow compliance, speed inthe swing follow through. This samecyclic interplay between relaxation forspeed and contraction for stiffness ismeasured in the best sprinters in theworld, the best strikers and kickers inmixed martial arts, the best lifters,and so on. Thus, the rate of musclecontraction is only important whenthe muscle can be released just asquickly—only a few in the world areable to do this.

These examples show why traditionalstrength training is usually a detrimentto performance. Techniques of ‘‘super-stiffness’’ used by strength athletes areimportant to understand when beingmindful of the lower functioning clientwho may be able to grasp some ofthese concepts and, for the first time,

Figure 8. The superman is a common extensor exercise but imposes double thecompressive load on a spine, which is hyperextended compared with themuch more tolerable birddog exercise. The capacity to train the supermanexercise is greatly compromised because pain is usually developed beforehigh levels of training can be achieved. Thus, it is rarely a good choice ofexercise.

Figure 9. During the birddog exercise, making a fist and cocontracting the arm and shoulder is a progression that enhances thecontraction levels in the upper erector spinae (a). This is a better exercise than the superman because the spine loads arelower; the muscle contraction level can be similar using the ‘‘squares’’ technique (b), and the spine is neutral, nothyperextended that lowers the load tolerance.


perhaps be able to rise from the toiletunassisted. In my consulting, I am oftenasked ‘‘How do you design a trainingprogram for a gymnast or wrester’’who must produce high force witha deviated spine posture? There areseveral potential strategies, and thechoice depends on the body type,injury history, current fitness level,and fitness goals of the athlete (toname a few). Sometimes, it is necessaryto avoid the injury mechanism (de-viated spine posture) in training andsave the ‘‘bending’’ for the competition.In this way, rigorous training can reachhigher levels without injury. An exam-ple of this approach can be found withcricket bowlers in Australia who havereduced injury rates and maintainedperformance by limiting the number ofbowling reps but still train otheractivities. These newest concepts arecompiled (40).

Eight essential components ofsuperstiffness

1. Use rapid contraction, then relaxationof muscle. Speed results from relaxa-tion for speed but also stiffness insome body regions (e.g., core) to but-tress the limb joints to initiate motionor enhance impact (of a golf club,hockey stick, fist, and the like) (50).

2. Tune the muscles. Storage and re-covery of elastic energy in the mus-cles require optimal stiffness, whichis tuned by the activation level.In the core, this is about 25% ofmaximum voluntary contractionfor many activities (4,8,5).

3. Enhance muscular binding andweaving. When several musclescontract together, they form a com-posite structure where the totalstiffness is higher than the sum ofthe individual contributing muscles(6). This is particularly important in

the abdominal wall formed by theinternal and external obliques andtransverse abdominis, highlightingthe need to contract them togetherin a bracing pattern (15).

4. Direct neuronal overflow. Strengthis enhanced at one joint by con-tractions at other joints—martialartists call this ‘‘eliminating the softspots.’’ Professional strongmen usethis to buttress weaker joints usingcore strength (53).

5. Eliminate energy leaks. Leaks arecaused when weaker joints areforced into eccentric contractionby stronger joints. For example,when jumping or changing runningdirection, the spine bending whenthe hip musculature rapidly con-tracts forms a loss of propulsion.The analogy ‘‘you can push a stonebut you cannot push a rope’’ exem-plifies this principle.

Figure 10. There are many progressions of exercises to stiffen and balance the anterior chain in a spine sparing way such asa staggered hand push-up (a) and the rollout (b).

Figure 11. Posterior chain progressions usually begin with pull-ups with the body stiffened.



6. Get through the sticking points. Thetechnique of ‘‘spreading the bar’’during the sticking point in thebench press is an example ofstiffening weaker joints.

7. Optimize the passive tissue connec-tive system. Stop inappropriate

passive stretching. Turn your ath-letes into Kangaroos. For example,reconsider if a runner should bestretched outside of their runningrange of motion. Many of the greatrunners use elasticity to spare theirmuscles or to potentiate them to

pulse with each stride. However, doconsider stretching to correct left/right asymmetries shown to be pre-dictive of future injury.

8. Create shock waves. Make theimpossible lifts possible by initiatinga shock wave with the hips that istransmitted through a stiff core toenhance lifts, throws, strikes, and thelike.

ORGANIZING THE LATE-STAGEPROGRAM

Finally, consider exercises such as thesquat. Interestingly, when we measureworld-class strongmen carrying weightor National Football League playersrunning planting the foot and cutting—-neither of these are exclusively trainedby the squat (see Ref. (44)). This isbecause these exercises do not train thequadratus lumborum and abdominalobliques, which are so necessary forthese tasks (53).

In contrast, spending less time undera bar squatting and redirecting some ofthis activity with asymmetric carriessuch as the farmers’ walk (or bottoms-up kettlebell carry—see Figure 12) (53)builds the athleticism needed for

Figure 12. The asymmetric kettlebell carry uniquely challenges the lateral musculature (quadratus lumborum and obliqueabdominal wall) in a way never possible with a squat. Yet this creates necessary ability for any person who runs and cuts,carries a load, and so on. The suitcase carry is another variation suitable for many advanced clients.

Figure 13. The lateral cable hold begins first with the hands close to the core and thenplaced further increases the twisting torque challenge (note no twist isallowed). Different levels and distance of the handles to the body modifiesthe challenge.


higher performance in these activitiesin a much more ‘‘spine friendly’’ way.The core is never a power generator asmeasuring the great athletes alwaysshows that the power is generated inthe hips and transmitted through thestiffened core. They use the torsomuscles as antimotion controllers,rarely motion generators (of course,there are exceptions for throwers andthe like, but the ones who create forcepulses with larger deviations in spineposture are the ones who injure first).Thus, the core musculature must bevery strong and capable of control tooptimize training of other body regionsand to facilitate best performance. Butpower training should be reserved forthe hips, not the core.

Once your client has excellent move-ment patterns and the appropriateblend of stiffening and mobility, theymay progress from corrective to per-formance enhancing exercise. Here,you may consider organizing trainingto include a push, pull, lift, carry, anda torsional buttressing task. The exactexercises are tuned to the client. Forexample, a push may be a push-up(14,49,51) or a one-armed cable pushwith a controlled and stiffened core.A pull may be a pull-up or a sleddrag (13). A carry may be a one-armed suitcase carry, which uniquelytrains the quadratus lumborum andlateral musculature, or a one-handed

bottoms-up kettlebell carry to enhancecore stiffening and the skill of steerageof strength through the linkage. A liftmay be a bar lift, kettlebell swing, orsnatch. A torsional task is not a twistbut a torsional challenge with no spinetwisting, such as a lateral cable holdwhere the arms are moved to differentpositions anteriorly (see Figure 13)(44). Finally, composite exercises maybe introduced for special situations thatrequire core strength, endurance, andcontrol but then assist the developmentof rapid force (see Figure 14) (46).

I am concerned that this short articleshortchanges the reader as it simplycannot convey the components neces-sary to be an elite trainer but, at least, itmay elevate awareness of some of theissues. I wish you a similarly enjoyablejourney as I have enjoyed in conduct-ing scientific studies and application ofthe principles to reduce pain andenhance performance.

Stuart McGill

is a professor ofspine biome-chanics at theUniversity ofWaterloo.

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Core Training: Evidence Translating to Better …...Core Training: Evidence Translating to Better Performance and Injury Prevention Stuart McGill, PhD Spine Biomechanics, Department