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The Myth of Triple Extension Applied Jump Mechanics

By Matt Brughelli

Two major factors that determine athletic ability are: running ability and jumping ability. If you can run faster and jump higher you’ll become a better athlete. The bottom line is “Speed Kills”. Any coach will tell you this, regardless of the sport. As coaches and athletes we need to find ways of improving sprinting and jumping performance. So where do we start? The first step is to examine the mechanics of each movement. There is some very good literature (scientific studies) on sprinting and jumping mechanics that began in the late 80’s. A team out of Free University (Amsterdam), which is led by Maarten Bobbert, has make huge contributions in this area. What can we learn from studying the mechanics of sprinting and jumping? It basically all comes down to discovering which exercises and methods are better than others. When you train sprinting and jumping movements, you can either: 1) add resistance – and thus attempt to develop more force at the same speed, or 2) take away resistance – and thus attempt to increase the speed of movement at the same force levels. Training should involve both of these techniques. Ultimately you are trying to do 3 things: increase peak force, increase the rate of force development, and increase the speed of movement.

There are a few things we’ve learned from the literature, some more controversial than others. We know that we cannot significantly increase sprint ability by simply jumping. And we cannot significantly

increase jump ability by simply sprinting. Resistance either needs to be added or taken away to get a cross-over effect. However, by adding resistance when sprinting (vests, cords, chutes) it is possible that sprint mechanics will be altered and performance will suffer. Also, taking away resistance during sprinting (over-speed, downhill) can possibly alter sprint mechanics and decrease performance. Thus sprint training may not be the best approach to improving athletic ability. On the other hand, jump mechanics will not be altered if you add or take away resistance. In fact, they are more likely to be improved. This is where the literature on jump mechanics is so important. Jump training improves both sprint and jump ability.

The final reason you need to know about jump mechanics is to avoid making mistakes. The greatest example of this is the mythical, over-simplified idea of “Triple Extension”. That’s right, triple extension is a myth. For some reason every textbook, training manual, and article define triple extension as “the simultaneous extension/lengthening of the hips, knees, and ankles”. Sorry guys, this is not how it works. The hips, knees, and ankles do not extend simultaneously with jumping movements, ever! The hips extend first, followed by the knees, which are followed by the ankles, then the toes. This article will explain how and why the joints extend in a sequence, explain jump mechanics in detail, and explain why this is important to know. I will also give implications for developing exercises and evaluating potential athletes. Optimal Pattern Jumping patterns do not change between different types of people. Despite differences in age, skill level, gender, or ability, we all jump the same way. Even if jumps are initiated with different levels of muscle activation, or from different starting positions a similar stereotypical pattern of extending joints will occur (1,2). This optimal pattern involves the extension of joints in a proximal to distal sequence (table 1). Researches have been struggling with this concept for many years. The jumping movement involves many joints in different planes, which increases the degrees of freedom and thus the chance for error. Somehow our bodies have learned to coordinate the timing, velocities, forces, and movements on every attempt. Of course the elite athlete can jump much higher and create more force than the average athlete, but the patterns are the same. Table 1. P/D Sequence of Extending Joints Step 1 Hip Extension Step 2 Knee Extension Step 3 Ankle Extension Step 4 Toe Extension The P/D sequence of extending joints allows power to be transferred between joints. The hips create and transfer power to the knees, which do the same for the ankles, and then to the toes. So why don’t our joints extend simultaneously as triple extension is defined? A few reasons, simultaneous extension of the hips, knees, and ankles would increase the chance of injury and decrease performance. When a joint is fully

extended, the velocity at that joint needs to be zero. Otherwise damage may occur when the joint is hyper-extended. In this case, the muscles would be inactivated early to prevent injury and therefore performance would suffer. From an applied standpoint, full extension would never be reached if our joints extended simultaneously. Muscle models of jumping have shown that when joints extended simultaneously a pre-mature take off will occur (3). Jumping involves accelerating the bodies’ center of mass (CM) in a vertical direction. If the acceleration of the bodies CM can surpass the acceleration due to gravity (AoG), a takeoff will occur. If the acceleration of the bodies CM does not surpass the AoG, takeoff will not occur. This is why we don’t leave the ground when we stand up. The instant the CM is equal to the AoG is the instant takeoff occurs. During jumping, as the segments rotate around their joints a centripetal acceleration is created. This centripetal acceleration acts in a downward direction and counters the upward, vertical acceleration of the bodies CM. If the segments all rotated at the same time, the centripetal acceleration becomes great and a takeoff will occur with the joints in a flexed position (4). Reaching full extension during jumping while preventing injury is a major challenge in jumping and can only be accomplished with the P/D sequence of extending joints. The P/D sequence of extending joints allows the segments to rotate in a sequence, thus keeping the bodies CM raised. In the P/D sequence each joint will raise the acceleration of CM, and the extension of each subsequent joint will keep the acceleration of CM above the acceleration of gravity until the last joint (toes) finishes extending. This allows the muscles to produce the greatest amount of work and power, and the transfer of power between joints. Power Transfer This article will focus of how power is transferred between joints. Power is the product of force, distance, and time. Power can be increased with either increasing the distance a segment (trunk, thigh, lower leg) travels, or the force created by the muscles. Decreasing the amount of time is takes to perform a movement can also increase power. With jumping and the P/D sequence, as one joint increases the distance traveled by its segments (increases power) and another joint simultaneously decreases the distance its segments travel (decreases power), power is thought to be transferred between the joints. As the jump is initiated, the hip joint begins to extend and creates power. Then the hip joint slows its extension as the knee joint begins its extension, and so on down to the toes. So, as the extension of the hip slows, its segments travel a shorter distance in a larger amount of time. And, as the extension of the knees increases, its segments travel a larger distance in a shorter amount of time. Think of the example of an isometric contraction (no movement of the joint), the segments do not travel any distance, thus power is greatly reduced. As each subsequent joint slows its extension, the power output is reduced as they come closer to being an isometric contraction. The P/D sequence involves a series of extending joints increasing and then decreasing their velocities and power outputs. Bi-Articular Muscles Many researches have been fascinated by the unique actions of the bi-articulatar muscles. Bi-articular muscles (Bi-Mus) cross two joints and have different actions at the separate joints. The hamstring muscle is a Bi-Mus that attaches at the pelvis and inserts below the knee (table 2). Table 2. Bi Articular Muscles

Muscle Actions Actions Hamstrings Hip Extension Knee Flexion Rectus Femoris Hip Flexion Knee ExtensionGastrocnemius Knee Flexion Ankle Extension The actions of the hamstring are to extend the hip and to flex the knee. In many athletic movements the hamstring will be stretched with knee extension and simultaneously shortened with hip extension (jumping,

running, cleans). The opposite will occur with landing and thus, in both examples, the length of the Bi-Mus remains relatively (to the mono-articulate muscles) unchanged (5). The P/D sequence and power transfer can only occur with the unique actions of the Bi-Mus. The Mono-articular muscles (Mono-Mus) cross only one joint and are only involved in generating positive work (table 3). Table 3. Mono Articulate MusclesMuscle Action Gluteals Hip Extension Quadriceps Knee Extension Soleus Ankle Extension We will now see how the Bi-Mus initiate the jump from a static position and how they are involved in tranferring power between joints. As the jump is initiated from the bottom position, the bodies CM needs to travel in a forward and upward direction. If either the knee or ankle joint were to extend first, the CM would travel in a backward and upward direction. Only with the hips extending first can a forward displacement of the CM occur (2). The hamstring muscles are ideally suited for this task. As the hamstrings contract (hip extension and knee flexion) the hip joint extends while the knee joint is held in a flexed position. Next, hip extension will need to be decreased, while knee extension is increased. The Rectus Femorus (hip flexion and knee extension) is activated for this task. The RF has the role of decreasing the extension of the hip and increasing extension of the knee. Then, the Gastrocnemius (knee flexion and ankle extension) slows extension of the knee while increasing the extension of the ankle. So now it is easy to see how power is transferred between joints. As the jump is initiated power is first generated at the hip joint, then transferred to the knee, then to the ankle and finally the toes. This sequence prevents a pre-mature take off, allows for maximum work and power to be produced by the muscles, and prevents injury at the joints. Any alterations to this P/D sequence will lead to less than optimal performance. Bobberts 01, has shown than by initiating the jump with the soleus muscle first (muscle models), jump height and efficiency will suffer. This is one reason coaches advocate training movements as opposed to training muscles. Strength without motor control will not improve performance. Heavy Segments and Implications The design of the musuloskeletal system is often modeled with different segments. The biggest and heaviest segments are placed furthest from the point of contact (the ground). This design allows for the maximum amount of power to be produced and maximizes efficiency. In a model simulation, by placing the heaviest segments closest to the ground jump height and efficiency was reduced. So why do we need to know this and how does it affect us? Two reasons, this knowledge can help us evaluate potential athletes and develop more effective exercises. When an athlete performs a vertical jump, the goal is to raise their CM as high as possible. Genetics plays a role in determining the height of an athletes CM. An athlete with a higher resting CM will have an easier time raising their CM and will have a higher end position of their CM, thus will jump higher. Imagine the female body vs. the male body. The female body has more weight distributed at the hips, the male body has more weight on the upper body (shoulders). The male body inherently has a higher CM than the female body. These differences are apparent between athletes of the same gender as well. Lets compare a high jumper (Athletes 2&4) with a sprinter (Athletes 1&3). The high jumper has narrow hips and a narrow waistline with little difference between the two circumferences. The high jumper also has relatively much wider shoulders, thus their CM

will be very high. The sprinter has wider hips, well-developed thighs and glutes, and a narrow waistline. The sprinter has more weight distributed at the lower body and thus has a lower CM. With sprinting, the goal is to keep the CM low and traveling in a horizontal direction.

Athlete 1 (Low CM) Athlete 2 (High CM)

Athlete 3 (Low CM) Athlete 4 (High CM) *Athletes 1& 3 (sprinters) have more weight distributed around the legs and hips, with less around the waist. Notice how the shoulders are not that much wider than the hips. These athletes have a lowered CM. *Athletes 2&4 (high jumpers) have more weight distributed around the shoulders and upper body. They are very narrow hips and waist. Notice how the shoulders are much wider than their hips. These athletes have a raised CM.

So, when given a large number of athletes, by evaluating body types it is possible to predict which athletes will be responders to either jump training or sprint training. Of course the goal of most sports is to improve both jumping and sprinting and there are many more factors that determine how fast an athlete will run, or how high one will jump. Most athletes will be a combination of these two types, but there are the extremes out there. This is not an exact science, but in my experience the athletes with the first body type are the super responders in the vertical jump measures and the athletes with the second body type are the super responders in the short sprint and agility measures. When developing exercises for an athlete, and understanding of jump mechanics is very important. The distribution of resistance can make a big difference in the squat jump, as well as in most sprinting and jumping movements. Currently, the common sites of added resistance for squat jumps are on the hips (weighted shorts), ankles, or shoulders (vest, or barbells), or holding dumbbells. With the ankle weights, since the hips and knees extend before the ankles, the resistance won’t be felt until too late. With the weighted shorts, as the ankle bends down the extra weight at the hips will create an extra downward and backwards force. To counter this force the muscles that affect knee and ankle extension may be activated early, and thus throw off the P/D sequence of extension. In my opinion, weighted jumps should be performed with resistance on the shoulders or held with the hands. Other modes of training (heavy, Olympic style, plyometrics), are not effected by mass distribution as much as weighted jumps. I feel that weighted jumps should be used for training athletes any sport. References:

1) Jacobs. Journal of Biomechanics, 29(4): 512, 1996 2) Bobbert. Med Sci Sports Exerc, 31(2): 303, 1999 3) Bobbert. Exerc Sport Sci Re, 29(3): 95, 2001 4) Bobbert. Journal of Biomechanics, 21: 249, 1988 5) Prilutsky. Journal of Biomechanics, 27(1): 25, 1994