Understanding how the muscle and tendon work together in movement is an integral part of program design. Depending on how you move, what you are doing and the speed at which you are doing it, the tendon/muscle may play a different role.

 

In short, the muscle and tendon act to compliment each other. When one is taught, the other is compliant (compliant meaning changes in length). These roles can flip when depending on the movement being performed. For example, during repeat pogo hops, the tendon becomes compliant and deforms upon ground contact, while the muscle becomes stiff and the fascicles do not go through much of a change. However, the opposite is true for lifting. When lifting weights, the tendon is taught and the muscle fascicle lengths go through large changes in length. Thus, depending on the type of exercise, the role of the tendon and the muscle may change.

Why Does This Matter?

 

Well, if we know that these roles differ during movements, we then can assume different movements will result in different types of tissue stresses and adaptations. Thus, we can probably say that doing too much of anything is not a good thing and a nice balance for that given sport is what we need to seek.

 

Lets look at hopping quickly. It has been shown that during repeat hops, the tendon acts as a spring and the muscle becomes stiff. However, as someone fatigues this is not quite the case. When the muscle can no longer stiffen with enough force, fascicle lengths change and the roles begin to slowly reverse. Knowing this, one can quickly see the importance of muscular strength. Fatigue reduces muscular strength, so if we extrapolate this to a more demanding movement with higher velocities, we can see that isometric strength at these positions is what keeps the muscle stiff and allows the tendon to act like a spring. From this, we can see why strength training is so important. However, at the same time we see that strength training is not the only part of the answer.

 

When doing the repetitive hops, the tendon needs to act like a spring, thus handle and transmit high forces. The tendon does not go under these same type of stressors when lifting weights, because the movements are too slow. Thus, in order to train the tendon action, we need to integrate hops, bounds and other plyometric work.

 

It might seem obvious “duh we need to lift weights and do plyometrics”, but if we understand how the muscle tendon unit works in dynamic action, we see that its first limiting factor is muscular strength. This explains why we need some base level of strength before handling such intense movements. Otherwise, the muscle will not be strong enough to remain stiff and the recoil energy will be lost.

However, what we also see is that regardless of how strong the muscle is, the tendon itself needs to be exposed to lower level plyometric demands in order to stress it in a proper fashion. By understanding the interaction of the muscle and the tendon, we see that there is a unique interplay between the two that demand a symbiotic relationship from both parties.

 

In short, the muscle and then tendon rely on each other. One cannot be deemed more important than the other. In order for one aspect of the unit to function at its highest level, the other aspect needs to be functional optimally as well. Thus, the importance of conjunctional development of both qualities is necessary for sport.