Tendon stiffness from exercise, is it really bad?

Today I was doing more research into tendon adaptation and performance and ran across the abstract below.   Without reading too much into the results, this study points out the contribution of the triceps surae (basically the calf) tendon/aponeurosis (I will just say tendon or tendons for the balance of this writing) to locomotion.

I will admit that for many years I have not really understood the full extent of the contribution tendons make to human movement.  I, of course, knew that they anchor the muscles to bone thus allowing movement.  What I did not realize until a few years ago, and even more so until very recently, was their true contribution to force production.  In other words, I used to envision them as essentially passive conduits of the force created by the contracting muscles.  As I now know, nothing could be further from the truth.

Tendons are significant contributors to expressed force production.  They enhance total force output and make movement more economic by reducing the force requirements of the muscle.

Tendons do not produce force; rather they store and release it through their elastic properties.

This brings me back to a video I recently made with which I hoped to shine a clarifying light on the current mobility/flexibility craze seen in the strength training and athletic world.  In short, increased tendon stiffness from training (especially strength training) is nearly universally viewed these days as a negative adaptation.  People are told to “correct” it.  What very few realize is that the increased stiffness is actually a POSITIVE adaptation assuming it does not get to the point it impedes one’s range of motion for a sport specific task etc.

The increased tendon stiffness, in real world application, results in a greater storage and release of potential energy which directly contributes to work being performed.  An example would be when a lifter is bench pressing.  Increased tendon stiffness in the pectoralis major will result in a greater maximum pressing ability and greater strength endurance with lighter loads as the elastic component of the tendons is able to store and release a greater amount of force.

So, the take home message is once again that increased tendon stiffness from training is ONLY a negative if it impedes your ability to complete a full range of motion for your given sport or form of exercise. It is, otherwise, a BENEFICIAL adaptation.

Exercise-induced changes in triceps surae tendon stiffness and muscle strength affect running economy in humans.
Albracht K, Arampatzis A.
Institute of Biomechanics and Orthopaedics, German Sport University, Cologne, Germany, albracht@dshs-koeln.de.
The purpose of the present study was to investigate whether increased tendon-aponeurosis stiffness and contractile strength of the triceps surae (TS) muscle-tendon units induced by resistance training would affect running economy. Therefore, an exercise group (EG, n = 13) performed a 14-week exercise program, while the control group (CG, n = 13) did not change their training. Maximum isometric voluntary contractile strength and TS tendon-aponeurosis stiffness, running kinematics and fascicle length of the gastrocnemius medialis (GM) muscle during running were analyzed. Furthermore, running economy was determined by measuring the rate of oxygen consumption at two running velocities (3.0, 3.5 ms(-1)). The intervention resulted in a ∼7 % increase in maximum plantarflexion muscle strength and a ∼16 % increase in TS tendon-aponeurosis stiffness. The EG showed a significant ∼4 % reduction in the rate of oxygen consumption and energy cost, indicating a significant increase in running economy, while the CG showed no changes. Neither kinematics nor fascicle length and elongation of the series-elastic element (SEE) during running were affected by the intervention. The unaffected SEE elongation of the GM during the stance phase of running, in spite of a higher tendon-aponeurosis stiffness, is indicative of greater energy storage and return and a redistribution of muscular output within the lower extremities while running after the intervention, which might explain the improved running economy.
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One Response to Tendon stiffness from exercise, is it really bad?

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