The length-tension relationship is an important consideration in Achilles tendinopathy rehabilitation. The Achilles rehab programs is different to the patellar tendon in that people tend to exercise into end of range, unless they have insertional pain and in that case only to neutral or 90 degrees foot to leg position

Given it does go into end of range and the eccentric component is isolated it is likely that one of the potential mechanisms is increased muscle compliance, ie less muscle resistance to stretch. In a 2008 study Mahieu and co-workers showed that calf compliance increased after 6 weeks of Alfredson type eccentric calf muscle training. This study was among normals and eccentric training was not loaded but it is possible that there is a similar effect among patients performing the Afredson program, and this may explain some of the benefit.

Another related muscle-tendon unit property that may change is length-tension relationship (see figure). It is well known from the work of Proske (see Brockett study) and others that joint range were peak force can be produced increased (ie the length tension curve shift to the right) following eccentric muscle training. What is not clear is whether this is specifically related to contraction type or the range through which the muscle is exercises, as similar effects have been shown with concentric muscle training (Blazevich 2007).

The clinical significance of all of this is that change in these muscle-tendon properties (compliance, length-tension) may be important mechanisms in Achilles tendinopathy eccentric muscle training, but as yet this outcome has not been investigated in clinical studies. Clinically, patients who are weaker in end of range may benefit more from exercise into end of range.

 

References

Mahieu NN, McNair P, Cools A, et al. Effect of eccentric training on the plantar flexor muscle-tendon tissue properties. Med Sci Sports Exerc 2008; 40:117-23

Brockett CL, Morgan DL, Proske U. Human hamstring muscles adapt to eccentric exercise by changing optimum length. Medicine & Science in Sports & Exercise 2001; 33:783-90

Blazevich AJ, Cannavan D, Coleman DR, et al. Influence of concentric and eccentric resistance training on architectural adaptation in human quadriceps muscles. J Appl Physiol 2007; 103:1565-75