Mechanical Eccentric Loading Changes Tendons
Shortened Achilles' tendons can be painful and reduce an athlete's performance. Stretching may help but studies show that eccentric training works very well. During an eccentric muscle contraction, the muscle and its tendon starts in a shortened position and then lengthen as the body part moves.
It's not clear why this type of training works so well for Achilles' tendinopathy. Tendinopathy refers to any injury of the tendon. This may include microtears and inflammation. In this study, researchers from Belgium and New Zealand team up together to understand the reason why eccentric mechanical loading is a successful rehab technique for this problem.
Two groups of healthy adults were included. All subjects were recreational athletes. One group followed an eccentric training program focused on the calf muscles for six weeks. Heel drop exercises were done daily. The second was a control group. They did not do the exercises or any special program.
The results were measured by comparing ankle motion and Achilles' tendon stiffness before and after the program. Ultrasound and dynamometer measurements were also used. These tools showed how much stretch occurred within the tendon structure.
The authors report that dorsiflexion ankle motion was increased in the eccentric-training group. Dorsiflexion is the movement that decreases the angle between the foot and the leg. During dorsiflexion, the toes are moved toward the knee. It is the opposite motion to plantar flexion (pointing the toes).
At the same time, the passive resistance torque of the plantar flexor muscles was decreased. Torque refers to the force on the ankle by the Achilles' tendon. Increased torque keeps the ankle from full dorsiflexion.
Decreased torque increases the ankle motion. Along with reduced torque, decreased stiffness and increased relaxation of the muscle and tendon fibers allow for greater dorsiflexion.
These findings support the idea that structural changes occur in the plantar flexor muscles as a result of the eccentric exercise program. A similar exercise program may be helpful in preventing Achilles' tendinopathy. More study is needed to confirm this idea.
Nele Nathalie Mahieu, PhD, et al. Effect of Eccentric Training on the Plantar Flexor Muscle-Tendon Tissue Properties. In Medicine & Science in Sports & Exercise. January 2008. Vol. 40. No. 1. Pp. 117-123.