Abstract
Degenerative disorders of tendons present an enormous clinical challenge. They are extremely common, prone to recur and existing medical and surgical treatments are generally unsatisfactory. Recently eccentric, but not concentric, exercises have been shown to be highly effective in managing tendinopathy of the Achilles (and other) tendons. The mechanism for the efficacy of these exercises is unknown although it has been speculated that forces generated during eccentric loading are of a greater magnitude. Our objective was to determine the mechanism for the beneficial effect of eccentric exercise in Achilles tendinopathy. Seven healthy volunteers performed eccentric and concentric loading exercises for the Achilles tendon. Tendon force and length changes were determined using a combination of motion analysis, force plate data and real-time ultrasound. There was no significant difference in peak tendon force or tendon length change when comparing eccentric with concentric exercises. However, high-frequency oscillations in tendon force occurred in all subjects during eccentric exercises but were rare in concentric exercises (P < 0.0001). These oscillations provide a mechanism to explain the therapeutic benefit of eccentric loading in Achilles tendinopathy and parallels recent evidence from bone remodelling, where the frequency of the loading cycles is of more significance than the absolute magnitude of the force.
Highlights
The management of degenerative disorders of tendons is an enormous clinical challenge
By simultaneously determining Achilles tendon (AT) length and the force acting through the tendon during both concentric and eccentric loading exercises, we directly compared the physiological stimulus with the AT during the two exercises
For the concentric exercises peak force occurs at the start of the exercise, and for eccentric exercises peak force occurs at the end of the exercise
Summary
The management of degenerative disorders of tendons is an enormous clinical challenge. It was believed that tendons were fairly inert structures and rest or immobilization was suggested as a treatment. Over time the negative effects of rest and immobilization have become recognized and there has been a move towards early functional treatment [4, 5]. It is appreciated that chronic tendon disorders are predominantly degenerative in nature and anti-inflammatory strategies are largely ineffective [1, 6]. Various suggestions have been made to account for the pain in chronic tendinopathy. Histological assessment of chronic tendinopathy is devoid of inflammatory cells [7]. Why degenerative tendinopathy is only sometimes painful remains unknown
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