Eccentric rehabilitation exercise increases peritendinous type I collagen synthesis in humans with Achilles tendinosis

It has been shown that 12 weeks of eccentric heavy resistance training can reduce pain in runners suffering from chronic Achilles tendinosis, but the mechanism behind the effectiveness of this treatment is unknown. The present study investigates the local effect of an eccentric training regime on elite soccer players suffering from chronic Achilles tendinosis on the turnover of the peritendinous connective tissue. Twelve elite male soccer players, of whom six suffered from unilateral tendinosis and six were healthy controls, participated in this study. All participants performed 12 weeks of heavy-resistance eccentric training apart from their regular training and soccer activity. Before and after the training period the tissue concentration of indicators of collagen turnover was measured by the use of the microdialysis technique. After training, collagen synthesis was increased in the initially injured tendon (n=6; carboxyterminal propeptide of type I collagen (PICP): pre 3.9 +/- 2.5 mu g/L to post 19.7 +/- 5.4 mu g/L, P < 0.05). The collagen synthesis was unchanged in healthy tendons in response to training (n=6; PICP: pre 8.3 +/- 5.2 mu g/L to post 11.5 +/- 5.0 mu g/L, P > 0.05). Collagen degradation, measured as carboxyterminal telopeptide region of type I collagen (ICTP), was not affected by training neither in the injured nor in the healthy tendons. The clinical effect of the 12 weeks of eccentric training was determined by using a standardized loading procedure of the Achilles tendons showing a decrease in pain in all the chronic injured tendons (VAS before 44 +/- 9, after 13 +/- 9; P < 0.05), and all subjects were back playing soccer following the eccentric training regime. The present study demonstrates that chronically injured Achilles tendons respond to 12 weeks of eccentric training by increasing collagen synthesis rate. In contrast, the collagen metabolism in healthy control tendons seems not to be affected by eccentric training. These findings could indicate a relation between collagen metabolism and recovery from injury in human tendons.