Structural analysis of rat patellar tendon in response to resistance and endurance training.

Little is known about tendon adaptations induced by mechanical loading. Our goal was to evaluate the effects of two different exercise training protocols on adult rat patellar tendon. Ninety-six male Wistar rats were divided into a sedentary group (control), a resistance-trained group and an endurance-trained group. The examinations were performed after 15, 30 and 45 days of training and after 2 weeks of rest since training was stopped. The content of collagen fibers and the cell nuclei number were quantified on tendon cross sections. In order to assess the training effectiveness, we evaluated the heart/body weight ratio, which was higher in 45 day-trained rats than their controls (P<0.01), showing the presence of cardiac hypertrophy. An increase in the content of collagen fibers was observed in the 45 day-trained groups and after 2 weeks of rest in the endurance group. Moreover, both trained groups showed a decrease in cell nuclei number after 30 and 45 days of training and 2 weeks of rest (P<0.05). Endurance and resistance training induces a tendon tissue remodeling that depends on the length and intensity of workload rather than the training type. Further studies are necessary to evaluate whether these structural modifications are associated with an increase in the mechanical strength of tendon.