Changes in stiffness induced by hindlimb suspension in rat Achilles tendon

The aim of this study was to measure the effects of hindlimb suspension on mechanical properties of the rat Achilles tendon. Adult male Wistar rats we re randomly assigned to groups to be either suspended, or a control. After 21 days, Achilles tendons were removed for mechanical analysis. Classical t ests of tensile performance were made, and mechanical parameters were deriv ed from a stress-strain relationship. The tendons of animals that had been suspended presented values for maximal stress and tangent modulus which wer e 37.5% (P < 0.01) and 41% (P < 0.01), respectively, lower than the tendons of the central rats. In a similar way, the energy absorption capacity had largely decreased in animals that had been suspended. However, the maximal strain was similar in the two groups. These results showed that hindlimb su spension in rats has an important detrimental effect on mechanical properti es of the Achilles tendon. Differences in tendon stiffness obtained here, a long with those found by other investigators, encourage the hypothesis that homeostatic responses of soft tissues are due to changes in limb loadings. This study may be useful in providing a better understanding of the adapta tion of human skeletal muscle when exposed to microgravity.