Effects of sprint and endurance training on passive stress-strain relation of fast- and slow-twitch skeletal muscle in Wistar rat.

Abstract

We investigated the effects of endurance and sprint training on the passive mechanical properties of fast-twitch (FT) and slow-twitch (ST) skeletal muscles. Eight-week-old male Wistar rats (n=18) were divided into three groups: control (C), sprint-trained (S) and endurance-trained (E). The trained animals exercised for 10 weeks on a treadmill. Under anaesthesia, Plantaris and Soleus muscles were deformed cyclically in vivo at 0.33 mm x s(-1) with length increments of 1 mm in successive cycles until rupture. The rupture of muscle occurs at belly. Stress-strain relation were constructed using the maximum stress and maximum strain in each cycle. The data were fitted to an S-shaped curve. The curve-fitting parameters for trained and untrained muscles showed significant statistical differences. Stress and strain at rupture and maximum deformation energy were statistically greater for trained ST muscles (both groups) than for the controls. The changes induced by the present training protocols were not significant in Plantaris. The above results suggest the plasticity of passive structure caused by activity-demands.