Training increases the in vivo strength of the lower leg: An experimental study in the rat

Abstract

The effect of training on bone strength has been investigated in rats. After 7 weeks of training, fracture strength of the tibia in vivo during muscle contraction and after resection was assessed. A group of 30 male rats 11 weeks old were randomized to exercise on a treadmill, sedentary (ordinary caging), and inactivity (right-sided patellar tendonectomy) groups. The training group ran on a treadmill with a 10% inclination for 1 h per day. After 4 weeks the animals in all groups were anesthetized and the right lower legs loaded in three-point ventral bending until fracture during electrically induced muscle contraction. The contralateral tibiae were tested correspondingly after resection. Ultimate bending moment, energy absorption to failure, bending stiffness, and deflection were assessed for the in vivo and the resected tibiae. The body weight gain was 37% higher in the sedentary and 57% higher in the inactive animals than in the training group (P < 0.05), indicating a physiologic effect of the training. In the dissected tibiae there were no significant group differences in any of the mechanical parameters, indicating that neither training nor inactivity changed the structural capacity of the tibiae per se. In contrast, there were significant differences between the in vivo tibiae. Ultimate bending moment was 12% higher in the training group than in the sedentary and inactive groups (P = 0.03). Energy absorption in the training group was 11 and 12% higher (not significant) than in the sedentary and inactivity groups, respectively. Bending stiffness was 7 and 17% higher in the training group compared to sedentary and inactivity groups (P = 0.018). These results indicate that muscle training protects against fracture in vivo.