Effects of jump training on passive mechanical stress and stiffness in rabbit skeletal muscle: role of collagen.

AIMS: This study evaluated the effect of a 15-week jump training period on mechanical parameters and collagen concentration of different muscle types in rabbits, at 50, 90 and 140 days of age. METHODS: Trained (T) animals were made to jump over obstacles in order to get food and water. The height of the obstacle was increased according to the animal's age. Control (C) animals were sedentary. Mechanical parameters (force, stress, stiffness) and collagen concentration were measured in Extensor Digitorum Longus (EDL), Rectus Femoris (RF), Semimembranosus Proprius (SMP) and Psoas Major (PSOAS). RESULTS: Both EDL and RF collagen concentrations and passive mechanical parameters increased between 50 and 140 days of age (P<0.001), whereas SMP and PSOAS collagen concentrations decreased (P<0.001). Soluble collagen concentration decreased similarly with age in all muscles and groups. Exercise training at 140 days induced a significant increase in force (EDL 20.4% and RF 15.3%, 0.01