抄録
We investigated the effects of repeated eccentric exercise for rat medial gastrocnemius muscle on ankle joint stiffness and muscle connectin (titin) isoform composition (longer form, α-connectin; shorter form, β-connectin). Male Wistar rats were trained on a custom-made, isokinetic dynamometer (eccentric-exercise group, n = 6; sham-operated group, n = 6). The exercise session consisted of twenty eccentric contractions elicited by submaximal electric stimulations under anesthesia. The contracting muscle was forcibly lengthened by an isokinetic dorsi-flexion of the ankle joint (velocity, 30°/s; range of motion, 45°). Rats in eccentric-exercise group were trained every two days for 20 days (10 sessions in total). Static passive resistive torque (PRT) at ankle joint of 45° was used as a measure of the joint stiffness, and was determined before and after the experimental period. After 10 sessions of eccentric exercise, the wet weight of medial gastrocnemius muscle significantly increased (P < 0.05), whereas the static PRT significantly decreased (P < 0.05) in eccentric-exercise group, when compared to the sham-operated group. Myosin-ATPase staining showed a decrease in the number of type IIb/IId fibers (P < 0.001) and an increase in the number of type IIa fibers (P < 0.05). However, no significant difference was seen in the connectin (titin) isoform composition between eccentric-exercise group and sham-operated group, suggesting that the reduction in PRT was not due to change in resting mechanical properties of muscle fibers.
