Effects of Eccentric Exercise on Joint Stiffness and Muscle Connectin (Titin) Isoform in the Rat Hindlimb

Abstract

Abstract: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 20 eccentric contractions elicited by submaximal electric stimulations under anesthesia. The contracting muscle was forcibly lengthened by an isokinetic dorsiflexion of the ankle joint (velocity, 30°/s; range of motion, 45°). Rats in the eccentric-exercise group were trained every two days for 20 days (10 sessions in total). The static passive resistive torque (PRT) of 45° at the ankle joint 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 the 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 the eccentric-exercise group and the sham-operated group, suggesting that the reduction in PRT was not due to change in resting mechanical properties of muscle fibers.

Does weightlifting increase residual force enhancement?

“…This is in agreement with human studies examining no influence of a 15 week (Kyrolainen et al, 2005) or 8 week (McGuigan et al, 2003) training program including stretch-shortening cycles on titin isoform expression. The findings were additionally confirmed by an eccentric training study (20 days) using rat M. gastrocnemius medialis (Ochi et al, 2007). In contrast, differential expression of titin isoforms was observed in weight-and powerlifters in comparison to untrained non-athletic individuals .…”

Effect of Intermittent Low-Frequency Electrical Stimulation on the Rat Gastrocnemius Muscle

“…In the red portion, intramuscular glycogen was depleted in the HFS group, but clear staining was observed after LFS treatment. The HFS protocol in our experiment is essentially the same as that used by previous studies [18, 27, 28], and this condition led to a supramaximal activation of gastrocnemius muscles. On the other hand, we observed that the exerted force and work volume in the LFS group was about less than 50% of that in the HFS group.…”

Effects of repeated lengthening contractions on skeletal muscle adaptations in female rats

“…However, since collagen cross-link content did not increase in the Achilles tendons of trained rats, tendon stiffness would not be expected to change even with an increase in collagen content. Interestingly, however, evidence of a decrease in joint stiffness was observed in male rats trained with lengthening contractions over a 20-day period [33].…”