title: Effects of eccentric exercise on joint stiffness and muscle connectin (titin) isoform in the rat hindlimb.
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, alpha-connectin; shorter form, beta-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 dorsi-flexion of the ankle joint (velocity, 30 degrees/s; range of motion, 45 degrees). 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 degrees 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.
authors.affiliation: Department of Life Sciences, Graduate School of Arts and Sciences, University of Tokyo, Meguro-ku, Tokyo, Japan 153-8902. cc47703@mail.ecc.u-tokyo.ac.jp
authors.forename: Eisuke
authors.initials: E
authors.lastname: Ochi
authors.forename: Koichi
authors.initials: K
authors.lastname: Nakazato
authors.forename: Naokata
authors.initials: N
authors.lastname: Ishii
mesh_terms: D000818:Animals; D000843:Ankle Joint / Q000502:physiology*; D064211:Connectin; D004558:Electric Stimulation; D006614:Hindlimb; D008297:Male; D009119:Muscle Contraction; D018656:Muscle Fibers, Fast-Twitch / Q000378:metabolism; D009124:Muscle Proteins / Q000378:metabolism*; D053580:Muscle Strength; D018482:Muscle, Skeletal / Q000033:anatomy & histology / Q000378:metabolism*; D009218:Myosins / Q000378:metabolism; D009929:Organ Size; D010805:Physical Conditioning, Animal; D020033:Protein Isoforms / Q000378:metabolism; D011494:Protein Kinases / Q000378:metabolism*; D016059:Range of Motion, Articular; D051381:Rats; D017208:Rats, Wistar; D013997:Time Factors; D019415:Torque
chemical_list: D064211:Connectin; D009124:Muscle Proteins; D020033:Protein Isoforms; D011494:Protein Kinases; D009218:Myosins