?Repetitive strain Injury and Aging: Is Resistance Training Strategy Helpful

Purpose: Repetitive strain injury (RSI) is accompanied by an increase in extracellular matrix (ECM), atrophy, and reduces the muscle power particularly in the elderly. Resistance training (RT) have potential positive effects on muscle function and morphology in elderly. Firstly, this study investigates changes in muscle tissues resulting from performance of a 6-weeks chronic eccentric contraction in aged rats. Using this model, the effects of eight-week therapeutic resistance training on recovery of pathological changes after chronic strain injury were examined. contraction. Methodology: in an experimental design, 48 elderly male Wistar rats were divided into six groups randomly. Three RSI groups underwent 6weeks (5 set of 10 repetitions, 5 days/week) of fast velocity submaximal eccentric contractions (5 sec trains of 0.2 msec pulses, voltage 40 V at 70 Hz), while the three control (CTL) groups were inactive. After 14 days, one of the RSI (RSI-1) and one of the control (CTL-1) were sacrificed for initial assessment of RSI-induced adaptations. Both RSI-RT and CTL-RT groups performed 8 weeks progressive resistance training (1 set of 6 repetitions using 50-100% 1RM, 3 days/week) and the other two groups (RSI-Re CTL-2) were inactive without any modalities. Gastrocnemius muscle response was assessed by isometric force(IF) and muscle wet mass. Quantitative histopathological analysis and immunoblotting of myogenin protein were also done in all groups. Results: Raw and relative (percent to body weight) measures of isometric force and wet muscle mass of gastrocnemius in CTL-1 group are significantly greater than RSI-1 group. Masson Trichrome and Hematoxylin eosin (H E) stains also showed histopathologic changes were present in RSI-1 group that included increase in fibrosis and non-contractile area, and decrease of myofiber area (MA). After 10 weeks of injury protocol, fibrosis and decrease in MA and IF of gastrocnemius were remained in RSI-Re group, but muscle wet mass was recovered. RT significantly improved IF and MA in both training groups, but non-contractile area was not changed. Only in RSI-RT, the protein level of myogenin was greater than control group. Conclusion: These results suggest that in aged rat force deficit and histopathological changes of gastrocnemius muscle after chronic strain injury were reminded after 10 weeks. Therapeutic Resistance training with an emphasis on concentric phase, low velocity and adequate rest can attenuate functional and histopathological changes in muscle after chronic strain injury in elderly rats.