Stiffening of the extracellular matrix in skeletal muscle of aged rats and the effect on muscle fiber mechanotransduction
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Sarcopenia is a growing problem and will continue as the aging population of the United States increases. Reduced adaptation of elderly skeletal muscle to exercise is likely to contribute to sarcopenia. The mechanism by which response to exercise is reduced is unclear, but altered mechanotransduction could be occurring. The extracellular matrix of muscle become stiffer with age and this could impair normal mechanotransduction. This could impair elderly individuals from responding to exercise programs, but may also contribute to strength loss. It was hypothesized that age, muscle stiffness, and glycation would be significant predictors of gene expression, and that muscle stiffness would best predict gene expression. Male Fisher Brown Norway hybrid rats aged 6 to 37 months completed 3 sets of 10 concentric contractions of the dorsiflexor muscles on a rat dynamometer through stimulation of the peroneal nerve. Rats were sacrificed eight hours post exercise, and the tibialis anterior and extensor digitorum longus muscles of both hindlimbs were excised. A significant inverse relationship was found between age and myogenin gene expression (myogenin = -0.502*(age) + 2.180, p=0.012). An interesting finding was that muscle stiffness of elderly rats was highly variable with five out of eleven old rats far outside the normal range. While muscle stiffness was not shown to be a significant predictor of response to exercise, this could have been from the generally small response. Future studies should investigate higher intensity exercise or more sensitive measures of response.