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The Role of the Extracellular Matrix in Mediating Muscle Soreness

The goal of this dissertation was to examine the role of the extracellular matrix (ECM) in muscle soreness. Study 1 examined how the disruption of the ECM from a minor surgery (e.g. muscle biopsy) affected muscle soreness. Study 1 showed that soreness levels increased at 24 h post-biopsy compared to baseline and resolved within 96 h. However, the level of muscle soreness at 24 h post-biopsy (20 mm) was lower than that reported for performing a strenuous and naïve exercise (40–80 mm). These results will help review boards at institutions where muscle biopsies are performed understand how a muscle biopsy affects individuals. Additionally, these results will help investigators better articulate the effects of a muscle biopsy to a study volunteer. Study 2 examined the molecular changes of ECM molecules in response to a single and repeated bout of exercise. Muscle biopsies were analyzed from baseline, 24 h post-Bout 1, and 24 h post-Bout 2 using qRT-PCR, western blotting, and zymography techniques. In this study, eight individuals (4 men and 4 women) performed the exercise—descending 10 flights of stairs 15 times—and four individuals (2 men and 2 women) were controls and did not exercise. The exercise and control group both had changes in gene expression and in one protein compared to baseline. However, no differences were found for either group in zymography. These results indicate that gene expression is the prominent alteration ECM molecules in skeletal muscle at 24 h after eccentric exercise. Study 3 used microarray analysis to examine the difference in gene expression between individuals (n=30, men) who presented with high-soreness levels (n=5) compared to low-soreness levels (n=7) after eccentric exercise. Muscle biopsies for microarray analysis were collected from the exercised leg at 3 h post-exercise and the non-exercised leg served as control. The 546 genes differentially regulated were imported into Ingenuity Pathway Analysis, which created networks and allowed for the identification of the top 100 up- and down-regulated genes. Despite finding that the up-regulated genes had more significant correlations and a greater number of genes with significant correlations compared to the down-regulated genes, these up-regulated genes were not more commonly found in one pathway compared to another. These results might suggest that the variability of muscle soreness after eccentric exercise is a consequence of the variability in the repair and adaptation of skeletal muscle after eccentric exercise.
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