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Heat shock proteins (HSP's) are expressed in response to various stressors, such as physical exercise, therefore this study investigated the role of these proteins in skeletal muscle remodeling in response to resistance training. First, we determined the time course of HSP response as a result of a single bout of damaging contractions characterized by non-recoverable force deficit. The next study investigated HSP expression in 3 month old and 30 month old rats in response to a 4.5-week, chronic resistance training program that was designed to elicit muscle hypertrophy. Moreover, we analyzed the gene expression of four hsp70 genes to determine whether resistance training differentially affects the transcription of these genes. The results of the first study showed that HSP25 and HSP72 proteins increased significantly (p < 0.01) in the injured TA muscles compared to control muscles by 48 h and remained elevated at 240h post-injury. Isometric force was significantly lower than control levels 48h post injury but it returned to control measures by 120h and continued to recover by 240h post-injury. This study demonstrated that skeletal muscle injury induced the expression of HSP25 and HSP72, which remained elevated even after the full recovery of isometric force to pre-injury levels. These data are consistent with the hypothesis that HSP's have a role in skeletal muscle remodeling following eccentric contraction-induced damage. The second investigation indicated that muscle wet weight of the left TA increased by 15.6% in young animals compared to the untrained side, while the aged rats demonstrated no significant hypertrophy based on muscle wet weight. A significant training effect was found for both stress proteins. On the other hand, there was no training by age interaction for HSP72, while a significant training by age effects were found in muscles for HSP25. We demonstrated in this investigation that both young and old animals are capable of increasing HSP72 expression in response to high intensity stress. However, it is possible that the underlying cellular mechanisms of stress protein induction might differ between these age groups.