Age Affects Skeletal Muscle Response to an Acute Exposure of Stretch-Shortening Contractions

Abstract

Previous studies have shown that aging increased susceptibility to contraction-induced injury in skeletal muscle and impaired recovery after injury. PURPOSE: To investigate the effect of an acute stretch-shortening contraction (SSC) exposure on the temporal skeletal muscle response of young and old rats. METHODS: The left dorsiflexor muscles of young (12 wks age, N = 30) and old (30 mo age, N = 30) male Fischer 344 × Brown Norway rats were exposed to an acute protocol of 80 maximal SSCs (60 deg/s, 50 deg range of motion) in vivo using a custom-fabricated dynamometer. Performance was characterized by isometric performance, negative and positive work, and stretch-shortening parameters (peak eccentric force and minimum pre-stretch force) pre-exposure and at 6 hrs, 24 hrs, 48 hrs, 72 hrs, and 120 hrs after exposure (N= 6 young and 6 old animals at each time point). RESULTS: The isometric force, peak force, minimum force, negative work and positive work were not statistically different between groups before the exposure. However, after the SSC exposure, older age negatively affected the isometric performance (p = 0.0001), minimum force (p < 0.0001), peak eccentric force (p = 0.0002), negative work (p = 0.0005), and positive work (p < 0.0001). The isometric performance and dynamic performance (minimum force, peak force, negative work and positive work) differed most between the age groups 72 hours and 120 hours after the SSC exposure. At the 72 hour and 120 hour time points, the older group exhibited lower isometric force (p = 0.0125 and 0.0051, respectively), minimum force (p = 0.0149 and 0.0005, respectively), peak force (p = 0.0018 and 0.0239, respectively), negative work (p = 0.0050 and 0.0298, respectively), and positive work (p = 0.0190 and 0.0054, respectively) than their younger counterparts. CONCLUSIONS: Age negatively affected both the isometric and dynamic performance measures temporally after an acute exposure to SSCs, particularly at the later time points. These findings suggest that aging impairs the ability of skeletal muscle to adapt to an acute exposure of SSCs. Disclaimer: “The findings and conclusions in this report (abstract/presentation) have not been formally disseminated by the National Institute for Occupational Safety and Health and should not be construed to represent any agency determination or policy.”