A novel combination of methods to assess sarcopenia and muscle performance in mice

A novel combination of assays was developed to assess sarcopenia and muscle performance. Three techniques were tested to assess muscle function both during and upon termination of treatments designed to induce sarcopenia. In unsuspended (US) and hindlimb suspended (HS) mice, a Hindlimb Exertion Force Test (HEFT), cage wheel running, and in vitro muscle electrophysiology were performed. Twelve-week old, mature male C57BL/6J mice were HS (n = 24) for two weeks, or served as US controls (n = 26). Both groups were subjected to a HEFT on day 13; that is, the maximum force exerted against a beam force transducer (2 lb. linear range, Transducer Techniques, Temecula CA) following applied tail shock stimulus (0.15 mA, 300 msec). This test primarily evaluated the hindlimb muscles used for an escape response (i.e., hamstrings, quadriceps and calf muscles). Mice (n = 10-11/group) were given voluntary access to running wheels for 7 days post treatment to evaluate muscle endurance. On day 13, HS mice showed a mean 18.9% (p = 0.002) decrease in the maximum force exerted compared to US mice. After 7 days of wheel running, HS running distance tended to decrease (13.2%, p = 0.084). HS mice ran an average of 2.0 km/day less than US control mice, with similar running patterns: distance declined on day 2 following completion of HS but increased steadily thereafter. With in vitro testing, the maximum soleus tetanus response decreased by 31.8% (p = 0.01) with HS, in agreement with the changes observed by the other assays. These three assays, combined, appear to provide effective and complementary ways to measure muscle performance and functional differences.