The repeated‐bout effect is compromised in the tibialis anterior muscles of mdx mice

Abstract

The purpose of this study was to test the hypothesis that skeletal muscles from mdx mice would have a reduced ability to adapt to eccentric muscle contractions (EC). Tibialis anterior (TA) muscles from male C57BL/6N and mdx mice 8–10 weeks of age were exposed to either a single or multiple bouts of EC separated by 14 days. Serum creatine kinase (CK) values were measured prior to EC, and immediately, 24, and 48 hours post exercise. Resting membrane potentials (RMP) were also measured immediately following a single or multiple bouts of EC. CK values were significantly greater in mdx mice compared to C57BL/6N mice prior to performing EC. Immediately following a single bout of EC, CK values were significantly greater than pre‐exercise in both C57BL/6N and mdx mice. At 24 and 48 hours neither group was different than their respective pre‐exercise values. Immediately following a second bout of EC, CK values were not different in C57BL/6N mice, but were significantly elevated in mdx mice when compared to pre‐exercise values. Neither group was different from pre‐exercise values at 24 and 48 hours after the second bout of EC. Measurement of RMP resulted in a similar trend. Both groups were significantly depolarized following a single bout of EC. After a second bout of EC cells from C57BL/6N mice were significantly less depolarized than following a single bout, while mdx muscles had a similar significant level of depolarization as measured after a single bout of EC. Together these results indicate a significant reduction of the repeated‐bout effect in TA muscles from mdx mice.