Time Course Changes In Muscle Torque Development After Single-leg Fatiguing Exercise Training In Mice

PURPOSE: To investigate whether involuntary single-leg fatiguing exercise training mimicking high-intensity resistance exercise can change maximal torque in mice expressing tdTomato fluorescent protein in muscle satellite cells. METHODS: Transgenic adult male mice (12 weeks old, n = 8 mice) expressing Td-Tomato fluorescent protein in Pax7+ (i.e., satellite cells) cells (Pax7CreER-Ai9) were treated with tamoxifen (2 mg/day, i.p.) for 5 days. Three days later, mice were single-leg exercise trained (i.e stimulation of the peroneal nerve of the right leg of each mouse to evoke fused tetanic contractions [100 Hz] of the anterior crural muscles), 3x per week for either 1 week (n = 4 mice) or 2 weeks (n = 4 mice). Each training session was composed of 3-s contractions with 7 s recovery between contractions, 10 contractions each set, 5 sets with 5 min rest between sets. Before the first training session and 3 days after the last training session (1 week or 2 weeks training), torque produced by the ankle was measured at different frequencies of pulse-stimulation (1-200 Hz), mice were euthanized, and muscles were frozen for histological measurements. Results are shown as Mean ± SD. RESULTS: During each session of training, peak torque developed at the last contraction was decreased by 54 ± 26 % (58 ± 22 Nmm/kg to 25 ± 12 Nmm/kg, P < 0.001) of the initial contraction suggesting fatigue development. Between sessions of training, initial torque was not significantly different suggesting that muscle recovered function between sessions. Torque measurements at different frequencies of stimulation 3 days after 1 week or 2 weeks of training showed a decrease in maximal tetanic torque relative to the mice body weight, after 1 week of training (83 ± 32 Nmm/kg to 61 ± 20 Nmm/kg, P < 0.05) but torque was recovered at 2 weeks of training (70 ± 22 Nmm/kg to 65 ± 25 Nmm/kg, not significant). CONCLUSION: Resistance exercise training in mice by using single-leg electrical stimulations leads to a fast (i.e., 1 week) decrease in muscle force development which is recovered by an additional week of training. Support: TRDRP grant # T29KT0397CA (to L.N.) T29KT0397CA (to L.N.)