Neuromuscular fatigue and recovery dynamics following prolonged continuous run at anaerobic threshold

Objective: The aim of this study was to determine the influence of intensive aerobic running on some muscle contractile characteristics and the dynamics of their recovery during a 2 hour period afterwards. Methods: Seven well trained runners performed a 6 km run at anaerobic threshold (VOBLA). Knee torque during single twitch, low and high frequency electrical stimulation (ES), maximum voluntary knee extension, and muscle activation level test of the quadriceps femoris muscles were measured before and immediately after the run, and at several time points during a 120 minute interval that followed the run. Results: After exercise, the mean ( SE) maximum twitch torque ( T-TW) and torque at ES with 20 Hz ( low frequency ES; T-F20) dropped by 14.1 ( 5.1)% ( p < 0.05) and 20.6 (7.9)% ( p < 0.05) respectively, while torque at stimulation with 100 Hz ( high frequency ES; T-F100), maximum isometric knee extension torque ( maximum voluntary contraction torque; T-MVC), and activation level did not change significantly. Twitch contraction time was shortened by 8 ( 2)% ( p < 0.05). Ten minutes after the run, TTW was 40% higher than immediately after the run and 10% ( p < 0.05) higher than before the run. T-F20, T-F100, and T-MVC remained lower for 60 minutes ( p < 0.05) than before the run. Conclusions: A 6 km continuous run at VOBLA caused peripheral fatigue by impairing excitation contraction coupling. Twitch torque recovered very quickly. However, the process of torque restoration at maximum isometric knee extension torque and at high and low frequency ES took much longer.