Time course of changes in neuromuscular responses during rides to exhaustion above and below critical power

Objectives: To examine the time course of changes in electromyographic (EMG) and mechanomyographic (MMG) amplitude (AMP) and mean power frequency (MPF) responses during cycle ergometry to exhaustion performed above (CP_+10%) and below (CP_-10%) critical power (CP) to infer motor unit activation strategies used to maintain power output. Methods: Participants performed a 3-min all out test to determine CP, and 2 randomly ordered, continuous rides to exhaustion at CP_+10% and CP_-10%. V^. O₂, EMG AMP, EMG MPF, MMG AMP, MMG MPF, and time to exhaustion (T_lim) were recorded. Responses at CP_-10% and CP_+10% were analyzed separately. Results: At CP_-10%, EMG and MMG AMP were significantly greater than the initial 5% timepoint at 100% T_lim. EMG MPF and MMG MPF reflected a downward trend that resulted in no significant difference between timepoints. At CP_+10%, EMG AMP was significantly greater than the initial 5% timepoint from 60% to 100% T_lim. MMG AMP was less than the initial 5% timepoint at only 50% T_lim. EMG and MMG MPF were significantly less than the initial 5% timepoint at 20% T_lim and 100% T_lim, respectively. Conclusions: The timecourse of changes in EMG and MMG signals were different at CP_-10% and CP_+10%, but responses observed indicated cycle ergometry to exhaustion relies on similar motor unit activation strategies.