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%). V̇O(2), 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 time-course 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.