Muscle Recruitment Patterns Above Critical Power

Abstract

Critical power (CP) represents an exercise intensity that above which exercise tolerance is limited and can be predicted. As the muscle fatigues during constant‐load exercise above CP, muscle motor unit recruitment is increased to meet the exercise demand. Our laboratory has shown that at task failure in small muscle mass handgrip exercise, muscle recruitment is not different across exercise intensities above CP.PurposeTo test the hypotheses that 1) end‐exercise muscle recruitment is not intensity‐dependent during whole body exercises above CP, and 2) at exercise intensities above CP muscle recruitment does not reach steady state, but continuously increases until task failure occurs.MethodsTo date, four healthy, young men (23.5 ± 2.0 yrs; 92.6 ± 4.2 kg, 175 ± 4 cm) completed five exercise bouts to task failure on separate days. During the first session, subjects performed an incremental test on a cycle ergometer to determine peak power (Ppeak). The subjects then performed four constant load cycle tests on subsequent days. The power outputs during the constant load tests were selected to elicit task failure within the pre‐determined time range of 2–15 min to ensure all tests were above CP. Electromyography (EMG) was measured on the L vastus lateralis to quantify potential increases in muscle recruitment and were reported as 20 contraction averages.ResultsAverage Ppeak was 300 ± 31 W. Work rate at which CP occurred was 178 ± 17W (59.4% ± 2.3 % Ppeak). There were no significant differences in end‐exercise iEMG (p=0.078) among exercise intensities above CP. Further, for each exercise intensity all subjects demonstrated a progressive increase in iEMG until task failure.ConclusionsConfirming our hypotheses, the current data suggest that during cycling exercise above CP, muscle recruitment at task failure is similar across exercise intensities.