Muscle metabolic and neuromuscular determinants of fatigue during cycling in different exercise intensity domains.

This is the author accepted manuscript. The final version is available from American Physiological Society via the DOI in this record.The lactate or gas exchange threshold (GET) and the critical power (CP) are closely associated with human exercise performance. We tested the hypothesis that the limit of tolerance (Tlim) during cycle exercise performed within the exercise intensity domains demarcated by GET and CP is linked to discrete muscle metabolic and neuromuscular responses. Eleven males performed a ramp incremental exercise test, 4-5 severe-intensity (SEV; >CP) constant-work-rate (CWR) tests until Tlim, a heavy-intensity (HVY; GET) CWR test until Tlim, and a moderate-intensity (MOD; 0.05) muscle metabolic milieu (i.e., low pH and [PCr] and high [lactate]) was attained at Tlim (~2-14 min) for all SEV exercise bouts. The muscle metabolic perturbation was greater at Tlim following SEV compared to HVY, and also following SEV and HVY compared to MOD (all P0.05). Neural drive to the VL increased during SEV (4±4%; P0.05). During SEV and HVY, but not MOD, the rates of change in M-wave amplitude and neural drive were correlated with changes in muscle metabolic ([PCr], [lactate]) and blood ionic/acid-base status ([lactate], [K(+)]) (P