Intensity-dependent Contribution of Neuromuscular Fatigue after Constant-Load Cycling.

Purpose: We tested the hypothesis that central and peripheral fatigue after constant-load cycling exercise would vary with exercise intensity and duration. Methods: Twelve, well-trained male cyclists (V[Combining Dot Above]O2max, 4.49+/-0.35 L[middle dot]min-1) completed three constant-load cycling trials to the limit of tolerance in a randomized, crossover design. Exercise intensities were set according to the respiratory responses to a preliminary ramp test to elicit cardiorespiratory and metabolic responses consistent with exercise in the severe and heavy exercise domains; 1) at power at V[Combining Dot Above]O2max (S+, 379+/-31 W), 2) at 60% of the difference between gas exchange threshold and V[Combining Dot Above]O2max (S-, 305+/-23 W) and 3) at the respiratory compensation point (RCP, 254+/-26 W). Pre- and post-exercise twitch responses from the quadriceps to electrical stimulation of the femoral nerve and magnetic stimulation of the motor cortex were recorded to assess neuromuscular and corticospinal function, respectively. Results: Exercise time was 3.14+/-0.59 min, 11.11+/-1.86 min and 42.14+/-9.09 min for S+, S- and RCP respectively. All trials resulted in similar reductions in maximum voluntary force (P=0.61). However, the degree of peripheral fatigue varied in an intensity-dependent manner, with greater reductions in potentiated twitch force after S+ (-33+/-9%) compared to both S- (-16+/-9%, P

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