Influence of extreme pedal rates on pulmonary O2 uptake kinetics during transitions to high-intensity exercise from an elevated baseline

We used extreme pedal rates to investigate the influence of muscle fibre recruitment on pulmonary V˙O2 kinetics during unloaded-to-moderate-intensity (U → M), unloaded-to-high-intensity (U → H), and moderate-intensity to high-intensity (M → H) cycling transitions. Seven healthy men completed transitions to 60% of the difference between gas-exchange threshold and peak V˙O2 from both an unloaded and a moderate-intensity (95% GET) baseline at cadences of 35 and 115 rpm. Pulmonary gas exchange was measured breath-by-breath and iEMG of the m. vastus lateralis and m. gluteus maximus was measured during all tests. At 35 rpm, the phase II time constant (τp) values for U → M, U → H, and M → H were 26 ± 7, 31 ± 7 and 36 ± 8 s with the value for M → H being longer than for U → M (P < 0.05). At 115 rpm, the τp values for U → M, U → H, and M → H were 29 ± 8, 48 ± 16 and 53 ± 20 s with the value for U → M being shorter than for the other two conditions (P < 0.05). The V˙O2 slow component was similar at both cadences, but iEMG only increased beyond minute 2 during high-intensity cycling at 115 rpm. These results demonstrate that V˙O2 kinetics are influenced by an interaction of exercise intensity and pedal rate and are consistent with the notion that changes in muscle fibre recruitment are responsible for slower phase II V˙O2 kinetics during high-intensity and work-to-work exercise transitions.