Influence of extreme pedal rates on pulmonary O(2) 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(O)(2) 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(O)(2) from both an unloaded and a moderate-intensity (95% GET) baseline at cadences of 35 and 115rpm. 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 35rpm, the phase II time constant (tau(p)) values for U-->M, U-->H, and M-->H were 26+/-7, 31+/-7 and 36+/-8s with the value for M-->H being longer than for U-->M (P<0.05). At 115rpm, the tau(p) values for U-->M, U-->H, and M-->H were 29+/-8, 48+/-16 and 53+/-20s with the value for U-->M being shorter than for the other two conditions (P<0.05). The V(O)(2) slow component was similar at both cadences, but iEMG only increased beyond minute 2 during high-intensity cycling at 115rpm. These results demonstrate that V(O)(2) 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(O)(2) kinetics during high-intensity and work-to-work exercise transitions.