Effect of pedal rate on primary and slow-component oxygen uptake responses during heavy-cycle exercise

We hypothesized that a higher pedal rate (assumed to result in a greater proportional contribution of type II motor units) would be associated with an increased amplitude of the O-2 uptake ((V) over dot O-2) Slow component during heavy-cycle exercise. Ten subjects (mean +/- SD, age 26 +/- 4 yr, body mass 71.5 +/- 7.9 kg) completed a series of square-wave transitions to heavy exercise at pedal rates of 35, 75, and 115 rpm. The exercise power output was set at 50% of the difference between the pedal rate-specific ventilatory threshold and peak (V) over dot O-2, and the baseline power output was adjusted to account for differences in the O-2 cost of unloaded pedaling. The gain of the (V) over dot O-2 primary component was significantly higher at 35 rpm compared with 75 and 115 rpm (mean +/- SE, 10.6 +/- 0.3, 9.5 +/- 0.2, and 8.9 +/- 0.4 ml . min(-1) . W-1, respectively; P < 0.05). The amplitude of the (V) over dot O-2 slow component was significantly greater at 115 rpm (328 +/- 29 ml/min) compared with 35 rpm (109 +/- 30 ml/min) and 75 rpm (202 -_ 38 ml/min) (P < 0.05). There were no significant differences in the time constants or time delays associated with the primary and slow components across the pedal rates. The change in blood lactate concentration was significantly greater at 115 rpm (3.7 +/- 0.2 mM) and 75 rpm (2.8 +/- 0.3 mM) compared with 35 rpm (1.7 +/- 0.4 mM) (P < 0.05). These data indicate that pedal rate influences (V) over dot O-2 kinetics during heavy exercise at the same relative intensity, presumably by altering motor unit recruitment patterns.