1. The influence of pedal rate on ventilatory response and breathing pattern during cycle exercise was studied in twelve untrained female subjects performing 15 W/min incremental work on a bicycle at 30 and 60 r.p.m. Comparisons were made within the range of aerobic work rate to avoid additional influences of a developing lactic acidosis. 2. At each pedal rate, CO2 excretion (VCO2) increased progressively to a level of 1.2 1/min with incrementally loaded cycling. With increasing VCO2, minute ventilation (VE), respiratory frequency (f), tidal volume (VT) and end-tidal PCO2 progressively increased. The inspiratory (TI) and expiratory (TE) durations decreased sharply on the transition from rest to unloaded cycling; further decreases occurred during incrementally loaded cycling. 3. Compared to 30 r.p.m., cycle exercise at 60 r.p.m. resulted in greater increases in VE and lower levels of end-tidal PCO2 at any given levels of VCO2. The greater ventilatory responses were due mostly to greater increases in f, which were in turn due to greater decreases in TE. The decrease in TI during cycling was little affected by changes in pedal rate. 4. The different magnitudes of ventilatory and PCO2 responses under the two pedal rate conditions suggest that neurogenic stimuli, central and/or peripheral in origin, participate in the control of exercise hyperpnoea in the non-steady-state phase. The possibility that the ventilatory response to cycle exercise is affected by the way that pedal rate is changed is discussed.
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