Ventilatory responses during varied stride and pedal frequencies

The effects of limb movement frequency during walking and running and cycling at 60 and 90 rpm on the ventilatory responses were studied in 19 male subjects. Ten of the subjects were trained runners whereas nine of the subjects were trained cyclists. The runners completed walk and run exercise trials at equal levels of CO2 excretion (VCO2) and low (approximately 60) rpm and high (approximately 90) rpm cycling trials at equal VCO2 levels. The cyclists completed low and high rpm cycling trials at equal VCO2 levels. The cyclists were not tested on the walk/run trials as they had been tested previously and had been shown to have similar ventilatory responses when walking and running at equal VCO2 levels. Minute ventilation (VE), tidal volume (VT), breathing frequency (f), end-tidal CO2 (PETCO2) and O2 (PETO2) tensions, and inspiratory (TI) and expiratory (TE) times were not found to differ significantly between the low and high pedal frequency trials for either the cyclists or the runners. No significant differences were found in estimated arterial CO2 tensions (PaCO2) or estimated alveolar ventilation (VA) between the cycling trials for either the runners or the cyclists. When comparing running to walking, the runners were found to have a greater VE and estimated VA. This was mediated by an increase in f as VT was found to decrease. The increased f was associated with a shortened TI as TE was not significantly different between the walk and run trials. End-tidal CO2 tension and estimated PaCO2 was significantly lower during the run trial as compared to the walk trial. These results suggest some form of neurogenic stimuli influencing ventilation in the runners while running. This same neurogenic influence is not present when cyclists run and when either cyclists or runners exercise on the bicycle. A possible source for the neurogenic stimuli is discussed.