Ventilatory responses when altering stride frequency at a constant oxygen uptake

Ten women completed a slow walk (SW), fast walk (FW) and a slow run (R) on a motor driven treadmill to evaluate the effect of varying stride frequency on ventilatory responses. The treadmill grade was adjusted during the walks such that the oxygen uptake was the same as during running at 0% grade. Stride frequencies averaged 59, 69 and 80 strides/min for the SW, FW and R, respectively. Oxygen uptake was similar for all three trials (1.78 L/min); as were heart frequencies (154.6 beats/min). Mean blood pressure was unaffected by changing stride frequency. Minute ventilation was similar for all three trials (ca. 47.3 L/min). Significant differences in respiratory frequency were observed (SW = 33.2, FW = 35.4, R = 37.2 breaths/min). Tidal volumes were significantly greater during the slow walk (1417 ml) than either the fast walk (1331 ml) or the run (1301 ml). CO2 output was significantly greater during the run compared to either of the walking trials. End-tidal CO2 was 38.6 mm Hg during the slow walk and was significantly reduced during the fast walk (36.3) and run (36.0). The results suggest the existence of a mild hypocapnia during the fast walk and running exercise. These results further suggest that variations in ventilatory patterns exist during walking and running that are not totally accountable by blood pressure or CO2 and may be related to extra-metabolic stimuli.