EFFECT OF PEDAL RATE ON CARDIORESPIRATORY RESPONSES DURING CONTINUOUS EXERCISE

The role of cycle ergometer pedal rate on the gradual increase in ventilation (V(E)), heart rate (HR), and oxygen uptake (VO2) accompanying continuous submaximal exercise is unknown. To examine this problem, five trained Males (VO2peak = 4.00 +/- 0.27 l . min-1) performed 45 min of moderate intensity (MI, 127 W) and high-moderate intensity (HMI, 166 W) cycle ergometry both at pedal rates of 60 rpm and 90 rpm. Power output and pedal mte had an additive effect on the overall mean responses for V(E), HR, and VO2, producing significantly higher values as power output and pedal rate increased. During continuous exercise, V(E), HR, and VO2 increased progressively from the 10th to the 45th minute for all tests. However, the rates of increase and factors modifying the V(E), HR, and VO2 responses were different. HR increased during all exercise tests an average of 10.8% independent of power output and pedal rate. V(E) increased 7.4% during MI exercise and 10% during HMI exercise independent of pedal rate. Similar power output dependent responses were observed for rectal temperature (T(r)) and blood lactate. VO2 increased 4.4% for MI and HMI exercise at 60 rpm, and 8.2% for the same power outputs at 90 rpm, respectively. Increases in T(r), the oxygen cost of pulmonary ventilation and fat oxidation, and lactate removal were estimated to account for only 31-36% of the slow rise in VO2 for any single test. This suggests that 64-69% of the rise in VO2 was due to factors related to muscle use. Our findings suggest that increases in HR during continuous exercise are influenced by thermoregulatory factors independent of exercise intensity and leg pedal rate. However, fast pedal rates potentiate the rate of VO2 increase, while power output potentiates the rate of increase for V(E). These findings suggest that gradual increases in respiration and energy expenditure during continuous cycle ergometry are influenced differentially by neuromuscular reflex mechanisms related to power output and pedal rate.