VARIABILITY OF SUBSTRATE UTILIZATION DURING EXERCISE RELATIVE TO VO2VT AND VO2MAX By

PURPOSE: The purpose of this study was to determine to the stability of ventilatory threshold (VT) as a set point for prescription of exercise intensity. METHODS: Fifty-eight healthy adults (males n = 28, females n = 30) performed VO2max and steady state testing. The VO2max test used a treadmill ramp protocol to determine VO2max and VO2vt. The results were used to determine workload exercise relative to VO2vt and VO2max (70 % VO2vt ≈ 40 % VO2max, 90 % VO2vt ≈ 50 % VO2max, 125 % VO2vt ≈ 65% VO2max). During the steady state test, subjects walked for 4 minutes at each of the workloads associated with the six exercise intensities. These stages were sequentially completed in the order of increasing intensity. Ventilation (VE), respiratory gas-exchange ratio (RER), VO2, and VCO2 were measured continuously and heart rate and rate of perceived exertion (RPE) were collected each minute. RESULTS: The mean overall variance of RER at the %VO2vt intensities was significantly less than at the %VO2max intensities (%VO2vt = 0.030±0.025, %VO2max = 0.041±0.029, p<0.001). The mean RER variance was not different between genders relative to %VO2vt (p>0.05). For males and females, the variance in RER was significantly less when evaluated at 70