Alterations in the VO2-Power Relationship above the Lactate Threshold during a Graded Bicycling Exercise Protocol

Purpose: The purpose of this study was to examine the changes in VO2-power and energy expenditure-power relationships below (BLT) and above (ALT) the lactate threshold (LT). Methods: Thirty active subjects (15 males, 15 females) performed a graded exercise protocol on a bicycle ergometer. Initial power outputs were determined based upon subject size and training status. Workloads were increased by 30-Watt increments every 4 minutes until exhaustion. Indirect calorimetry and blood lactate measures were performed during each stage. Linear regressions were developed BLT and ALT for VO2-power and energy expenditure-power (EE-power) relationships. Only 18 subjects (13 males, 5 females) had a sufficient number of data points BLT and ALT to adequately describe the linear regressions. Results: The individual R2 values for VO2-power and EE-power relationships at both BLT and ALT were 0.93 or higher. The mean (±SD) VO2-power slope (mlO2/min/Watt) and intercept (mlO2/min) for ALT were significantly (p\u3c0.01) steeper and lower than the mean BLT slope and intercept (Slope: ALT = 12.7±2.9 vs. BLT = 8.8±1.7; Intercept: ALT = -146.2±617.1 vs. BLT = 656.2±186.8). The mean EE-power slope (kcal/min/Watt) and intercept (kcal/min) for ALT were significantly (p\u3c0.01) steeper and lower than the mean BLT slope and intercept (Slope: ALT = 0.067±0.015 vs. BLT = 0.045±0.009; Intercept: ALT = -1.624±3.248 vs. BLT = 2.934±0.917). No sex effect was observed on the changes in slope or intercept for either VO2-power or EE-power. Conclusion: The relationship between power and either VO2 or energy expenditure during a graded bicycle test suggests an increased oxidative energy requirement relative to power above the lactate threshold