Adjustment for gas exchange threshold enhances precision of heart rate-derived VO2 estimates during heavy exercise

Abstract

Overestimates of oxygen uptake (VO2) are derived from the heart rate reserve – VO2 reserve (HRR–VO2R) model. We tested the hypothesis that adjusting for differences above and below gas exchange threshold (HRR–GET model) would tighten the precision of HR-derived VO2 estimates during heavy exercise. Seven men and 7 women of various VO2 max levels, on 2 separate days, cycled for 6 min at intensities equal to power at GET, 15% the difference between GET and VO2 max (15% above), and at 30% above GET. A second bout at 15% above GET (15% above (bout 2)) after 3 min of recovery was performed to assess estimates during interval training. Actual VO2 was compared with estimates derived from the HRR–VO2R and the HRR–GET. VO2 values were summed over the 6 min duration of data collection (6 min LO2) and compared with Bland–Altman plots. HRR–VO2R yielded 6 min LO2 (±2 SD) overestimates of 2.0 (±2.5), 1.9 (±2.7), and 1.3 (±3.3) for GET, 15% over, and 30% over, respectively, whereas corresponding 6 min LO2 difference values for the HRR–GET model were –0.42 (±1.6), –0.23 (±1.1), and –0.55 (±1.8), respectively. For 15% above (bout 2), the 6 min LO2 difference for HRR–VO2R was 1.8 (±2.9), whereas the difference for HRR–GET was 0.17 (±1.4). The 6 min LO2 values relative to the subjects’ VO2 max did not vary (r = 0.05 to 0.36); therefore, fitness level did not affect estimates. Sex did not affect accuracy of either estimate model (sex X estimate model interaction, p > 0.95). We observed accurate estimates from the HRR–GET model during heavy exercise.