Influence of exercise modality on agreement between gas exchange and heart rate variability thresholds

Abstract

The main purpose of this study was to investigate the level of agreement between the gas exchange threshold (GET) and heart rate variability threshold (HRVT) during maximal cardiopulmonary exercise testing (CPET) using three different exercise modalities. A further aim was to establish whether there was a 1:1 relationship between the percentage heart rate reserve (%HRR) and percentage oxygen uptake reserve (%VO2 R) at intensities corresponding to GET and HRVT. Sixteen apparently healthy men 17 to 28 years of age performed three maximal CPETs (cycling, walking, and running). Mean heart rate and VO2 at GET and HRVT were 16 bpm (P<0.001) and 5.2 mL · kg(-1) · min(-1) (P=0.001) higher in running than cycling, but no significant differences were observed between running and walking, or cycling and walking (P>0.05). There was a strong relationship between GET and HRVT, with R2 ranging from 0.69 to 0.90. A 1:1 relationship between %HRR and % VO2 R was not observed at GET and HRVT. The %HRR was higher during cycling (GET mean difference=7%; HRVT mean difference=11%; both P<0.001), walking (GET mean difference=13%; HRVT mean difference=13%; both P<0.001), or running (GET mean difference=11%; HRVT mean difference=10%; both P<0.001). Therefore, using HRVT to prescribe aerobic exercise intensity appears to be valid. However, to assume a 1:1 relationship between %HRR and % VO2 R at HRVT would probably result in overestimation of the energy expenditure during the bout of exercise.

Figure 1. Graphic illustration of the methods used to determine the gas exchange threshold (GET; ventilatory equivalents method, excess CO₂ method, V-slope method) and heart rate variability threshold (HRVT; Poincare plot method).

Figure 2. Bland-Altman plots showing within-subject differences between the gas exchange threshold (GET) and heart rate variability threshold (HRVT) plotted against means of GET and HRVT for percentage heart rate reserve (%HRR) and percentage V˙O2 reserve (%V˙O2 R) obtained in the cardiopulmonary exercise tests (cycling, walking, and running). The dashed lines represent the mean bias and 95% limits of agreement (n=16).

Figure 3. Mean±SD percentage of heart rate reserve (%HRR), oxygen uptake reserve (%V˙O2 R), and difference between %HRR-%V˙O2 R at the gas exchange threshold (GET) and heart rate variability threshold (HRVT) (n=16). Sidak-adjusted P values indicate significant differences between %HRR and %V˙O2 R.