Comparisons of the metabolic intensities at heart rate, gas exchange, and ventilatory thresholds

International Journal of Exercise Science 13(2): 455-469, 2020. PURPOSE: This study compared the V̇ O₂ corresponding to the critical heart rate (CHRV̇ O₂) and the physical working capacity at the heart rate fatigue threshold (PWC_hrtV̇ O₂) to the gas exchange threshold (GET), ventilatory threshold (VT), and respiratory compensation point (RCP). METHODS: Nine runners (mean ± SD, age 23 ± 3 years) completed an incremental test on a treadmill to determine V̇ O_2peak, GET, VT, and RCP. The CHRV̇ O₂ and PWC_hrtV̇ O₂ were determined from 4 separate constant velocity treadmill runs to exhaustion and HR and time to exhaustion were recorded. Differences among the thresholds were examined with a one-way repeated measures ANOVA (p ≤ 0.05). RESULTS: The GET (38.44 mL•kg^-1 •min^-1, 78% V̇̇ O_2peak), VT (37.36 mL•kg^-1 •min^-1, 76% V̇ O_2peak), and PWC_hrtV̇ O₂ (38.26 mL•kg^-1•min^-1, 77% V̇ O_2peak) were not different, but were lower than the RCP (44.70 mL•kg^-1 •min^-1, 90% V̇ O_2peak; p = 0.010, p < 0.001, p = 0.001, respectively). The CHRV̇ O₂ (40.09 mL•kg^-1 •min^-1, 81% V̇ O_2peak) was not different from the GET (p = 1.000), VT (p = 0.647), PWC_hrtV̇ O₂ (p = 1.000), or RCP (p = 0.116). CONCLUSIONS: These results indicated that the initial metabolic intensities at CHR and PWC_hrt lie within the heavy and moderate intensity domains, respectively. Therefore, the PWC_hrt may provide a relative intensity more appropriate for untrained populations, while the CHR may be more appropriate for more trained populations.