Comparisons of the Metabolic Intensities at Heart Rate, Gas Exchange, and Ventilatory Thresholds

This study compared the V̇O corresponding to the critical heart rate (CHRV̇O ) and the physical working capacity at the heart rate fatigue threshold (PWC_hrt V̇O ) to the gas exchange threshold (GET), ventilatory threshold (VT), and respiratory compensation point (RCP).

Nine runners (mean ± SD, age 23 ± 3 years) completed an incremental test on a treadmill to determine V̇O _peak, GET, VT, and RCP. The CHRV̇O and PWC_hrt V̇O 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).

The GET (38.44 mL×kg^-1×min^-1, 78% V̇O _peak), VT (37.36 mL×kg^-1×min^-1, 76% V̇O _peak), and PWC_hrt V̇O (38.26 mL×kg^-1×min^-1, 77% V̇O _peak) were not different, but were lower than the RCP (44.70 mL×kg^-1×min^-1, 90% V̇O _peak; p = 0.010, p < 0.001, p = 0.001, respectively). The CHRV̇O (40.09 mL×kg^-1×min^-1, 81% V̇O _peak) was not different from the GET (p = 1.000), VT (p = 0.647), PWC_hrt V̇O (p = 1.000), or RCP (p = 0.116).

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.