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

Pasquale J Succi, Taylor K Dinyer, M Travis Byrd, Haley C Bergstrom, Pasquale J Succi, Taylor K Dinyer, M Travis Byrd, Haley C Bergstrom

Abstract

Purpose: This study compared the V̇O 2 corresponding to the critical heart rate (CHRV̇O 2 ) and the physical working capacity at the heart rate fatigue threshold (PWChrt V̇O 2 ) 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 V̇O 2 peak, GET, VT, and RCP. The CHRV̇O 2 and PWChrt V̇O 2 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% V̇O 2 peak), VT (37.36 mL×kg-1×min-1, 76% V̇O 2 peak), and PWChrt V̇O 2 (38.26 mL×kg-1×min-1, 77% V̇O 2 peak) were not different, but were lower than the RCP (44.70 mL×kg-1×min-1, 90% V̇O 2 peak; p = 0.010, p < 0.001, p = 0.001, respectively). The CHRV̇O 2 (40.09 mL×kg-1×min-1, 81% V̇O 2 peak) was not different from the GET (p = 1.000), VT (p = 0.647), PWChrt V̇O 2 (p = 1.000), or RCP (p = 0.116).

Conclusions: These results indicated that the initial metabolic intensities at CHR and PWChrt lie within the heavy and moderate intensity domains, respectively. Therefore, the PWChrt may provide a relative intensity more appropriate for untrained populations, while the CHR may be more appropriate for more trained populations.

Keywords: Critical heart rate; PWChrt; critical power; endurance training; fatigue thresholds.

Figures

Figure 1
Figure 1
Example of the gas exchange threshold (GET) determination for a representative subject. The GET was defined as the breakpoint in the V̇CO2 (L×min−1) versus V̇O2 (L×min−1) graph.
Figure 2
Figure 2
Example of the ventilatory threshold (VT) determination for a representative subject. The VT was defined as the breakpoint in the V̇E (L×min−1) versus V̇O2 (L×min−1) graph.
Figure 3
Figure 3
Example of the respiratory compensation point (RCP) determination for a representative subject. The RCP was defined as the breakpoint in the V̇E (L×min−1) versus V̇CO2 (L×min−1) graph.
Figure 4
Figure 4
Example derivation of critical heart rate (CHR) for a representative subject. CHR is defined as the slope of the linear regression line of the total heart beats (HBLim) versus limit time (TLim).
Figure 5A
Figure 5A
Example of the determination of the physical working capacity at the heart rate threshold (PWChrt) for a representative subject. First the slope coefficients were derived from the heart rate (b·min−1) versus time (min) to exhaustion relationship for four, constant velocity runs.
Figure 5B
Figure 5B
The PWChrt was defined as the y-intercept of the velocity (km·hr−1) versus slope coefficients relationship for each velocity.
Figure 6
Figure 6
Visual representation of the mean ± SD for each of the thresholds determined from the incremental treadmill test and constant velocity runs. *significantly greater than GET, VT, and PWChrtV̇O2 (p < 0.05).

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