A Test for Determining Critical Heart Rate Using the Critical Power Model

The purposes of this study were to (a) determine if the mathematical model that has previously been used to estimate the critical power (CP) was applicable to heart rate (HR) to estimate the critical heart rate (CHR), and (b) compare the CHR to the HR values at the CP (CP(HR)), ventilatory threshold (VT(HR)), and respiratory compensation point (RCP(HR)). Fifteen women (mean age ± SD = 21.7 ± 2.1 years) performed an incremental test to exhaustion to determine VO₂peak, VT(HR), and RCP(HR). The subjects also performed 4 exhaustive workbouts at different power outputs for the determination of CP and CHR. For each power output, the total number of heart beats (HB(lim)) was calculated as the product of the average 5-second HR (bpm) and total time to exhaustion (T(lim) in minutes). The HB(lim) and total work (W(lim) in kilograms-meters) were plotted as a function of the T(lim) at each power output, and the slope coefficients of the regression lines between HB(lim) or W(lim) and T(lim) were defined as the CHR and CP, respectively. A 1-way repeated-measures analysis of variance (ANOVA) indicated that CHR (172 ± 11 bpm, 92.9 ± 2.7%HRmax) was similar to RCP(HR) (172 ± 9 bpm, 92.9 ± 2.2%HRmax) but was higher (p < 0.05) than CP(HR) (154 ± 10 bpm, 83.2 ± 4.0%HRmax) and VT(HR) (152 ± 12 bpm, 82.1 ± 4.3%HRmax). The relationship between HR and T(lim) from the CHR test can be described by the CP model. The CHR test may be a practical method for estimating RCP without the need to measure expired gas samples. Furthermore, like the RCP, the CHR test may be used to demarcate the heavy from severe exercise intensity domains, predict endurance exercise performance, and prescribe a training intensity for competitive cyclists.