Verification of the heart rate threshold

Abstract

Among the methods for determining anaerobic threshold (AT), the heart rate (HR) method seems to be the simplest. On the other hand, many conflicting results from comparing this method with others have been presented over the last 10 years. Therefore, the aim of this study was to compare the heart rate threshold (HRT) with the lactate turn point (LTP) —“second” break point of dependence of lactate (LA) to power output, ventilatory threshold (VT) and threshold determined by electromyography (EMG_AT), all determined by the same exercise test and evaluated by the same computer algorithm. A group of 24 female students [mean age 20.5 (SD 1.6) years, maximal oxygen consumption 48.8 (SD 4.7) ml · kg⁻¹ · min⁻¹ performed an incremental exercise test on a cycle ergometer (modified Conconi test) starting with an initial power output (PO) of 40 W with intensity increments of 10 W · min⁻¹ until the subjects were exhausted. The HRT, LTP and EMG_AT determination was done by computer-aided break-point regression analysis from dependence of functional measures on PO. The same computer algorithm was used for VT determination from the relationship between ventilation (V) and oxygen uptake ($\dot V$O₂) or carbon dioxide output ($\dot V$CO₂). Nonsignificant differences were found between HRT [$\dot V$O₂ 35.2 (SD 4.2) ml · kg⁻¹ · min⁻¹; HR 170.8 (SD 5.5) beats min⁻¹; LA 4.01 (SD 1.03) mmol · l⁻¹; PO 2.27 (SD 0.33) W · kg⁻¹ VT [$\dot V$O₂ 35.1 (SD 3.7) ml · kg⁻¹ · min⁻¹ HR 168.3 (SD 4.8) beats · min⁻¹; LA 3.87 (SD 1:17) mmol · l⁻¹; PO 2.22 (SD 0.27) W · kg⁻¹ EMG_AT [$\dot V$O₂35.6 (SD 4.1) ml · kg⁻¹ · min⁻¹ HR 171.0 (SD 5.4) beats · min⁻¹; LA 4.11 (SD 0.98) mmol · l⁻¹; PO 2.30 (SD 0.31) W · kg⁻¹] and LTP [$\dot V$O₂) 35.3 (SD 4.1) ml · kg⁻¹ · min⁻¹; HR 170.1 (SD 6.0) beats · min⁻¹; LA 3.99 (SD 0.76) mmol · l⁻¹; PO 2.27 (SD 0.29) W · kg⁻¹]. Highly significant correlations (P < 0.01 in all cases) were found among all measurements made at threshold level in all the thresholds investigated. Correlation coefficients ranged in selected variables at different threshold levels from 0.842 to 0.872 in $\dot V$O₂ measured in ml · kg⁻¹ · min⁻¹, from 0.784 to 0.912 for LA, from 0.648 to 0.857 for HR, and from 0.895 to 0.936 for PO measured in W · kg⁻¹. These findings have led us to conclude that HRT could be used as an alternative method of determining anaerobic threshold in untrained subjects.