VERIFICATION OF THE HEART-RATE THRESHOLD

Among the methods for determining anaerobic threshold (AT), the heart rate (HR) method seems to be the simplest. On the other hand, many con flicting results from comparing this method with others have been pres ented over the last 10 years. Therefore, the aim of this study was to compare the heart rate threshold (HRT) with the lactate turn point (LT P) - ''second'' break point of dependence of lactate (LA) to power out put, ventilatory threshold (VT) and threshold determined by electromyo graphy (EMG(AT)), all determined by the same exercise test and evaluat ed 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 er gometer (modified Conconi test) starting with an initial power output (PO) of 40 W with intensity increments of 10 W . min-1 until the subje cts were exhausted. The HRT, LTP and EMG(AT) determination was done by computer-aided break-point regression analysis from dependence of fun ctional measures on PO. The same computer algorithm was used for VT de termination from the relationship between ventilation (Ti) and oxygen uptake (VO2) or carbon dioxide output (VCO2). Nonsignificant differenc es were found between HRT [VO2 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 [VO2 35.1 (SD 3.7) ml . kg(-1) min(-1); HR 16 8.3 (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) [VO2 35.6 (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 [VO2 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 threshol d level in all the thresholds investigated. Correlation coefficients r anged in selected variables at different threshold levels from 0.842 t o 0.872 in VO2 measured in ml . kg(-1) min(-1), from 0.784 to 0.912 fo r LA, from 0.648 to 0.857 for HR, and from 0.895 to 0.936 for PO measu red in W . kg(-1). These findings have led us to conclude that HRT cou ld be used as an alternative method of determining anaerobic threshold in untrained subjects.