%HRmax target heart rate is dependent on heart rate performance curve deflection

The percent of maximal heart rate (%HRmax) model is widely used to determine training intensities in healthy subjects and patients when prescribing training intensities in these groups of subjects. Purpose: The aim of the study was to investigate the influence of the time course of the heart rate performance curve (HRPC) on the accuracy of target training heart rate. Methods: Sixty-two young healthy male subjects performed an incremental cycle ergometer exercise test until voluntary exhaustion. Subjects were then divided into four groups according to the time course of the HR-PC. Groups were classified in regular HR response (k(HR2) > 0.2), indifferent HR response (0 < k(HR2) < 0.2), linear HR response (k(HR2) = 0), and inverted HR response (k(HR2) < 0). The first and the second lactate turn point (LTP1, LTP2) as well as the heart rate turn point (HRTP) were determined as submaximal markers of performance. Linear regression lines were calculated for HR in the three regions of energy supply defined by LTP1, and LTP2. Results: HR at LTP1 and HRmax was not significantly different between all four groups. HR at LTP2 was dependent on the time course of the HRPC and was significantly lower (P < 0.05) as k(HR2) decreased. Power output and blood lactate concentration at LTP1, LTP2 and maximal workload (P-max) were not significantly different between the groups. Conclusion: From our data, we conclude that target training HR detected by means of the %HRmax method may be overestimated in cases where the HR response is not regular, as it was found in many of our subjects.