The objectives of this study were to determine whether the power output measured by physical working capacity at threshold heart rate (PWC THR) was equivalent to power output at the maximal steady state of heart rate (MSS HR), and to analyze the influence of exercise duration on the calculation of PWC THR. Seven subjects were submitted to a maximal progressive test and five bouts at constant power relative to the second metabolic threshold (Lim2). Heart rate (HR) and HR variability were estimated by linear regression and Poincaré plotting, respectively. There was a significant difference between PWC THR and MSS HR, irrespective of the intensity used. Additionally, intensities higher than 50% of Lim2 did not result in HR stabilization. However, the latter finding did not depend on cardiovascular autonomic control since there was no difference in SD1 or SD1/SD2 as a function of duration of the effort. Thus, PWC THR does not represent MSS HR in physically active young adults. Furthermore, the lack of HR stabilization seems to be independent of neural mechanisms.
Heart rate; Physical exercise; Autonomic nervous system