Prediction of exhaustion time from heart rate drift

Beaury and Eclache (1978) proposed to extrapolate the drift of the heart rate up to maximal heart rate (Hrmax measured during an incremental maximal test) as a convenient way of estimation of the exhaustion tim (tlim) of an exercise at constant power (75 or 80% of Maximal Aerobic Power (MAP)). The purpose of this study was to evaluate this method of estimation of exhaustion time for a large range of power (60, 73, 86, 100 and 120% MAP). We compared the exercise duration calculated with this method (1limtheo) and the actual exhaustion time (tlim). The results showed that the subjects did not reach their maximal heart rate (Hrmax) at tlim and consequently that tlimtheo, calculated by extrapolation of heart rate drift, overestimated tlim, for all the loads in our study. The difference between tlimtheo and tlim (delta tlim expressed as a percentage of tlim) is significantly lower at 86% MAP than delta tlim at the other loads. It is likely that delta tlim is minimal around 80% MAP, i.e. the loads used in the study by Beaury and Eclache (1978). The values of heart rate (Hrlim), oxygen uptake (VO2lim) and oxygen puls (O2pulslim) measured at exhaustion suggested that the high level of energy cost is one of the main limiting factors at 86% MAP, in contrast with other loads.