PREDICTION OF EXHAUSTION TIME FROM HEART-RATE DRIFT

BEAURY and ECLACHE (1978) proposed to extrapolate the drift of the hea rt rate up to maximal heart rate (Hr(max) measured during an increment al maximal test) as a convenient way of estimation of the exhaustion t im (t(lim)) of an exercise at constant power (75 or 80% of Maximal Aer obic Power (MAP)). The purpose of this study was to evaluate this meth od 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 (l(limtheo)) and the actual exhaustion time (t(lim)). The results showed that the subjects did not reach their maximal hear t rate (Hr(max)) at t(lim) and consequently that t(limtheo), calculate d by extrapolation of heart rate drift, overestimated t(lim), for all the loads in our study. The difference between t(limtheo) and t(lim) ( DELTAt(lim) expressed as a percentage of t(lim)) is significant lower at 86% MAP than DELTAt(lim) at the other loads. It is likely that DELT At(lim) is minimal around 80% MAP, i.e. the loads used in the study by BEAURY and ECLACHE (1978). The values of heart rate (Hr(lim)), oxygen uptake (V(O2lim)) and oxygen PUIS (O2puls(lim)) measured at exhaustio n suggested that the high level of energy cost is one of the main limi ting factors at 86% MAP, in contrast with other loads.