Work-exhaustion time relationships and the critical power concept. A critical review.

The present review is focused on the physiological meanings of the critical power concept proposed by Scherrer in 1954 and its applications to general exercises such as running, cycling and swimming. Since the first studies on the critical power of local exercises, many studies have found that critical power is correlated with indices which are related to aerobic endurance such as maximal oxygen uptake, ventilatory threshold, OBLA or maximal lactate steady state. In fact, the relationship between exhaustion time t(lim) and the Work Wlim (or Distance Dlim) performed at exhaustion is not exactly linear and, consequently, the power-t(lim) equation is not a true hyperbola. The effect of the range of t(lim), used in the calculation of the slope of the Wlim-t(lim) relationship (called critical power) are discussed. When critical power is calculated from short supramaximal exercises, this power is higher than the power output which corresponds to a lactate steady state (or an oxygen uptake steady state) and does not correspond to a power output which can be sustained a long time. The authors present experimental data collected during local (knee extension) and general (running and cycling) exercises which suggest that critical power could correspond to a steady state provided that critical power is calculated from heavy submaximal exercises only (t(lim) ranging between 6 and 30 min). It is difficult to predict exhaustion time from critical power or critical velocity because of the hyperbolic nature of the power-t(lim) relationship. On the other hand, a large error in the measure of t(lim) should have a small effect on the calculation of critical power or velocity. In contrast, the value of Y intercept of the Wlim-t(lim) (or Dlim-(t(lim)) relationship should be sensitive to errors in t(lim).