Experimental validation of the 3-parameter critical power model in cycling

PurposeThe three-parameter model of critical power (3-p) implies that in the severe exercise intensity domain time to exhaustion (T-lim) decreases hyperbolically with power output starting from the power asymptote (critical power, ?(cr)) and reaching 0s at a finite power limit (?(0)) thanks to a negative time asymptote (k). We aimed to validate 3-p for short T-lim and to test the hypothesis that ?(0) represents the maximal instantaneous muscular power.MethodsTen subjects performed an incremental test and nine constant-power trials to exhaustion on an electronically braked cycle ergometer. All trials were fitted to 3-p by means of non-linear regression, and those with T-lim greater than 2min also to the 2-parameter model (2-p), obtained constraining k to 0s. Five vertical squat jumps on a force platform were also performed to determine the single-leg (i.e., halved) maximal instantaneous power.ResultsT(lim) ranged from 264s to 15.7 +/- 4.9min. In 3-p, with respect to 2-p, ?(cr) was identical (177 +/- 26W), while curvature constant W' was higher (17.0 +/- 4.3 vs 15.9 +/- 4.2kJ, p<0.01). 3-p-derived ?(0) was lower than single-leg maximal instantaneous power (1184 +/- 265 vs 1554 +/- 235W, p<0.01).Conclusions3-p is a good descriptor of the work capacity above ?(cr) up to T-lim as short as 20s. However, since there is a discrepancy between estimated ?(0) and measured maximal instantaneous power, a modification of the model has been proposed.