Effect of recovery duration from prior exhaustive exercise on the parameters of the power-duration relationship

The physiological equivalents of the curvature constant (W') of the high-intensity power-duration (P-t(LIM)) relationship are poorly understood, although they are presumed to reach maxima/minima at exhaustion. In an attempt to improve our understanding of the determinants of W', we therefore aimed to determine its recovery kinetics following exhaustive exercise (which depletes W') concomitantly with those of O(2) uptake (V(O(2)), a proxy for the kinetics of phosphocreatine replenishment) and blood lactate concentration ([L(-)]). Six men performed cycle-ergometer exercise to t(LIM): a ramp and four constant-load tests, at different work rates, for estimation of lactate threshold, W', critical power (CP), and maximum V(O(2)). Three further exhausting tests were performed at different work rates, each preceded by an exhausting "conditioning" bout, with intervening recoveries of 2, 6, and 15 min. Neither prior exhaustion nor recovery duration altered V(O(2)) or [L(-)] at t(LIM). Postconditioning, the P-t(LIM) relationship remained well characterized by a hyperbola, with CP unchanged. However, W' recovered to 37 +/- 5, 65 +/- 6, and 86 +/- 4% of control following 2, 6, and 15 min of intervening recovery, respectively. The W' recovery was curvilinear [interpolated half time (t(1/2)) = 234 +/- 32 s] and appreciably slower than V(O(2)) recovery (t(1/2) = 74 +/- 2 s) but faster than [L(-)] recovery (t(1/2) = 1,366 +/- 799 s). This suggests that W' determines supra-CP exercise tolerance, its restitution kinetics are not a unique function of phosphocreatine concentration or arterial [L(-)], and it is unlikely to simply reflect a finite energy store that becomes depleted at t(LIM).