Effect of oral creatine ingestion on parameters of the work rate-time relationship and time to exhaustion in high-intensity cycling

The relationship between work rate ((W) over dot) and time to exhaustion (t) during intense exercise is commonly described by either a hyperbolic function (NLin), t = W'/((W) over dot-(W) over dot(cp)), or by its linear equivalent (LinW) W-lim = W' + (W) over dot(cp)(t). The parameter (W) over dot(cp) (critical power) has been described as an inherent characteristic of the aerobic energy system, while W' has been shown to be a ralid estimate of anaerobic work capacity. Recent studies have demonstrated that oral supplementation of creatine monohydrate (CrH2O) increases total muscle creatine stores, and have linked these increases to improved performances in intense intermittent exercise. This study was conducted to determine the effect of CrH2O supplementation on estimates of W' and (W) over dot(cp) derived from the NLin and LinW equations, and to determine the effect of CrH2O on t in exhaustive constant power exercise of different intensities. Fifteen active but untrained university students completed three phases of testing on a cycle ergometer: (1) familiarization, three learning trials, (2) baseline determination of W' and (W) over dot(cp), four bouts performed at a (W) over dot selected to elicit fatigue in 90-600 s, and (3) experimental determination of W' and (W) over dot(cp), four bouts performed at the same (W) over dot as baseline, but performed after 5 days of ingesting either a placebo (4 x 6 g of glucose/day) or CrH2O (4 x 5 g of CrH2O and 1 g glucose/day). Testing was administered in a double-blind manner. Analyses of covariance revealed a significant effect for CrH2O on both estimates of W' (NLin, P = 0.04; LinW, P < 0.01), but not on estimates of (W) over dot(cp) (NLin, P = 0.37; LinW; P = 0.30). Within groups, t was significantly different for only CrH2O at the two highest (W) over dots (P = 0.04). It is concluded that oral ingestion of CrH2O increases estimates of W' due to an improved t at the shorter, more intense exercise bouts.