Creatine supplementation improves performance above critical power but does not influence the magnitude of neuromuscular fatigue at task failure.

Schäfer, L U; Hayes, M; Dekerle, J

NEW FINDINGS What is the central question of this study? Does the magnitude of neuromuscular fatigue depend on the amount of work done (W') at task failure when cycling above critical power (CP)? What is the main finding and its importance? Creatine supplementation increases W' and enhances supra-CP performance, but induces similar magnitudes of neuromuscular fatigue at task failure compared to placebo. Increased W' does not lead to higher levels of neuromuscular fatigue. This supports the notion of a critical level of neuromuscular fatigue at task failure and challenges a direct causative link between W' depletion and neuromuscular fatigue. ABSTRACT The present study examined the effect of creatine supplementation on neuromuscular fatigue and exercise tolerance when cycling above critical power (CP). Eleven males performed an incremental cycling test, 4-5 constant-load trials to task failure (TTF) to obtain asymptote (CP) and curvature constant (W') of the power-duration relationship, followed by three constant-load supra-CP trials: 1) one TTF following placebo supplementation (PLA); 2) one TTF following creatine supplementation (CRE); and 3) one trial of equal duration to PLA following creatine supplementation (ISO). Neuromuscular assessment of the right knee extensors was performed pre- and post-exercise to measure maximal voluntary contraction (MVC), twitch forces evoked by single (Qpot ) and paired high- (PS100) and low-frequency (PS10) stimulations and voluntary activation. Creatine supplementation increased TTF in CRE vs. PLA by ∼11% (P = 0.017) and work done above CP by ∼10% (P = 0.015), with no difference (P > 0.05) in reductions in MVC (-24 ± 8 vs. -20 ± 9%), Qpot (-39 ± 13 vs. -32 ± 14%), PS10 (-42 ± 14 vs. -36 ± 13%), PS100 (-25 ± 10 vs. -18 ± 12%) and voluntary activation (-7 ± 8 vs. -5 ± 7%) in CRE vs. PLA. No significant difference were found between ISO and both PLA and CRE (P > 0.05). These findings suggest similar levels of neuromuscular fatigue can be found following supra-CP cycling despite increases in performance time and amount of work done above CP, supporting the notion of a critical level of neuromuscular fatigue and challenging a direct causative link between W' depletion and neuromuscular fatigue. This article is protected by copyright. All rights reserved.