Dietary creatine supplementation and muscular adaptation to resistive overload.

Abstract

This study examined the influence of dietary creatine (CR) supplementation upon mechanical and hypertrophic responses to a well-defined conditioning stimulus provided by electromyostimulation (EMS). Eighteen resistance-trained subjects were assigned CR or a placebo (PL) in a randomized, double-blind fashion. After CR loading (20 g x d(-1) for 7 d), CR supplementation (5 g x d(-1)) or PL was continued for 8 wk. During supplementation, EMS (3--5 sets of 10 coupled eccentric and concentric actions) was applied to the left m. quadriceps femoris (QF) twice weekly while subjects continued voluntary resistance training of both lower limbs unsupervised. Cross-sectional area (CSA) of each QF was assessed with magnetic resonance imaging (MRI). Torque during EMS was analyzed to assess muscle loading and fatigue resistance. Maximal torque and the torque time integral increased markedly over training (P < or = 0.0001). These responses reflected activation of more muscle as EMS current was increased (about 16%), greater recovery between sets (P < or = 0.0423), and less fatigue during sets over training (P = 0.0002). CR did not influence these responses (P = 0.8093). In accord with these results, the increase in CSA for the stimulated QF (11%) was comparable for CR and PL (P = 0.2190). CSA in the nonstimulated QF increased 5% in CR (P = 0.0091) but did not change in PL. We conclude that CR supplementation did not augment the mechanical or hypertrophic response to a precisely measured conditioning stimulus that attenuated but did not ameliorate fatigue. We suggest that enhanced fatigue resistance may not explain the apparent ergogenic effect of CR during voluntary training.