SKELETAL-MUSCLE METABOLISM DURING SHORT-DURATION HIGH-INTENSITY EXERCISE - INFLUENCE OF CREATINE SUPPLEMENTATION

Seven male subjects performed repeated bouts of high-intensity exercis e, on a cycle ergometer, before and after 6 d of creatine supplementat ion (20 g Cr H2O day(-1)). The exercise protocol consisted of five 6-s exercise periods performed at a fixed exercise intensity, intersperse d with 30-s recovery periods (Part I), followed (40 s later) by one 10 s exercise period (Part II) where the ability to maintain power outpu t was evaluated. Muscle biopsies were taken from m. vastus lateralis a t rest, and immediately after (i) the fifth 6 s exercise period in Par t I and (ii) the 10 s exercise period in Part II. In addition, a serie s of counter movement (CMJ) and squat (SJ) jumps were performed before and after the administration period. As a result of the creatine supp lementation, total muscle creatine [creatine (Cr)+phosphocreatine (PCr )] concentration at rest increased from (mean +/- SEM) 128.7 (4.3) to 151.5 (5.5) mmol kg(-1) dry wt (P < 0.05). This was accompanied by a 1 .1 (0.5) kg increase in body mass (P < 0.05). After the fifth exercise bout in Part I of the exercise protocol, PCr concentration was higher [69.7 (2.3) vs. 45.6 (7.5) mmol kg(-1) dry wt, P < 0.05], and muscle lactate was lower [26.2 (5.5) vs. 44.3 (9.9) mmol kg(-1) dry wt, P < 0 .05] after vs. before supplementation. In Part II, after creatine supp lementation, subjects mere better able to maintain power output during the 10-s exercise period (P < 0.05). There was no change in jump perf ormance as a result of the creatine supplementation (P > 0.05). These findings show that enhanced fatigue resistance during short duration h igh-intensity exercise following creatine supplementation is associate d with a greater availability of PCr and a lower accumulation of lacta te in the muscle. The finding that jump performance was not enhanced s uggests that short-term creatine feeding does not influence peak power output.