Creatine continues to be a popular dietary supplement, with prevalence of use as high as 75% in some sports. Creatine ingestion and the subsequent increase in skeletal muscle creatine content may result in enhanced resistance to fatigue during intense exercise or increased lean body mass. Increased muscle creatine and phosphocreatine with oral creatine ingestion can be accomplished using two different approaches. In the first method, a ‘‘loading’’ dose of creatine, usually about 20 to 25 g/d (0.3 g $ kg 1 $ d 1), for 5 to 7 d is ingested [1]. In the second method, lower doses of creatine, usually about 2 to 5 g/d (0.03 g $ kg 1 $ d 1), for about 4 wk are ingested. This second protocol was based on the seminal work by Hultman et al. [1] who demon-strated that low doses of creatine supplementation could increase muscle creatine levels given adequate time. However, the minimal amount of creatine to have an effect (i.e., increased muscle creatine) and whether or not this can influence performance have not been clearly defined.
Although many drugs have a rapid onset of action, nutrients such as creatine have a delayed onset of action, because it must accumulate in skeletal muscle over time to exert its effect. Subsequently, any increase in muscle creatine after supplementation is a function of dose and duration. Although the commonly used high-dose creatine loading protocol (20 g/d for 5 d) results in about a 20% to 25% increase in muscle creatine, the majority of the ingested creatine is excreted in the urine. For example, Rawson et al. [2] previously reported that during high-dose creatine ingestion (20 g/d for 5 d), about 47% can be recovered in the urine. In this investigation, nearly 50% of the ingested creatine was lost in the urine by day 3 of supplementation [2]. Similarly, Law et al. [3] reported 48% and 55% urinary creatine excretions on days 3 and 6 of a typical creatine loading protocol (20 g/d for 5 d). Recently, Sale et al. [4] reported that 20 g of creatine ingestion per day in frequent low doses (20 g/d in 20 1-g doses) or a more traditional loading protocol (20 g/d in four 5-g doses) resulted in 49% and 62% of the creatine being excreted, respectively. Although these investigators were able to modify body creatine retention by altering dosing frequency throughout the day, the majority of creatine was still excreted in the urine.
Some groups have reported that lower doses of creatine can be ergogenic [5,6], although others have reported no effect [7,8]. These discordant findings likely resulted from differences in supplementation duration, training status of the participants, creatine formulation, and exercise test selection (e.g., single bout versus repeated bouts). A gap in the literature exists regarding the effects of low-dose creatine ingestion on high-intensity exercise performance and body composition when dosing is based on body size and administered over a period of time that would allow sufficient muscle uptake. The purpose of the present study was to examine the effects of low-dose creatine supple-mentation on body composition, muscle function, and body creatine retention. We hypothesized that very low-dose creatine ingestion, when ingested over a sufficient period, would improve muscle function.
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