KEYWORDS: supplements, creatine, strength, muscle mass, timing
ABSTRACT: Resistance training is a potent stimulus to enhance skeletal muscle hypertrophy and strength. Combining creatine supplementation with resistance training may be an effective strategy to enhance the physiological adaptations from resistance training alone. Emerging evidence suggests that the timing of creatine supplementation may be an important regulator of muscle hypertrophy and strength. Creatine ingested before and after resistance training sessions appear to be an effective strategy to increase muscle mass and strength, with slightly greater benefits if creatine is consumed after exercise compared to before. This brief review will evaluate the literature pertaining to the strategic ingestion of creatine and resistance training resulting in practical creatine supplementation strategies.
It is well established that the mechanical stimuli from resistance training increases muscle protein synthesis (1). Although the machinery for stimulating muscle protein synthesis is increased after resistance training (2), the anabolic response may be delayed post-exercise (3). The combination of creatine supplementation and resistance training may lead to greater muscle benefits than resistance training alone in young and older adults (4, 5). Furthermore, the timing of creatine ingestion may be an important factor for creating an anabolic environment for muscle growth (5). Emerging evidence suggests that creatine supplementation, in close proximity to resistance training sessions, may provide superior benefits compared to creatine intake at other times of the day (6, 7). While the mechanistic actions explaining the greater benefits from timed creatine ingestion are unknown, it is possible that blood flow kinetics and creatine transport are involved (8, 9). Therefore, the purpose of this review is to 1) briefly outline the potential beneficial effects of creatine supplementation, 2) review the emerging evidence involving the timing of creatine supplementation combined with resistance training, and 3) outline creatine supplementation strategies.
Creatine, methyl-guanidino acetic acid, is a naturally occurring nitrogen-containing compound (5, 10, 11). Creatine excretion occurs at a rate of ~2 g·d-1 (12). Creatine can be replaced via endogenous synthesis (1-2 g·d-1) in the kidneys, liver, and pancreas or through dietary intake, typically ~1-3 g·d-1 (11, 12). Creatine is found in high concentrations in red meat and seafood (12). Ninety-five percent of creatine is stored in skeletal muscle, of which 60-70 percent is phosphorylated (i.e. phosphocreatine)(13). Phosphocreatine rapidly resynthesizes adenosine diphopshate to help maintain adenosine triphosphate (ATP) during high intensity exercise such as resistance training (13). Theoretically, elevated phosphocreatine stores (via creatine supplementation) may increase exercise training intensity and the volume of work performed leading to greater muscle accretion and strength (reviewed in Branch (14); Rawson & Volek (15)). Several purported mechanisms exists which may help explain the typical increase in muscle mass and strength from creatine (4, 5, 10). Creatine supplementation elevates skeletal phosphocreatine and total creatine stores (16) which...