by NSCA’s Guide to Sport and Exercise Nutrition
Kinetic Select September 2019
The following is an exclusive excerpt from the book NSCA’s Guide to Sport and Exercise Nutrition, published by Human Kinetics. All text and images provided by Human Kinetics.
The sport supplement creatine has been the gold standard to which other nutritional supplements are compared (Greenwood, Kalman, and Antonio 2008) because it improves performance, increases lean body mass, and has an excellent safety profile when consumed in recommended dosages (Greenwood, Kalman, and Antonio 2008). Creatine is one of the most widely researched sport nutrition supplements on the market. Among several methods of ingestion, the most common is to mix creatine as a powder into a drink. Creatine is also commonly ingested in the form of a capsule.
Chemically, creatine is derived from the amino acids glycine, arginine, and methionine; it is obtained from the ingestion of meat or fish and is also synthesized in the kidney, liver, and pancreas (Balsom, Soderlund, and Ekblom 1994; Heymsfield et al. 1983). When creatine enters the muscle cell, it accepts a high-energy phosphate and forms phosphocreatine. Phosphocreatine is the storage form of high-energy phosphate, which is used by the skeletal muscle cell to rapidly regenerate adenosine triphosphate (ATP) during bouts of maximal muscular contraction (Hirvonen et al. 1987). The conversion of ATP into adenosine diphosphate (ADP) and a phosphate group generates the energy needed by the muscles during short-term, high-intensity exercise. The energy for all-out maximal-effort exercise lasting up to approximately 6 seconds (typical duration of activity for a strength and power athlete) is primarily derived from limited stores of ATP in the muscle. Phosphocreatine availability in the muscles is vitally important in energy production since ATP cannot be stored in excessive amounts within the muscle and is rapidly depleted during bouts of exhaustive or high-intensity exercise.
Oral creatine monohydrate supplementation has been reported to increase muscle creatine and phosphocreatine content by 15% to 40%, enhance the cellular bioenergetics of the phosphagen system, improve the shuttling of high-energy phosphates between the mitochondria and cytosol via the creatine phosphate shuttle, and enhance the activity of various metabolic pathways (Kreider 2003a). Relative to dosage, the majority of published studies on creatine supplementation divided the typical dosage pattern into two phases: a loading phase and a maintenance phase. A typical loading phase comprises 20 g of creatine (or 0.3 g/kg body weight) in divided doses four times a day for two to seven days; this is followed by a maintenance dose of 2 to 5 g daily (or 0.03 g/kg body weight) for several weeks to months at a time.
➤➤ phosphagen system—The quickest and most powerful source of energy for muscle movement.
Scientific studies indicate that creatine supplementation is an effective and safe nutritional strategy to promote gains in strength and muscle mass during resistance training—both important attributes for the strength and power athlete (Greenwood et al. 2000; Kreider 2003a, 2003b; Stout et al. 2000; Volek et al. 1997). Specific to lean body mass, creatine supplementation has been shown to be effective in several cohorts, including males, females, and the elderly (Branch 2003; Brose, Parise, and Tarnopolsky 2003; Chrusch et al. 2001; Kreider et al. 1998; van Loon et al. 2003). Short-term
creatine supplementation increases total body mass by approximately 0.8 to 1.7 kg (~1.8 to 3.7 pounds). Longer-term creatine supplementation (e.g., six to eight weeks) in conjunction with resistance training increased lean body mass by approximately 2.8 to 3.2 kg (~7 pounds) (Greenwood, Kalman, and Antonio 2008; Earnest et al. 1995; Kreider et al. 1996; Stout, Eckerson, and Noonan 1999).
Unequivocally, one of the most visible effects of creatine supplementation is an increase in body mass. However, for the strength and power athlete, an increase in body mass will impart benefit only if the weight gain is in the form of lean tissue. Fortunately, several scientific investigations have demonstrated that gains in body mass are partially attributable to actual increases in the cellular protein content of muscle tissue (Volek et al. 1999; Willoughby and Rosene 2001). For more information on the changes in skeletal muscle protein content and overall changes in body composition in response to creatine supplementation, refer to chapter 10.
Creatine can also be advantageous to strength athletes given its ability to promote strength gains during training. Studies indicate that creatine supplementation during training can increase gains in 1-repetition maximum (1RM) strength and power. Peeters, Lantz, and Mayhew (1999) investigated the effect of creatine monohydrate and creatine phosphate supplementation on strength, body composition, and blood pressure over a six-week period. Strength tests performed were the 1RM bench press, 1RM leg press, and maximal repetitions on the seated preacher bar curl with a fixed amount of weight. Subjects were matched for strength and placed into one of three groups—a placebo, creatine monohydrate, or creatine phosphate group. All subjects performed a standardized strength training regimen and ingested a loading dosage of 20 g/day for the first three days of the study, followed by a maintenance dose of 10 g/day for the remainder of the six-week supplementation period. Significant differences were noted between the placebo group and the two creatine groups for changes in lean body mass, body weight, and 1RM bench press. Eckerson and colleagues (2004) also studied the effects of two and five days of creatine loading on anaerobic working capacity using the critical power test. Ten physically active women randomly received two treatments separated by a five-week washout period: (a) 18 g dextrose as placebo or (b) 5 g creatine plus 18 g dextrose taken four times a day for five days. Ingesting the placebo resulted in no significant changes in anaerobic working capacity; however, creatine ingestion significantly increased anaerobic working capacity by 22.1% after five days of loading.
Elsewhere, Kreider and colleagues (1998) conducted a study in which 25 National Collegiate Athletic Association Division IA football players supplemented their diet for 28 days with creatine or a placebo during resistance and agility training. Before and after the supplementation protocol, the football players performed a maximal-repetition test on the isotonic bench press, squat, and power clean and also performed a high-intensity cycle ergometer sprint test. The creatine group showed significantly greater gains in bench press lifting volume; the sum of bench press, squat, and power clean lifting volume; and total work performed during the first five 6-second cycle ergometer sprints. Ingestion of creatine promoted greater gains in fat-free mass, isotonic lifting volume, and sprint performance during intense resistance and agility training.
The studies reviewed here are only a few among dozens that have shown an increase in strength, power, and high-intensity performance. Combined, these three studies indicate that creatine supplementation can increase maximal strength, high-intensity exercise performance, and lifting volume. The International Society of Sports Nutrition (Buford et al. 2007) stated in its comprehensive review on creatine supplementation and position stand:
NSCA’s Guide to Sport and Exercise Nutrition will lead you through the key concepts of sport and exercise nutrition so that you can assess an individual’s nutrition status and—if it falls within your scope of practice—develop customized nutrition plans. The book is available in bookstores everywhere, as well as online at the NSCA Store.