Creatine monohydrate is the form generally used and tested. In practice, this is available in three different forms, which differ according to particle size (granular, powder and micronised), in the belief that smaller particles are more fully absorbed and cause less gastric distress. ERGOGENIC AID
Creatine supplementation has become one of the most widely used supplements taken by athletes and is touted by some as the only truly effective ergogenic aid besides carbohydrate loading. It is used by athletes engaged in sprint disciplines (e.g. 100 m run or 50 m swim), strength disciplines (e.g. weight lifting) or high-intensity, repetitive burst exercise (e.g. tennis, hockey, football, soccer) separated by short bouts of recovery. Its use is based on the assumption that supplementation at doses above dietary levels will increase energy and power output and also enhance recovery
Hundreds of small studies have attempted to evaluate the effects of creatine supplementation on exercise capacity and muscle physiology in various populations.
A 2003 review of the literature concluded that approximately 300 studies have evaluated its potential as an ergogenic aid, with about 70% of studies reporting statistically significant positive results (Kreider 2003).
Who will respond? The observation that not every athlete responds to creatine supplementation with improved strength, performance and recovery has prompted investigation into identifying key features of responders. One study identified that responders had the lowest initial levels of muscle creatine, greatest percentage of type 2 fibres, greatest preload muscle fibre cross-sectional area and fat free mass in comparison to non-responders (Syrotuik & Bell 2004). Other factors that are likely to influence an individual's response to creatine include training status, diet, age and the bioavailability of the creatine supplement being used. Not taking these factors into account may partly explain the inconsistent results obtained in randomised studies. Short duration, high-intensity exercise Most, but not all, controlled studies have shown that supplementation improves performance and delays muscle fatigue (Balsom et al 1995, Becque et al 2000, Burke et al 1996, Cox et al 2002, Finn et al 2001, Gilliam et al 2000, Kreider et al 1998, Maganaris & Maughan 1998, Mujika & © 2007 Elsevier Australia
Padilla 1997, Mujika et al 2000, Tarnopolsky & MacLennan 2000, Williams & Branch 1998). Studies have been conducted in a variety of athletes, such as sprint cyclists, soccer players and sprint swimmers, and generally used a dose of 20 g daily. Lean body mass Creatine increases exercise-related gains in lean body mass (Chrusch et al 2001, Jowko et al 2001, Stone et al 1999), although some of these apparent gains may actually represent water retention in the muscles. Enhanced power Many studies show that creatine supplementation in conjunction with resistance training augments gains in muscle strength and size, although the effect is not consistent for everybody (Spriet & Gibala 2004, Volek & Rawson 2004). Creatine supplementation increases muscle fibre hypertrophy, myosin heavy chain expression and swelling of myocytes, which may in turn affect carbohydrate and protein metabolism. Supplementation also increases acute weightlifting performance and training volume, which may allow for greater overload and adaptation to training.
A 2003 review of 22 studies estimated that the average increase in muscle strength following creatine supplementation as an adjunct to resistance training was 8% greater than for placebo (20% vs 12%) (Rawson & Volek 2003). Similarly, the average increase in weightlifting performance (maximal repetitions at a given percentage of maximal strength) following creatine supplementation plus resistance training was 14% greater than placebo (26% vs 12%).
Reducing strength decline in the elderly The effects of supplemental creatine in older adults has been investigated in a few studies, overall producing positive results (Brose et al 2003, Chrusch et al 2001, Kreider et al 1998). One randomised, doubleblind study involving 30 older men (>70 years) showed that resistance training combined with creatine supplementation produced significantly greater increases in lean tissue mass, leg strength, endurance and average power than placebo (Chrusch et al 2001). The dose regimen used was 0.3 g/kg for the first 5 days followed by 0.07 g/kg thereafter. Another double-blind study in 28 men and women aged over 65 years showed that creatine supplementation (5 g daily) combined with resistance training enhanced the increase in total and fat-free mass, and gains in several indices of isometric muscle strength (Brose et al 2003).
Cervical level spinal cord injury According to a randomised, double-blind, placebo controlled crossover trial, creatine supplementation enhances upper extremity work capacity in subjects with complete cervical-level spinal cord injury (Jacobs etal 2002).
Clinical note — The Australian Institute of Sport Supplement Program
TheAIS is world renowned for Its professionalism and high-quality training programs. In 2000, a project called the AIS Sports Supplement Program was developed to ensure that athletes use supplements correctly and confidently, and receive 'cutting edge' advice on nutritional practices. In order to streamline the information available, a panel of experts categorised some of the most popular sports supplements into various classes to clarify which are approved or recommended and which are directly banned by international doping rules. Some of the approved supplements recommended for use include creatine, antioxidants (vitamins C and E), multivitamins, iron, calcium supplements and sports drinks.
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