Popular Ergogenic Drugs and Supplements in Young Athletes
Ryan Calfee, MD and Paul Fadale, MD
Brown University School of Medicine, Providence, Rhode Island (PEDIATRICS Vol. 117 No. 3 March 2006, pp. e577-e589)
CREATINE
Physiology
Creatine is formed from glycine, arginine, and methionine and is naturally produced by the liver, kidneys, and pancreas. After production, creatine is transported to muscle, heart, and brain, with 95% of bodily stores remaining in muscle. Creatine is also naturally present in the diet, mainly in meat and fish. The daily requirement of creatine is 2 g, with this amount provided half from endogenous production and half from normal diet.74 Muscle creatine stores are in a balanced equilibrium with creatine and phosphocreatine interconverted via creatine kinase. Phosphocreatine provides energy to the muscle via its dephosphorylation, which donates a phosphate to adenosine diphosphate producing adenosine triphosphate (Fig 2). Aerobic recovery time then allows for the restoration of phosphocreatine.9 Phosphocreatine availability is considered the limiting factor in short, high-intensity activities, as it provides muscle with the major energy source over the first 10 seconds of anaerobic activity after free adenosine triphosphate is consumed in the first 1 second of action (Fig 3). 75,76
Investigations into the tissue level effects of oral creatine seem to show several changes. Supplementation can cause an 20% increase in muscle phosphocreatine stores, quicken the replenishment of phosphocreatine during recovery, and buffer lactic acid as hydrogen ions are consumed during the dephosphorylation of phosphocreatine, which potentially delays fatigue onset (Fig 2).77–79
Dosing
Creatine is recommended to be taken first in a loading phase, with athletes consuming 5 g 4 times per day for the first 4 to 6 days. The standard dosing then is 2 g/day for the next 3 months. Creatine taken in excess of this amount seems to be excreted via the kidneys.80 A month of abstinence is standard practice after each use cycle. The Physician's Desk Reference notes that athletes should consume 6 to 8 glasses of water per day while taking creatine to prevent dehydration.81 Absorption of oral creatine does vary with diet. Carbohydrate-rich fluids tend to increase creatine absorption, whereas caffeine impairs its uptake.82,83
Effects
Creatine supplementation does appear to have athletic benefits. However, nearly 30% of athletes do not see benefits with creatine use, thereby falling into a category of "nonresponders" who are theorized to have already maximal phosphocreatine stores.9 Most common, performance effects are seen in increasing strength and outcomes in short-duration, anaerobic events. Studies do not show improved endurance performance as expected given that prolonged muscle activity depends on aerobic glycolysis.84 In a well-controlled setting, Volek et al85 performed a double-blinded study that examined 12 weeks of creatine use including standard loading and maintenance phases in recreational weightlifters. In those athletes who were taking creatine, significant increases in fat-free body mass; bench press maximal lift; peak power production in sets of repeated jump squats; and biopsied type I, IIA, and IIAB muscle fibers were demonstrated.
Adverse Effects
Athletes who take creatine commonly experience early weight gain of 1.6 to 2.4 kg, which can be detrimental in purely speed-based events. It is also common for athletes to report minor gastrointestinal discomfort and muscle cramps, although these generally do not curb use.4 There have been 2 case reports of renal function compromise. One was an athlete who had previously diagnosed focal segmental glomerulosclerosis and experienced a transient 50% loss of glomerular filtration rate, and 1 previously healthy athlete reported transient interstitial nephritis.86,87 However, at least 1 study of self-reported use over several years did not show adverse renal effects.88 Three highly publicized deaths have occurred in college wrestlers who were known to take creatine, although official autopsy results indicated that dehydration and weight loss were at fault, not creatine.81 Additional questions remain, as there are no data to judge the effects of supplementation on the other tissues that store creatine (heart and brain), the effects of chronic use, or the effects of creatine use in minors.
Legal/Sports Aspects
Creatine remains a legal nutritional supplement today. Despite at least 1 brand's name, Teen Advantage, the American College of Sports Medicine has recommended explicitly that it is not to be used by anyone who is younger than 18 years.79 Collegiate teams, including trainers and coaches, are prohibited from supplying creatine or other supplements directly to their student athletes.
Eli yllaoleva (turhankin pitka patka) on tiivistelma tutkimuksista kreatiinin suhteen. Mulla oli mutu tuosta krean hiilareitten kanssa vetamisesta, eli pelkka voda ei ole ideaali. Samaten kertoo uudemman kerran tuosta kofeiinista, etta ei ole hyva idea -kumoaa vaikutuksen. Vaittaa myos, etta 3g riittaisi loadin jalkeen (jos nostaa 20% kropassa olevan kreafosfaatin maaraa ja se maara vakiona on about gramma, niin siina tapauksessa would make sense). Mielenkiintoista oli myos havaita, etta noin 30% ihmisista ei reagoi kreaan, jossain muualla luin syyksi sen, etta ilmeisesti heidan kropan kreafosfaatti on jo maksimissa eika lisakrea tuota muutosta mihinkaan. Ja olihan tuossa noita muitakin pointteja reilumminkin, lukekaa jos jaksatte.
