Title: Oral Creatine and Exercise
Key words: creatine monohydrate, glycine, arginine, phosphocreatine, muscle fatigue, exercise performance, high intensity exercise, ATP, glycolysis, ergogenic
Date: Aug 2000
Category: 12. Sports
Author: Dr van Rhijn
Oral Creatine and Exercise
Creatine monohydrate, a nitrogen containing compound abundant in meat and fish but also synthesized by liver, kidney and pancreas (from amino acids glycine & arginine), is mostly stored in skeletal muscle (95%) as phosphocreatine (PCr)1 and involved in production of energy for high intensity activity. The scientific rational for creatine (Cr) supplementation, by competitive athletes to increase body stores in order to prevent muscle fatigue and enhance exercise performance, will be discussed.
Ingestion of 5g of Creatine will increase plasma levels from approximately 30 to 800 mmol/l within an hour, gradually returning to baseline levels over a period of 6-7 hours. Animal studies confirm increased muscle uptake with plasma concentrations above 500 mmol/l. Further studies show beneficial effects of supplementation (dose: 5-6 grams taken 4 times per day), achieving maximum muscle stores saturation (127–149 mmol/kg dry muscle) after 4-5 days2. Subsequently, stores can be maintained by an intake of 2 gram per day3, and muscle stores will decline gradually over 6-8 weeks following supplementation of this regime. Vegetarians (responders) benefit most, as they tend to have a lower muscle Cr content4. The kidney rapidly disposes excess plasma Cr levels, reducing the danger of side effects. No toxicity has been observed in short-term supplementation at these levels.
Creatine is indispensable to muscle contraction. Supplementation extends the capacity to maintain a specific level of high intensity, intermittent exercise5, and may benefit competitors participating in sports requiring short-term6, repeated7,8, explosive bursts of maximum effort with short recovery periods in between9, such as swimming, sprinting or football. It maximises the training effect, enhances strength10 & peak performance11,12,13 as well as total work output14,15 by delaying or preventing fatigue16 in repeated bouts of high-intensity exercise17,18.
Research evidence tends to show that Cr supplementation exhibits small but significant physiological and performance changes in healthy young adult male subjects. However, the evidence is not written in stone as therapeutic doses (>2g/day)19 are required to show an effect and various studies fail to show any benefit on velocity20 or performance21,22,23. Cr supplementation does not increase maximal isometric strength, rate of maximal force production, nor aerobic endurance exercise performance24.
The need for high energy production is vital in high intensity sport performance and one of the most commonly designated energy systems, the immediate ATP-CP phosphagen system25, provides the explosive power in final thrust or sprint work. PCr breakdown provides by far the most ATP synthesis26,27 to fulfil this demand, as ATP alone is too slow to produce the necessary energy.
PCr + ADP + H+ « ATP + Cr
Oral Cr supplementation probably assists sporting performance by increasing the total PCr stores28,29, thereby blunting ATP decline and by making PCr more readily available for resynthesis30,31 (temporal & spatial energy buffering)32 of substances for muscular enhanced energy production (high energy phosphate bond release). Stores are usually depleted after 20 seconds. It may also act as a proton buffer against lactic acid production33 (reduce accumulation and pH), therefore reducing muscle fatigue (facilitate recovery) during high intensity activities. The subsequent delayed and reduced reliance on the short term, anaerobic glycolysis to contribute to ATP production may be a factor here34. Cr is also an osmotically active substance, increasing the intracellular hydration, enhancing protein synthesis and increasing fat-free body mass35,36, thereby improving muscular performance.
On balance, Cr may probably classify as a true ergogenic aid in short, intense intermittent work bouts. Therapeutic levels of Cr supplementation are relatively new and very popular. It is advisable to take supplements only under appropriate medical supervision, as little data is available at present regarding the long-term side effects37.
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