Creatine

Phosphocreatine (creatine) is a substance stored in muscles; it supplies phosphate to ATP and thus rapidly restores ATP during anaerobic muscle contraction. It is synthesized inside the liver from arginine, glycine, and methionine; dietary sources include milk, steak, and some fish.

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Pharmacodynamics

• Increases energy for high-intensity physical activity.
• Increases muscle mass.

Theoretical foundations

Creatine (Cr), or methylguanidinoacetic acid, is an amine made up of three amino acids (glycine, arginine, and methionine). CrP and adenosine triphosphate (ATP) provide most of the energy for short-term maximal exercise.

The average amount of creatine in skeletal muscle is 125 mmol kg-1 of dry muscle mass and ranges from 90-160 mmol kg-1 of dry muscle mass. Approximately 60% of muscle creatine is in the form of CrP. A portion of the creatine in CrP can be obtained from dietary creatine (primarily from meat products) or synthesized from the amino acids glycine and arginine. Muscle creatine is replenished at a rate of 2 g per day after its irreversible conversion to creatinine. The availability of CrP is important during short-term, high-intensity exercise because depletion of CrP prevents ATP resynthesis at the required rate. Theoretically, the ergogenic effect of CrP is due to the ability of CrP to rephosphorylate adenosine diphosphate (ADP) for ATP resynthesis during anaerobic metabolism. Creatine supplements are used to increase the speed and power extracted from the ATP-CrP energy system.

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Research results

Greenhaff noted that consuming 20-25 grams of creatine monohydrate per day (four to five 5-gram doses) for 5-7 days can produce a 20% increase in muscle creatine levels, of which about 20% is CrP. After this loading dose, a dose of 2-5 grams per day should maintain elevated creatine levels.

Numerous studies have examined the effects of Cr supplementation on athletic performance. Volek et al. examined the effects of Cr supplementation on muscle performance during repeated high-intensity resistance exercise. Groups receiving creatine and placebo performed bench press and bent-leg long jumps. The interventions were conducted three times (T1, T2, and T3) with an interval of 6 days. Before the T1 test, the groups did not receive supplements. Between T1 and T2, both groups received placebo. Between T2 and T3, one group received 25 g of creatine (5 doses of 5 g) per day, while the other continued to receive placebo. Creatine supplementation significantly increased peak power during all five jump sets and significantly improved the number of repetitions during the five bench press sets. The researchers concluded that resistance-trained athletes may benefit from taking creatine supplements because they can make their workouts more intense.

Additional studies have confirmed the ergogenic effect of Cr for a variety of high-power exercises. Creatine supplementation has been associated with increased strength in seated resistance exercises in women and in soccer players, increased maximal power in treadmill sprints, improved performance in single and repeated short bursts, and increased cycling time to exhaustion.

Engelhardt et al. looked at the effects of creatine supplementation on performance in triathlon athletes. After taking 20 g of creatine or placebo for 5 days, athletes were tested on endurance performance (30-minute cycle) with intervals of 15 s cycling and 45 s rest. The results showed that supplementation significantly (18%) increased power performance but had no effect on endurance performance.

However, not all studies have found positive results. In some studies, creatine supplementation failed to show even minimal ergogenic effects on strength and snatch performance. Creatine was also ineffective in endurance exercises.

Creatine supplementation also appears to increase lean mass. Is the increase in lean mass due to increased protein synthesis or fluid retention? Most studies report increases in body mass of 0.7 to 1.6 kg after short-term supplementation. Kreidor et al. studied total body mass versus total body water in soccer players over a 28-day supplementation period and in a control group of athletes. The creatine group increased total body mass by an average of 2.42 kg and had no significant increase in water volume. Further studies are needed to determine the effects of creatine supplementation on protein synthesis and fluid retention.

Claimed effect of phosphocreatine (creatine)

Creatine is believed to improve physical and athletic performance and reduce fatigue. Some studies suggest that creatine is effective in increasing workloads performed at short maximal effort (e.g., sprinting, weightlifting). It has been shown to be therapeutic in muscle phosphorylase deficiency (glycogen storage disease type 2) and choroidal and retinal atrophy; preliminary data also suggest possible adverse effects in Parkinson's disease and amyotrophic lateral sclerosis.

Dosing and administration

Many reports have noted that creatine supplementation has resulted in increased muscle cramps, muscle and tendon strains, muscle damage, and delayed recovery from injury. However, studies evaluating trained athletes during strenuous exercise have not reported such adverse effects.

Concerns that creatine supplements may put additional stress on the kidneys and liver have not been confirmed in the doses of creatine studied in healthy individuals. The only documented side effect of creatine supplementation is weight gain.

There is no evidence of long-term safety effects of creatine. The NCAA Competition and Medical Aspects of Sport Committee has initiated research into the long-term use of supplements and whether some people are susceptible to negative side effects.

The current recommended dose is 20-25g per day for 5-7 days, then 5g per day. If there is no need for further supplementation, the creatine washout period to achieve normal muscle levels lasts approximately 4 weeks.

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Side effects creatine

Creatine may cause weight gain, possibly due to increased muscle mass and apparent increases in serum creatinine levels. Minor gastrointestinal symptoms, dehydration, electrolyte imbalances, and muscle cramps have also been reported.

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