Creatine supplementation does not improve sprint performance in competitive swimmers

Creatine supplementation protocols with or without training interventions on body composition: a GRADE-assessed systematic review and dose-response meta-analysis

BACKGROUND

Despite the robust evidence demonstrating positive effects from creatine supplementation (primarily when associated with resistance training) on measures of body composition, there is a lack of a comprehensive evaluation regarding the influence of creatine protocol parameters (including dose and form) on body mass and estimates of fat-free and fat mass.

METHODS

Randomized controlled trials (RCTs) evaluating the effect of creatine supplementation on body composition were included. Electronic databases, including PubMed, Web of Science, and Scopus were searched up to July 2023. Heterogeneity tests were performed. Random effect models were assessed based on the heterogeneity tests, and pooled data were examined to determine the weighted mean difference (WMD) with a 95% confidence interval (CI).

RESULTS

From 4831 initial records, a total of 143 studies met the inclusion criteria. Creatine supplementation increased body mass (WMD: 0.86 kg; 95% CI: 0.76 to 0.96, I2 = 0%) and fat-free mass (WMD: 0.82 kg; 95% CI: 0.57 to 1.06, I2 = 0%) while reducing body fat percentage (WMD: -0.28 %; 95% CI: -0.47 to -0.09; I2 = 0%). Studies that incorporated a maintenance dose of creatine or performed resistance training in conjunction with supplementation had greater effects on body composition.

CONCLUSION

Creatine supplementation has a small effect on body mass and estimates of fat-free mass and body fat percentage. These findings were more robust when combined with resistance training.

Creatine Supplementation in Women's Health: A Lifespan Perspective

Despite extensive research on creatine, evidence for use among females is understudied. Creatine characteristics vary between males and females, with females exhibiting 70–80% lower endogenous creatine stores compared to males. Understanding creatine metabolism pre- and post-menopause yields important implications for creatine supplementation for performance and health among females. Due to the hormone-related changes to creatine kinetics and phosphocreatine resynthesis, supplementation may be particularly important during menses, pregnancy, post-partum, during and post-menopause. Creatine supplementation among pre-menopausal females appears to be effective for improving strength and exercise performance. Post-menopausal females may also experience benefits in skeletal muscle size and function when consuming high doses of creatine (0.3 g·kg⁻¹·d⁻¹); and favorable effects on bone when combined with resistance training. Pre-clinical and clinical evidence indicates positive effects from creatine supplementation on mood and cognition, possibly by restoring brain energy levels and homeostasis. Creatine supplementation may be even more effective for females by supporting a pro-energetic environment in the brain. The purpose of this review was to highlight the use of creatine in females across the lifespan with particular emphasis on performance, body composition, mood, and dosing strategies.

Supplements and Nutritional Interventions to Augment High-Intensity Interval Training Physiological and Performance Adaptations-A Narrative Review

High-intensity interval training (HIIT) involves short bursts of intense activity interspersed by periods of low-intensity exercise or rest. HIIT is a viable alternative to traditional continuous moderate-intensity endurance training to enhance maximal oxygen uptake and endurance performance. Combining nutritional strategies with HIIT may result in more favorable outcomes. The purpose of this narrative review is to highlight key dietary interventions that may augment adaptations to HIIT, including creatine monohydrate, caffeine, nitrate, sodium bicarbonate, beta-alanine, protein, and essential amino acids, as well as manipulating carbohydrate availability. Nutrient timing and potential sex differences are also discussed. Overall, sodium bicarbonate and nitrates show promise for enhancing HIIT adaptations and performance. Beta-alanine has the potential to increase training volume and intensity and improve HIIT adaptations. Caffeine and creatine have potential benefits, however, longer-term studies are lacking. Presently, there is a lack of evidence supporting high protein diets to augment HIIT. Low carbohydrate training enhances the upregulation of mitochondrial enzymes, however, there does not seem to be a performance advantage, and a periodized approach may be warranted. Lastly, potential sex differences suggest the need for future research to examine sex-specific nutritional strategies in response to HIIT.

Caffeine and Bicarbonate for Speed. A Meta-Analysis of Legal Supplements Potential for Improving Intense Endurance Exercise Performance

A 1% change in average speed is enough to affect medal rankings in intense Olympic endurance events lasting ~45 s to 8 min which for example includes 100 m swimming and 400 m running (~1 min), 1,500 m running and 4000 m track cycling (~4 min) and 2,000 m rowing (~6-8 min). To maximize the likelihood of winning, athletes utilizes legal supplements with or without scientifically documented beneficial effects on performance. Therefore, a continued systematic evidence based evaluation of the possible ergogenic effects is of high importance. A meta-analysis was conducted with a strict focus on closed-end performance tests in humans in the time domain from 45 s to 8 min. These test include time-trials or total work done in a given time. This selection criterion results in a high relevance for athletic performance. Only peer-reviewed placebo controlled studies were included. The often applied and potentially ergogenic supplements beta-alanine, bicarbonate, caffeine and nitrate were selected for analysis. Following a systematic search in Pubmed and SportsDiscuss combined with evaluation of cross references a total of 7 (beta-alanine), 25 (bicarbonate), 9 (caffeine), and 5 (nitrate) studies was included in the meta-analysis. For each study, performance was converted to an average speed (km/h) from which an effect size (ES; Cohens d with 95% confidence intervals) was calculated. A small effect and significant performance improvement relative to placebo was observed for caffeine (ES: 0.41 [0.15–0.68], P = 0.002) and bicarbonate (ES: 0.40 [0.27–0.54], P < 0.001). Trivial and non-significant effects on performance was observed for nitrate (ES: 0.19 [−0.03–0.40], P = 0.09) and beta-alanine (ES: 0.17 [−0.12–0.46], P = 0.24). Thus, caffeine's and bicarbonate's ergogenic effect is clearly documented for intense endurance performance. Importantly, for all supplements an individualized approach may improve the ergogenic effect on performance.

"Nutraceuticals" in relation to human skeletal muscle and exercise

Skeletal muscles have a fundamental role in locomotion and whole body metabolism, with muscle mass and quality being linked to improved health and even lifespan. Optimizing nutrition in combination with exercise is considered an established, effective ergogenic practice for athletic performance. Importantly, exercise and nutritional approaches also remain arguably the most effective countermeasure for muscle dysfunction associated with aging and numerous clinical conditions, e.g., cancer cachexia, COPD, and organ failure, via engendering favorable adaptations such as increased muscle mass and oxidative capacity. Therefore, it is important to consider the effects of established and novel effectors of muscle mass, function, and metabolism in relation to nutrition and exercise. To address this gap, in this review, we detail existing evidence surrounding the efficacy of a nonexhaustive list of macronutrient, micronutrient, and "nutraceutical" compounds alone and in combination with exercise in relation to skeletal muscle mass, metabolism (protein and fuel), and exercise performance (i.e., strength and endurance capacity). It has long been established that macronutrients have specific roles and impact upon protein metabolism and exercise performance, (i.e., protein positively influences muscle mass and protein metabolism), whereas carbohydrate and fat intakes can influence fuel metabolism and exercise performance. Regarding novel nutraceuticals, we show that the following ones in particular may have effects in relation to 1) muscle mass/protein metabolism: leucine, hydroxyl β-methylbutyrate, creatine, vitamin-D, ursolic acid, and phosphatidic acid; and 2) exercise performance: (i.e., strength or endurance capacity): hydroxyl β-methylbutyrate, carnitine, creatine, nitrates, and β-alanine.

Effect of 10 week beta-alanine supplementation on competition and training performance in elite swimmers

Although some laboratory-based studies show an ergogenic effect with beta-alanine supplementation, there is a lack of field-based research in training and competition settings. Elite/Sub-elite swimmers (n = 23 males and 18 females, age = 21.7 ± 2.8 years; mean ± SD) were supplemented with either beta-alanine (4 weeks loading phase of 4.8 g/day and 3.2 g/day thereafter) or placebo for 10 weeks. Competition performance times were log-transformed, then evaluated before (National Championships) and after (international or national selection meet) supplementation. Swimmers also completed three standardized training sets at baseline, 4 and 10 weeks of supplementation. Capillary blood was analyzed for pH, bicarbonate and lactate concentration in both competition and training. There was an unclear effect (0.4%; ± 0.8%, mean, ± 90% confidence limits) of beta-alanine on competition performance compared to placebo with no meaningful changes in blood chemistry. While there was a transient improvement on training performance after 4 weeks with beta-alanine (-1.3%; ± 1.0%), there was an unclear effect at ten weeks (-0.2%; ± 1.5%) and no meaningful changes in blood chemistry. Beta-alanine supplementation appears to have minimal effect on swimming performance in non-laboratory controlled real-world training and competition settings.

Nutritional supplements: prevalence of use and contamination with doping agents

Based upon recent sales numbers, nutritional supplements play a key role in the lifestyle of a substantial proportion of the population. As well as products such as vitamins or minerals, several precursors of anabolic steroids are marketed as nutritional supplements. Another group of commercially available supplements are products for weight loss based upon herbal formulations originating from Ephedra species. Apart from supplements indicating the presence of these active compounds, numerous non-hormonal nutritional supplements were found that were contaminated with non-labelled anabolic steroids. Stimulating agents other than naturally occurring analogues of ephedrine were detected. A major group using dietary supplements are sportsmen, ranging from amateur level to elite athletes. Besides the possible health risks associated with the use of dietary supplements, athletes should take care not to violate the rules of the World Anti-Doping Agency because athletes remain responsible for substances detected in their biofluids, irrespective of their origin. Several analytical methods have been developed to determine the presence of doping agents as contaminants. The present review attempts to address the issues concerning the use of nutritional supplements and the detection of doping agents as contaminants in dietary supplements.

Sports doping in the adolescent: the Faustian conundrum of Hors de Combat

The drive toward success in sports and the need for a cosmetically acceptable appearance have driven many adolescents to take a wide variety of so-called doping substances. The consumption of these chemicals in the hope and hype of improved sports performance, fueled by the easing of government restrictions on their proof of safety and efficacy, has resulted in an explosion of so-called ergogenic products available to our youth. Agents that have been used include anabolic steroids, anabolic-like agents, designer steroids, creatine, protein and amino acid supplements, minerals, antioxidants, stimulants, blood doping, erythropoietin, beta-blockers, and others. The use of these agents has considerable potential to cause physical and psychological damage. Use and misuse of drugs in this sports doping process should be discouraged. This discussion reviews some of the agents that are currently being used. Clinicians providing sports medicine care to youth, whether through anticipatory guidance or direct sports medicine management, should educate their young patients about the hype and hyperbole of these products that may keep them out instead of in the game at considerable financial cost to the unwary consumer.

Global and targeted gene expression and protein content in skeletal muscle of young men following short-term creatine monohydrate supplementation

Creatine monohydrate (CrM) supplementation has been shown to increase fat-free mass and muscle power output possibly via cell swelling. Little is known about the cellular response to CrM. We investigated the effect of short-term CrM supplementation on global and targeted mRNA expression and protein content in human skeletal muscle. In a randomized, placebo-controlled, crossover, double-blind design, 12 young, healthy, nonobese men were supplemented with either a placebo (PL) or CrM (loading phase, 20 g/day x 3 days; maintenance phase, 5 g/day x 7 days) for 10 days. Following a 28-day washout period, subjects were put on the alternate supplementation for 10 days. Muscle biopsies of the vastus lateralis were obtained and were assessed for mRNA expression (cDNA microarrays + real-time PCR) and protein content (Kinetworks KPKS 1.0 Protein Kinase screen). CrM supplementation significantly increased fat-free mass, total body water, and body weight of the participants (P < 0.05). Also, CrM supplementation significantly upregulated (1.3- to 5.0-fold) the mRNA content of genes and protein content of kinases involved in osmosensing and signal transduction, cytoskeleton remodeling, protein and glycogen synthesis regulation, satellite cell proliferation and differentiation, DNA replication and repair, RNA transcription control, and cell survival. We are the first to report this large-scale gene expression in the skeletal muscle with short-term CrM supplementation, a response that suggests changes in cellular osmolarity.

Effect of creatine supplementation on training for competition in elite swimmers

PURPOSE

The study was conducted to examine the effects of oral creatine supplementation on training for competition in 20 elite swimmers.

METHODS

Subjects performed a maximal sprint test (8 x 50 yd (45.72 m), T1) before loading with creatine (Cr, 20 g.d Cr monohydrate for 5 d), 1 wk later (T2), and following a 22- to 27-wk period of training and competition (T3). Following T2, subjects supplemented with either Cr (3 g + glucose 7 g.d) or placebo (glucose 10 g.d; double blind) for the remainder of the 22- to 27-wk season and then both groups supplemented once more with 20 g.d Cr monohydrate for 5 d before their major competition. Venous and capillary blood samples were obtained pre- and posttest during the repeated sprint tests to determine blood metabolites and hormones. Competition times were recorded, and changes in subjects' best times were used to compare the effect of training and supplementation on competitive performance.

RESULTS

Mean competition times in the Cr and control groups changed by+1.90 +/-1.91 and+0.72+/-1.64% for short course (SC, 25-m pool) and by+0.14+/-1.14 and -0.59+/-0.82% long course (LC, 50-m pool), respectively (Cr vs control, NS). No differences between groups were found in blood metabolites, although the human growth hormone (hGH) response to repeated sprints was blunted following Cr loading (T1, 30.42+/-14.60 and 28.95+/-18.27 microg.L; T2, 21.48+/-13.96 and 14.24+/-7.32 microg.L for Cr and control groups, respectively P<0.05).

CONCLUSION

No statistically significant differences in performance were observed between groups after long-term maintenance during training, although small differences were observed that might be meaningful for elite performers.

Influence of creatine supplementation on 800 m wheelchair performance: a pilot study

STUDY DESIGN

Double-blind, placebo-controlled, randomly assigned, crossover.

OBJECTIVE

To assess the influence of a short-term oral creatine supplementation on 800 m wheelchair performance.

SETTING

Swiss Paraplegic Centre, Nottwil, Switzerland.

SUBJECTS

In total, six (four male, two female subjects) competitive wheelchair athletes participated in the study. Their age was 33.0+/-9.1 years, height 171.5+/-7.7 cm and weight 63.1+/-6.2 kg. Average weekly training volume was 10.0+/-3.7 h. All of them have been engaged in regular training for over 10.5+/-7.2 years.

METHODS

During the two treatment periods, subjects ingested 4 x 5 g of creatine monohydrate or placebo (maltodextrin) daily during 6 days in a randomised order. A washout period of 4 weeks lay in-between the two supplementation periods. Before and after each treatment period athletes performed an all-out 800 m wheelchair test on a training roller. Time to complete 800 m, rate of perceived exertion (RPE), lactate concentrations and heart rate were measured. Before each test, body weight was determined.

RESULTS

Times to complete 800 m before and after creatine supplementation (102.8+/-13.9 versus 100.5+/-11.3 s) compared to before and after placebo supplementation (101.6+/-15.6 versus 99.5+/-13.8 s) were not significantly different. Moreover, for all other parameters measured, no significant differences between creatine and placebo supplementation were found.

CONCLUSION

A short-term oral creatine supplementation compared to placebo seems not to enhance performance over 800 m in trained, spinal cord-injured, wheelchair athletes.

Creatine supplementation and performance in 6 consecutive 60 meter sprints

Creatine is an ergogenic aid used in individual and team sports. The aim of this study is to analyze the effect of monohydrate creatine supplementation on physical performance during 6 consecutive maximal speed 60 meter races, and the changes induced in some characteristic biochemical and ventilatory parameters. The study was carried out on nineteen healthy and physically active male volunteers, and randomly distributed into two groups: Group C received a supplement of creatine monohydrate (20 g/day for 5 days) and group P received placebo. Tests were performed before and after supplementation. No significant changes were observed in weight or body water measured by bioimpedance or the sum of 7 skinfold or performance during the 60 meter races. Group C showed a statistically significant increase in plasma creatinine from 69.8 +/- 12.4 to 89.3 +/- 12.4 micromol x L(-1) (p<0.05). In group C in the second control day (after creatine supplementation), expiratory volume V(E), O2 uptake and CO2 production were lower after 2 minutes of active recovery period. These results indicate that creatine monohydrate supplementation does not appear to improve the performance in 6 consecutive 60 meter repeated races but may modify ventilatory dynamics during the recovery after maximal effort.

Ergogenic aids: a review of basic science, performance, side effects, and status in sports

The use of drugs and supplements to enhance performance has become a part of mainstream athletics. Many team physicians and sports medicine practitioners are unfamiliar with the benefits and risks of these products and thus are unable to educate young athletes on this topic. In spite of numerous reports on the health risks of anabolic steroid use, 1 to 3 million Americans have used them. Human growth hormone has been tried by up to 5% of 10th graders, although no scientific study has shown that it is an effective performance-enhancing drug. Amphetamines and similar compounds may be the most widely abused drug in baseball; recently, they have come under increased scrutiny in sport. Erythropoietin is a highly effective aerobic enhancer that has been linked to multiple deaths in cyclists and other endurance athletes. The neutraceutical industry, led by supplements such as creatine, ephedra, and androstenedione, remains unregulated by the Food and Drug Administration and has serious issues with quality and side effects. An understanding of these products is essential for the sports medicine practitioner to provide sound, safe advice to the athlete.

Effects of creatine supplementation on the performance and body composition of competitive swimmers

The objective of this study was to determine the effect of creatine supplementation on performance and body composition of swimmers. Eighteen swimmers were evaluated in terms of post-performance lactate accumulation, body composition, creatine and creatinine excretion, and serum creatinine concentrations before and after creatine or placebo supplementation. No significant differences were observed in the marks obtained in swimming tests after supplementation, although lactate concentrations were higher in placebo group during this period. In the creatine-supplemented group, urinary creatine, creatinine, and body mass, lean mass and body water were significantly increased, but no significant difference in muscle or bone mass was observed. These results suggest that creatine supplementation cannot be considered to be an ergogenic supplement ensuring improved performance and muscle mass gain in swimmers.

Popular sports supplements and ergogenic aids

This article reviews the evidence-based ergogenic potential and adverse effects of 14 of the most common products in use by recreational and elite athletes today. Both legal and prohibited products are discussed. This is an aggressively marketed and controversial area of sports medicine worldwide. It is therefore prudent for the clinician to be well versed in the more popular supplements and drugs reputed to be ergogenic in order to distinguish fact from fiction.Antioxidants, proteins and amino acids are essential components of diet, but additional oral supplementation does not increase endurance or strength. Caffeine is ergogenic in certain aerobic activities. Creatine is ergogenic in repetitive anaerobic cycling sprints but not running or swimming. Ephedrine and pseudoephedrine may be ergogenic but have detrimental cardiovascular effects. Erythropoietin is ergogenic but increases the risk of thromboembolic events. beta-Hydroxy-beta-methylbutyrate has ergogenic potential in untrained individuals, but studies are needed on trained individuals. Human growth hormone and insulin growth factor-I decrease body fat and may increase lean muscle mass when given subcutaneously. Pyruvate is not ergogenic. The androgenic precursors androstenedione and dehydroepiandrosterone have not been shown to increase any parameters of strength and have potentially significant adverse effects. Anabolic steroids increase protein synthesis and muscle mass but with many adverse effects, some irreversible. Supplement claims on labels of product content and efficacy can be inaccurate and misleading.

Creatine supplementation and athletic performance

Nutritional supplements and other ergogenic aids have gained widespread use among professional, amateur, recreational, and student athletes for their potential to enhance athletic performance and provide a competitive edge. Creatine monohydrate is one of the more commonly used and potentially beneficial supplements that currently is viewed to be safe. Supplementation with oral creatine augments skeletal muscle creatine concentrations in most individuals, which has been shown to promote gains in lean body mass when used in conjunction with resistance training, to enhance power and strength, and to improve performance in intense exercise, especially during repeated bouts. Young athletes, however, must be cautious about taking creatine because its effects on growth and development are unknown and long-term safety has not been established. Variability in research study designs and small sample sizes have left many questions unanswered regarding the safety and efficacy of chronic supplementation. This is an active area of clinical investigation and the results of ongoing and future research should guide the appropriate use of creatine to enhance athletic performance among athletes of all ages.

Oral creatine supplementation and skeletal muscle metabolism in physical exercise

Creatine is the object of growing interest in the scientific literature. This is because of the widespread use of creatine by athletes, on the one hand, and to some promising results regarding its therapeutic potential in neuromuscular disease on the other. In fact, since the late 1900s, many studies have examined the effects of creatine supplementation on exercise performance. This article reviews the literature on creatine supplementation as an ergogenic aid, including some basic aspects relating to its metabolism, pharmacokinetics and side effects. The use of creatine supplements to increase muscle creatine content above approximately 20 mmol/kg dry muscle mass leads to improvements in high-intensity, intermittent high-intensity and even endurance exercise (mainly in nonweightbearing endurance activities). An effective supplementation scheme is a dosage of 20 g/day for 4-6 days, and 5 g/day thereafter. Based on recent pharmacokinetic data, new regimens of creatine supplementation could be used. Although there are opinion statements suggesting that creatine supplementation may be implicated in carcinogenesis, data to prove this effect are lacking, and indeed, several studies showing anticarcinogenic effects of creatine and its analogues have been published. There is a shortage of scientific evidence concerning the adverse effects following creatine supplementation in healthy individuals even with long-term dosage. Therefore, creatine may be considered as a widespread, effective and safe ergogenic aid.

Human, rat and chicken small intestinal Na+ - Cl- -creatine transporter: functional, molecular characterization and localization

In spite of all the fascinating properties of oral creatine supplementation, the mechanism(s) mediating its intestinal absorption has(have) not been investigated. The purpose of this study was to characterize intestinal creatine transport. [(14)C] creatine uptake was measured in chicken enterocytes and rat ileum, and expression of the creatine transporter CRT was examined in human, rat and chicken small intestine by reverse transcription-polymerase chain reaction, Northern blot, in situ hybridization, immunoblotting and immunohistochemistry. Results show that enterocytes accumulate creatine against its concentration gradient. This accumulation was electrogenic, Na(+)- and Cl(-)-dependent, with a probable stoichiometry of 2 Na(+): 1 Cl(-): 1 creatine, and inhibited by ouabain and iodoacetic acid. The kinetic study revealed a K(m) for creatine of 29 microM. [(14)C] creatine uptake was efficiently antagonized by non-labelled creatine, guanidinopropionic acid and cyclocreatine. More distant structural analogues of creatine, such as GABA, choline, glycine, beta-alanine, taurine and betaine, had no effect on intestinal creatine uptake, indicating a high substrate specificity of the creatine transporter. Consistent with these functional data, messenger RNA for CRT was detected only in the cells lining the intestinal villus. The sequences of partial clones, and of the full-length cDNA clone, isolated from human and rat small intestine were identical to previously cloned CRT cDNAs. Immunological analysis revealed that CRT protein was mainly associated with the apical membrane of the enterocytes. This study reports for the first time that mammalian and avian enterocytes express CRT along the villus, where it mediates high-affinity, Na(+)- and Cl(-)-dependent, apical creatine uptake.

Nutrition and sports supplements: fact or fiction

BACKGROUND

In an age of highly competitive sports, whether it be the high school student, the weekend warrior, or the professional athlete, more individuals are using "performance-enhancing" nutritional supplements. Many feel they are gaining a "competitive edge," without thinking of the potential consequences. Consumers are inundated with claims of strength, weight loss, and improved body definition, but they are rarely given information on the potentially harmful side effects. There are few large, multicenter, randomized trials of these various nutritional supplements that look at the purported claims and potential side effects.

STUDY

We reviewed the available studies, including case reports, and researched data on five of the most popular performance-enhancing supplements, including androstenedione, creatine, chromium, ephedra, and protein and amino acid supplements.

CONCLUSIONS

Of the reviewed supplements, only creatine may be marginally beneficial. The potential benefit would probably only be useful to the professional athlete and not the average person. All of the supplements reviewed have potentially harmful side effects; however, certain supplements clearly show harmful effects, and use should strongly be cautioned. In addition, ephedra should be withdrawn from the marketplace. At this time, without better-designed studies, these agents cannot be recommended.

Sports doping in the adolescent athlete the hope, hype, and hyperbole

A well-balanced diet with appropriate training is the key to maximizing athletic performance. Nutritional counseling should be an essential part of anticipatory guidance, especially for certain teens, such as those who are vegetarians or those with low-calorie intakes. Other considerations for anticipatory guidance are listed in Box 8. Adequate hydration before, during, and after practice or a game is important to maintain hemodynamic balance, prevent heat disorders, and optimize performance. Cool water is adequate for short-duration activities, while carbohydrate-electrolyte fluids are more desirable for long-term activities, especially those lasting more than an hour. Such drinks are also more palatable and the athlete is more likely to consume them. Carbohydrates (meaning hydrates of carbon) are an important part of the athlete's diet; carbohydrates are rapidly broken down and their energy is quickly supplied to the body. The body stores only a small amount of carbohydrates in the form of glycogen in the liver, while muscle glycogen is an immediate source of energy. Thus, carbohydrate loading has been used to increase glycogen stores and aid the athlete involved in endurance events.

Creatine loading and resting skeletal muscle phosphocreatine flux: a saturation-transfer NMR study

31P saturation-transfer nuclear magnetic resonance spectroscopy was used to study skeletal muscle phosphocreatine (PCr) flux in healthy male volunteers. Data analysis included consideration of effects from incomplete saturation and radiofrequency spillover. Spectra were recorded from the resting gastrocnemius muscle before and after 6 days of creatine monohydrate (Cr-H2O) intake (20 g/day). Parallel to an improved muscle performance during maximal intermittent exercise following Cr-H2O supplementation, the concentration of PCr increased (P=0.01) by 23% (34.9+/-2.8 mmol/l vs. 28.6+/-2.7 mmol/l), whereas other metabolites were unaffected (inorganic phosphate: 4.3+/-1.4 mmol/l, free intracellular Mg(2+): 1.1+/-0.7 mmol/l, cytosolic pH: 7.04+/-0.02). Forward and reverse fluxes through the creatine kinase (CK) reaction did not change significantly from their baseline levels (v(for): 11.8+/-5.4 mmol/l per second vs. 15.3+/-6.8 mmol/l per second, (v(rev): 9.5+/-3.4 mmol/l per second vs. 10.9+/-3.7 mmol/l per second). The rate of PCr resynthesis in resting muscle is not limited by the CK reaction, which is near equilibrium. Consequently, the post-load increase in total creatine has no effect on the unidirectional CK reaction rates.

Creatine use among a select population of high school athletes

OBJECTIVE

To determine the prevalence, frequency, and patterns of creatine use among a local population of high school athletes.

SUBJECTS AND METHODS

Male and female high school athletes completed an anonymous questionnaire on creatine use during the August 1999 preparticipation examinations at a single institutional sports medicine center.

RESULTS

A total of 328 students (182 males and 146 females) aged 14 to 18 years (mean +/- SD 15.2 +/- 1.3 years) completed the survey (100% response rate), although not all athletes answered each question. Twenty-seven athletes (8.2% of total group), 1 of whom was female, reported creatine use. Of these 27 athletes, 14 (52%) were taking creatine at the time of the survey. The frequency of creatine use among past and current users was equally distributed among rarely (30%), weekly (35%), and daily (35%). Creatine users were older than nonusers (mean 16.5 +/- 1.2 vs 15.0 +/- 1.3 years; P < .001). Of creatine users, 21 (78%) were male football players. Nineteen of 24 respondents (79%) believed creatine improved their performance. Overall, 78% of users either did not know how much creatine they were taking (12/22 respondents) or were taking greater than the recommended doses (5/22 respondents). Minor gastrointestinal side effects or muscle cramps were reported by 5 (20%) of 25 respondents. Creatine users were more likely than nonusers to know other creatine users (81% vs 22%; P < .001) and to use other supplements (67% vs 9%; P < .001). Creatine users obtained creatine information primarily from friends (74%) and purchased creatine predominantly from health food stores (86%).

CONCLUSIONS

High school male and female athletes as young as 14 years use creatine. Of high school athletes participating in our study, 8.2% reported creatine use. Relatively minor side effects, diarrhea, cramps, and loss of appetite, were reported. Creatine users seem to believe that creatine improves their performance, but they may lack sufficient information to make informed decisions regarding creatine use. Further larger scale study is warranted.

Effect of creatine supplementation on muscle metabolic response to a maximal treadmill exercise test in Standardbred horses

The aim of the present study was to investigate the effect of creatine (Cr) supplementation on muscle metabolic response in connection with a maximal treadmill exercise test, known to cause a marked anaerobic metabolic response and adenine nucleotide degradation. First, 6 Standardbred trotters performed a standardised maximal exercise test until fatigue (baseline test). The test used was an inclined incremental treadmill test in which the speed was increased by 1 m/s, starting at 7 m/s, every 60 s until the horse could no longer keep pace with the treadmill. After this baseline test, the horses were separated into 2 equal groups. One half received a dose of 25 g creatine monohydrate twice daily, and the other group were given the same dose of lactose (placebo). The supplementation period was 6.5 days, after which the maximal treadmill exercise test was performed again. A washout period of 14 days was allowed before treatments were switched between groups and a new supplementation period started. After this second supplementation period a new maximal exercise test was performed. After supplementation with creatine or placebo, horses were stopped after performing the same number of speed steps and duration of exercise as they had in the baseline test. Blood samples for analysis of plasma lactate, creatine (Cr), creatinine, hypoxanthine, xanthine and uric acid concentrations were collected at rest, during each speed step and during recovery. The total blood volume (TBV) was also determined. Muscle biopsies for analysis of muscle metabolites (adenosine triphosphate [ATP], adenosine diphosphate [ADP], adenosine monophosphate [AMP], inosine monophosphate [IMP], creatine phosphate [CP], lactate [La] and glycogen) were taken at rest, immediately post exercise and after 15 min recovery. The results showed no significant increase in plasma Cr or muscle total creatine concentration (TCr) after supplementation with Cr. At the end of exercise ATP and CP concentrations had decreased and IMP and lactate concentrations increased in muscle in all groups. Plasma lactate concentration increased during exercise and recovery and plasma uric acid concentration increased during recovery in all groups. No influence could be found in TBV after supplementation with creatine. These results show that creatine supplementation in the dosage used in this study had no influence on muscle metabolic response or TBV.

Adverse effects of creatine supplementation: fact or fiction?

The consumption of oral creatine monohydrate has become increasingly common among professional and amateur athletes. Despite numerous publications on the ergogenic effects of this naturally occurring substance, there is little information on the possible adverse effects of this supplement. The objectives of this review are to identify the scientific facts and contrast them with reports in the news media, which have repeatedly emphasised the health risks of creatine supplementation and do not hesitate to draw broad conclusions from individual case reports. Exogenous creatine supplements are often consumed by athletes in amounts of up to 20 g/day for a few days, followed by 1 to 10 g/day for weeks, months and even years. Usually, consumers do not report any adverse effects, but body mass increases. There are few reports that creatine supplementation has protective effects in heart, muscle and neurological diseases. Gastrointestinal disturbances and muscle cramps have been reported occasionally in healthy individuals, but the effects are anecdotal. Liver and kidney dysfunction have also been suggested on the basis of small changes in markers of organ function and of occasional case reports, but well controlled studies on the adverse effects of exogenous creatine supplementation are almost nonexistent. We have investigated liver changes during medium term (4 weeks) creatine supplementation in young athletes. None showed any evidence of dysfunction on the basis of serum enzymes and urea production. Short term (5 days), medium term (9 weeks) and long term (up to 5 years) oral creatine supplementation has been studied in small cohorts of athletes whose kidney function was monitored by clearance methods and urine protein excretion rate. We did not find any adverse effects on renal function. The present review is not intended to reach conclusions on the effect of creatine supplementation on sport performance, but we believe that there is no evidence for deleterious effects in healthy individuals. Nevertheless, idiosyncratic effects may occur when large amounts of an exogenous substance containing an amino group are consumed, with the consequent increased load on the liver and kidneys. Regular monitoring is compulsory to avoid any abnormal reactions during oral creatine supplementation.

Does dietary creatine supplementation play a role in skeletal muscle metabolism and performance?

Fatigue sustained during short-term, high-intensity exercise in humans is associated with the inability of skeletal muscle to maintain a high rate of anaerobic ATP production from phosphocreatine hydrolysis. Ingestion of creatine monohydrate at a rate of 20 g/d for 5-6 d was shown to increase the total creatine concentration of human skeletal muscle by approximately 25 mmol/kg dry mass, some 30% of this in phosphorylated form as phosphocreatine. A positive relation was then shown between muscle creatine uptake and improvements in performance during repeated bouts of maximal exercise. However, there is no evidence that increasing intake > 20-30 g/d for 5-6 d has any potentiating effect on creatine uptake or performance. In individuals in whom the initial total creatine concentration already approached 150 mmol/kg dry mass, neither creatine uptake nor an effect on phosphocreatine resynthesis or performance was found after supplementation. Loss of ATP during heavy anaerobic exercise was found to decline after creatine ingestion, despite an increase in work production. These results suggest that improvements in performance are due to parallel improvements in ATP resynthesis during exercise as a consequence of increased phosphocreatine availability. Creatine uptake is augmented by combining creatine supplementation with exercise and with carbohydrate ingestion.

Role of plasma membrane transporters in muscle metabolism

Muscle plays a major role in metabolism. Thus it is a major glucose-utilizing tissue in the absorptive state, and changes in muscle insulin-stimulated glucose uptake alter whole-body glucose disposal. In some conditions, muscle preferentially uses lipid substrates, such as fatty acids or ketone bodies. Furthermore, muscle is the main reservoir of amino acids and protein. The activity of many different plasma membrane transporters, such as glucose carriers and transporters of carnitine, creatine and amino acids, play a crucial role in muscle metabolism by catalysing the influx or the efflux of substrates across the cell surface. In some cases, the membrane transport process is subjected to intense regulatory control and may become a potential pharmacological target, as is the case with the glucose transporter GLUT4. The goal of this review is the molecular characterization of muscle membrane transporter proteins, as well as the analysis of their possible regulatory role.

Creatine and creatinine metabolism

The goal of this review is to present a comprehensive survey of the many intriguing facets of creatine (Cr) and creatinine metabolism, encompassing the pathways and regulation of Cr biosynthesis and degradation, species and tissue distribution of the enzymes and metabolites involved, and of the inherent implications for physiology and human pathology. Very recently, a series of new discoveries have been made that are bound to have distinguished implications for bioenergetics, physiology, human pathology, and clinical diagnosis and that suggest that deregulation of the creatine kinase (CK) system is associated with a variety of diseases. Disturbances of the CK system have been observed in muscle, brain, cardiac, and renal diseases as well as in cancer. On the other hand, Cr and Cr analogs such as cyclocreatine were found to have antitumor, antiviral, and antidiabetic effects and to protect tissues from hypoxic, ischemic, neurodegenerative, or muscle damage. Oral Cr ingestion is used in sports as an ergogenic aid, and some data suggest that Cr and creatinine may be precursors of food mutagens and uremic toxins. These findings are discussed in depth, the interrelationships are outlined, and all is put into a broader context to provide a more detailed understanding of the biological functions of Cr and of the CK system.

Is there a rationale for the use of creatine either as nutritional supplementation or drug administration in humans participating in a sport?

Even though no unambiguous proof for enhanced performance during high-intensity exercise has yet been reported, the creatine administration is charged to improve physical performance and has become a popular practice among subjects participating in different sports. Appropriate creatine dosage may be also used as a medicinal product since, in accordance with the Council Directive 65/65/CEE, any substance which may be administered with a view to restoring, correcting or modifying physiological functions in human beings is considered a medicinal product. Thus, quality, efficacy and safety must characterize the substance. In biochemical terms, creatine administration enhances both creatine and phosphocreatine concentrations, allowing for an increased total creatine pool in skeletal muscle. In thermodynamics terms, creatine interferes with the creatine-creatine kinase-phosphocreatine circuit, which is related to the mitochondrial function as a highly organized system for the energy control of the subcellular adenylate pool. In pharmacokinetics terms, creatine entry into skeletal muscle is initially dependent on the extracellular concentration, but the creatine transport is subsequently down-regulated. In pharmacodynamics terms, the creatine enhances the possibility to maintain power output during brief periods of high-intensity exercises. In spite of uncontrolled daily dosage and long-term administration, no research on creatine safety in humans has been set up by specific standard protocol of clinical pharmacology and toxicology, as currently occurs in phase I for the products for human use. More or less documented side effects induced by creatine are weight gain; influence on insulin production; feedback inhibition of endogenous creatine synthesis; long-term damages on renal function. A major point that related to the quality of creatine products is the amount of creatine ingested in relation to the amount of contaminants present. During the production of creatine from sarcosine and cyanamide, variable amounts of contaminants (dicyandiamide, dihydrotriazines, creatinine, ions) are generated and, thus, their tolerable concentrations (ppm) must be defined by specific toxicological researches. Creatine, as the nutritional factors, can be used either at supplementary or therapeutic levels as a function of the dose. Supplementary doses of nutritional factors usually are of the order of the daily turnover, while therapeutic ones are three or more times higher. In a subject with a body weight of 70 kg with a total creatine pool of 120 g, the daily turnover is approximately 2 g. Thus, in healthy subjects nourished with a fat-rich, carbohydrate-, protein-poor diet and participating in a daily recreational sport, the oral creatine supplementation should be on the order of the daily turnover, i.e. less than 2.5-3 g per day, bringing the gastrointestinal absorption to account. In healthy athletes submitted daily to high-intensity strength- or sprint-training, the maximal oral creatine supplementation should be on the order of two times the daily turnover, i.e. less than 5-6 g per day for less than 2 weeks, and the creatine supplementation should be taken under appropriate medical supervision. The oral administration of more than 6 g per day of creatine should be considered as a therapeutic intervention because the dosage is more than three times higher than the creatine daily turnover and more than six times higher than the creatine daily allowance. In this case, creatine administration should be prescribed by physicians only in the cases of suspected or proven deficiency, or in conditions of severe stress and/or injury. 2000 Academic Press@p$hr

Creatine supplementation increases muscle total creatine but not maximal intermittent exercise performance

This study investigated creatine supplementation (CrS) effects on muscle total creatine (TCr), creatine phosphate (CrP), and intermittent sprinting performance by using a design incorporating the time course of the initial increase and subsequent washout period of muscle TCr. Two groups of seven volunteers ingested either creatine [Cr; 6 x (5 g Cr-H(2)O + 5 g dextrose)/day)] or a placebo (6 x 5 g dextrose/day) over 5 days. Five 10-s maximal cycle ergometer sprints with rest intervals of 180, 50, 20, and 20 s and a resting vastus lateralis biopsy were conducted before and 0, 2, and 4 wk after placebo or CrS. Resting muscle TCr, CrP, and Cr were unchanged after the placebo but were increased (P < 0.05) at 0 [by 22.9 +/- 4.2, 8.9 +/- 1.9, and 14.0 +/- 3.3 (SE) mmol/kg dry mass, respectively] and 2 but not 4 wk after CrS. An apparent placebo main effect of increased peak power and cumulative work was found after placebo and CrS, but no treatment (CrS) main effect was found on either variable. Thus, despite the rise and washout of muscle TCr and CrP, maximal intermittent sprinting performance was unchanged by CrS.

Effects of creatine supplementation on exercise performance

While creatine has been known to man since 1835, when a French scientist reported finding this constitutent of meat, its presence in athletics as a performance enhancer is relatively new. Amid claims of increased power and strength, decreased performance time and increased muscle mass, creatine is being hailed as a true ergogenic aid. Creatinine is synthesised from the amino acids glycine, arginine and methionine in the kidneys, liver and pancreas, and is predominantly found in skeletal muscle, where it exists in 2 forms. Approximately 40% is in the free creatine form (Crfree), while the remaining 60% is in the phosphorylated form, creatine phosphate (CP). The daily turnover rate of approximately 2 g per day is equally met via exogenous intake and endogenous synthesis. Although creatine concentration (Cr) is greater in fast twitch muscle fibres, slow twitch fibres have a greater resynthesis capability due to their increased aerobic capacity. There appears to be no significant difference between males and females in Cr, and training does not appear to effect Cr. The 4 roles in which creatine is involved during performance are temporal energy buffering, spatial energy buffering, proton buffering and glycolysis regulation. Creatine supplementation of 20 g per day for at least 3 days has resulted in significant increases in total Cr for some individuals but not others, suggesting that there are 'responders' and 'nonresponders'. These increases in total concentration among responders is greatest in individuals who have the lowest initial total Cr, such as vegetarians. Increased concentrations of both Crfree and CP are believed to aid performance by providing more short term energy, as well as increase the rate of resynthesis during rest intervals. Creatine supplementation does not appear to aid endurance and incremental type exercises, and may even be detrimental. Studies investigating the effects of creatine supplementation on short term, high intensity exercises have reported equivocal results, with approximately equal numbers reporting significant and nonsignificant results. The only side effect associated with creatine supplementation appears to be a small increase in body mass, which is due to either water retention or increased protein synthesis.

Creatine supplementation. Its role in human performance

Creatine supplementation is the most popular nutritional supplement today. Although many questions remain regarding the use and benefits of creatine supplementation, a fast-growing body of literature is starting to define both its acute and chronic effects on human and physiologic performance. The initial data indicate that this energetic boost of the phosphagen energy system also helps to enhance strength and power training. Few documented side effects have been demonstrated in the medical and scientific literature, but further investigation is still required as to long-term use (i.e., beyond several months).