Effects of acute creatine monohydrate supplementation on leucine kinetics and mixed-muscle protein synthesis

Legal pre-event nutritional supplements to assist energy metabolism

Physical training and proper nutrition are paramount for success in sport. A key tissue is skeletal muscle, as the metabolic pathways that produce energy or ATP allow the muscles to complete the many activities critical to success in sport. The energy-producing pathways must rapidly respond to the need for ATP during sport and produce energy at a faster rate or for a longer duration through training and proper nutrition which should translate into improved performance in sport activities. There is also continual interest in the possibility that nutritional supplements could further improve muscle metabolism and the provision of energy during sport. Most legal sports supplements do not improve performance following oral ingestion. However, three legal supplements that have received significant attention over the years include creatine, carnitine and sodium bicarbonate. The ingestion of large amounts of creatine for 4–6 days increases skeletal muscle creatine and phosphocreatine contents. The majority of the experimental evidence suggests that creatine supplementation can improve short-term exercise performance, especially in sports that require repeated short-term sprints. It may also augment the accretion of skeletal muscle when taken in combination with a resistance-exercise training programme. Supplementary carnitine has been touted to increase the uptake and oxidation of fat in the mitochondria. However, muscle carnitine levels are not augmented following oral carnitine supplementation and the majority of well-controlled studies have reported no effect of carnitine on enhancing fat oxidation, V̇o2max or prolonged endurance exercise performance. The ingestion of sodium bicarbonate before intense exercise decreases the blood [H+] to potentially assist the efflux of H+ from the muscle and temper the metabolic acidosis associated with intense exercise. Many studies have reported performance increases in laboratory-based cycling tests and simulated running races in the field following sodium bicarbonate ingestion where the need for ATP from substrate phosphorylation is high. However, other studies have reported no benefit and the incidence of negative side effects is high.

The impact of nutritional and exercise strategies for aging bone and muscle

This symposium addressed recent evidence suggesting that nutritional intervention and resistance-training strategies may be important for aging bone and muscle. The physiological consequences of aging and the potential mechanistic actions of nutritional aids during resistance training were emphasized.

Timing of creatine or protein supplementation and resistance training in the elderly

Muscle loss with age has a negative effect on strength and functional independence. Age-related loss of muscle is the result of decreased muscle fiber number and size, which are functions of altered hormonal status, physical inactivity, and variations in nutritional intake. Resistance training has a positive effect on muscle mass and strength in the elderly. Studies of protein or creatine supplementation for increasing muscle mass and strength in older individuals are equivocal. The timing of nutritional supplementation may be more important than the absolute daily intake of supplements. Protein or creatine ingestion proximate to resistance-training sessions may be more beneficial for increasing muscle mass and strength than ingestion of protein or creatine at other times of the day, possibly because of increased blood flow and therefore increased transport of amino acids and creatine to skeletal muscle.

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.

Creatine monohydrate and conjugated linoleic acid improve strength and body composition following resistance exercise in older adults

Aging is associated with lower muscle mass and an increase in body fat. We examined whether creatine monohydrate (CrM) and conjugated linoleic acid (CLA) could enhance strength gains and improve body composition (i.e., increase fat-free mass (FFM); decrease body fat) following resistance exercise training in older adults (>65 y). Men (N = 19) and women (N = 20) completed six months of resistance exercise training with CrM (5g/d)+CLA (6g/d) or placebo with randomized, double blind, allocation. Outcomes included: strength and muscular endurance, functional tasks, body composition (DEXA scan), blood tests (lipids, liver function, CK, glucose, systemic inflammation markers (IL-6, C-reactive protein)), urinary markers of compliance (creatine/creatinine), oxidative stress (8-OH-2dG, 8-isoP) and bone resorption (Ν-telopeptides). Exercise training improved all measurements of functional capacity (P<0.05) and strength (P<0.001), with greater improvement for the CrM+CLA group in most measurements of muscular endurance, isokinetic knee extension strength, FFM, and lower fat mass (P<0.05). Plasma creatinine (P<0.05), but not creatinine clearance, increased for CrM+CLA, with no changes in serum CK activity or liver function tests. Together, this data confirms that supervised resistance exercise training is safe and effective for increasing strength in older adults and that a combination of CrM and CLA can enhance some of the beneficial effects of training over a six-month period. Trial Registration. ClinicalTrials.gov NCT00473902

Efeitos da suplementação de creatina e do treinamento de potência sobre a performance e a massa corporal magra de ratos

INTRODUÇÃO: A creatina é um dos suplementos mais usados por atletas para incrementar a síntese protéica e aumentar a massa e força muscular. OBJETIVO: Investigou-se os efeitos da suplementação de creatina associada a um programa de treinamento de potência (saltos verticais) sobre a performance e a composição da massa corporal magra de ratos Wistar. MÉTODOS: Ratos Wistar adultos foram distribuídos em quatro grupos: SSC (sedentário sem creatina); SC (sedentário com creatina); ESC (exercício sem creatina) e EC (exercício com creatina). Os animais receberam água e ração ad libitum. Os grupos SC e EC ingeriam dose de creatina diariamente, adotando o procedimento de carga (0,430g/kg p.c. por 7 dias) e manutenção (0,070g/kg p.c. por 6 semanas). Os grupos EC e ESC foram submetidos a um regime progressivo de saltos verticais (5x10 saltos com 1 min de intervalo) em tanque com água, 5 dias/semana, durante 7 semanas. A performance foi avaliada pelo tempo de execução das 5 séries de 10 saltos verticais e a composição da massa corporal magra (músculos e ossos) foi avaliada pelas porções: água, proteína e gordura. RESULTADOS: A performance não foi afetada pela ingestão de creatina (p > 0,05). Os animais suplementados tiveram o percentual de proteína elevado e o de gordura reduzido (p < 0,05), independente do treinamento. Os animais exercitados exibiram maior percentual de proteína, e menor de gordura, além de menor ganho de peso corporal, comparados com os sedentários, independente da suplementação (p < 0,05). Não houve diferença para o percentual de água e consumo alimentar (p > 0,05). CONCLUSÃO: A suplementação de creatina não afetou a performance dos animais, mas alterou a massa corporal magra. A suplementação de creatina e o programa de treinamento de potência, de forma independente, elevaram o percentual de proteína dos músculos e ossos e reduziram o percentual de gordura, sem alterar o percentual de água.

Measurement of human mixed muscle protein fractional synthesis rate depends on the choice of amino acid tracer

The goal of this study was to discover whether using different tracers affects the measured rate of muscle protein synthesis in human muscle. We therefore measured the mixed muscle protein fractional synthesis rate (FSR) in the quadriceps of older adults during basal, postabsorptive conditions and mixed meal feeding (70 mg protein x kg fat-free mass(-1) x h(-1) x 2.5 h) by simultaneous intravenous infusions of [5,5,5-(2)H(3)]leucine and either [ring-(13)C(6)]phenylalanine or [ring-(2)H(5)]phenylalanine and analysis of muscle tissue samples by gas chromatography-mass spectrometry. Both the basal FSR and the FSR during feeding were approximately 20% greater (P < 0.001) when calculated from the leucine labeling in muscle tissue fluid and proteins (fasted: 0.063 +/- 0.005%/h; fed: 0.080 +/- 0.007%/h) than when calculated from the phenylalanine enrichment data (0.051 +/- 0.004 and 0.066 +/- 0.005%/h, respectively). The feeding-induced increase in the FSR ( approximately 20%; P = 0.011) was not different with leucine and phenylalanine tracers (P = 0.69). Furthermore, the difference between the leucine- and phenylalanine-derived FSRs was independent of the phenylalanine isotopomer used (P = 0.92). We conclude that when using stable isotope-labeled tracers and the classic precursor product model to measure the rate of muscle protein synthesis, absolute rates of muscle protein FSR differ significantly depending on the tracer amino acid used; however, the anabolic response to feeding is independent of the tracer used. Thus different precursor amino acid tracers cannot be used interchangeably for the evaluation of muscle protein synthesis, and data from studies using different tracer amino acids can be compared qualitatively but not quantitatively.

The effect of creatine supplementation on mass and performance of rat skeletal muscle

This study investigated the effect of dietary creatine supplementation on hypertrophy and performance of rat skeletal muscle. Male Sprague-Dawley rats underwent either tibialis anterior ablation or partial ablation of the plantaris/gastrocnemius to induce compensatory hypertrophy of the extensor digitorum longus (EDL) or soleus respectively, or sham surgery. Creatine (300 mg/kg) was administered to one half of each group for 5 weeks, after which force production was measured. With the leg fixed at the knee and ankle, the distal tendon of the EDL or soleus was attached to a force transducer and the muscle was electrically stimulated via the sciatic nerve. Synergist ablation resulted in a significant increase in EDL mass and in soleus mass relative to control muscles. However, no effect of creatine supplementation on muscle mass or performance was found between control and either group of creatine-treated rats. Despite an apparent increase in muscle creatine content, creatine supplementation did not augment muscle hypertrophy or force production in rat EDL or soleus muscle, providing evidence that the potential benefits of creatine supplementation are not due to a direct effect on muscle but rather to an enhanced ability to train.

Nutritional strategies to influence adaptations to training

This article highlights new nutritional concerns or practices that may influence the adaptation to training. The discussion is based on the assumption that the adaptation to repeated bouts of training occurs during recovery periods and that if one can train harder, the adaptation will be greater. The goal is to maximize with nutrition the recovery/adaptation that occurs in all rest periods, such that recovery before the next training session is complete. Four issues have been identified where recent scientific information will force sports nutritionists to embrace new issues and reassess old issues and, ultimately, alter the nutritional recommendations they give to athletes. These are: (1) caffeine ingestion; (2) creatine ingestion; (3) the use of intramuscular triacylglycerol (IMTG) as a fuel during exercise and the nutritional effects on IMTG repletion following exercise; and (4) the role nutrition may play in regulating the expression of genes during and after exercise training sessions. Recent findings suggest that low doses of caffeine exert significant ergogenic effects by directly affecting the central nervous system during exercise. Caffeine can cross the blood-brain barrier and antagonize the effects of adenosine, resulting in higher concentrations of stimulatory neurotransmitters. These new data strengthen the case for using low doses of caffeine during training. On the other hand, the data on the role that supplemental creatine ingestion plays in augmenting the increase in skeletal muscle mass and strength during resistance training remain equivocal. Some studies are able to demonstrate increases in muscle fibre size with creatine ingestion and some are not. The final two nutritional topics are new and have not progressed to the point that we can specifically identify strategies to enhance the adaptation to training. However, it is likely that nutritional strategies will be needed to replenish the IMTG that is used during endurance exercise. It is not presently clear whether the IMTG store is chronically reduced when engaging in daily sessions of endurance training or if this impacts negatively on the ability to train. It is also likely that the increased interest in gene and protein expression measurements will lead to nutritional strategies to optimize the adaptations that occur in skeletal muscle during and after exercise training sessions. Research in these areas in the coming years will lead to strategies designed to improve the adaptive response to training.

Creatine supplementation attenuates corticosteroid-induced muscle wasting and impairment of exercise performance in rats

The objective of the present study was to investigate whether creatine (Cr) could attenuate the deleterious effects of high doses of dexamethasone (Dexa) on body mass, exercise performance, and respiratory variables of rodents. Forty-four Wistar rats performed incremental maximal exercise tests. They were then assigned to four groups: G1: subcutaneous (SC) and intraperitoneal (IP) saline; G2: SC saline and IP Cr (250 mg·kg−1·day−1); G3: SC Dexa (7.5 mg·kg−1·day−1) and IP saline; G4: SC Dexa and IP Cr. New exercise tests and analysis of the respiratory pattern under resting conditions and after stimulation with doxapram (2 mg/kg IP) were performed after 18 days. Post- minus pretreatment differences were compared between groups. G3 and G4 showed a significant impairment in body mass gain compared with G1 and G2 ( P < 0.05) (G1: 65.3 ± 26.1, G2: 93.1 ± 27.4, G3: −18.4 ± 20.1, G4: 9.8 ± 23.1 kg × 10−3). Similar results were observed for maximal oxygen consumption (G1: 9.5 ± 8.5, G2: 25.8 ± 14.5, G3: −25.5 ± 6.0, G4: −4.8 ± 9.5 ml·kg−1·min−1) and test duration (G1: 43.0 ± 45.0, G2: 72.0 ± 59.5, G3: −165.0 ± 60.6, G4: −48.0 ± 48.5 s). Simultaneous use of Cr significantly attenuated the Dexa-induced impairment of the last two variables. Cr attenuated Dexa-induced gastrocnemius and diaphragm muscle weight losses and the atrophy of gastrocnemius type IIb fibers. Cr supplementation had only small effects on Dexa-induced respiratory changes. These results suggest that Cr may play a role in the prophylaxis or treatment of steroid-induced myopathy.

Creatine for treating muscle disorders

BACKGROUND

Progressive muscle weakness is a main symptom of most hereditary muscle diseases. Creatine is a popular nutritional supplement among athletes. It improves muscle performance in healthy individuals and might be helpful for treating myopathies.

OBJECTIVES

To evaluate the efficacy of oral creatine supplementation in muscle diseases.

SEARCH STRATEGY

We searched the Cochrane Neuromuscular Disease Group Register in May 2004 for randomised trials using the search term 'creatine'. We also searched the Cochrane Central Register of Controlled Trials (The Cochrane Library, Issue 2, 2005) using the same search term. We adapted this strategy to search MEDLINE (PubMed, from January 1966 to September 2005) and EMBASE (from January 1980 to May 2004). We reviewed the bibliographies of the randomised trials identified, contacted the authors and known experts in the field and approached pharmaceutical companies to identify additional published or unpublished data.

SELECTION CRITERIA

Types of studies: randomised or quasi-randomised controlled trials.

TYPES OF PARTICIPANTS

people of all ages with hereditary muscle disease. Types of intervention: any creatine supplementation of at least 0.03 g/kg body weight/day.

PRIMARY OUTCOME MEASURE

change in muscle strength measured by quantitative muscle testing.

SECONDARY OUTCOME MEASURES

change in muscle strength measured by manual muscle testing, change in energy parameters assessed by 31 phosphorous spectroscopy, change in muscle mass or a surrogate for muscle mass, adverse events.

DATA COLLECTION AND ANALYSIS

Two authors independently applied the selection criteria, assessed trial quality and extracted data. Some missing data were obtained from investigators.

MAIN RESULTS

Twelve trials, including 266 participants, met the selection criteria. One trial compared creatine and glutamine treatment with placebo. In trials with 138 participants with muscular dystrophies treated with creatine, there was a significant increase in maximum voluntary contraction in the creatine group compared to placebo, with a weighted mean difference of 8.47% (95% confidence intervals 3.55 to 13.38). There was also an increase in lean body mass during creatine treatment compared to placebo (weighted mean difference 0.63 kg, 95% confidence intervals 0.02 to 1.25). No trial reported any clinically relevant adverse event. In trials with 33 participants with metabolic myopathies treated with creatine, there was no significant difference in maximum voluntary contraction between the creatine and placebo group (weighted mean difference -2.26%, confidence intervals -6.29 to 1.78). One trial reported a significant increase in muscle pain during high-dose creatine treatment (150 mg/kg body weight) in glycogen storage disease type V.

AUTHORS' CONCLUSIONS

Evidence from randomised controlled trials shows that short- and medium-term creatine treatment improves muscle strength in people with muscular dystrophies, and is well-tolerated. Evidence from randomised controlled trials does not show significant improvement in muscle strength in metabolic myopathies. High-dose creatine in glycogenosis type V increased muscle pain.

Safety of creatine supplementation

The literature on creatine supplementation supporting its efficacy has grown rapidly and has included studies in both healthy volunteers and patient populations. However, the first rule in the development of therapeutic agents is safety. Creatine is well-tolerated in most individuals in short-term studies. However, isolated reports suggest creatine may be associated with various side effects affecting several organ systems including skeletal muscle, the kidney and the gastrointestinal tract. The majority of clinical studies fail to find an increased incidence of side effects with creatine supplementation. To date, studies have not found clinically significant deviations from normal values in renal, hepatic, cardiac or muscle function. Few data are available on the long-term consequences of creatine supplementation.

Basal muscle intracellular amino acid kinetics in women and men

Sexual dimorphism in skeletal muscle mass is apparent, with men having more muscle mass and larger individual muscle cells. However, no sex-based differences have been detected in blood forearm phenylalanine turnover, although whole body leucine oxidation has been reported to be greater in men than in women. We hypothesized that sex differences in intracellular amino acid turnover may account for these discrepancies, with men having a higher intracellular turnover than women. We studied young, healthy women (women, n = 8) and men (men, n = 10) following an overnight fast. Phenylalanine, leucine, and alanine muscle intracellular kinetics were assessed using stable isotope methodologies, femoral arteriovenous blood sampling, and muscle biopsies. Muscle intracellular amino acid kinetics were reported relative to both leg volume and lean leg mass because of sex differences in leg volume and in muscle and fat distribution. When expressed per leg volume (nmol.min(-1).100 ml leg volume(-1)), phenylalanine net balance (women: -16 +/- 4, men: -31 +/- 5), release from proteolysis in the blood (women: 46 +/- 9, men: 75 +/- 10) and intracellular availability (women: 149 +/- 23, men: 241 +/- 35), and alanine production, utilization, and intracellular availability were higher in men (P < 0.05). However, when the kinetic parameters were normalized per unit of lean leg mass, all differences disappeared. Muscle fractional synthetic rate was also not different between women and men. We conclude that there are no sex-based differences in basal muscle intracellular amino acid turnover when the data are normalized by lean mass. It remains to be determined if there are sex differences in intracellular amino acid metabolism following anabolic or catabolic stimuli.

Nutritional aspects of women strength athletes

Strength training elicits sports related and health benefits for both men and women. Although sexual dimorphism is observed in exercise metabolism, there is little information outlining the specific nutritional needs of women strength athletes. Many women athletes restrict energy intake, specifically fat consumption, in order to modify body composition, but this nutritional practice is often counter-productive. Compared to men, women appear to be less reliant on glycogen during exercise and less responsive to carbohydrate mediated glycogen synthesis during recovery. Female strength athletes may require more protein than their sedentary and endurance training counterparts to attain positive nitrogen balance and promote protein synthesis. Therefore, women strength athletes should put less emphasis on a very high carbohydrate intake and more emphasis on quality protein and fat consumption in the context of energy balance to enhance adaptations to training and improve general health. Attention to timing of nutrient ingestion, macronutrient quality, and dietary supplementation (for example, creatine) are briefly discussed as important components of a nutritionally adequate and effective strength training diet for women.

Insights into muscle atrophy and recovery pathway based on genetic models

PURPOSE OF REVIEW

Muscle atrophy is a pervasive problem that occurs with disuse, aging, and a myriad of disease conditions. The purposes of this review are to describe recent advances in studying muscle atrophy that have elucidated pathways involved at the molecular level; to compare different types of atrophy--primary (e.g. bed rest, immobilization) and secondary (when the atrophy is related to pathology as well as disuse, e.g. injury, sepsis etc.) and their multiple common features; to review progress in studying the recovery process and clinical status.

RECENT FINDINGS

Major advances have been made at the molecular level. There are two phenotypes for muscle atrophy--primary, which is mainly related to disuse (e.g. bed), and secondary, when the atrophy is related to pathology as well as disuse. It appears that the two forms have multiple elements in common. Studies on the recovery process reveal a very complex sequence of events that are not the simple reverse of the muscle loss process. In contrast to the progress at the molecular level, progress in treating muscle atrophy or accelerating recovery has been disappointing.

SUMMARY

Although nutritional supplementation and pharmacological agents continue to have the potential to minimize muscle atrophy, given its minimal risks, exercise sets a very high standard for treatment options when medically appropriate. Identification of pathways and control points offers the potential for new approaches.

Creatine Monohydrate Supplementation Does Not Improve Functional Recovery After Total Knee Arthroplasty

OBJECTIVE

To determine if creatine monohydrate supplementation can improve body composition and enhance recovery after total knee arthroplasty (TKA).

DESIGN

Randomized trial in which creatine monohydrate or placebo was administered.

SETTING

Public primary care facility.

PARTICIPANTS

Thirty-seven adults (17 men, 20 women) with osteoarthritis undergoing TKA. Intervention Subjects received creatine monohydrate (10 g/d x 10 d presurgery to 5 g/d x 30 d postsurgery) or placebo.

MAIN OUTCOME MEASURES

Body composition (dual-energy x-ray absorptiometry scanning), muscle metabolite concentrations (adenosine triphosphate, phosphocreatine, creatine, total creatine [phosphocreatine + creatine]), muscle histomorphometery, quadriceps, ankle dorsiflexion and handgrip strength, and functional capacity. All measurements were completed preoperatively (-7 d) and 30 days postoperatively, except for that of muscle metabolites. Muscle metabolite samples were collected during surgery (0 d) and at 30 days.

RESULTS

A significant decrease in quadriceps and ankle dorsiflexion strength was observed at 30 days postoperatively (P < .01). There were no significant effects of creatine monohydrate supplementation on any of the measured outcome variables.

CONCLUSIONS

Creatine monohydrate supplementation did not improve body composition or muscle strength when given before surgery, nor did it enhance recovery after TKA.

Scientific basis and practical aspects of creatine supplementation for athletes

A large number of studies have been published on creatine supplementation over the last decade. Many studies show that creatine supplementation in conjunction with resistance training augments gains in muscle strength and size. The underlying physiological mechanism(s) to explain this ergogenic effect remain unclear. Increases in muscle fiber hypertrophy and myosin heavy chain expression have been observed with creatine supplementation. Creatine supplementation increases acute weightlifting performance and training volume, which may allow for greater overload and adaptations to training. Creatine supplementation may also induce a cellular swelling in muscle cells, which in turn may affect carbohydrate and protein metabolism. Several studies point to the conclusion that elevated intramuscular creatine can enhance glycogen levels but an effect on protein synthesis/degradation has not been consistently detected. As expected there is a distribution of responses to creatine supplementation that can be largely explained by the degree of creatine uptake into muscle. Thus, there is wide interest in methods to maximize muscle creatine levels. A carbohydrate or carbohydrate/protein-induced insulin response appears to benefit creatine uptake. In summary, the predominance of research indicates that creatine supplementation represents a safe, effective, and legal method to enhance muscle size and strength responses to resistance training.

Targeting cellular energy production in neurological disorders

The concepts of energy dysregulation and oxidative stress and their complicated interdependence have rapidly evolved to assume primary importance in understanding the pathophysiology of numerous neurological disorders. Therefore, neuroprotective strategies addressing specific bioenergetic defects hold particular promise in the treatment of these conditions (i.e., amyotrophic lateral sclerosis, Huntington's disease, Parkinson's disease, Friedreich's ataxia, mitochondrial cytopathies and other neuromuscular diseases), all of which, to some extent, share 'the final common pathway' leading to cell death through either necrosis or apoptosis. Compounds such as creatine monohydrate and coenzyme Q(10) offer substantial neuroprotection against ischaemia, trauma, oxidative damage and neurotoxins. Miscellaneous agents, including alpha-lipoic acid, beta-OH-beta-methylbutyrate, riboflavin and nicotinamide, have also been shown to improve various metabolic parameters in brain and/or muscle. This review will highlight the biological function of each of the above mentioned compounds followed by a discussion of their utility in animal models and human neurological disease. The balance of this work will be comprised of discussions on the therapeutic applications of creatine and coenzyme Q(10).

The role of creatine in the management of amyotrophic lateral sclerosis and other neurodegenerative disorders

Creatine is consumed in the diet and endogenously synthesised in the body. Over the past decade, the ergogenic benefits of synthetic creatine monohydrate have made it a popular dietary supplement, particularly among athletes. The anabolic properties of creatine also offer hope for the treatment of diseases characterised by weakness and muscle atrophy. Moreover, because of its cellular mechanisms of action, creatine offers potential benefits for diseases involving mitochondrial dysfunction. Recent data also support the hypothesis that creatine may have a neuroprotective effect. Amyotrophic lateral sclerosis (ALS) is characterised by progressive degeneration of motor neurons, resulting in weakening and atrophy of skeletal muscles. In patients with this condition, creatine offers potential benefits in terms of facilitating residual muscle contractility as well as improving neuronal function. It may also help stabilise mitochondrial dysfunction, which plays a key role in the pathogenesis of ALS. Indeed, the likely multifactorial aetiology of ALS means the combined pharmacodynamic properties of creatine offer promise for the treatment of this condition. Evidence from available animal models of ALS supports the utility of treatment with creatine in this setting. Limited data available in other neuromuscular and neurodegenerative diseases further support the potential benefit of creatine monohydrate in ALS. However, few randomised, controlled trials have been conducted. To date, two clinical trials of creatine monohydrate in ALS have been completed without demonstration of significant improvements in overall survival or a composite measure of muscle strength. These trials have also posed unanswered questions about the optimal dosage of creatine and its beneficial effects on muscle fatigue, a measure distinct from muscle strength. A large, multicentre, clinical trial is currently underway to further investigate the efficacy of creatine monohydrate in ALS and address these unresolved issues. Evidence to date shows that creatine supplementation has a good safety profile and is well tolerated by ALS patients. The purpose of this article is to provide a short, balanced review of the literature concerning creatine monohydrate in the treatment of ALS and related neurodegenerative diseases. The pharmacokinetics and rationale for the use of creatine are described along with available evidence from animal models and clinical trials for ALS and related neurodegenerative or neuromuscular diseases.

Potential ergogenic effects of arginine and creatine supplementation

The rationale for the use of nutritional supplements to enhance exercise capacity is based on the assumption that they will confer an ergogenic effect above and beyond that afforded by regular food ingestion alone. The proposed or advertised ergogenic effect of many supplements is based on a presumptive metabolic pathway and may not necessarily translate to quantifiable changes in a variable as broadly defined as exercise performance. L-arginine is a conditionally essential amino acid that has received considerable attention due to potential effects on growth hormone secretion and nitric oxide production. In some clinical circumstances (e.g., burn injury, sepsis) in which the demand for arginine cannot be fully met by de novo synthesis and normal dietary intake, exogenous arginine has been shown to facilitate the maintenance of lean body mass and functional capacity. However, the evidence that supplemental arginine may also confer an ergogenic effect in normal healthy individuals is less compelling. In contrast to arginine, numerous studies have reported that supplementation with the arginine metabolite creatine facilitates an increase in anaerobic work capacity and muscle mass when accompanied by resistance training programs in both normal and patient populations. Whereas improvement in the rate of phosphocreatine resynthesis is largely responsible for improvements in acute work capacity, the direct effect of creatine supplementation on skeletal muscle protein synthesis is less clear. The purpose of this review is to summarize the role of arginine and its metabolite creatine in the context of a nutrition supplement for use in conjunction with an exercise stimulus in both healthy and patient populations.

Effect of Creatine Ingestion after Exercise on Muscle Thickness in Males and Females

Muscles exercised before creatine (Cr) supplementation have a greater elevation of intramuscular Cr than nonexercised muscles.

PURPOSE

To determine whether preferential increase of muscle thickness could be achieved by ingesting Cr immediately after exercise of specific muscles over 6 wk. Another purpose was to determine if the increase in lean tissue mass (LTM) with Cr supplementation is greater in males than females.

METHODS

Subjects randomly assigned to Cr (six males, five females, 0.2 g Cr x kg(-1)) and placebo (PL; five males, five females) performed single-limb training with one side of the body two times per week and with the opposite limbs two times per week. Cr was consumed after training of one side of the body and PL after training the opposite side. Subjects on PL always consumed PL after exercise. Elbow flexors and knee extensors muscle thickness, LTM, fat, and bone mass, and single-limb bench and leg press one-repetition maximum (1-RM) were assessed before and after 6 wk.

RESULTS

Within the Cr group, elbow flexors muscle thickness increased more in the limbs trained on days Cr was supplemented compared with limbs trained on days PL was supplemented (P < 0.02). All other measures changed to a similar extent between limbs. Males on Cr had the greatest increase in LTM (P < 0.05) with no difference between females on Cr and PL. Bench press 1-RM increased more in Cr than PL groups (P < 0.01). All other measures changed to a similar extent between groups. Males increased bone mass (P < 0.01) with no effect of Cr supplementation.

CONCLUSION

Supplementing with Cr after training of the arms resulted in greater increase in muscle thickness of the arms. Males have a greater increase in LTM with Cr supplementation than females.

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.

Drug treatment for facioscapulohumeral muscular dystrophy

BACKGROUND

Facioscapulohumeral muscular dystrophy is a progressive muscle disease which has no agreed treatment. Early suggestions that corticosteroids might be helpful were not supported by a subsequent open label study. The beta 2 adrenergic agonist albuterol, also known as salbutamol, is known to have anabolic effects which might be beneficial for facioscapulohumeral muscular dystrophy. Creatine has been used as a muscle performance enhancer by athletes and it might be helpful in muscular dystrophies including facioscapulohumeral muscular dystrophy.

OBJECTIVES

The objective of the review was to determine whether there is any drug treatment which alters the progression of facioscapulohumeral muscular dystrophy.

SEARCH STRATEGY

We searched the Cochrane Neuromuscular Disease Group specialised register (searched August 2003), MEDLINE (January 1966 to August 2003) and EMBASE (January 1980 to August 2003) for any references to facioscapulohumeral muscular dystrophy. Abstracts from the major neurological meetings and trial bibliographies were also searched for further references to trials. Experts were contacted for information regarding unpublished trials or trials in progress.

SELECTION CRITERIA

We included all randomised or quasi-randomised trials of any drug treatment for facioscapulohumeral muscular dystrophy, in adults with a recognised diagnosis of facioscapulohumeral muscular dystrophy. Trials had to include an assessment of muscle strength at one year.

DATA COLLECTION AND ANALYSIS

All identified trials were independently assessed by both reviewers to ensure that they fulfilled the selection criteria and were then rated for their quality. Trial data were extracted and entered by one reviewer and checked by the other. If appropriate data existed a weighted treatment effect was to be calculated across trials using the Cochrane statistical package, Review Manager. The results were to have been expressed as relative risks and 95% confidence intervals and risk differences and 95% confidence intervals for dichotomous outcomes, and weighted mean differences and 95% confidence intervals for continuous outcomes.

MAIN RESULTS

Two published high quality randomised controlled trials fulfilled the selection criteria. One compared creatine supplementation with placebo and the other compared high and low-dose albuterol with placebo. A further unpublished randomised controlled trial of albuterol in facioscapulohumeral muscular dystrophy was identified. The creatine trial showed a non-significant difference in favour of creatine. The albuterol trial showed no significant difference in muscle strength at one year but some secondary measures such as lean body mass and handgrip strength did improve.

REVIEWERS' CONCLUSIONS

There is no evidence from randomised controlled trials to support any drug treatment for facioscapulohumeral muscular dystrophy but only two randomised controlled trials have been published.

The effects of creatine supplementation on muscular performance and body composition responses to short-term resistance training overreaching

To determine the effects of creatine supplementation during short-term resistance training overreaching on performance, body composition, and resting hormone concentrations, 17 men were randomly assigned to supplement with 0.3 g/kg per day of creatine monohydrate (CrM: n=9) or placebo (P: n=8) while performing resistance exercise (5 days/week for 4 weeks) followed by a 2-week taper phase. Maximal squat and bench press and explosive power in the bench press were reduced during the initial weeks of training in P but not CrM. Explosive power in the bench press, body mass, and lean body mass (LBM) in the legs were augmented to a greater extent in CrM ( P<or=0.05) by the end of the 6-week period. A tendency for greater 1-RM squat improvement ( P=0.09) was also observed in CrM. Total testosterone (TT) and the free androgen index (TT/SHBG) decreased in CrM and P, reaching a nadir at week 3, whereas sex hormone binding globulin (SHBG) responded in an opposite direction. Cortisol significantly increased after week 1 in CrM (+29%), and returned to baseline at week 2. Insulin was significantly depressed at week 1 (-24%) and drifted back toward baseline during weeks 2-4. Growth hormone and IGF-I levels were not affected. Therefore, some measures of muscular performance and body composition are enhanced to a greater extent following the rebound phase of short-term resistance training overreaching with creatine supplementation and these changes are not related to changes in circulating hormone concentrations obtained in the resting, postabsorptive state. In addition, creatine supplementation appears to be effective for maintaining muscular performance during the initial phase of high-volume resistance training overreaching that otherwise results in small performance decrements.

Dairy products, meat and sports performance

Creatine supplementation improves repetitive, short-term performance. It has not been shown that exclusion of meat from the diet would impair repetitive short-term performance. In contrast, reduction of protein intake and a concomitant increase of carbohydrate intake during a period of 3-5 days improves anaerobic (2-7 minutes) performance. The protein intake in a mixed or lacto-vegetarian diet is adequate even for elite athletes, providing that energy requirements are met. Many dietary supplements have been suggested to increase muscle mass and/or to decrease fat mass. Although the effects of conjugated linoleic acid on body composition in athletes are not clear, some positive findings in untrained, obese individuals call for more studies. Strenuous training may impair immune function and increase the susceptibility to infections. Exclusion of meat from the diet does not seem to have adverse effects on immune function. Glutamine supplementation (>3-6 g/day) may improve immune function, but more studies are needed. Similarly, more studies on the possible effects of whey protein and probiotic supplementation on immune function and performance in physically highly active individuals are warranted. Vitamin and mineral balance are not usually a problem among athletes. Notable exceptions may be calcium and iron in some females. Increased calcium intake in athletes with hormonal and menstrual disturbances could theoretically help in maintaining bone status; however, no data are available. A diet with meat may help in maintaining adequate iron stores.

No effect of creatine supplementation on human myofibrillar and sarcoplasmic protein synthesis after resistance exercise

Muscle hypertrophy during resistance training is reportedly increased by creatine supplementation. Having previously failed to find an anabolic effect on muscle protein turnover at rest, either fed or fasted, we have now examined the possibility of a stimulatory effect of creatine in conjunction with acute resistance exercise. Seven healthy men (body mass index, 23 +/- 2 kg/m2, 21 +/- 1 yr, means +/- SE) performed 20 x 10 repetitions of leg extension-flexion at 75% one-repetition maximum in one leg, on two occasions, 4 wk apart, before and after ingesting 21 g/day creatine for 5 days. The subjects ate approximately 21 g maltodextrin + 6 g protein/h for 3 h postexercise. We measured incorporation of [1-13C]leucine into quadriceps muscle proteins in the rested and exercised legs. Leg protein breakdown (as dilution of [2H5]phenylalanine) was also assessed in the exercised and rested leg postexercise. Creatine supplementation increased muscle total creatine by approximately 21% (P < 0.01). Exercise increased the synthetic rates of myofibrillar and sarcoplasmic proteins by two- to threefold (P < 0.05), and leg phenylalanine balance became more positive, but creatine was without any anabolic effect.

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.

Histological assessment of intermediate- and long-term creatine monohydrate supplementation in mice and rats

Creatine monohydrate (CrM) supplementation appears to be relatively safe based on data from short-term and intermediate-term human studies and results from several therapeutic trials. The purpose of the current study was to characterize pathological changes after intermediate-term and long-term CrM supplementation in mice [healthy control and SOD1 (G93A) transgenic] and rats (prednisolone and nonprednisolone treated). Histological assessment (18-20 organs/tissues) was performed on G93A mice after 159 days, and in Sprague-Dawley rats after 365 days, of CrM supplementation (2% wt/wt) compared with control feed. Liver histology was also evaluated in CD-1 mice after 300 days of low-dose CrM supplementation (0.025 and 0.05 g x kg-1x day-1) and in Sprague-Dawley rats after 52 days of CrM supplementation (2% wt/wt) with and without prednisolone. Areas of hepatitis were observed in the livers of the CrM-supplemented G93A mice (P < 0.05), with no significant inflammatory lesions in any of the other 18-20 tissues/organs that were evaluated. The CD-1 mice also showed significant hepatic inflammatory lesions (P < 0.05), yet there was no negative effect of CrM on liver histology in the Sprague-Dawley rats after intermediate-term or long-term supplementation nor was inflammation seen in any other tissues/organs (P = not significant). Dietary CrM supplementation can induce inflammatory changes in the liver of mice, but not rats. The observed inflammatory changes in the murine liver must be considered in the evaluation of hepatic metabolism in CrM-supplemented mice. Species differences must be considered in the evaluation of toxicological and physiological studies.

Factors influencing creatine loading into human skeletal muscle

This review describes several factors involved in regulating skeletal muscle creatine uptake and total creatine content. Skeletal muscle total creatine content increases with oral creatine supplementation, although the response is variable. Factors that may account for this variation are carbohydrate intake, physical activity, training status, and possibly fiber type.

Creatine supplementation has no effect on human muscle protein turnover at rest in the postabsorptive or fed states

Dietary creatine supplementation is associated with increases in muscle mass, but the mechanism is unknown. We tested the hypothesis that creatine supplementation enhanced myofibrillar protein synthesis (MPS) and diminished muscle protein breakdown (MPB) in the fed state. Six healthy men (26 +/- 7 yr, body mass index 22 +/- 4 kg/m(2)) were studied twice, 2-4 wk apart, before and after ingestion of creatine (21 g/day, 5 days). We carried out two sets of measurements within 5.5 h of both MPS (by incorporation of [1-(13)C]leucine in quadriceps muscle) and MPB (as dilution of [1-(13)C]leucine or [(2)H(5)]phenylalanine across the forearm); for the first 3 h, the subjects were postabsorptive but thereafter were fed orally (0.3 g maltodextrin and 0.083 g protein. kg body wt(-1) x h(-1)). Creatine supplementation increased muscle total creatine by approximately 30% (P < 0.01). Feeding had significant effects, doubling MPS (P < 0.001) and depressing MPB by approximately 40% (P < 0.026), but creatine had no effect on turnover in the postabsorptive or fed states. Thus any increase in muscle mass accompanying creatine supplementation must be associated with increased physical activity.

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.

Effect of dietary supplements on lean mass and strength gains with resistance exercise: a meta-analysis

The purpose of this study was to quantify which dietary supplements augment lean mass and strength gains during resistance training. Peer-reviewed studies between the years 1967 and 2001 were included in the analysis if they met a predetermined set of experimental criteria, among which were at least 3-wk duration and resistance-training 2 or more times a week. Lean mass and strength were normalized for meta-analysis by conversion to percent change per week and by calculating the effect size for each variable. Of the 250 supplements examined, only 6 had more than 2 studies that met the criteria for inclusion in the meta-analysis. Creatine and beta-hydroxy-beta-methylbutyrate (HMB) were found to significantly increase net lean mass gains of 0.36 and 0.28%/wk and strength gains of 1.09 and 1.40%/wk (P < 0.05), respectively. Chromium, dehydroepiandrosterone, androstenedione, and protein did not significantly affect lean gain or strength. In conclusion, two supplements, creatine and HMB, have data supporting their use to augment lean mass and strength gains with resistance training.

Creatine supplementation enhances isometric strength and body composition improvements following strength exercise training in older adults

We sought to determine whether creatine monohydrate (CrM) supplementation would enhance the increases in strength and fat-free mass that develop during resistance exercise training in older adults. Twenty-eight healthy men and women over the age of 65 years participated in a whole-body resistance exercise program 3 days per week for 14 weeks. The study participants were randomly allocated, in a double-blind fashion, to receive either CrM (5 g/d + 2 g of dextrose; n = 14) or placebo (7 g of dextrose; n = 14). The primary outcome measurements included the following: total body mass, fat-free mass, one-repetition maximum strength for each body part, isometric knee extension, handgrip, and dorsiflexion strength, chair stand performance, 30-m walk test, 14-stair climb performance, muscle fiber type and area, and intramuscular total creatine. Fourteen weeks of resistance exercise training resulted in significant increases in all measurements of strength and functional tasks and muscle fiber area for both groups (p <.05). CrM supplementation resulted in significantly greater increases in fat-free mass and total body mass, as compared with placebo (p <.05). The CrM group also showed a greater increase in isometric knee extension strength in men and women, as compared with placebo (p <.05), and also greater gains in isometric dorsiflexion strength (p <.05), but in men only. There was a significant increase in intramuscular total creatine in the CrM group (p <.05). Finally, there were no significant side effects of treatment or exercise training. This study confirms that supervised heavy resistance exercise training can safely increase muscle strength and functional capacity in older adults. The addition of CrM supplementation to the exercise stimulus enhanced the increase in total and fat-free mass, and gains in several indices of isometric muscle strength.

Creatine monohydrate supplementation does not increase muscle strength, lean body mass, or muscle phosphocreatine in patients with myotonic dystrophy type 1

Creatine monohydrate (CrM) supplementation may increase strength in some types of muscular dystrophy. A recent study in myotonic muscular dystrophy type 1 (DM1) did not find a significant treatment effect, but measurements of muscle phosphocreatine (PCr) were not performed. We completed a randomized, double-blind, cross-over trial using 34 genetically confirmed adult DM1 patients without significant cognitive impairment. Participants received CrM (5 g, approximately 0.074 g/kg daily) and a placebo for each 4-month phase with a 6-week wash-out. Spirometry, manual muscle testing, quantitative isometric strength testing of handgrip, foot dorsiflexion, and knee extension, handgrip and foot dorsiflexion endurance, functional tasks, activity of daily living scales, body composition (total, bone, and fat-free mass), serum creatine kinase activity, serum creatinine concentration and clearance, and liver function tests were completed before and after each intervention, and muscle PCr/beta-adenosine triphosphate (ATP) ratios of the forearm flexor muscles were completed at the end of each phase. CrM supplementation did not increase any of the outcome measurements except for plasma creatinine concentration (but not creatinine clearance). Thus, CrM supplementation at 5 g daily does not have any effects on muscle strength, body composition, or activities of daily living in patients with DM1, perhaps because of a failure of the supplementation to increase muscle PCr/beta-ATP content.

Dietary creatine supplementation and exercise performance: why inconsistent results?

Over the past few years there has been considerable interest in both the use of creatine (Cr) supplementation by athletes and the documentation of its effects by scientists. Some believe that this nitrogen-containing compound found in meat and fish has a performance-enhancing capability as important for brief intense exercise efforts as dietary carbohydrate is for activities where glycogen supplies limit performance. The mechanisms thought to be responsible for any ergogenic effect of acute (few d) Cr supplementation include: increased stores of muscle phosphocreatine (PCr), faster regeneration of PCr during exercise recovery, enhanced adenosine triphosphate (ATP) production from glycolysis secondary to increased hydrogen ion buffering, and/or possible shortened post contraction muscle relaxation time. With chronic (wk mo) supplementation when combined with strength training, Cr may alter muscle protein metabolism directly (via decreasing protein breakdown or increasing synthesis) and/or indirectly as a result of a greater training load made possible by its acute ergogenic effects on strength and power. Cr supplementation is not banned by the International Olympic Committee and, with the exception of a small increase in body mass (approximately 1 kg) over the initial 36 d, does not appear to have any adverse side effects, at least with short-term use. Few scientific data are available for more prolonged use (mo or y) but considering the large numbers of athletes using Cr over the past 6+ y and the absence of reported problems, it may be that the often discussed somewhat nebulous long term adverse effects are presently being overestimated. Intakes of 285-300 mg Cr/kg body mass 1 over 36 d or 3050 mg/kg body mass 1 over approximately 4 wk are sufficient to produce benefits (muscle mass and high intensity power gains); however, not all study results are consistent. The focus of this review is to outline some possible explanations for the inconsistent observations reported in the literature. Clearly, if proven to be consistent the benefits of Cr supplementation could extend far beyond the athletic arena to include individuals who experience muscle weakness for a variety of other reasons (e.g., age/disuse, muscle disease, exposure to microgravity, etc).

Resistance-training-induced adaptations in skeletal muscle protein turnover in the fed state

Resistance training changes the balance of muscle protein turnover, leading to gains in muscle mass. A longitudinal design was employed to assess the effect that resistance training had on muscle protein turnover in the fed state. A secondary goal was investigation of the potential interactive effects of creatine (Cr) monohydrate supplementation on resistance-training-induced adaptations. Young (N = 19, 23.7 +/- 3.2 year), untrained (UT), healthy male subjects completed an 8-week resistance-training program (6 d/week). Supplementation with Cr had no impact on any of the variables studied; hence, all subsequent data were pooled. In the UT and trained (T) state, subjects performed an acute bout of resistance exercise with a single leg (exercised, EX), while their contralateral leg acted as a nonexercised (NE) control. Following exercise, subjects were fed while receiving a primed constant infusion of [d5]- and [15N]-phenylalanine to determine the fractional synthetic and breakdown rates (FSR and FBR), respectively, of skeletal muscle proteins. Acute exercise increased FSR (UT-NE, 0.065 +/- 0.025 %/h; UT-EX, 0.088 +/- 0.032 %/h; P < 0.01) and FBR (UT-NE, 0.047 +/- 0.023 %/h; UT-EX, 0.058 +/- 0.026 %/h; P < 0.05). Net balance (BAL = FSR - FBR) was positive in both legs (P < 0.05) but was significantly greater (+65%) in the EX versus the NE leg (P < 0.05). Muscle protein FSR and FBR were greater at rest following T (FSR for T-NE vs. UT-NE, +46%, P < 0.01; FBR for T-NE vs. UT-NE, +81%, P < 0.05). Resistance training attenuated the acute exercise-induced rise in FSR (T-NE vs. T-EX, +20%, P = 0.65). The present results demonstrate that resistance training resulted in an elevated resting muscle protein turnover but an attenuation of the acute response of muscle protein turnover to a single bout of resistance exercise.