Effects of ingesting supplements designed to promote lean tissue accretion on body composition during resistance training

Creatine for Exercise and Sports Performance, with Recovery Considerations for Healthy Populations

Creatine is one of the most studied and popular ergogenic aids for athletes and recreational weightlifters seeking to improve sport and exercise performance, augment exercise training adaptations, and mitigate recovery time. Studies consistently reveal that creatine supplementation exerts positive ergogenic effects on single and multiple bouts of short-duration, high-intensity exercise activities, in addition to potentiating exercise training adaptations. In this respect, supplementation consistently demonstrates the ability to enlarge the pool of intracellular creatine, leading to an amplification of the cell's ability to resynthesize adenosine triphosphate. This intracellular expansion is associated with several performance outcomes, including increases in maximal strength (low-speed strength), maximal work output, power production (high-speed strength), sprint performance, and fat-free mass. Additionally, creatine supplementation may speed up recovery time between bouts of intense exercise by mitigating muscle damage and promoting the faster recovery of lost force-production potential. Conversely, contradictory findings exist in the literature regarding the potential ergogenic benefits of creatine during intermittent and continuous endurance-type exercise, as well as in those athletic tasks where an increase in body mass may hinder enhanced performance. The purpose of this review was to summarize the existing literature surrounding the efficacy of creatine supplementation on exercise and sports performance, along with recovery factors in healthy populations.

Nutrition Recommendations for Bodybuilders in the Off-Season: A Narrative Review

Many nutrition practices often used by bodybuilders lack scientific support and can be detrimental to health. Recommendations during the dieting phase are provided in the scientific literature, but little attention has been devoted to bodybuilders during the off-season phase. During the off-season phase, the goal is to increase muscle mass without adding unnecessary body fat. This review evaluated the scientific literature and provides nutrition and dietary supplement recommendations for natural bodybuilders during the off-season phase. A hyper-energetic diet (~10–20%) should be consumed with a target weight gain of ~0.25–0.5% of bodyweight/week for novice/intermediate bodybuilders. Advanced bodybuilders should be more conservative with the caloric surplus and weekly weight gain. Sufficient protein (1.6–2.2 g/kg/day) should be consumed with optimal amounts 0.40–0.55 g/kg per meal and distributed evenly throughout the day (3–6 meals) including within 1–2 hours pre- and post-training. Fat should be consumed in moderate amounts (0.5–1.5 g/kg/day). Remaining calories should come from carbohydrates with focus on consuming sufficient amounts (≥3–5 g/kg/day) to support energy demands from resistance exercise. Creatine monohydrate (3–5 g/day), caffeine (5–6 mg/kg), beta-alanine (3–5 g/day) and citrulline malate (8 g/day) might yield ergogenic effects that can be beneficial for bodybuilders.

Dietary Protein for Training Adaptation and Body Composition Manipulation in Track and Field Athletes

Track and field athletes engage in vigorous training that places stress on physiological systems requiring nutritional support for optimal recovery. Of paramount importance when optimizing recovery nutrition are rehydration and refueling which are covered in other papers in this volume. Here, we highlight the benefits for dietary protein intake over and above requirements set out in various countries at ∼0.8-1.0 g·kg body mass (BM)^-1·day^-1 for training adaptation, manipulating body composition, and optimizing performance in track and field athletes. To facilitate the remodeling of protein-containing structures, which are turning over rapidly due to their training volumes, track and field athletes with the goal of weight maintenance or weight gain should aim for protein intakes of ∼1.6 g·kg BM^-1·day^-1. Protein intakes at this level would not necessarily require an overemphasis on protein-containing foods and, beyond convenience, does not suggest a need to use protein or amino acid-based supplements. This review also highlights that optimal protein intakes may exceed 1.6 g·kg BM^-1·day^-1 for athletes who are restricting energy intake and attempting to minimize loss of lean BM. We discuss the underpinning rationale for weight loss in track and field athletes, explaining changes in metabolic pathways that occur in response to energy restriction when manipulating protein intake and training. Finally, this review offers practical advice on protein intakes that warrant consideration in allowing an optimal adaptive response for track and field athletes seeking to train effectively and to lose fat mass while energy restricted with minimal (or no) loss of lean BM.

Hematological and Hemodynamic Responses to Acute and Short-Term Creatine Nitrate Supplementation

In a double-blind, crossover, randomized and placebo-controlled trial; 28 men and women ingested a placebo (PLA), 3 g of creatine nitrate (CNL), and 6 g of creatine nitrate (CNH) for 6 days. Participants repeated the experiment with the alternate supplements after a 7-day washout. Hemodynamic responses to a postural challenge, fasting blood samples, and bench press, leg press, and cycling time trial performance and recovery were assessed. Data were analyzed by univariate, multivariate, and repeated measures general linear models (GLM). No significant differences were found among treatments for hemodynamic responses, clinical blood markers or self-reported side effects. After 5 days of supplementation, one repetition maximum (1RM) bench press improved significantly for CNH (mean change, 95% CI; 6.1 [3.5, 8.7] kg) but not PLA (0.7 [-1.6, 3.0] kg or CNL (2.0 [-0.9, 4.9] kg, CNH, p = 0.01). CNH participants also tended to experience an attenuated loss in 1RM strength during the recovery performance tests following supplementation on day 5 (PLA: -9.3 [-13.5, -5.0], CNL: -9.3 [-13.5, -5.1], CNH: -3.9 [-6.6, -1.2] kg, p = 0.07). After 5 days, pre-supplementation 1RM leg press values increased significantly, only with CNH (24.7 [8.8, 40.6] kg, but not PLA (13.9 [-15.7, 43.5] or CNL (14.6 [-0.5, 29.7]). Further, post-supplementation 1RM leg press recovery did not decrease significantly for CNH (-13.3 [-31.9, 5.3], but did for PLA (-30.5 [-53.4, -7.7] and CNL (-29.0 [-49.5, -8.4]). CNL treatment promoted an increase in bench press repetitions at 70% of 1RM during recovery on day 5 (PLA: 0.4 [-0.8, 1.6], CNL: 0.9 [0.35, 1.5], CNH: 0.5 [-0.2, 0.3], p = 0.56), greater leg press endurance prior to supplementation on day 5 (PLA: -0.2 [-1.6, 1.2], CNL: 0.9 [0.2, 1.6], CNH: 0.2 [-0.5, 0.9], p = 0.25) and greater leg press endurance during recovery on day 5 (PLA: -0.03 [-1.2, 1.1], CNL: 1.1 [0.3, 1.9], CNH: 0.4 [-0.4, 1.2], p = 0.23). Cycling time trial performance (4 km) was not affected. Results indicate that creatine nitrate supplementation, up to a 6 g dose, for 6 days, appears to be safe and provide some ergogenic benefit.

International Society of Sports Nutrition position stand: safety and efficacy of creatine supplementation in exercise, sport, and medicine

Creatine is one of the most popular nutritional ergogenic aids for athletes. Studies have consistently shown that creatine supplementation increases intramuscular creatine concentrations which may help explain the observed improvements in high intensity exercise performance leading to greater training adaptations. In addition to athletic and exercise improvement, research has shown that creatine supplementation may enhance post-exercise recovery, injury prevention, thermoregulation, rehabilitation, and concussion and/or spinal cord neuroprotection. Additionally, a number of clinical applications of creatine supplementation have been studied involving neurodegenerative diseases (e.g., muscular dystrophy, Parkinson's, Huntington's disease), diabetes, osteoarthritis, fibromyalgia, aging, brain and heart ischemia, adolescent depression, and pregnancy. These studies provide a large body of evidence that creatine can not only improve exercise performance, but can play a role in preventing and/or reducing the severity of injury, enhancing rehabilitation from injuries, and helping athletes tolerate heavy training loads. Additionally, researchers have identified a number of potentially beneficial clinical uses of creatine supplementation. These studies show that short and long-term supplementation (up to 30 g/day for 5 years) is safe and well-tolerated in healthy individuals and in a number of patient populations ranging from infants to the elderly. Moreover, significant health benefits may be provided by ensuring habitual low dietary creatine ingestion (e.g., 3 g/day) throughout the lifespan. The purpose of this review is to provide an update to the current literature regarding the role and safety of creatine supplementation in exercise, sport, and medicine and to update the position stand of International Society of Sports Nutrition (ISSN).

A buffered form of creatine does not promote greater changes in muscle creatine content, body composition, or training adaptations than creatine monohydrate

Background

Creatine monohydrate (CrM) has been consistently reported to increase muscle creatine content and improve high-intensity exercise capacity. However, a number of different forms of creatine have been purported to be more efficacious than CrM. The purpose of this study was to determine if a buffered creatine monohydrate (KA) that has been purported to promote greater creatine retention and training adaptations with fewer side effects at lower doses is more efficacious than CrM supplementation in resistance-trained individuals.

Methods

In a double-blind manner, 36 resistance-trained participants (20.2 ± 2 years, 181 ± 7 cm, 82.1 ± 12 kg, and 14.7 ± 5% body fat) were randomly assigned to supplement their diet with CrM (Creapure® AlzChem AG, Trostberg, Germany) at normal loading (4 x 5 g/d for 7-days) and maintenance (5 g/d for 21-days) doses; KA (Kre-Alkalyn®, All American Pharmaceutical, Billings, MT, USA) at manufacturer’s recommended doses (KA-L, 1.5 g/d for 28-days); or, KA with equivalent loading (4 x 5 g/d for 7-days) and maintenance (5 g/d) doses of CrM (KA-H). Participants were asked to maintain their current training programs and record all workouts. Muscle biopsies from the vastus lateralis, fasting blood samples, body weight, DEXA determined body composition, and Wingate Anaerobic Capacity (WAC) tests were performed at 0, 7, and 28-days while 1RM strength tests were performed at 0 and 28-days. Data were analyzed by a repeated measures multivariate analysis of variance (MANOVA) and are presented as mean ± SD changes from baseline after 7 and 28-days, respectively.

Results

Muscle free creatine content obtained in a subgroup of 25 participants increased in all groups over time (1.4 ± 20.7 and 11.9 ± 24.0 mmol/kg DW, p = 0.03) after 7 and 28-days, respectively, with no significant differences among groups (KA-L −7.9 ± 22.3, 4.7 ± 27.0; KA-H 1.0 ± 12.8, 9.1 ± 23.2; CrM 11.3 ± 23.9, 22.3 ± 21.0 mmol/kg DW, p = 0.46). However, while no overall group differences were observed (p = 0.14), pairwise comparison between the KA-L and CrM groups revealed that changes in muscle creatine content tended to be greater in the CrM group (KA-L −1.1 ± 4.3, CrM 11.2 ± 4.3 mmol/kg DW, p = 0.053 [mean ± SEM]). Although some significant time effects were observed, no significant group x time interactions (p > 0.05) were observed in changes in body mass, fat free mass, fat mass, percent body fat, or total body water; bench press and leg press 1RM strength; WAC mean power, peak power, or total work; serum blood lipids, markers of catabolism and bone status, and serum electrolyte status; or, whole blood makers of lymphocytes and red cells. Serum creatinine levels increased in all groups (p < 0.001) with higher doses of creatine promoting greater increases in serum creatinine (p = 0.03) but the increases observed (0.1 – 0.2 mg/dl) were well within normal values for active individuals (i.e., <1.28 ± 0.2 mg/dl). Serum LDL was decreased to a greater degree following ingesting loading doses in the CrM group but returned to baseline during the maintenance phase. No side effects were reported.

Conclusions

Neither manufacturers recommended doses of KA (1.5 g/d) or KA with equivalent loading (20 g/d for 7-days) and maintenance doses (5 g/d for 21-days) of CrM promoted greater changes in muscle creatine content, body composition, strength, or anaerobic capacity than CrM (20 g/d for 7-days, 5 g/d for 21-days). There was no evidence that supplementing the diet with a buffered form of creatine resulted in fewer side effects than CrM. These findings do not support claims that consuming a buffered form of creatine is a more efficacious and/or safer form of creatine to consume than creatine monohydrate.

Effect of nutritional intervention on body composition and performance in elite athletes

Strength training and positive energy intake are the most important factors related to lean body mass (LBM) gain. Most studies investigating weight-gain interventions are based recreationally active subjects and less is known about optimal weight-gain protocols in elite athletes. The purpose of this study was to evaluate the effect of nutritional guidance in an 8- to 12-week weight-gain period in elite athletes. Thirty-nine elite athletes were randomised to either a 'nutritional counseling group' (NCG, n=21, 19.1±2.9 years, 70.9±8.9 kg) or 'ad libitum group' (ALG, n=18, 19.6±2.7 years, 75.0±5.9 kg). All athletes continued their sport-specific training which included an additional four strength-training sessions per week. NCG followed a meal plan providing a positive energy balance, while the ALG athletes had an ad libitum energy intake. Body weight (BW), body composition, one repetition maximum (1RM), 40 m sprint and counter movement jump (CMJ) were measured pre- and post-intervention. Energy intake was higher in the NCG than in the ALG (3585±601 vs. 2964±884 kcal) and consequently BW increased more in NCG than in ALG (3.9±0.6% vs. 1.5±0.4%). Fat mass (FM) increased more in NCG than in ALG (15±4 vs. 3±3%), but gain in LBM was not different between groups. All 1RM results improved in both groups (6-12%), whereas 40 m sprint and CMJ remained unchanged, except for a significant decrease in 40 m sprint for the athletes in NCG. Athletes with nutritional guidance increased BW more, however, excess energy intake in a weight-gain protocol should be considered carefully due to undesirable increases in body fat.

Long-term effect of nutritional counselling on desired gain in body mass and lean body mass in elite athletes

Lean body mass (LBM) is important in power-related sports. In athletes with heavy training loads and competitions, it may be difficult to increase and maintain LBM during the season. The purpose of this study was to evaluate the long-term effects on body composition after an 8-12 week weight-gain period with or without nutritional guidance. Twenty-one elite athletes where randomized to 1 of 2 groups: the nutritional counselling group (NCG; n = 12, 18.5 ± 1.7 y, 67.8 ± 7.4 kg) and the ad libitum group (ALG; n = 9, 19.6 ± 2.7 y, 74.2 ± 5.7 kg). The NCG followed a meal plan that provided a surplus of 506 ± 84 kcal·day(-1), whereas the ALG had an ad libitum energy intake (EI) during the strength-training (4 sessions per week) intervention. Body mass (BM) and body composition were measured pre- and postintervention, and 6 and 12 months after the intervention. EI in the NCG was normalized after 12 months, whereas EI in the ALG was unchanged during or after the intervention. BM increased more in the NCG than in the ALG during the intervention (4.3% ± 0.9% vs. 1.0% ± 0.6%) and after 12 months (6.0% ± 0.9% vs. 1.8% ± 0.7%). LBM increased in the NCG during the intervention (2.8% ± 0.5%) and after 12 months (4.4% ± 1.0%), whereas LBM in the ALG was unchanged. The NCG managed to maintain and increase BM and LBM after the intervention period. Hence, the focus on nutritional guidance, in addition to strength training, seems to be preferable for obtaining the long-term effect of weight gain in athletes.

Analysis of the efficacy, safety, and regulatory status of novel forms of creatine

Creatine has become one of the most popular dietary supplements in the sports nutrition market. The form of creatine that has been most extensively studied and commonly used in dietary supplements is creatine monohydrate (CM). Studies have consistently indicated that CM supplementation increases muscle creatine and phosphocreatine concentrations by approximately 15–40%, enhances anaerobic exercise capacity, and increases training volume leading to greater gains in strength, power, and muscle mass. A number of potential therapeutic benefits have also been suggested in various clinical populations. Studies have indicated that CM is not degraded during normal digestion and that nearly 99% of orally ingested CM is either taken up by muscle or excreted in urine. Further, no medically significant side effects have been reported in literature. Nevertheless, supplement manufacturers have continually introduced newer forms of creatine into the marketplace. These newer forms have been purported to have better physical and chemical properties, bioavailability, efficacy, and/or safety profiles than CM. However, there is little to no evidence that any of the newer forms of creatine are more effective and/or safer than CM whether ingested alone and/or in combination with other nutrients. In addition, whereas the safety, efficacy, and regulatory status of CM is clearly defined in almost all global markets; the safety, efficacy, and regulatory status of other forms of creatine present in today’s marketplace as a dietary or food supplement is less clear.

Low-dose creatine combined with protein during resistance training in older men

PURPOSE

To determine whether low-dose creatine and protein supplementation during resistance training (RT; 3 d x wk(-1); 10 wk) in older men (59-77 yr) is effective for improving strength and muscle mass without producing potentially cytotoxic metabolites (formaldehyde).

METHODS

Older men were randomized (double-blind) to receive 0.1 g x kg(-1) creatine + 0.3 g x kg(-1) protein (CP; n = 10), creatine (C; n = 13), or placebo (PLA; n = 12) on training days. Measurements before and after RT included lean tissue mass (air-displacement plethysmography), muscle thickness (ultrasound) of elbow, knee, and ankle flexors and extensors, leg and bench press strength, and urinary indicators of cytotoxicity (formaldehyde), myofibrillar protein degradation [3-methylhistidine (3-MH)],and bone resorption [cross-linked N-telopeptides of type I collagen (NTx)].

RESULTS

Subjects in C and CP groups combined experienced greater increases in body mass and total muscle thickness than PLA (P < 0.05). Subjects who received CP increased lean tissue mass (+5.6%) more than C (+2.2%) or PLA (+1.0%; P < 0.05) and increased bench press strength (+25%) to a greater extent than C and PLA combined (+12.5%; P < 0.05). CP and C did not differ from PLA for changes in formaldehyde production (+24% each). Subjects receiving creatine (C and CP) experienced a decrease in 3-MH by 40% compared with an increase of 29% for PLA (P < 0.05) and a reduction in NTx (-27%) versus PLA (+13%; P = 0.05).

CONCLUSIONS

Low-dose creatine combined with protein supplementation increases lean tissue mass and results in a greater relative increase in bench press but not leg press strength. Low-dose creatine reduces muscle protein degradation and bone resorption without increasing formaldehyde production.

Impact of differing protein sources and a creatine containing nutritional formula after 12 weeks of resistance training

OBJECTIVE

We evaluated whether colostrum (Col) or an isocaloric and isonitrogenous blend of whey and casein in addition to creatine (Cr) affects body composition, muscular strength and endurance, and anaerobic performance during resistance training.

METHODS

Forty-nine resistance-trained subjects participated in a standardized 12-wk total body resistance training program. In a double-blind and randomized manner, subjects supplemented their diet with a protein control (Pro), Pro/Col, Pro/Cr, or Col/Cr. Supplements were isocaloric and isonitrogenous and provided 60 g/d of casein/whey (Pro) or Col as the protein source. At 0, 8, and 12 wk of supplementation, subjects were weighed, had body composition determined using dual-energy X-ray absorptiometry (DXA), performed one-repetition maximum (1RM) and 80% of 1RM tests on the bench press and leg press, and 30-s anaerobic sprint capacity tests. Data (mean +/- SD) were analyzed by repeated measures analysis of variance and reported as raw data in all tables and as changes from baseline for all figures for the Pro, Pro/Col, Pro/Cr, and Col/Cr groups, respectively.

RESULTS

Resistance training increased 1RM strength, muscular endurance, and anaerobic sprint capacity equally in all groups. Significant main and interaction effects (P < 0.05) were found for body mass, DXA total scanned mass, and fat-free mass (FFM; lean plus bone), whereas no changes (P > 0.05) were noted for fat mass, percent fat, or bone content. Post hoc analysis showed that, compared with Pro, subjects ingesting Pro/Col, Pro/Cr, and Col/Cr showed greater gains in body mass and DXA total scanned mass. Subjects ingesting Pro/Cr and Col/Cr had greater increases in FFM during training in comparison with Pro/Col.

CONCLUSION

In conjunction with 12 wk of resistance training, ingestion of Col or a blend of whey and casein protein with a vitamin/mineral supplement containing Cr resulted in greater improvements in FFM in comparison with Pro and Pro/Col.

Nutrient administration and resistance training

Skeletal muscle tissue is tightly regulated throughout our bodies by balancing its synthesis and breakdown. Many factors are known to exist that cause profound changes on the overall status of skeletal muscle, some of which include exercise, nutrition, hormonal influences and disease. Muscle hypertrophy results when protein synthesis is greater than protein breakdown. Resistance training is a popular form of exercise that has been shown to increase muscular strength and muscular hypertrophy. In general, resistance training causes a stimulation of protein synthesis as well as an increase in protein breakdown, resulting in a negative balance of protein. Providing nutrients, specifically amino acids, helps to stimulate protein synthesis and improve the overall net balance of protein. Strategies to increase the concentration and availability of amino acids after resistance exercise are of great interest and have been shown to effectively increase overall protein synthesis. 123 After exercise, providing carbohydrate has been shown to mildly stimulate protein synthesis while addition of free amino acids prior to and after exercise, specifically essential amino acids, causes a rapid pronounced increase in protein synthesis as well as protein balance.13 Evidence exists for a dose-response relationship of infused amino acids while no specific regimen exists for optimal dosing upon ingestion. Ingestion of whole or intact protein sources (e.g., protein powders, meal-replacements) has been shown to cause similar improvements in protein balance after resistance exercise when compared to free amino acid supplements. Future research should seek to determine optimal dosing of ingested intact amino acids in addition to identifying the cellular mechanistic machinery (e.g. transcriptional and translational mechanisms) for causing the increase in protein synthesis.

The potential value and toxicity of chromium picolinate as a nutritional supplement, weight loss agent and muscle development agent

The element chromium apparently has a role in maintaining proper carbohydrate and lipid metabolism in mammals. As this role probably involves potentiation of insulin signalling, chromium dietary supplementation has been postulated to potentially have effects on body composition, including reducing fat mass and increasing lean body mass. Because the supplement is absorbed better than dietary chromium, most studies have focused on the use of chromium picolinate [Cr(pic)(3)]. Cr(pic)(3) has been amazingly popular with the general public, especially with athletes who may have exercise-induced increased urinary chromium loss; however, its effectiveness in manifesting body composition changes has been an area of intense debate in the last decade. Additionally, claims have appeared that the supplement might give rise to deleterious effects. However, over a decade of human studies with Cr(pic)(3) indicate that the supplement has not demonstrated effects on the body composition of healthy individuals, even when taken in combination with an exercise training programme. Recent cell culture and in vivo rat studies have indicated that Cr(pic)(3) probably generates oxidative damage of DNA and lipids and is mutagenic, although the significance of these results on humans taking the supplement for prolonged periods of time is unknown and should be a focus for future investigations. Given that in vitro studies suggest that other forms of chromium used as nutritional supplements, such as chromium chloride, are unlikely to be susceptible to generating this type of oxidative damage, the use of these compounds, rather than Cr(pic)(3), would appear warranted. Potential neurological effects (both beneficial and deleterious) from Cr(pic)(3) supplementation require further study.

Effect of creatine manipulation on fast-twitch skeletal muscle of the mouse

1. The effect of short-term, reversible alteration of muscle total creatine content (Crtot) on force development was sought in fast-twitch extensor digitorum longus (EDL) muscles of female mice. 2. Three in vivo interventions were investigated: 1% creatine-supplementation, treatment with the creatine-uptake inhibitor beta-guanidino propionic acid (beta-GPA; 1%) or beta-GPA treatment followed by creatine supplementation for 5 days. 3. The Crtot of isolated muscles, determined using reverse-phase high-performance liquid chromatography, was 133 +/- 38 mmol/kg dry in 11 EDL control muscles and was not significantly affected by dietary creatine-supplementation (152 +/- 25 mmol/kg dry; n = 8). Significant creatine depletion was observed in the beta-GPA-fed group (65 +/- 6 mmol/kg dry; n = 9) and this was reversed by 5 days of creatine supplementation (133 +/- 21 mmol/kg dry; n = 10). 4. Creatine depletion did not affect maximum tetanic stress. However, when muscle creatine was restored by creatine supplementation, a substantial increase in tetanic stress was observed. Significant correlations were observed between Crtot and maximum tetanic stress (r = 0.56) and relaxation rate (r = 0.43). The enhancement of force was not due to effects of creatine on muscle fibre type because neither mechanical tests of fibre characteristics nor the fibre types of the muscles were affected. 5. We conclude that, in muscles that contain large numbers of fast-twitch fibres, maximum tetanic stress is determined, in part, by muscle creatine stores.

Creatine supplementation combined with resistance training in older men

PURPOSE

To study the effect of creatine (Cr) supplementation combined with resistance training on muscular performance and body composition in older men.

METHODS

Thirty men were randomized to receive creatine supplementation (CRE, N = 16, age = 70.4 +/- 1.6 yr) or placebo (PLA, N = 14, age = 71.1 +/- 1.8 yr), using a double blind procedure. Cr supplementation consisted of 0.3-g Cr.kg(-1) body weight for the first 5 d (loading phase) and 0.07-g Cr.kg(-1) body weight thereafter. Both groups participated in resistance training (36 sessions, 3 times per week, 3 sets of 10 repetitions, 12 exercises). Muscular strength was assessed by 1-repetition maximum (1-RM) for leg press (LP), knee extension (KE), and bench press (BP). Muscular endurance was assessed by the maximum number of repetitions over 3 sets (separated by 1-min rest intervals) at an intensity corresponding to 70% baseline 1-RM for BP and 80% baseline 1-RM for the KE and LP. Average power (AP) was assessed using a Biodex isokinetic knee extension/flexion exercise (3 sets of 10 repetitions at 60 degrees.s(-1) separated by 1-min rest). Lean tissue (LTM) and fat mass were assessed using dual energy x-ray absorptiometry.

RESULTS

Compared with PLA, the CRE group had significantly greater increases in LTM (CRE, +3.3 kg; PLA, +1.3 kg), LP 1-RM (CRE, +50.1 kg; PLA +31.3 kg), KE 1-RM (CRE, +14.9 kg; PLA, +10.7 kg), LP endurance (CRE, +47 reps; PLA, +32 reps), KE endurance (CRE, +21 reps; PLA +14 reps), and AP (CRE, +26.7 W; PLA, +18 W). Changes in fat mass, fat percentage, BP 1-RM, and BP endurance were similar between groups.

CONCLUSION

Creatine supplementation, when combined with resistance training, increases lean tissue mass and improves leg strength, endurance, and average power in men of mean age 70 yr.

Creatine-dextrose and protein-dextrose induce similar strength gains during training

BACKGROUND

Creatine supplementation during resistance exercise training has been reported to induce greater increases in fat-free mass (FFM), muscle fiber area, and strength when compared with a placebo. We have recently shown that timing of nutrient delivery in the postexercise period can have positive effects on whole body protein turnover (B. D. Roy et al., Med Sci Sports Exerc. 32(8):1412-1418, 2000).

PURPOSE

We tested the hypothesis that a postexercise protein-carbohydrate supplement would result in similar increases in FFM, muscle fiber area, and strength as compared with creatine monohydrate (CM), during a supervised 2-month resistance exercise training program in untrained men.

METHODS

Young healthy male subjects were randomized to receive either CM and glucose (N = 11; CM 10 g + glucose 75 g [CR-CHO] (CELL-Tech)) or protein and glucose (N = 8; casein 10 g + glucose 75 g [PRO+CHO]), using double-blinded allocation. Participants performed 8 wk of whole body split-routine straight set weight training, 1 h.d(-1), 6 d.wk(-1). Measurements, pre- and post-training were made of fat-free mass (FFM; DEXA), total body mass, muscle fiber area, isokinetic knee extension strength (45 and 240 degrees.s(-1)), and 1 repetition maximal (1RM) strength for 16 weight training exercises.

RESULTS

Total body mass increased more for CR-CHO (+4.3 kg, 5.4%) as compared with PRO-CHO (+1.9 kg, 2.4%) (P < 0.05 for interaction) and FFM increased after training (P < 0.01) but was not significantly different between the groups (CR-CHO = +4.0 kg, 6.4%; PRO-CHO = +2.6 kg, 4.1%) (P = 0.11 for interaction). Muscle fiber area increased similarly after training for both groups (approximately 20%; P < 0.05). Training resulted in an increase in 1RM for each of the 16 activities (range = 14.2-39.9%) (P < 0.001), isokinetic knee extension torque (P < 0.01), with no treatment effects upon any of the variables.

CONCLUSIONS

We concluded that postexercise supplementation with PRO-CHO resulted in similar increases in strength after a resistance exercise training program as compared with CR-CHO. However, the greater gains in total mass for the CR-CHO group may have implications for sport-specific performance.

Evaluation of creatine transport using Caco-2 monolayers as an in vitro model for intestinal absorption

Creatine is a nutraceutical that has gained popularity in both well-trained and casual athletes for its performance-enhancing or ergogenic properties. The major disadvantages of creatine monohydrate formulations are poor solubility and oral bioavailability. In the present study, creatine transport was examined using Caco-2 monolayers as an in vitro model for intestinal absorption. Confluent monolayers of Caco-2 cells (passage 25-35) were used for the permeability studies. Monolayers were placed in side-by-side diffusion chambers. (14)C-Creatine (0.1-0.5 microCi/mL) was added to either the apical or basolateral side, and the transport of the creatine across the Caco-2 monolayer was measured over a 90-min period. The apical to basolateral transport of (14)C-creatine was small, ranging from 0.2-3% of the original amount appearing on the receiver side in a 90-min period. Interestingly, the basolateral to apical permeability of radiolabeled creatine was substantially greater than that observed in the apical to basolateral direction. Studies with drug efflux transport inhibitors indicate that neither the P-glycoprotein nor multidrug resistance-associated protein is involved in the enhanced basolateral to apical transport of creatine.

Dietary creatine supplementation and muscular adaptation to resistive overload

PURPOSE

This study examined the influence of dietary creatine (CR) supplementation upon mechanical and hypertrophic responses to a well-defined conditioning stimulus provided by electromyostimulation (EMS).

METHODS

Eighteen resistance-trained subjects were assigned CR or a placebo (PL) in a randomized, double-blind fashion. After CR loading (20 g x d(-1) for 7 d), CR supplementation (5 g x d(-1)) or PL was continued for 8 wk. During supplementation, EMS (3--5 sets of 10 coupled eccentric and concentric actions) was applied to the left m. quadriceps femoris (QF) twice weekly while subjects continued voluntary resistance training of both lower limbs unsupervised. Cross-sectional area (CSA) of each QF was assessed with magnetic resonance imaging (MRI). Torque during EMS was analyzed to assess muscle loading and fatigue resistance.

RESULTS

Maximal torque and the torque time integral increased markedly over training (P < or = 0.0001). These responses reflected activation of more muscle as EMS current was increased (about 16%), greater recovery between sets (P < or = 0.0423), and less fatigue during sets over training (P = 0.0002). CR did not influence these responses (P = 0.8093). In accord with these results, the increase in CSA for the stimulated QF (11%) was comparable for CR and PL (P = 0.2190). CSA in the nonstimulated QF increased 5% in CR (P = 0.0091) but did not change in PL.

CONCLUSION

We conclude that CR supplementation did not augment the mechanical or hypertrophic response to a precisely measured conditioning stimulus that attenuated but did not ameliorate fatigue. We suggest that enhanced fatigue resistance may not explain the apparent ergogenic effect of CR during voluntary training.

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.

Creatine supplementation and exercise performance: an update

Creatine, a natural nutrient found in animal foods, is alleged to be an effective nutritional ergogenic aid to enhance sport or exercise performance. Research suggests that oral creatine monohydrate supplementation may increase total muscle creatine [TCr], including both free creatine [FCr] and phosphocreatine [PCr]. Some, but not all, studies suggest that creatine supplementation may enhance performance in high-intensity, short-term exercise tasks that are dependent primarily on PCr (i.e., < 30 seconds), particularly laboratory tests involving repeated exercise bouts with limited recovery time between repetitions; additional corroborative research is needed regarding its ergogenic potential in actual field exercise performance tasks dependent on PCr. Creatine supplementation has not consistently been shown to enhance performance in exercise tasks dependent on anaerobic glycolysis, but additional laboratory and field research is merited. Additionally, creatine supplementation has not been shown to enhance performance in exercise tasks dependent on aerobic glycolysis, but additional research is warranted, particularly on the effect of chronic supplementation as an aid to training for improvement in competitive performance. Short-term creatine supplementation appears to increase body mass in males, although the initial increase is most likely water. Chronic creatine supplementation, in conjunction with physical training involving resistance exercise, may increase lean body mass. However, confirmatory research data are needed. Creatine supplementation up to 8 weeks has not been associated with major health risks, but the safety of more prolonged creatine supplementation has not been established. Creatine is currently legal and its use by athletes is not construed as doping.