Effect of creatine supplementation on creatine and glycogen content in rat skeletal muscle

Sarcopenia and type 2 diabetes: Pathophysiology and potential therapeutic lifestyle interventions

AIMS

Sarcopenia generally refers to the age-related reduction in muscle strength, functional ability, and muscle mass. Sarcopenia is a multifactorial condition associated with poor glucose disposal, insulin resistance, and subsequently type 2 diabetes (T2D). The pathophysiological connection between sarcopenia and T2D is complex but likely involves glycemic control, inflammation, oxidative stress, and adiposity.

METHODS AND RESULTS

Resistance exercise and aerobic training are two lifestyle interventions that may improve glycemic control in older adults with T2D and counteract sarcopenia. Further, there is evidence that dietary protein, Omega-3 fatty acids, creatine monohydrate, and Vitamin D hold potential to augment some of these benefits from exercise.

CONCLUSIONS

The purpose of this narrative review is: (1) discuss the pathophysiological link between age-related sarcopenia and T2D, and (2) discuss lifestyle interventions involving physical activity and nutrition that may counteract sarcopenia and T2D.

Effects of Creatine Supplementation on Histopathological and Biochemical Parameters in the Kidney and Pancreas of Streptozotocin-Induced Diabetic Rats

Diabetes mellitus (DM) is a worldwide health concern, and projections state that cases will reach 578 million by 2030. Adjuvant therapies that can help the standard treatment and mitigate DM effects are necessary, especially those using nutritional supplements to improve glycemic control. Previous studies suggest creatine supplementation as a possible adjuvant therapy for DM, but they lack the evaluation of potential morphological parameters alterations and tissue injury caused by this compound. The present study aimed to elucidate clinical, histomorphometric, and histopathological consequences and the cellular oxidative alterations of creatine supplementation in streptozotocin (STZ)-induced type 1 DM rats. We could estimate whether the findings are due to DM or the supplementation from a factorial experimental design. Although creatine supplementation attenuated some biochemical parameters, the morphological analyses of pancreatic and renal tissues made clear that the supplementation did not improve the STZ-induced DM1 injuries. Moreover, creatine-supplemented non-diabetic animals were diagnosed with pancreatitis and showed renal tubular necrosis. Therefore, even in the absence of clinical symptoms and unaltered biochemical parameters, creatine supplementation as adjuvant therapy for DM should be carefully evaluated.

Evaluation of chronic toxicity of cyclocreatine in beagle dogs after oral gavage administration for up to 23 weeks

Cyclocreatine (LUM-001) was evaluated for chronic toxicity (23 weeks) in beagle dogs to support clinical development in patients with creatine transporter deficiency (CTD) disorder. Deionized water (vehicle control) or cyclocreatine was administered by oral gavage twice daily (12 ± 1 h apart) at 20, 40 and 75 mg/kg/dose followed by a recovery period. Due to severe toxicity, the study was terminated earlier than the planned 39 weeks of dosing. Animals in the 20, 40 and 75 mg/kg/dose groups completed 160, 106, and 55 days of dosing, respectively, followed by 30, 55 and 106 days of a recovery period, respectively. Three (25%), 7 (58%), and 7 (58%) animals were euthanized and/or found dead in the 40, 80, and 150 mg/kg/day dose groups, respectively. Clinical signs observed were inappetence, frequent emesis, stool abnormalities, weight loss, lethargy and respiratory distress. Histopathological evaluation revealed congestion, edema, cellular infiltration, fibrin, and/or hemorrhage in the lungs of all dose groups. Additionally, animals in all cyclocreatine treatment groups had perinuclear cytoplasmic vacuoles in the heart, kidneys, skeletal and smooth muscles. After the recovery period, the vacuoles were still observed in the cardiac and renal tissues. Cyclocreatine was absorbed rapidly with mean Tmax within 1 to 2 h and half-life ranged between 2.17 and 2.79 h on Day 1, however, on the final day of dosing, it ranged between 5.80 and 8.77 h (males) and 10.3 to 13.1 h (females). To conclude, in this study the lungs, kidneys, heart, skeletal and smooth muscles were identified as the target organs of cyclocreatine toxicity in beagle dogs.

Effect of Creatine Supplementation on Functional Capacity and Muscle Oxygen Saturation in Patients with Symptomatic Peripheral Arterial Disease: A Pilot Study of a Randomized, Double-Blind Placebo-Controlled Clinical Trial

The aim of the study was to verify the effects of creatine (Cr) supplementation on functional capacity (walking capacity; primary outcome) and calf muscle oxygen saturation (StO2) (secondary outcome) in symptomatic peripheral arterial disease (PAD) patients. Twenty-nine patients, of both sexes, were randomized (1:1) in a double-blind manner for administration of placebo (PLA, n = 15) or creatine monohydrate (Cr, n = 14). The supplementation protocol consisted of 20 g/day for 1 week divided into four equal doses (loading phase), followed by single daily doses of 5 g in the subsequent 7 weeks (maintenance phase). Functional capacity (total walking distance) was assessed by the 6 min walk test, and calf muscle StO2 was assessed through near infrared spectroscopy. The measurements were collected before and after loading and after the maintenance phase. The level of significance was p < 0.05. No significant differences were found for function capacity (total walking distance (PLA: pre 389 ± 123 m vs. post loading 413 ± 131 m vs. post maintenance 382 ± 99 m; Cr: pre 373 ± 149 m vs. post loading 390 ± 115 m vs. post maintenance 369 ± 115 m, p = 0.170) and the calf muscle StO2 parameters (p > 0.05). Short- and long-term Cr supplementation does not influence functional capacity and calf muscle StO2 parameters in patients with symptomatic PAD.

Evaluation of chronic toxicity of cyclocreatine, a creatine analog, in Sprague Dawley rat after oral gavage administration for up to 26 weeks

Cyclocreatine (LUM-001), a creatine analog, was evaluated for its nonclinical toxicity in Sprague Dawley (SD) rats. Deionized water as a vehicle control article or cyclocreatine was administered by oral gavage twice daily (approximately 12 ± 1 h apart) at 30, 100 and 300 mg/kg/dose levels in rats up to 26 weeks followed by a 28-day recovery period. Due to an increased incidence of seizures, the 600 mg/kg/day dose group males were dosed only for 16-weeks followed by a 14-week recovery period. Thirteen males and four females from 600 mg/kg/day dose group were sacrificed at interim on Day 113 to study plausible brain lesions and not due to moribundity. There was a dose dependent increase in the number of seizure incidences in ≥60 mg/kg/day males and 600 mg/kg/day females. Microscopically, higher incidences of vacuoles in the brain at 600 mg/kg/day in both sexes, thyroid follicular atrophy and follicular cell hypertrophy at ≥200 mg/kg/day in males and 600 mg/kg/day in females, and seminiferous tubular degeneration and/or interstitial edema in testes at ≥200 mg/kg/day were observed. Mean plasma half-life of cyclocreatine was between 3.5 and 6.5 h. In conclusion, chronic administration of cyclocreatine by oral gavage in Sprague Dawley rats induced the seizures and microscopic lesions in the brain, testes and thyroid. Based on the results of this study the highest tested dose of 600 mg/kg/day (mean C_max of 151.5 μg/mL; AUC_0-24 of 1970 h*μg/mL) was considered the maximum tolerated dose (MTD) in SD rats.

Short-term creatine supplementation changes protein metabolism signaling in hindlimb suspension

The effect of a short-term creatine supplementation on hindlimb suspension (HS)-induced muscle atrophy was investigated. Creatine monohydrate (5 g/kg b.w. per day) or placebo, divided in 2 daily doses, was given by oral gavage for 5 days. Rats were maintained in HS with dietary supplementation concomitantly for 5 days. Body weight, soleus and EDL muscle masses, and cross-sectional areas (CSA) of the muscle fibers were measured. Signaling pathways associated with skeletal muscle mass regulation (FST, MSTN, FAK, IGF-1, MGF, Akt, mTOR, atrogin-1, and MuRF1 expressions, and Akt, S6, GSK3B, and 4EBP1 proteins) were evaluated in the muscles. Soleus muscle exhibited more atrophy than the EDL muscle due to HS. Creatine supplementation attenuated the decrease of wet weight and increased p-4EBP1 protein in the EDL muscle of HS rats. Also, creatine increased mTOR and atrogin-1 expressions in the same muscle and condition. In the absence of HS, creatine supplementation increased FAK and decreased MGF expressions in the EDL muscle. Creatine attenuated the increase in FST expression due to HS in the soleus muscle. MuRF1 expression increased in the soleus muscle due to creatine supplementation in HS animals whereas atrogin-1 expression increased still further in this group compared with untreated HS rats. In conclusion, short-term creatine supplementation changed protein metabolism signaling in soleus and EDL muscles. However, creatine supplementation only slightly attenuated the mass loss of both muscles and did not prevent the CSA reduction and muscle strength decrease induced by HS for 5 days.

ISSN exercise & sports nutrition review update: research & recommendations

Background

Sports nutrition is a constantly evolving field with hundreds of research papers published annually. In the year 2017 alone, 2082 articles were published under the key words ‘sport nutrition’. Consequently, staying current with the relevant literature is often difficult.

Methods

This paper is an ongoing update of the sports nutrition review article originally published as the lead paper to launch the Journal of the International Society of Sports Nutrition in 2004 and updated in 2010. It presents a well-referenced overview of the current state of the science related to optimization of training and performance enhancement through exercise training and nutrition. Notably, due to the accelerated pace and size at which the literature base in this research area grows, the topics discussed will focus on muscle hypertrophy and performance enhancement. As such, this paper provides an overview of: 1.) How ergogenic aids and dietary supplements are defined in terms of governmental regulation and oversight; 2.) How dietary supplements are legally regulated in the United States; 3.) How to evaluate the scientific merit of nutritional supplements; 4.) General nutritional strategies to optimize performance and enhance recovery; and, 5.) An overview of our current understanding of nutritional approaches to augment skeletal muscle hypertrophy and the potential ergogenic value of various dietary and supplemental approaches.

Conclusions

This updated review is to provide ISSN members and individuals interested in sports nutrition with information that can be implemented in educational, research or practical settings and serve as a foundational basis for determining the efficacy and safety of many common sport nutrition products and their ingredients.

Use and Effectiveness of Performance-Enhancing Substances

The use and effects of selected performance-enhancing drugs and nutritional supplements are reviewed. Recent sports medicine studies are mostly double blind and placebo controlled but contain relatively small sample sizes. Their data appear reliable and are reported in reputable journals. Definitions and methods used in sports medicine are provided to enhance the understanding of this literature. The use of performance-enhancing substances is probably under-reported. Anabolic-androgenic steroids are reportedly used in 0% to 1% of women, 0.5% to 3% of high school girls, 1% to 5% of men, 1% to 12% of high school boys, and up to 67% of some groups of elite athletes. The use of combinations of performance-enhancing substances is common. Carbohydrate loading, adequate protein intake, creatine, blood doping, and erythropoietin (epoetin alfa) appear to enhance performance. Anabolic-androgenic steroids enhance performance, but health risks limit their use. Growth hormones and β2 -selective adrenergic agonists may enhance performance, but additional studies are needed. Androstenedione, caffeine, amphetamines, and nonprescription sympathomimetics do not appear to enhance performance. Performance-enhancing drugs have shown some benefit in diseased patients with malnutrition and/or decreases in physical ability. Pharmacists and other health care providers have opportunities to improve the understanding, use, and monitoring of performance-enhancing substances.

Creatine supplementation and glycemic control: a systematic review

The focus of this review is the effects of creatine supplementation with or without exercise on glucose metabolism. A comprehensive examination of the past 16 years of study within the field provided a distillation of key data. Both in animal and human studies, creatine supplementation together with exercise training demonstrated greater beneficial effects on glucose metabolism; creatine supplementation itself demonstrated positive results in only a few of the studies. In the animal studies, the effects of creatine supplementation on glucose metabolism were even more distinct, and caution is needed in extrapolating these data to different species, especially to humans. Regarding human studies, considering the samples characteristics, the findings cannot be extrapolated to patients who have poorer glycemic control, are older, are on a different pharmacological treatment (e.g., exogenous insulin therapy) or are physically inactive. Thus, creatine supplementation is a possible nutritional therapy adjuvant with hypoglycemic effects, particularly when used in conjunction with exercise.

Creatine ingestion augments dietary carbohydrate mediated muscle glycogen supercompensation during the initial 24 h of recovery following prolonged exhaustive exercise in humans

Muscle glycogen availability can limit endurance exercise performance. We previously demonstrated 5 days of creatine (Cr) and carbohydrate (CHO) ingestion augmented post-exercise muscle glycogen storage compared to CHO feeding alone in healthy volunteers. Here, we aimed to characterise the time-course of this Cr-induced response under more stringent and controlled experimental conditions and identify potential mechanisms underpinning this phenomenon. Fourteen healthy, male volunteers cycled to exhaustion at 70 % VO_2peak. Muscle biopsies were obtained at rest immediately post-exercise and after 1, 3 and 6 days of recovery, during which Cr or placebo supplements (20 g day⁻¹) were ingested along with a prescribed high CHO diet (37.5 kcal kg body mass⁻¹ day⁻¹, >80 % calories CHO). Oral-glucose tolerance tests (oral-GTT) were performed pre-exercise and after 1, 3 and 6 days of Cr and placebo supplementation. Exercise depleted muscle glycogen content to the same extent in both treatment groups. Creatine supplementation increased muscle total-Cr, free-Cr and phosphocreatine (PCr) content above placebo following 1, 3 and 6 days of supplementation (all P < 0.05). Creatine supplementation also increased muscle glycogen content noticeably above placebo after 1 day of supplementation (P < 0.05), which was sustained thereafter. This study confirmed dietary Cr augments post-exercise muscle glycogen super-compensation, and demonstrates this occurred during the initial 24 h of post-exercise recovery (when muscle total-Cr had increased by <10 %). This marked response ensued without apparent treatment differences in muscle insulin sensitivity (oral-GTT, muscle GLUT4 mRNA), osmotic stress (muscle c-fos and HSP72 mRNA) or muscle cell volume (muscle water content) responses, such that another mechanism must be causative.

Metabogenic and Nutriceutical Approaches to Address Energy Dysregulation and Skeletal Muscle Wasting in Duchenne Muscular Dystrophy

Duchenne Muscular Dystrophy (DMD) is a fatal genetic muscle wasting disease with no current cure. A prominent, yet poorly treated feature of dystrophic muscle is the dysregulation of energy homeostasis which may be associated with intrinsic defects in key energy systems and promote muscle wasting. As such, supplementative nutriceuticals that target and augment the bioenergetical expansion of the metabolic pathways involved in cellular energy production have been widely investigated for their therapeutic efficacy in the treatment of DMD. We describe the metabolic nuances of dystrophin-deficient skeletal muscle and review the potential of various metabogenic and nutriceutical compounds to ameliorate the pathological and clinical progression of the disease.

The effect of creatine supplementation on myocardial function, mitochondrial respiration and susceptibility to ischaemia/reperfusion injury in sedentary and exercised rats

AIM

To investigate the effects of dietary creatine supplementation alone and in combination with exercise on basal cardiac function, susceptibility to ischaemia/reperfusion injury and mitochondrial oxidative function. There has been an increase in the use of creatine supplementation among sports enthusiasts, and by clinicians as a therapeutic agent in muscular and neurological diseases. The effects of creatine have been studied extensively in skeletal muscle, but not in the myocardium.

METHODS

Male Wistar rats were swim-trained for 8 weeks, 5 days per week. Hearts were excised and either freeze-clamped for biochemical analysis or perfused on the isolated heart perfusion system to assess function and ischaemia/reperfusion tolerance. Mechanical function was documented in working heart and retrograde mode. The left coronary artery was ligated and infarct size determined. Mitochondrial oxidative capacity was quantified.

RESULTS

Aortic output recovery of hearts from the sedentary controls (CSed) was significantly higher than those from creatine-supplemented sedentary (CrSed), creatine-supplemented exercised (CrEx) as well as control exercised (CEx) groups. Ischaemic contracture of hearts from CrEx was significantly higher than that of CSed. There were no differences in infarct size and mitochondrial oxygen consumption.

CONCLUSION

This study suggests that creatine supplementation has no effects on basal cardiac function but reduces myocardial tolerance to ischaemia in hearts from exercise-trained animals, by increasing the ischaemic contracture and decreasing reperfusion aortic output. Exercise training alone also significantly decreased aortic output recovery. However, the exact mechanisms for these adverse myocardial effects are unknown and need further investigation.

Detection of creatine in rat muscle by FTIR spectroscopy

There is a current lack of clarity regarding the use of Fourier-transform infrared spectroscopy (FT-IR) to evaluate intramuscular concentrations of creatine (Cr). Thus, the aim of this study was to assess the FT-IR spectral features of tibialis anterior muscle in rats submitted in conditions that were expected to perturb the Cr pool. First, an experiment was performed to ensure that FT-IR was able to detect the Cr intramuscular in sedentary and supplemented rats (Experiment 1). The effect of physical exercise on spectral muscle features was then examined, especially in relation to the spectroscopy markers (Experiment 2). Using pure Cr (control), it was possible to verify that only the peaks centered at 1308 and 1396 cm(-1) of all the spectra showed the same peak positions, indicating these FT-IR shifts as indirect markers of Cr intramuscular content. Experiment 2 revealed a higher Cr content for the Cr-supplemented and exercised animals than the rats of other groups. In conclusion, it was demonstrated that FT-IR spectroscopy using 1396 cm(-1) and mainly 1308 band was able to monitor Cr muscle content in rats sedentary, Cr-supplemented, and submitted to physical training. Besides, FT-IR could be a feasible method for the nondestructive assessment of Cr skeletal muscle content.

Exercise-induced, but not creatine-induced, decrease in intramyocellular lipid content improves insulin sensitivity in rats

The effect of creatine supplementation, alone or in combination with exercise training, on insulin sensitivity, intramyocellular lipid content (IMCL) and fatty acid translocase (FAT)/CD36 content was investigated in rats fed a sucrose-rich cafeteria diet during 12 weeks. Five experimental conditions were CON, receiving normal pellets; CAF, fed the cafeteria diet; CAF(TR), fed the cafeteria diet together with exercise training in weeks 8-12 and CAF(CR) and CAF(CRT) that were analogous to CAF and CAF(TR), respectively, but which received daily 2.5% of creatine monohydrate. During intravenous glucose tolerance test, compared with CON, whole-body glucose tolerance was reduced in CAF and CAF(CR) but not in CAF(TR) and CAF(CRT). Insulin-stimulated glucose transport in perfused red gastrocnemius muscles was impaired in CAF and CAF(CR) but not in the trained groups. IMCL content in soleus and extensor digitorum longus muscles was higher in CAF than in CON, but not in CAF(TR), CAF(CR) and CAF(CRT). Compared with CON and CAF, FAT/CD36 protein content in m. soleus, was ~40% lower in CAF(CR), CAF(TR) and CAF(CRT). The fraction of fecal fat, as determined in a 3-week post hoc study, was 25% higher in CAF(CR) than in CON. Moreover, in CAF(CR), triglyceride concentration in blood and liver were significantly lower than in CAF. It is concluded that creatine supplementation in rats on a cafeteria diet inhibits IMCL accumulation via inhibition of gastrointestinal lipid absorption together with lower muscle FAT/CD36 content. Furthermore, exercise-induced but not creatine-induced reduction of IMCL is associated with improved insulin action on glucose transport in muscle cells.

The effects of a pre-workout supplement containing caffeine, creatine, and amino acids during three weeks of high-intensity exercise on aerobic and anaerobic performance

Background

A randomized, single-blinded, placebo-controlled, parallel design study was used to examine the effects of a pre-workout supplement combined with three weeks of high-intensity interval training (HIIT) on aerobic and anaerobic running performance, training volume, and body composition.

Methods

Twenty-four moderately-trained recreational athletes (mean ± SD age = 21.1 ± 1.9 yrs; stature = 172.2 ± 8.7 cm; body mass = 66.2 ± 11.8 kg, VO₂max = 3.21 ± 0.85 l·min^-1, percent body fat = 19.0 ± 7.1%) were assigned to either the active supplement (GT, n = 13) or placebo (PL, n = 11) group. The active supplement (Game Time^®, Corr-Jensen Laboratories Inc., Aurora, CO) was 18 g of powder, 40 kcals, and consisted of a proprietary blend including whey protein, cordyceps sinensis, creatine, citrulline, ginseng, and caffeine. The PL was also 18 g of powder, 40 kcals, and consisted of only maltodextrin, natural and artificial flavors and colors. Thirty minutes prior to all testing and training sessions, participants consumed their respective supplements mixed with 8-10 oz of water. Both groups participated in a three-week HIIT program three days per week, and testing was conducted before and after the training. Cardiovascular fitness (VO₂max) was assessed using open circuit spirometry (Parvo-Medics TrueOne^® 2400 Metabolic Measurement System, Sandy, UT) during graded exercise tests on a treadmill (Woodway, Pro Series, Waukesha, WI). Also, four high-speed runs to exhaustion were conducted at 110, 105, 100, and 90% of the treadmill velocity recorded during VO₂max, and the distances achieved were plotted over the times-to-exhaustion. Linear regression was used to determine the slopes (critical velocity, CV) and y-intercepts (anaerobic running capacity, ARC) of these relationships to assess aerobic and anaerobic performances, respectively. Training volumes were tracked by summing the distances achieved during each training session for each subject. Percent body fat (%BF) and lean body mass (LBM) were assessed with air-displacement plethysmography (BOD POD^®, Life Measurement, Inc., Concord, CA).

Results

Both GT and PL groups demonstrated a significant (p = 0.028) increase in VO₂max from pre- to post-training resulting in a 10.3% and 2.9% improvement, respectively. CV increased (p = 0.036) for the GT group by 2.9%, while the PL group did not change (p = 0.256; 1.7% increase). ARC increased for the PL group by 22.9% and for the GT group by 10.6%. Training volume was 11.6% higher for the GT versus PL group (p = 0.041). %BF decreased from 19.3% to 16.1% for the GT group and decreased from 18.0% to 16.8% in the PL group (p = 0.178). LBM increased from 54.2 kg to 55.4 kg (p = 0.035) for the GT group and decreased from 52.9 kg to 52.4 kg in the PL group (p = 0.694).

Conclusion

These results demonstrated improvements in VO₂max, CV, and LBM when GT is combined with HIIT. Three weeks of HIIT alone also augmented anaerobic running performance, VO₂max and body composition.

ISSN exercise & sport nutrition review: research & recommendations

Sports nutrition is a constantly evolving field with hundreds of research papers published annually. For this reason, keeping up to date with the literature is often difficult. This paper is a five year update of the sports nutrition review article published as the lead paper to launch the JISSN in 2004 and presents a well-referenced overview of the current state of the science related to how to optimize training and athletic performance through nutrition. More specifically, this paper provides an overview of: 1.) The definitional category of ergogenic aids and dietary supplements; 2.) How dietary supplements are legally regulated; 3.) How to evaluate the scientific merit of nutritional supplements; 4.) General nutritional strategies to optimize performance and enhance recovery; and, 5.) An overview of our current understanding of the ergogenic value of nutrition and dietary supplementation in regards to weight gain, weight loss, and performance enhancement. Our hope is that ISSN members and individuals interested in sports nutrition find this review useful in their daily practice and consultation with their clients.

Creatine supplementation spares muscle glycogen during high intensity intermittent exercise in rats

Background

The effects of creatine (CR) supplementation on glycogen content are still debatable. Thus, due to the current lack of clarity, we investigated the effects of CR supplementation on muscle glycogen content after high intensity intermittent exercise in rats.

Methods

First, the animals were submitted to a high intensity intermittent maximal swimming exercise protocol to ensure that CR-supplementation was able to delay fatigue (experiment 1). Then, the CR-mediated glycogen sparing effect was examined using a high intensity intermittent sub-maximal exercise test (fixed number of bouts; six bouts of 30-second duration interspersed by two-minute rest interval) (experiment 2). For both experiments, male Wistar rats were given either CR supplementation or placebo (Pl) for 5 days.

Results

As expected, CR-supplemented animals were able to exercise for a significant higher number of bouts than Pl. Experiment 2 revealed a higher gastrocnemius glycogen content for the CR vs. the Pl group (33.59%). Additionally, CR animals presented lower blood lactate concentrations throughout the intermittent exercise bouts compared to Pl. No difference was found between groups in soleus glycogen content.

Conclusion

The major finding of this study is that CR supplementation was able to spare muscle glycogen during a high intensity intermittent exercise in rats.

Exploring the therapeutic role of creatine supplementation

Creatine (Cr) plays a central role in energy provision through a reaction catalyzed by phosphorylcreatine kinase. Furthermore, this amine enhances both gene expression and satellite cell activation involved in hypertrophic response. Recent findings have indicated that Cr supplementation has a therapeutic role in several diseases characterized by atrophic conditions, weakness, and metabolic disturbances (i.e., in the muscle, bone, lung, and brain). Accordingly, there has been an evidence indicating that Cr supplementation is capable of attenuating the degenerative state in some muscle disorders (i.e., Duchenne and inflammatory myopathies), central nervous diseases (i.e., Parkinson's, Huntington's, and Alzheimer's), and bone and metabolic disturbances (i.e., osteoporosis and type II diabetes). In light of this, Cr supplementation could be used as a therapeutic tool for the elderly. The aim of this review is to summarize the main studies conducted in this field and to highlight the scientific and clinical perspectives of this promising therapeutic supplement.

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 supplementation reduces plasma levels of pro-inflammatory cytokines and PGE2 after a half-ironman competition

OBJECTIVE

The effect of creatine supplementation upon plasma levels of pro-inflammatory cytokines: Interleukin (IL) 1 beta and IL-6, Tumor Necrosis Factor alpha (TNFalpha), and Interferon alpha (INF alpha) and Prostaglandin E(2) (PGE(2)) after a half-ironman competition were investigated.

METHODS

Eleven triathletes, each with at least three years experience of participation in this sport were randomly divided between the control and experimental groups. During 5 days prior to competition, the control group (n = 6) was supplemented with carbohydrate (20 g x d(-1)) whereas the experimental group (n = 5) received creatine (20 g x d(-1)) in a double-blind trial. Blood samples were collected 48 h before and 24 and 48 h after competition and were used for the measurement of cytokines and PGE(2).

RESULTS

Forty-eight hours prior to competition there was no difference between groups in the plasma concentrations (pg x ml(-1), mean +/- SEM) of IL-6 (7.08 +/- 0.63), TNFalpha (76.50 +/- 5.60), INF alpha (18.32 +/- 1.20), IL-1 beta (23.42 +/- 5.52), and PGE(2) (39.71 +/- 3.8). Twenty-four and 48 h after competition plasma levels of TNFalpha, INF alpha, IL-1 beta and PGE(2) were significantly increased (P < 0.05) in both groups. However, the increases in these were markedly reduced following creatine supplementation. An increase in plasma IL-6 was observed only after 24 h and, in this case, there was no difference between the two groups.

CONCLUSION

Creatine supplementation before a long distance triathlon competition may reduce the inflammatory response induced by this form of strenuous of exercise.

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.

Effects of creatine supplementation on glucose tolerance and insulin sensitivity in sedentary healthy males undergoing aerobic training

Recent findings have indicated that creatine supplementation may affect glucose metabolism. This study aimed to examine the effects of creatine supplementation, combined with aerobic training, on glucose tolerance in sedentary healthy male. Subjects (n = 22) were randomly divided in two groups and were allocated to receive treatment with either creatine (CT) ( approximately 10 g . day over three months) or placebo (PT) (dextrose). Administration of treatments was double blind. Both groups underwent moderate aerobic training. An oral glucose tolerance test (OGTT) was performed and both fasting plasma insulin and the homeostasis model assessment (HOMA) index were assessed at the start, and after four, eight and twelve weeks. CT demonstrated significant decrease in OGTT area under the curve compared to PT (P = 0.034). There were no differences between groups or over time in fasting insulin or HOMA. The results suggest that creatine supplementation, combined with aerobic training, can improve glucose tolerance but does not affect insulin sensitivity, and may warrant further investigation with diabetic subjects.

Creatine supplementation does not enhance submaximal aerobic training adaptations in healthy young men and women

The benefits of dietary creatine supplementation on muscle performance are generally related to an increase in muscle phosphocreatine content. However, creatine supplementation may benefit endurance sports through increased glycogen re-synthesis following exercise. This study investigated the effect of creatine supplementation on muscle glycogen content, submaximal exercise fuel utilisation and endurance performance following 4 weeks of endurance training. Thirteen healthy, physically active, non-vegetarian subjects volunteered to take part and completed the study. Subjects were supplemented with either creatine monohydrate (CREAT, n = 7) or placebo-maltodextrin (CON, n = 6). Submaximal fuel utilisation and endurance performance were assessed before and after a 4 week endurance training program. Muscle biopsies were also collected before and following training for assessment of muscle creatine and glycogen content. Training increased quadriceps glycogen content to the same degree (approximately 20%) in both groups (P = 0.04). There was a significant training effect on submaximal fuel utilisation and improved endurance performance. However, there was no significant treatment effect of creatine supplementation. Creatine supplementation does not effect metabolic adaptations to endurance training.

Creatine supplementation augments the increase in satellite cell and myonuclei number in human skeletal muscle induced by strength training

The present study investigated the influence of creatine and protein supplementation on satellite cell frequency and number of myonuclei in human skeletal muscle during 16 weeks of heavy-resistance training. In a double-blinded design 32 healthy, male subjects (19-26 years) were assigned to strength training (STR) while receiving a timed intake of creatine (STR-CRE) (n=9), protein (STR-PRO) (n=8) or placebo (STR-CON) (n=8), or serving as a non-training control group (CON) (n=7). Supplementation was given daily (STR-CRE: 6-24 g creatine monohydrate, STR-PRO: 20 g protein, STR-CON: placebo). Furthermore, timed protein/placebo intake were administered at all training sessions. Muscle biopsies were obtained at week 0, 4, 8 (week 8 not CON) and 16 of resistance training (3 days per week). Satellite cells were identified by immunohistochemistry. Muscle mean fibre (MFA) area was determined after histochemical analysis. All training regimes were found to increase the proportion of satellite cells, but significantly greater enhancements were observed with creatine supplementation at week 4 (compared to STR-CON) and at week 8 (compared to STR-PRO and STR-CON) (P<0.01-0.05). At week 16, satellite cell number was no longer elevated in STR-CRE, while it remained elevated in STR-PRO and STR-CON. Furthermore, creatine supplementation resulted in an increased number of myonuclei per fibre and increases of 14-17% in MFA at week 4, 8 and 16 (P<0.01). In contrast, STR-PRO showed increase in MFA only in the later (16 week, +8%) and STR-CON only in the early (week 4, +14%) phases of training, respectively (P<0.05). In STR-CRE a positive relationship was found between the percentage increases in MFA and myonuclei from baseline to week 16, respectively (r=0.67, P<0.05). No changes were observed in the control group (CON). In conclusion, the present study demonstrates for the first time that creatine supplementation in combination with strength training amplifies the training-induced increase in satellite cell number and myonuclei concentration in human skeletal muscle fibres, thereby allowing an enhanced muscle fibre growth in response to strength training.

No effects of lifelong creatine supplementation on sarcopenia in senescence-accelerated mice (SAMP8)

Oral creatine supplementation can acutely ameliorate skeletal muscle function in older humans, but its value in the prevention of sarcopenia remains unknown. We evaluated the effects of lifelong creatine supplementation on muscle mass and morphology, contractility, and metabolic properties in a mouse model of muscle senescence. Male senescence-accelerated mice (SAMP8) were fed control or creatine-supplemented (2% of food intake) diet from the age of 10 to 60 wk. Soleus and extensor digitorum longus muscles were tested for in vitro contractile properties, creatine content, and morphology at weeks 25 and 60. Both muscle types showed reduced phosphocreatine content at week 60 that could not be prevented by creatine. Accordingly, age-associated decline in muscle mass and contractility was not influenced by treatment. Aged soleus muscles had fewer and smaller fast-twitch glycolytic fibers irrespective of treatment received. It is concluded that lifelong creatine supplementation is no effective strategy to prevent sarcopenia in senescence-accelerated mice.

AMP kinase expression and activity in human skeletal muscle: effects of immobilization, retraining, and creatine supplementation

The effects of leg immobilization and retraining in combination with oral creatine intake on muscle AMP-activated protein kinase (AMPK) protein expression and phosphorylation status were investigated. A double-blind trial was performed in young healthy volunteers ( n = 22). A cast immobilized the right leg for 2 wk, whereafter the knee-extensor muscles of that leg were retrained for 6 wk. Half of the subjects received creatine monohydrate throughout the study (Cr; from 15 g down to 2.5 g daily), and the others ingested placebo (P; maltodextrin). Before and after immobilization and retraining, needle biopsies were taken from the right and left vastus lateralis muscles. In the right leg of P and Cr, immobilization did not affect AMPK α1-, α2-, and β2-subunit expression or AMPK α-subunit phosphorylation status. However, irrespective of the treatment received, retraining increased the degree of α-subunit phosphorylation by ∼25% ( P < 0.05) and increased AMPK α1-subunit expression ( P < 0.05) in both groups. From the start to the end of the study, AMPK subunit protein expression and α-subunit phosphorylation status were unchanged in the contralateral control leg. It is concluded that immobilization-induced muscle inactivity for 2 wk does not alter AMPK α1-, α2-, and β2-subunit expression or α-AMPK phosphorylation status. Furthermore, the present observations indicate that AMPK probably is not implicated in the previously reported beneficial effects of oral creatine supplementation on muscle during immobilization and rehabilitative weight 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).

Creatine feeding increases GLUT4 expression in rat skeletal muscle

The purpose of this study was to investigate the potential role of creatine in GLUT4 gene expression in rat skeletal muscle. Female Wistar rats were fed normal rat chow (controls) or chow containing 2% creatine monohydrate ad libitum for 3 wk. GLUT4 protein levels of creatine-fed rats were significantly increased in extensor digitorum longus (EDL), triceps, and epitrochlearis muscles compared with muscles from controls (P < 0.05), and triceps GLUT4 mRNA levels were approximately 100% greater in triceps muscles from creatine-fed rats than in muscles from controls (P < 0.05). In epitrochlearis muscles from creatine-fed animals, glycogen content was approximately 40% greater (P < 0.05), and insulin-stimulated glucose transport rates were higher (P < 0.05) than in epitrochlearis muscles from controls. Despite no changes in [ATP], [creatine], [phosphocreatine], or [AMP], creatine feeding increased AMP-activated protein kinase (AMPK) phosphorylation by 50% in rat EDL muscle (P < 0.05). Creatinine content of EDL muscle was almost twofold higher for creatine-fed animals than for controls (P < 0.05). Creatine feeding increased protein levels of myocyte enhancer factor 2 (MEF2) isoforms MEF2A ( approximately 70%, P < 0.05), MEF2C ( approximately 60%, P < 0.05), and MEF2D ( approximately 90%, P < 0.05), which are transcription factors that regulate GLUT4 expression, in creatine-fed rat EDL muscle nuclear extracts. Electrophoretic mobility shift assay showed that DNA binding activity of MEF2 was increased by approximately 40% (P < 0.05) in creatine-fed rat EDL compared with controls. Our data suggest that creatine feeding enhances the nuclear content and DNA binding activity of MEF2 isoforms, which is concomitant with an increase in GLUT4 gene expression.

Effect of creatine on contractile force and sensitivity in mechanically skinned single fibers from rat skeletal muscle

Increasing the intramuscular stores of total creatine [TCr = creatine (Cr) + creatine phosphate (CrP)] can result in improved muscle performance during certain types of exercise in humans. Initial uptake of Cr is accompanied by an increase in cellular water to maintain osmotic balance, resulting in a decrease in myoplasmic ionic strength. Mechanically skinned single fibers from rat soleus (SOL) and extensor digitorum longus (EDL) muscles were used to examine the direct effects on the contractile apparatus of increasing [Cr], increasing [Cr] plus decreasing ionic strength, and increasing [Cr] and [CrP] with no change in ionic strength. Increasing [Cr] from 19 to 32 mM, accompanied by appropriate increases in water to maintain osmolality, had appreciable beneficial effects on contractile apparatus performance. Compared with control conditions, both SOL and EDL fibers showed increases in Ca2+ sensitivity (+0.061 ± 0.004 and +0.049 ± 0.009 pCa units, respectively) and maximum Ca2+-activated force (to 104 ± 1 and 105 ± 1%, respectively). In contrast, increasing [Cr] alone had a small inhibitory effect. When both [Cr] and [CrP] were increased, there was virtually no change in Ca2+ sensitivity of the contractile apparatus, and maximum Ca2+-activated force was ∼106 ± 1% compared with control conditions in both SOL and EDL fibers. These results suggest that the initial improvement in performance observed with Cr supplementation is likely due in large part to direct effects of the accompanying decrease in myoplasmic ionic strength on the properties of the contractile apparatus.

Creatine: are the benefits worth the risk?

Creatine monohydrate is a popular sports supplement used to maintain levels of high-energy phosphates during exercise. As a supplement, varying amounts are consumed per person corresponding to parameters such as body mass and level of training (i.e. maintenance versus loading doses). Numerous studies have reported beneficial effects including increased muscle mass during training and neural protection. However, negative reports have also been made of possible side effects, such as muscle cramping during exercise, and potential impurities. The present paper introduces the positive and negative aspects of creatine supplementation and focuses on the toxicological data of creatine, its metabolites and associated mutagenicity or carcinogenicity, genomeceutical effect(s), and any potential 'contaminants.' Additionally, the novel applications of creatine to the areas of neurology, cardiology, and diabetes are presented and discussed along with the representative data for sports nutrition.

Effect of muscle creatine content manipulation on contractile properties in mouse muscles

The effects of muscle creatine manipulation on contractile properties in oxidative and glycolytic muscles were evaluated. Whereas control mice (NMRi; n = 12) received normal chow (5 g daily), three experimental groups were created by adding creatine monohydrate (CR group; 5%, 1 week; n = 13); beta-guanidinoproprionic acid, an inhibitor of cellular creatine uptake (beta-GPA group; 1%, 2 weeks; n = 12); or CR following beta-GPA (beta-GPA+CR group; n = 11). Total creatine (TCr) and the contractile properties of incubated soleus and extensor digitorum longus (EDL) muscles were determined. For the soleus, compared with control, TCr increased in the CR group (+25%), decreased in beta-GPA group (-50%), and remained stable in the beta-GPA+CR group, whereas, for the EDL, TCr was similar in the CR, and lower in the beta-GPA (-40%) and beta-GPA+CR (-15%) groups. None of the experimental groups (CR, beta-GPA, or beta-GPA+CR) showed changes in peak tension (P(peak)), time to peak tension, or relaxation in soleus or EDL during twitch or tetanic stimulation. For the soleus, fatigue reduced P(peak) to approximately 60% of initial P(peak); 5 min of recovery restored P(peak) to values approximately 15% higher in CR than in controls. P(peak) recovery was not affected by beta-GPA or beta-GPA+CR in the soleus or any treatment in the EDL. Thus, peak tension recovery is enhanced by creatine intake in oxidative but not glycolytic muscles. This may be implicated in the beneficial action of creatine loading.

Creatine supplementation increases glucose oxidation and AMPK phosphorylation and reduces lactate production in L6 rat skeletal muscle cells

Recent observations have suggested that creatine supplementation might have a beneficial effect on glucoregulation in skeletal muscle. However, conclusive studies on the direct effects of creatine on glucose uptake and metabolism are lacking. The objective of this study was to investigate the effects of creatine supplementation on basal and insulin-stimulated glucose transporter (GLUT4) translocation, glucose uptake, glycogen content, glycogen synthesis, lactate production, glucose oxidation and AMP-activated protein kinase (AMPK) phosphorylation in L6 rat skeletal muscle cells. Four treatment groups were studied: control, insulin (100 nM), creatine (0.5 mM) and creatine + insulin. After 48 h of creatine supplementation the creatine and phosphocreatine contents of L6 myoblasts increased by approximately 9.3- and approximately 5.1-fold, respectively, but the ATP content of the cells was not affected. Insulin significantly increased 2-deoxyglucose uptake ( approximately 1.9-fold), GLUT4 translocation ( approximately 1.8-fold), the incorporation of D-[U-(14)C]glucose into glycogen ( approximately 2.3-fold), lactate production ( approximately 1.5-fold) and (14)CO(2) production ( approximately 1.5-fold). Creatine neither altered the glycogen and GLUT4 contents of the cells nor the insulin-stimulated rates of 2-DG uptake, GLUT4 translocation, glycogen synthesis and glucose oxidation. However, creatine significantly reduced by approximately 42% the basal rate of lactate production and increased by approximately 40% the basal rate of (14)CO(2) production. This is in agreement with the approximately 35% increase in citrate synthase activity and also with the approximately 2-fold increase in the phosphorylation of both alpha-1 and alpha-2 isoforms of AMPK after creatine supplementation. We conclude that 48 h of creatine supplementation does not alter insulin-stimulated glucose uptake and glucose metabolism; however, it activates AMPK, shifts basal glucose metabolism towards oxidation and reduces lactate production in L6 rat skeletal muscle cells.

Muscle creatine uptake and creatine transporter expression in response to creatine supplementation and depletion

The total creatine pool size [Cr(total); creatine (Cr) + phosphocreatine (PCr)] is crucial for optimal energy utilization in skeletal muscle, especially at the onset of exercise and during intense contractions. The Cr(total) likely is controlled by long-term modulation of Cr uptake via the sodium-dependent Cr transporter (CrT). To test this hypothesis, adult male Sprague-Dawley rats were fed 1% Cr, their muscle Cr(total) was reduced by approximately 85% [1% beta-guanidinoproprionic acid (beta-GPA)], or their muscle Cr(total) was repleted (1% Cr after beta-GPA depletion). Cr uptake was assessed by skeletal muscle (14)C-Cr accumulation to Cr and PCr by using hindlimb perfusion, and CrT protein content was assessed by Western blot. Cr uptake rate decreased with dietary Cr supplementation in the white gastrocnemius (WG; 45%) only. Depletion of muscle Cr(total) to approximately 15% of normal increased Cr uptake in the soleus (21%) and red gastrocnemius (22%), corresponding to 70-150% increases in muscle CrT content. In contrast, the inherently lower Cr uptake rate in the WG was unchanged with depletion of muscle Cr(total) even though CrT band density was increased by 230%. Thus there was no direct relationship between apparent muscle CrT abundance and Cr uptake rates. However, Cr uptake rates scaled inversely with decreases in muscle Cr(total) in the high-oxidative muscle types but not in the WG. This implies that factors controlling Cr uptake are different among fiber types. These observations may help explain the influence of initial muscle Cr(total), time dependency, and variations in muscle Cr(total) accumulation during Cr supplementation.

Creatine uptake and creatine transporter expression among rat skeletal muscle fiber types

Total creatine (Cr(total) = phosphocreatine + creatine) concentrations differ substantially among mammalian skeletal muscle. Because the primary means to add Cr(total) to muscle is uptake of creatine through the sodium-dependent creatine transporter (CrT), differences in creatine uptake and CrT expression could account for the variations in [Cr(total)] among muscle fiber types. To test this hypothesis, hindlimbs of adult rats were perfused with 0.05-1 mM [(14)C]creatine for up to 90 min. Creatine uptake rates at 1 mM creatine were greatest in the soleus (140 +/- 8.8 nmol x h(-1) x g(-1)), less in the red gastrocnemius (117 +/- 8.3), and least in the white gastrocnemius (97 +/- 10.7). These rates were unaltered by time, insulin concentration, or increased perfusate sodium concentration. Conversely, creatine uptake rates were correspondingly decreased among fiber types by lower creatine and sodium concentrations. The CrT protein content by Western blot analysis was similarly greatest in the soleus, less in the red gastrocnemius, and least in the white gastrocnemius, whereas CrT mRNA was not different. Creatine uptake rates differ among skeletal muscle fiber sections in a manner reasonably assigned to the 58-kDa band of the CrT. Furthermore, creatine uptake rates scale inversely with creatine content, with the lowest uptake rate in the fiber type with the highest Cr(total) and vice versa. This suggests that the creatine pool fractional turnover rate is not common across muscle phenotypes and, therefore, is differentially regulated.

Combined creatine and protein supplementation in conjunction with resistance training promotes muscle GLUT-4 content and glucose tolerance in humans

The present study was undertaken to explore the effects of creatine and creatine plus protein supplementation on GLUT-4 and glycogen content of human skeletal muscle. This was investigated in muscles undergoing a decrease (immobilization) and subsequent increase (resistance training) in activity level, compared with muscles with unaltered activity pattern. A double-blind, placebo-controlled trial was performed by 33 young healthy subjects. The subjects' right legs were immobilized with a cast for 2 wk, followed by a 6-wk resistance training program for the right knee extensor muscles. The participants were supplemented throughout the study with either placebo (Pl group) or creatine (Cr group) or with creatine during immobilization and creatine plus protein during retraining (Cr+P group). Needle biopsies were bilaterally taken from the vastus lateralis. GLUT-4 protein expression was reduced by the immobilization in all groups (P < 0.05). During retraining, GLUT-4 content increased (P < 0.05) in both Cr (+24%) and Cr+P (+33%), which resulted in higher posttraining GLUT-4 expression compared with Pl (P < 0.05). Compared with Pl, muscle glycogen content was higher (P < 0.05) in the trained leg in both Cr and Cr+P. Supplements had no effect on GLUT-4 expression or glycogen content in contralateral control legs. Area under the glucose curve during the oral glucose tolerance test was decreased from 232 +/- 23 mmol. l(-1). min(-1) at baseline to 170 +/- 23 mmol. l(-1). min(-1) at the end of the retraining period in Cr+P (P < 0.05), but it did not change in Cr or Pl. We conclude that creatine intake stimulates GLUT-4 and glycogen content in human muscle only when combined with changes in habitual activity level. Furthermore, combined protein and creatine supplementation improved oral glucose tolerance, which is supposedly unrelated to the changes in muscle GLUT-4 expression.

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 creatine ingestion on glucose tolerance and insulin sensitivity in men

PURPOSE

This study investigated whether acute (5 d) and/or short-term (28 d) creatine (Cr) ingestion altered glucose tolerance or insulin action in healthy, untrained men (aged 26.9 +/- 5.7 yr; SD).

METHODS

Subjects were randomly allocated to either a Cr ( N= 8) or placebo group (N = 9) and were tested in the control condition (presupplementation), and after 5 and a further 28 d of supplementation. The Cr group ingested 20 g and 3 g.d (-1) of Cr for the first 5 and following 28 d, respectively. The placebo group ingested similar amounts of glucose over the same time period. During each testing period, subjects underwent an oral glucose tolerance test (OGTT) to determine insulin sensitivity, and six subjects from each group underwent a muscle biopsy before each OGTT.

RESULTS

Cr supplementation resulted in an increased (P< 0.05) muscle TCr content after both the acute and short-term loading phase compared with placebo. Neither acute nor short-term Cr supplementation influenced skeletal muscle glycogen content, glucose tolerance, or measures of insulin sensitivity.

CONCLUSIONS

These findings demonstrated that acute Cr supplementation (20 g.d(-1) for 5 d) followed by short-term Cr supplementation (3 g.d(-1) for 28 d) did not alter insulin action in healthy, active untrained men.

The effect of creatine supplementation on glucose uptake in rat skeletal muscle

Glucose transport in muscle is a function of the muscle metabolic state, as evidenced by the increase in glucose transport which occurs with conditions of altered aerobic metabolism such as hypoxia or contractile activity. The energy state of the muscle can be determined by the muscle phosphocreatine concentration. Dietary supplementation of creatine has been shown to increase both phosphocreatine (PCr) and creatine (TCr) levels in muscle, although not in the same proportion, so that the PCr/TCr ratio falls suggesting an altered energy state in the cell. The purpose of this study was to determine the effect of increased creatine content on glucose uptake in muscle. PCr and TCr were determined in plantaris muscles from rats following five weeks of dietary supplementation of creatine monohydrate (300 mg/kg/day). (3)H-2-deoxyglucose uptake was measured in epitrochlearis muscles incubated in the presence or absence of a maximally stimulating dose of insulin. Despite a significant increase in creatine content in muscle, neither basal nor insulin-stimulated glucose uptake was altered in creatine supplemented rats. Since PCr levels were not increased with creatine supplementation, these results suggest that the actual concentration of PCr is a more important determinant of glucose uptake than the PCr/TCr ratio.

Creatine supplementation: exploring the role of the creatine kinase/phosphocreatine system in human muscle

The effect of oral creatine supplementation on high-intensity exercise performance has been extensively studied over the past ten years and its ergogenic potential in young healthy subjects is now well documented. Recently, research has shifted from performance evaluation towards elucidating the mechanisms underlying enhanced muscle functional capacity after creatine supplementation. In this review, we attempt to summarise recent advances in the understanding of potential mechanisms of action of creatine supplementation at the level of skeletal muscle cells. By increasing intracellular creatine content, oral creatine ingestion conceivably stimulates operation of the creatine kinase (CK)/phosphocreatine (PCr) system, which in turn facilitates muscle relaxation. Furthermore, evidence is accumulating to suggest that creatine supplementation can beneficially impact on muscle protein and glycogen synthesis. Thus, muscle hypertrophy and glycogen supercompensation are candidate factors to explain the ergogenic potential of creatine ingestion. Additional issues discussed in this review are the fibre-type specificity of muscle creatine metabolism, the identification of responders versus non-responders to creatine intake, and the scientific background concerning potential side effects of creatine supplementation.