Creatine supplementation and dynamic high-intensity intermittent exercise

Two intermittent high-intensity exercise protocols were performed before and after the administration of either creatine or a placebo, and performance characteristics and selected physiological responses were studied. Each exercise protocol consisted of 10 6-s bouts of high-intensity cycling at 2 exercise intensities (130 rev/min [EX₁₃₀]: ～820 W and 140 rev/min [EX₁₄₀)]: ～ 880 W) so that in EX₁₃₀ the same amount of exercise was performed before and after the administration period, whereas an exercise intensity in EX₁₄₀ was chosen to induce fatigue over the 10 exercise bouts. Sixteen healthy male subjects were randomly assigned to the 2 experimental groups. A double-blind design was used in this study. There were no significant changes in the placebo group for any of the measured parameters. Performance towards the end of each exercise bout in EX₁₄₀ was enhanced following creatine supplementation, as shown by a smaller decline in work output from baseline along the 10 trials. Although more work was performed in EX₁₄₀, after vs before the administration period, blood lactate accumulation decreased (mean and SEM), from 10.8 (0.5) to 9.1 (0.8) mmol·l^?1 and plasma accumulation of hypoxanthine decreased from 21.1 (0.4) to 16.7 (0.8) μmol·l^?1, but there was no change in oxygen uptake measured during 3 exercise and recovery periods [3.18 (0–1) vs 3.14 (0.1) l·min^?1]. In EX₁₃₀ blood lactate accumulation decreased, from 7.0 (0.5) to 5.1 (0.5) mmol·l^?1, and oxygen uptake was also lower, decreasing from 2.84 (0.1) to 2.78 (0.1) l·min^?1. A significant increase in body mass (11 kg: range 0.3 to 2.5 kg) was found in the creatine group. The mechanism responsible for the improved performance with creatine supplementation are postulated to be both a higher initial creatine phosphate content availability and an increased rate of creatine phosphate resynthesis during recovery periods. The lower blood lactate and hypoxanthine accumulation can also be explained by these mechanisms.     

Oral theophylline supplementation and high-intensity intermittent exercise

AIM: The present study was carried out to investigate whether oral theophylline supplementation exerts an ergogenic effect during intermittent high-intensity exercise. METHODS: Ten healthy subjects undertook intermittent exercise (1 min cycling at 120% of VO(2max) with 3 min of recovery until exhaustion). The exercise test was repeated twice, 1 week apart. On each occasion, the subject ingested, in a double blind setting, either theophylline (4.5 mg/kg) or placebo 90 min before commencing the exercise test. RESULTS: Three subjects could not complete both trials due to nausea and dizziness after theophylline had been administered. Time to exhaustion in the remaining subjects was slightly increased after theophylline administration (55.9+/-6 min vs 59.3+/-5.9 min; p<0.05). CONCLUSION: Present data indicate that oral theophylline supplementation delays fatigue onset during intermittent high-intensity exercise. The effect, although statistically significant, does not appear to be marked. The possibility of occurrence of negative side effects and the evidence for its ergogenic potential suggests the necessity to include theophylline in the International Olympic Committee (IOC) World Antidoping Agency (WADA) list as a banned or restricted substance.     

Effects of a supplementation during exercise and recovery

The present study was designed to investigate whether a protein hydrolysate enriched in branched chain amino acids and antioxidants, trace and mineral elements, and vitamins would affect performance and fatigue. Eighteen sportsmen underwent testing before and after 28 days supplementation with either treatment in protein hydrolysate or placebo. Testing included exhaustive aerobic and anaerobic exercises with determination of blood lactate concentration through exercise and recovery and antioxidant status, but also measurements of maximal oxidative capacity (V. (max)) and citrate synthase activity (CS) from a resting muscle biopsy. Protein hydrolysate resulted in a significant decrease in fatigue indices, without affecting performances. A significant increase in enzymatic antioxidant and a decrease in oxidative damage were observed at rest after treatment but not with a placebo. Decrease in maximal blood lactate and improvement of blood lactate removal were only observed after protein hydrolysate treatment. Furthermore, CS increased significantly, whereas no change was observed in V. (max). In conclusion, this protein hydrolysate treatment induced adaptations that may promote a decrease in fatigue during exercises, potentially explained by changes in parameters used to represent oxidative damage and antioxidant status at rest and changes in lactate metabolism.     

Antioxidant supplementation and immunoendocrine responses to prolonged exercise

PURPOSE: Antioxidant supplementation may modulate systemic cortisol and interleukin-6 (IL-6) responses to prolonged exercise, but it is unclear whether such effects are also associated with a reduction in the magnitude of immunodepression. The purpose of the present study was to examine the effects of daily vitamin C (L-ascorbic acid, 1000 mg x d(-1)) and vitamin E (RRR-alpha-tocopherol, 400 IU x d(-1)) supplementation on immunoendocrine responses to prolonged exercise. METHODS: Twenty healthy, recreationally active males cycled for 2.5 h at approximately 60% of maximal oxygen uptake after 4 wk of placebo (PLA, N=10) or antioxidant (AO, N=10) supplementation. RESULTS: A significant group x time interaction was observed for plasma cortisol concentration (P=0.008), and the postexercise increase was greater (P<0.05) in the PLA compared with AO group (approximately 170% compared with an approximately 120% increase above baseline). Plasma IL-6 concentration was significantly increased after exercise to a similar extent in both groups. Plasma free F2-isoprostane concentration was significantly increased after exercise and was unaffected by AO supplementation, whereas plasma TBARS was unaffected by exercise in the PLA group but was lower after exercise in the AO group than in the PLA group. Circulating neutrophil count was significantly increased after exercise, and in vitro bacteria-stimulated elastase release per neutrophil was significantly decreased to a similar extent in both groups. CONCLUSIONS: These results suggest that 4 wk of AO supplementation may blunt the cortisol response to a single 2.5-h bout of prolonged exercise independently of changes in oxidative stress or plasma IL-6 concentration, but it is not effective at modulating the exercise-induced neutrophilia or depression of neutrophil function.     

Creatine supplementation and exercise performance: recent findings

Creatine monohydrate (Cr) is perhaps one of the most widely used supplements taken in an attempt to improve athletic performance. The aim of this review is to update, summarise and evaluate the findings associated with Cr ingestion and sport and exercise performance with the most recent research available. Because of the large volume of scientific literature dealing with Cr supplementation and the recent efforts to delineate sport-specific effects, this paper focuses on research articles that have been published since 1999.Cr is produced endogenously by the liver or ingested from exogenous sources such as meat and fish. Almost all the Cr in the body is located in skeletal muscle in either the free (Cr: approximately 40%) or phosphorylated (PCr: approximately 60%) form and represents an average Cr pool of about 120-140 g for an average 70 kg person.It is hypothesised that Cr can act though a number of possible mechanisms as a potential ergogenic aid but it appears to be most effective for activities that involve repeated short bouts of high-intensity physical activity. Additionally, investigators have studied a number of different Cr loading programmes; the most common programme involves an initial loading phase of 20 g/day for 5-7 days, followed by a maintenance phase of 3-5 g/day for differing periods of time (1 week to 6 months). When maximal force or strength (dynamic or isotonic contractions) is the outcome measure following Cr ingestion, it generally appears that Cr does significantly impact force production regardless of sport, sex or age. The evidence is much more equivocal when investigating isokinetic force production and little evidence exists to support the use of Cr for isometric muscular performance. There is little benefit from Cr ingestion for the prevention or suppression of muscle damage or soreness following muscular activity.When performance is assessed based on intensity and duration of the exercises, there is contradictory evidence relative to both continuous and intermittent endurance activities. However, activities that involve jumping, sprinting or cycling generally show improved sport performance following Cr ingestion. With these concepts in mind, the focus of this paper is to summarise the effectiveness of Cr on specific performance outcomes rather than on proposed mechanisms of action.The last brief section of this review deals with the potential adverse effects of Cr supplementation. There appears to be no strong scientific evidence to support any adverse effects but it should be noted that there have been no studies to date that address the issue of long-term Cr usage.     

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 L-tryptophan supplementation on exercise performance

The performance of strenuous physical exercise is associated with discomfort and pain, the tolerance for that being modulated by the activity of the endogenous opioid systems. As 5-hydroxy-tryptamine (5-HT) affects nociception through its effects on the enkephalin-endorphin system, we have analyzed the effects of a moderate supplementation with L-tryptophan, the immediate precursor of 5-HT, on endurance and sensation of effort. Twelve healthy sportsmen were subjected to a work load corresponding to 80% of their maximal oxygen uptake on two separate trials, after receiving a placebo and after receiving the same amount of L-tryptophan. The subjects ran on a treadmill until exhaustion. Total exercise time, perceived exertion rate, maximum heart rate, peak oxygen consumption, pulse recovery rate, and excess post-exercise oxygen consumption were determined during the two trials. The total exercise time was 49.4% greater after receiving L-tryptophan than after receiving the placebo. A lower rate of perceived exertion was exhibited by the group while on tryptophan although the differences from the control group were not statistically significant. No differences were observed in the other parameters between the two trials. The longer exercise time als well at the total work load performed could be due to an increased pain tolerance as a result of L-tryptophan ingestion.     

Decrease in respiratory quotient during exercise following L-carnitine supplementation

This study was undertaken to determine the effects of L-carnitine addition to the diet during submaximal exercise in endurance-trained humans. Ten subjects (VO2max: 62 ml.kg-1.min-1) performed a control test (C) (45 min of cycling at 66% of VO2max) followed by 60 min of recovery in a sitting position. Each subject repeated this trial after 28 days of placebo (P) and L-carnitine (L-C) treatment (double-blinded cross-over design). The dose of each treatment was 2 g/day. There were no differences between the C and P tests. The respiratory quotient was lower (p less than 0.05) with treatment than with P or C during exercise. In addition, oxygen uptake, heart rate, blood glycerol, and resting plasma free fatty acid concentrations presented a nonsignificant trend toward higher values in L-C than in the C or P groups. These observations suggest an increased lipid utilization by muscle during exercise in the L-C-treated group. This effect has further possibilities for improving performance during submaximal exercise.     

Effect of vitamin B-6 supplementation on fuels, catecholamines, and amino acids during exercise in men

PURPOSE: In two separate but identical studies, the effect of vitamin B-6 supplementation was examined on plasma energy substrates, catecholamines, and 13 amino acid concentrations during exercise. METHODS: Eleven trained men performed two separate exhaustive exercise tests at 71.0+/-4.6% VO2max during two separate 9-d controlled diet periods. Exercise test 1 (T1C) occurred following a control diet, and test 2 (T2B6) occurred following a vitamin B-6 supplemented diet (20 mg PN.d(-1)). Blood was drawn pre, during (60 min), post, and post-60 min of exercise, and plasma was analyzed for glucose, lactate, glycerol, free fatty acids (FFA), catecholamines (N = 5), and amino acids (N = 5). RESULTS: Mean FFA concentrations changed over time in both tests (P < 0.001) and were lower in T2B6 compared to T1C at pre (P = 0.03), during (P = 0.05), and post-60 min (P = 0.04) of exercise. Mean lactate, glycerol, and catecholamine concentrations only changed over time (P < 0.0001). The only significant changes in amino acid concentrations were for lower tyrosine (P = 0.007) and methionine (P = 0.03) concentrations in T2B6 relative to TIC at post-60 min of exercise and postexercise, respectively. No differences were observed in exercise times to exhaustion between TIC (108+32.6 min) and T2B6 (109+51.2 min). CONCLUSIONS: These results indicate that vitamin B-6 supplementation can alter plasma FFA and amino acid concentrations during exhaustive endurance exercise without affecting endurance.     

The effects of magnesium supplementation on exercise performance

PURPOSE: To determine the effects of magnesium (Mg2+) supplementation on performance and recovery in physically active women using the sensitive and recently advanced measure of ionic Mg2+ (iMg). METHODS: Participants (N = 121) were screened for [iMg] in plasma, with 44 (36.4%) exhibiting [iMg] below the normal range of 0.53-0.67 mmol.L-1 (4). Thirty-two subjects (21 +/- 3 yr) representing a broad range of [iMg] (0.54 +/- 0.04 mmol.L-1) completed the main 14-wk study. At baseline, participants submitted to a resting blood pressure measurement, and they completed both an anaerobic treadmill test and an incremental (aerobic) treadmill test. For the latter, values for workload, oxygen uptake, and heart rate were obtained at both anaerobic threshold and maximal effort. Blood samples for iMg, total serum Mg2+ (TMg), erythrocyte Mg2+ (EMg), Ca2+, K+, Na+, hemoglobin, hematocrit, lactate, and glucose were also collected pretest, and 4, 10, 30 min, and 24 h posttest. Subjects received 212 mg.d-1 Mg oxide or placebo in a double-blind fashion and were retested after 4 wk. After a 6-wk washout period, the testing was repeated with a treatment crossover. RESULTS: Ionic Mg2+ increased with Mg2+ treatment versus placebo (P < 0.05); however, performance and recovery indices were not significantly affected. CONCLUSION: Four weeks of 212 mg.d-1 Mg oxide supplementation improves resting [iMg] levels but not performance or recovery in physically active women.     

Effects of creatine supplementation on exercise performance.

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

CNS fatigue and prolonged exercise: effect of glucose supplementation

INTRODUCTION: Ingestion of carbohydrates during prolonged exercise may improve endurance, whereas an insufficient supply of glucose results in hypoglycemia and fatigue. Fatigue, defined as a loss of force-generating capacity, may develop for a variety of reasons and involve both central and peripheral factors. This study investigated whether CNS activation of the skeletal muscles was affected by prolonged exercise with or without glucose supplementation. METHODS: Voluntary force production and central activation ratios, assessed by the twitch interpolation technique, were determined during a 2-min sustained maximal knee extension in eight endurance-trained males in a baseline condition and immediately after 3 h of cycling randomized to be with or without glucose supplementation. RESULTS: The exercise bout without glucose supplementation (placebo trial) reduced the blood glucose concentration from 4.5 +/- 0.2 to 3.0 +/- 0.2 mM, whereas blood glucose homeostasis was maintained during the glucose trial. The average force during the sustained maximal voluntary muscle contraction was 248 +/- 23 N at baseline, 222 +/- 20 N in the glucose trial, and 197 +/- 21 N in the placebo trial (P < 0.05 between conditions). In the placebo trial, the lowered force production was accompanied by a reduced level of CNS activation compared with the other two conditions (P < 0.05), whereas the central activation ratios were similar in the glucose trial as compared with baseline. CONCLUSION: Exercise-induced hypoglycemia attenuates CNS activation during a sustained maximal muscle contraction, whereas central activation appears to be unaffected by 3 h of moderately intense exercise in endurance-trained athletes when euglycemia is maintained by carbohydrate ingestion.     

Thyroid stunning in vivo and in vitro

AIM: To review published in-vivo and in-vitro quantitative dosimetric studies on thyroid stunning in order to derive novel data applicable in clinical practice. METHODS: A non-linear regression analysis was applied to describe the extent of thyroid stunning in thyroid remnants, as a function of the radiation absorbed dose of diagnostic radioiodine-131 (I), in thyroid cancer patients investigated in four in-vivo studies. The regression curves were fitted using individual patient absorbed doses or the mean absorbed doses for the groups of patients. Fitted curves were compared with two recent models, the first found in patients with benign thyroid disease and the second found in cultured thyroid cells after I irradiation. RESULTS: The extrapolated absorbed doses for the onset of thyroid stunning were 0 Gy delivered to thyroid cells in vitro, and < or =4 Gy and 34 Gy delivered to thyroid cells in vivo (malignant and benign conditions, respectively). Thyroid stunning amounted to roughly 50% in the case of 2 Gy delivered to thyroid cells in vitro, and in the case of < or =30 Gy and 472 Gy delivered to thyroid cells in vivo (malignant and benign conditions, respectively). CONCLUSIONS: There is no scintigraphically sufficient diagnostic amount of I that can be given prior to I therapy for thyroid cancer that does not cause thyroid stunning, i.e. it is not recommended to deliver pre-therapeutically more than a few gray (<5 Gy) into thyroid remnants. More investigations are required to confirm the proposed in-vitro and benign in-vivo models, but characteristic absorbed doses presented so far for in-vitro vs. in-vivo malignant vs. in-vivo benign thyroid environments differ roughly by an order of magnitude.     

Use of glycolytic energy sources by human skeletal muscle under anoxic conditions in vitro and during moderate exercise in vivo

To test a new in vitro model for investigations of muscle metabolism, the most important metabolites of muscle anaerobic metabolism (ATP, creatine phosphate, glucose, glycogen, and lactate) were measured in muscle biopsies from healthy male subjects, endurance-trained cyclists, strength-trained weight lifters, intensively trained long-distance runners, and speed-trained sprinters. The samples were taken at rest and after moderate muscle exercise for 30 s. These samples were analysed as such or after in vitro incubation for 30 s, 60 s, and 5 min under anoxic conditions. Anoxic conditions were created by incubating the muscle specimens in mineral oil through which N2 was bubbled. Under anoxic conditions in vitro, the concentrations of glycogen fell significantly in muscle specimens from sprinters and long-distance runners. The same tendency was observed in all other groups. The concentrations of high-energy phosphates. ATP and creatine phosphate, did not deplete under anoxic conditions. Under anoxic conditions, the rate of energy use, i.e., the metabolic rate calculated from the changes in the energy sources in terms of high-energy phosphate (P) use, was highest during the first 30 s, and declined to zero after 60 s. In the endurance-trained cyclists the metabolic rate was significantly lower than in any other group. In conclusion, muscle tissue behaves in quite a different way under anoxic conditions in vitro as compared with its behavior during exercise in vivo, and so the in vitro model is not suitable to compensate for studies of muscle metabolism in vivo. The in vitro model is of value, however, in, for example, determining the maximal metabolic rate of muscle.     

Creatine supplementation reduces muscle inosine monophosphate during endurance exercise in humans

INTRODUCTION: Creatine (Cr) supplementation has been shown to attenuate increases in plasma ammonia and hypoxanthine during intense endurance exercise lasting 1 h, suggesting that Cr supplementation may improve muscle energy balance (matching of ATP resynthesis to ATP demand) during such exercise. We hypothesized that Cr supplementation would improve muscle energy balance (as assessed by muscle inosine monophosphate (IMP) accumulation) during intense endurance exercise. METHODS: Seven well-trained men completed two experimental trials involving approximately 1 h of intense endurance exercise (cycling 45 min at 78+/-1% & OV0312;O2 peak followed by completion of 251+/-6 kJ as quickly as possible (performance ride)). Subjects ingested approximately 42 g.d dextrose for 5 d before the first experimental trial (CON), then approximately 21 g Cr monohydrate plus approximately 21 g.d dextrose for 5 d before the second experimental trial (CREAT). Trials were ordered because of the long washout time for Cr. Subjects were blinded to the order of the trials. RESULTS: Creatine supplementation significantly (P< 0.05) increased muscle total Cr (resting values: CREAT: 138.1+/-7.9; CON: 117.7+/- 6.5 mmol.kg dm). No difference was seen between treatments in any measured muscle or blood metabolite after the first 45 min of exercise. Despite the performance ride completion time being similar in the two treatments ( approximately 13.5 min, approximately 86% & OV0312;O2 peak), IMP at the end of the performance ride was significantly (P<0.05) lower in CREAT than in CON (CREAT: 1.2+/- 0.6; CON: 2.0+/- 0.7 mmol.kg dm). CONCLUSION:Raising muscle total Cr content before exercise appears to improve the ability of the muscle to maintain energy balance during intense aerobic exercise, but not during more moderate exercise intensities.