Gastrointestinal distress after creatine supplementation in athletes: are side effects dose dependent?

The main aim of the present study was to investigate the effects of two different creatine-supplementation protocols on incidence of gastrointestinal (GI) distress in top-level athletes. Data were collected from 59 top-level male soccer players who were allocated in a double-blind design to three randomly assigned trials: ingesting creatine supplement (C5: 2 x 5-g doses, and C10: 1 x 10-g dose) or placebo (P) for 28 days. In order to assess potential side effects of the supplementation regimen, all subjects were instructed to report any adverse effects of supplementation on their GI system. Survey questions covered perceived side effects on GI system linked with creatine supplementation. In all three treatment groups, the most frequent GI complaints were diarrhoea (39.0%), stomach upset (23.8%), and belching (16.9%). We did not find a significant difference between incidence of GI distress symptoms between C5 and the placebo group after the survey. Yet, significant differences were found for incidence of diarrhoea between the C5 and C10 groups (28.6% vs. 55.6%, respectively, p < 0.05). Moreover, diarrhoea was more frequent in the C10 group as compared with the placebo group (55.6% vs. 35.0%, p < 0.05). There is no reason to believe that short-term oral creatine supplementation for 28 days has any detrimental effect on the GI tract if taken in a recommended amount (10 g per day in two equal doses). The risk of diarrhoea may be increased, however, following intake of 10 grams of creatine per single serving.     

The effects of creatine supplementation on performance during the repeated bouts of supramaximal exercise

AIM: The aim of this study was to investigate the effects of creatine supplementation on performance during the repeated bouts of supramaximal exercise. METHODS: Twenty-three untrained young males participated in the study. A double blind design was used to create the creatine and placebo groups. Wingate test was performed 5 times with 90 g x kg(-1) body weight load with 2-min intervals. Peak power, mean power (MP), fatigue index (FI) were calculated. Capillary blood samples for lactate analysis were taken during the initial rest period and soon after the fifth Wingate test. For 6 days the creatine group (n=12) ingested 5 g creatine monohydrate, the placebo group (n=11) a flavored drink without creatine monohydrate 4 times daily. On the 7th day, the Wingate tests were repeated, as was the 1st day. RESULTS: In the creatine group, MP in the 3rd and 4th Wingate test, in the placebo group FI in the 1st and 2nd Wingate test significantly increased. While the total power output obtained from the five Wingate tests increased 7.6% from 366.3+/-65 W to 394+/-67.1 W, there was no change in the placebo group. CONCLUSIONS: It is concluded that creatine supplementation enhances total power output during the repeated bouts of supramaximal exercise separated by short resting intervals.     

Performance and muscle fiber adaptations to creatine supplementation and heavy resistance training.

PURPOSE: The purpose of this study was to examine the effect of creatine supplementation in conjunction with resistance training on physiological adaptations including muscle fiber hypertrophy and muscle creatine accumulation. METHODS: Nineteen healthy resistance-trained men were matched and then randomly assigned in a double-blind fashion to either a creatine (N = 10) or placebo (N = 9) group. Periodized heavy resistance training was performed for 12 wk. Creatine or placebo capsules were consumed (25 g x d(-1)) for 1 wk followed by a maintenance dose (5 g x d(-1)) for the remainder of the training. RESULTS: After 12 wk, significant (P < or = 0.05) increases in body mass and fat-free mass were greater in creatine (6.3% and 6.3%, respectively) than placebo (3.6% and 3.1%, respectively) subjects. After 12 wk, increases in bench press and squat were greater in creatine (24% and 32%, respectively) than placebo (16% and 24%, respectively) subjects. Compared with placebo subjects, creatine subjects demonstrated significantly greater increases in Type I (35% vs 11%), IIA (36% vs 15%), and IIAB (35% vs 6%) muscle fiber cross-sectional areas. Muscle total creatine concentrations were unchanged in placebo subjects. Muscle creatine was significantly elevated after 1 wk in creatine subjects (22%), and values remained significantly greater than placebo subjects after 12 wk. Average volume lifted in the bench press during training was significantly greater in creatine subjects during weeks 5-8. No negative side effects to the supplementation were reported. CONCLUSION: Creatine supplementation enhanced fat-free mass, physical performance, and muscle morphology in response to heavy resistance training, presumably mediated via higher quality training sessions.     

Oral creatine supplementation improves multiple sprint performance in elite ice-hockey players

BACKGROUND: The purpose of this study was to assess the effect of oral creatine monohydrate supplementation on multiple sprint cycle and skating performance in ice-hockey players. METHODS: Participants: sixteen elite ice-hockey players were selected as subjects. Experimental design: subjects were randomly assigned to either a creatine (Cr) (n = 8) or a placebo (P) group (n = 8) in a double blind design. After familiarization and baseline tests, subjects loaded with 5 g of creatine monohydrate or placebo (glucose) four times per day for 5 days, after which a maintenance dose of 5 g per day for 10 weeks was administered. At baseline, and after 10 days and 10 weeks of supplementation, subjects performed i) a cycle test involving 5 all-out sprints of 15 sec duration separated by 15 sec recovery with the resistance set at 0.075 body mass (kg), and ii) 6 timed 80-m skating sprints with the sprints initiated every 30 sec and a split time taken at 47 m. RESULTS: A two-way ANOVA demonstrated no significant change in any of the variables in the P group over the period of study. However, in the Cr group, average mean power output over the 5 sprints was significantly higher at 10 days (1074 +/- 241 W) and 10 weeks (1025 +/- 216 W) than at baseline (890 +/- 172 W), (p < 0.01). Average peak power output over the 5 sprints improved significantly from baseline (1294 +/- 311 W) to 10 days (1572 +/- 463 W), (p < 0.01). Average on-ice sprint performance to 47 m was significantly faster at 10 days (6.88 +/- 0.21 sec) and 10 weeks (6.96 +/- 0.19 sec) than at baseline (7.17 +/- 0.27 sec), (p < 0.005). CONCLUSIONS: This study demonstrates that creatine supplementation has an ergogenic effect in elite ice-hockey players.     

Creatine supplementation during resistance training in college football athletes

PURPOSE: This investigation assessed the effects of a 9-wk regimen of creatine monohydrate (Cr x H2O) supplementation coupled with resistance training on body composition and neuromuscular performance in NCAA Division I football athletes. METHODS: Twenty-five subjects were randomly assigned in a double-blind, randomized placebo-controlled design, to a treatment (Cr, N = 9), placebo (P, N = 8), or control group (C, N = 8). The Cr group received 20 g.d(-1) of creatine for the first 5 d in 5-g doses, four times daily, followed by 5 g.d(-1) for the remainder of the study. Each 5-g dose was mixed with 500 mL of glucose solution (Gatorade). The P group received a placebo (sodium phosphate monohydrate; NaH2PO4 x H2O) following the exact protocol as the Cr group. The C group received no supplementation. All subjects resistance trained 4 d.wk(-1). Measurements of neuromuscular performance and body composition were made pre- and post-training after supplementation while monitoring dietary intakes. RESULTS: Repeated measures ANOVA indicated significant differences occurred between the Cr group and the other two groups (P and C) for total body weight, lean body mass, cell hydration, strength, peak torque at 300 degrees.s(-1) knee flexion, percent torque decrement, and anaerobic power and capacity. However, percent body fat, peak torque during both knee flexion and extension at 60 and 180 degrees.s(-1), peak torque at 300 degrees.s(-1) during knee extension, global muscular strength (power clean), and extracellular fluid remained statistically unchanged for all groups. CONCLUSIONS: Our findings indicate that creatine, supplemented concurrently with resistance and anaerobic training, may positively affect cell hydration status and enhance performance variables further than augmentation seen with training alone.     

Effects of oral creatine supplementation on high intensity, intermittent exercise performance in competitive squash players.

The purpose of this study was to determine the effects of oral creatine supplementation on high intensity, intermittent exercise performance in competitive squash players. Nine squash players (mean +/- SEM VO2max = 61.9 +/- 2.1 ml x kg(-1) x min(-1); body mass = 73 +/- 3 kg) performed an on-court "ghosting" routine that involved 10 sets of 2 repetitions of simulated positional play, each set interspersed with 30 s passive recovery. A double blind, crossover design was utilised whereby experimental and control groups supplemented 4 times daily for 5 d with 0.075 g x kg(-1) body mass of creatine monohydrate and maltodextrine, respectively, and a 4 wk washout period separated the crossover of treatments. The experimental group improved mean set sprint time by 3.2 +/- 0.8% over and above the changes noted for the control group (P = 0.004 and 95% Cl = 1.4 to 5.1%). Sets 2 to 10 were completed in a significantly shorter time following creatine supplementation compared to the placebo condition (P < 0.05). In conclusion, these data support existing evidence that creatine supplementation improves high intensity, intermittent exercise performance. In addition, the present study provides new evidence that oral creatine supplementation improves exercise performance in competitive squash players.     

The effect of creatine monohydrate supplementation on sprint skating in ice-hockey players

AIM: Creatine monohydrate supplementation is beneficial for enhancing high-intensity exercise performance, especially activities that involve repeated sprints. Creatine monohydrate supplementation is common in ice-hockey players. The purpose of this study was to determine the effect of creatine monohydrate supplementation on sprint skating performance in Junior B and collegiate ice-hockey players. METHODS: Seventeen ice-hockey players were randomly assigned to receive creatine (0.3 g/kg body mass/day for 5 days) or placebo. Before and after supplementation players performed repeated sprints to exhaustion on a skating treadmill (repeated 10-s sprints; 30-s rest between sprints) while blood lactate was simultaneously collected. The time to exhaustion on the treadmill test was calculated as total amount of time, including partial intervals, before the player reached exhaustion. Players were also tested for peak torque and average power during knee extension/flexion (3 sets of 10 reps; 60-s rest between sets) on an isokinetic dynamometer at 60 degrees/s. RESULTS: The change in time to exhaustion from before to after supplementation averaged 20.6+/-7 s in the creatine group and 21.9+/-13 s in the placebo group, with no differences between groups. Likewise, there were no differences between groups for changes in isokinetic peak torque and average power. There were no differences between groups over time for blood lactate changes during the repeated sprints on the treadmill. CONCLUSIONS: We conclude that creatine was not effective for improving performance in these ice-hockey players.     

Electro-membrane microcurrent therapy reduces signs and symptoms of muscle damage

PURPOSE: Delayed onset muscle soreness (DOMS) occurs after unaccustomed physical activity or competitive sport, resulting in stiff, painful muscles with impaired function. Acustat electro-membrane microcurrent therapy has been used to treat postoperative pain and soft tissue injury; however, its efficacy in reducing symptoms of muscle damage is not known. METHODS: Thirty healthy men were recruited for a double-blind, placebo-controlled trial. The muscles of their nondominant arms were damaged using an eccentric-exercise protocol. Subjects were then randomly assigned to treatment with either Acustat or a matching placebo membrane for 96 h and monitored for a total of 168 h. RESULTS: Subjects in both groups experienced severe pain and swelling of the elbow flexors after the eccentric exercise. After 24 h, the elbow joint angle of the placebo group had increased significantly more than those in the Acustat group (13.7 +/- 8.9 degrees vs 7.5 +/- 5.5 degrees; placebo vs Acustat, P < 0.05), possibly as a consequence of the elbow flexor muscles shortening. For the first 48 h after exercise, maximum voluntary contraction of the elbow flexor muscles was significantly impaired in the placebo group by up to 25% (P < 0.05), whereas muscle function was unchanged in the Acustat group. Peak plasma creatine kinase activity was also lower in the Acustat group (peak = 777 +/- 1438 U.L-1) versus the placebo group (peak = 1918 +/- 2067 U.L-1; (P < 0.05). The membranes were well tolerated by the subjects in both groups without any adverse effects. CONCLUSION: These data show that treatment of muscle damage with Acustat electro-membrane microcurrent therapy reduces the severity of the symptoms. The mechanisms of action are unknown but are likely related to maintenance of intracellular Ca2+ homeostasis after muscle damaging exercise.     

Creatine supplementation improves muscular performance in older men

PURPOSE: Creatine supplementation has been shown to enhance muscle strength and power after only 5-7 d in young adults. Creatine supplementation could therefore benefit older individuals because aging is associated with a decrease in muscle strength and explosive power. METHODS: We examined the effects of 7 d of creatine supplementation in normally active older men (59-72 yr) by using a double-blind, placebo-controlled design with repeated measures. After a 3-wk familiarization period to minimize learning effects, a battery of tests was completed on three occasions separated by 7 d (T1, T2, and T3). After T1, subjects were matched and randomly assigned into creatine (N = 10) and placebo (N = 8) groups. After T2, subjects consumed supplements (0.3 g x kg(-1) x d(-1)) for 7 d until T3. All subjects were tested for maximal dynamic strength (one-repetition maximum leg press and bench press), maximal isometric strength (knee extension/flexion), upper- and lower-body explosive power (6 x 10-s sprints on a cycle ergometer), and lower-extremity functional ability (timed sit-stand test and tandem gait test). Body composition was assessed via hydrostatic weighing, and blood samples were obtained to assess renal and hepatic responses and muscle creatine concentrations. RESULTS: No significant increases in any performance measures were observed from T1 to T2 with the exception of isometric right-knee flexion in the placebo group indicating stability in the testing protocols. Significant group-by -time interactions indicated the responses from T2 to T3 were significantly greater (P 相似文献   

Effect of creatine supplementation on training for competition in elite swimmers

PURPOSE: The study was conducted to examine the effects of oral creatine supplementation on training for competition in 20 elite swimmers. METHODS: Subjects performed a maximal sprint test (8 x 50 yd (45.72 m), T1) before loading with creatine (Cr, 20 g.d Cr monohydrate for 5 d), 1 wk later (T2), and following a 22- to 27-wk period of training and competition (T3). Following T2, subjects supplemented with either Cr (3 g + glucose 7 g.d) or placebo (glucose 10 g.d; double blind) for the remainder of the 22- to 27-wk season and then both groups supplemented once more with 20 g.d Cr monohydrate for 5 d before their major competition. Venous and capillary blood samples were obtained pre- and posttest during the repeated sprint tests to determine blood metabolites and hormones. Competition times were recorded, and changes in subjects' best times were used to compare the effect of training and supplementation on competitive performance. RESULTS: Mean competition times in the Cr and control groups changed by+1.90 +/-1.91 and+0.72+/-1.64% for short course (SC, 25-m pool) and by+0.14+/-1.14 and -0.59+/-0.82% long course (LC, 50-m pool), respectively (Cr vs control, NS). No differences between groups were found in blood metabolites, although the human growth hormone (hGH) response to repeated sprints was blunted following Cr loading (T1, 30.42+/-14.60 and 28.95+/-18.27 microg.L; T2, 21.48+/-13.96 and 14.24+/-7.32 microg.L for Cr and control groups, respectively P<0.05). CONCLUSION: No statistically significant differences in performance were observed between groups after long-term maintenance during training, although small differences were observed that might be meaningful for elite performers.     

Creatine supplementation and health variables: a retrospective study

PURPOSE: Long-term safety of creatine supplementation has been questioned. This retrospective study was performed to examine markers related to health, the incidence of reported side effects and the perceived training benefits in athletes supplementing with creatine monohydrate. METHODS: Twenty-six athletes (18 M and 8 F, 24.7 +/- 9.2 y; 82.4 +/- 20.0 kg; 176.5 +/- 8.8 cm) from various sports were used as subjects. Blood was collected between 7:00 and 8:30 a.m. after a 12-h fast. Standard clinical examination was performed for CBC and 27 blood chemistries. Testosterone, cortisol, and growth hormone were analyzed using an ELISA. Subjects answered a questionnaire on dietary habits, creatine supplementation, medical history, training history, and perceived effects of supplementation. Body mass was measured using a medical scale, body composition was estimated using skinfolds, and resting heart rate and blood pressure were recorded. Subjects were grouped by supplementation length or no use: Gp1 (control) = no use (N = 7; 3 F, 4 M); Gp2 = 0.8-1.0 yr (N = 9; 2 F, 7 M); and Gp3 = 1(+) (N = 10; 3 F, 7 M). RESULTS: Creatine supplementation ranged from 0.8--4 yr. Mean loading dose for Gp2 and Gp3 was 13.7 +/- 10.0 and the maintenance dose was 9.7 +/- 5.7 g.d(-)1. Group differences were analyzed using one-way ANOVA. CONCLUSIONS: Expected gender differences were observed. Of the comparisons made among supplementation groups, only two differences for creatinine and total protein (P < 0.05) were noted. All group means fell within normal clinical ranges. There were no differences in the reported incidence of muscle injury, cramps, or other side effects. These data suggest that long-term creatine supplementation does not result in adverse health effects.     

Caffeine is ergogenic after supplementation of oral creatine monohydrate

PURPOSE: The purpose of this investigation was to assess the acute effects of caffeine ingestion on short-term, high-intensity exercise (ST) after a period of oral creatine supplementation and caffeine abstinence. METHODS: Fourteen trained male subjects performed treadmill running to volitional exhaustion (T(lim)) at an exercise intensity equivalent to 125% VO(2max). Three trials were performed, one before 6 d of creatine loading (0.3 g x kg x d(-1) baseline), and two further trials after the loading period. One hour before the postloading trials, caffeine (5 mg x kg(-1)) or placebo was orally ingested in a cross-over, double-blind fashion. Four measurements of rating of perceived exertion were taken, one every 30 s, during the first 120 s of the exercise. Blood samples were assayed for lactate, glucose, potassium, and catecholamines, immediately before and after exercise. RESULTS: Body mass increased (P < 0.05) over the creatine supplementation period, and this increase was maintained for both caffeine and placebo trials. There was no increase in the maximal accumulated oxygen deficit between trials; however, total VO(2) was significantly increased in the caffeine trial in comparison with the placebo trial (13.35 +/- 3.89 L vs 11.67 +/- 3.61 L). In addition, caffeine T(lim) (222.1 +/- 48.9 s) was significantly greater (P < 0.05) than both baseline (200.8 +/- 33.4 s) and placebo (198.3 +/- 45.4 s) T(lim). RPE was also lower at 90 s in the caffeine treatment (13.8 +/- 1.8 RPE points) in comparison with baseline (14.6 +/- 1.9 RPE points). CONCLUSION: As indicated by a greater T(lim), acute caffeine ingestion was found to be ergogenic after 6-d of creatine supplementation and caffeine abstinence.     

Physiological responses to short-term exercise in the heat after creatine loading.

PURPOSE: This investigation was designed to examine the influence of creatine (Cr) supplementation on acute cardiovascular, renal, temperature, and fluid-regulatory hormonal responses to exercise for 35 min in the heat. METHODS: Twenty healthy men were matched and then randomly assigned to consume 0.3 g.kg(-1) Cr monohydrate (N = 10) or placebo (N = 10) for 7 d in a double-blind fashion. Before and after supplementation, both groups cycled for 30 min at 60-70% VO2(peak) immediately followed by three 10-s sprints in an environmental chamber at 37 degrees C and 80% relative humidity. RESULTS: Body mass was significantly increased (0.75 kg) in Cr subjects. Heart rate, blood pressure, and sweat rate responses to exercise were not significantly different between groups. There were no differences in rectal temperature responses in either group. Sodium, potassium, and creatinine excretion rates obtained from 24-h and exercise urine collection periods were not significantly altered in either group. Serum creatinine was elevated in the Cr group but within normal ranges. There were significant exercise-induced increases in cortisol, aldosterone, renin, angiotensin I and II, atrial peptide, and arginine vasopressin. The aldosterone response was slightly greater in the Cr (263%) compared with placebo (224%) group. Peak power was greater in the Cr group during all three 10-s sprints after supplementation and unchanged in the placebo group. There were no reports of adverse symptoms, including muscle cramping during supplementation or exercise. CONCLUSION: Cr supplementation augments repeated sprint cycle performance in the heat without altering thermoregulatory responses.     

Effects of creatine on isometric bench-press performance in resistance-trained humans

PURPOSE: The purpose of this study was to investigate the effects of creatine (Cr) supplementation on force generation during an isometric bench-press in resistance-trained men. METHODS: 32 resistance-trained men were matched for peak isometric force and assigned in double-blind fashion to either a Cr or placebo group. Subjects performed an isometric bench-press test involving five maximal isometric contractions before and after 5 d of Cr (20 g.d-1 Cr + 180 g.d-1 dextrose) or placebo (200 g.d-1 dextrose). Body composition was measured before and after supplementation. Subjects completed 24-h urine collections throughout the study period; these were subsequently analyzed to provide total Cr and creatinine excretion. RESULTS: The amount of Cr retained over the supplementation period was 45 +/- 18 g (mean +/- SD), with an estimated intramuscular Cr storage of 43 (13-61) mmol x kg(-1) x dry weight muscle (median [range]). Four subjects in the Cr group were classified as "nonresponders" (< or =21 mmol x kg(-1) x dry weight muscle increase following Cr supplementation) and the remaining 17 subjects were classed as "responders" (> or =32 mmol x kg(-1) x dry weight muscle). For the Cr group, peak force and total force pre- or post-supplementation were not different from placebo. However, when the analysis was confined to the responders, both the change in peak force [Repetition 2: 59(81) N vs -26(85) N; Repetition 3: 45(59) N vs -26(64) N) and the change in total force (Repetition 1: 1471(1274) N vs 209(1517) N; Repetition 2: 1575(1254) N vs 196(1413) N; Repetition 3: 1278(1245) N vs -3(1118) N; Repetition 4: 918(935) N vs -83(1095) N] post-supplementation were significantly greater compared with the placebo group (P < 0.01). For the Cr group, estimated Cr uptake was inversely correlated with training status (r = -0.68, N = 21, P = 0.001). Cr significantly increased body weight (84.1 +/- 8.6 kg pre- vs 85.3 +/- 8.3 kg post-supplementation) and fat-free mass (71.8 +/- 6.0 kg pre- vs 72.6 +/- 6.0 kg post-supplementation), with the magnitude of increase being significantly greater in the responder group than in the placebo group. CONCLUSION: Five days of Cr supplementation increased body weight and fat-free body mass in resistance-trained men who were classified as responders. Peak force and total force during a repeated maximal isometric bench-press test were also significantly greater in the responders compared to the placebo group.     

Adverse effects of creatine supplementation: fact or fiction?

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

Effects of creatine supplementation on isometric force-time curve characteristics.

PURPOSE: To assess the effects of creatine monohydrate on isometric force-time curve parameters of sedentary college males aged 18-25 yr. METHODS: This double-blind study randomly assigned subjects to either a treatment (with creatine (Cr)) group (N = 11) or placebo group (P) (N = 8). The Cr group received 20 g x d(-1) of Cr for the first 5 d, in 5-g doses, four times daily (loading period) followed by a 5-g x d(-1) dose for the next 5 d (maintenance phase) and then no Cr ingestion for 7 d (washout period). Each 5-g dose was mixed with 250 mL of Gatorade. The P group received a placebo (cornstarch) following the exact same dosage regimen and protocol as the Cr group. All subjects were sedentary and had not used any nutritional supplements for 6 months before the study. Measurements of isometric force production of four muscle groups (elbow flexors and extensors; knee flexors and extensors) were characterized by a number of force-time parameters including strength (MF), time to maximal force (TMF), rate of force development (MRFD), and intermittent endurance (total impulse (TI) and percent force decrement (PFD)). Testing was done at pretreatment, after the 10-d loading and maintenance phases, and after the washout phase. RESULTS: Repeated measures ANOVA indicated no significant group effect for any muscle group concerning the maximal strength parameters and only two significant time effects for the knee flexors during MF and MRFD. Similarly, there were no significant group effects for any muscle group during the endurance trials; however, there was a significant time effect concerning TI for each muscle group tested. CONCLUSION: Our findings indicate that oral supplementation with creatine monohydrate in untrained males does not positively influence isometric strength but may enhance intermittent isometric muscular endurance.     

Chronic multivitamin-mineral supplementation does not enhance physical performance.

The effects on physical performance of 90 d of supplementation with a high potency multivitamin-mineral supplement were studied in a double-blind, placebo-controlled design. Twenty-two healthy, physically active men were randomly assigned to a supplement (S) or placebo (P) group; both groups had similar physical characteristics. Performance was assessed from maximal aerobic capacity, endurance capacity, and isokinetic tests. Supplementation did not affect maximal aerobic capacity: pre and after approximately 12 wk of supplementation values for maximal oxygen consumption (48.5 +/- 1.3 vs 46.2 +/- 1.1 ml.kg-1.min-1), maximal heart rate (186 +/- 2 vs 187 +/- 2 beats.min-1) or treadmill time (19.96 +/- 0.48 vs 19.99 +/- 0.37 min) did not differ in the S group; similar findings were noted in the P group. Performance during the 90-min endurance run, as assessed from heart rates, rectal temperatures, and plasma glucose, lactate and adrenocorticotropin values, was not affected by treatment. Similarly, muscle strength and endurance were not affected. Thus, supplementation did not affect physical performance in well-nourished men who maintained their physical activity.     

Effect of oral creatine supplementation on isokinetic torque production

PURPOSE: This study was conducted to examine the effect of oral creatine supplementation on the decline in peak isokinetic torque of the quadriceps muscle group during an endurance test. METHODS: Twenty-three active, but untrained, male subjects performed isokinetic strength tests on a Cybex II dynamometer at 180 degrees x s(-1). The protocol consisted of pre- and post-tests with five sets of 30 maximum volitional contractions with a 1-min rest period between sets. Subjects returned to perform the posttest after 5 d of placebo (4 x 6 g glucose x d(-1), N = 12) or creatine (4 x 5 g creatine + 1 g glucose x d(-1), N = 11) supplementation. Supplements and testing were administered in a double blind fashion. Peak torque was measured during each contraction and the 30 contractions were averaged for each set. RESULTS: A three-way mixed ANOVA with one between factor (placebo vs creatine) and two within factors (pre/post supplementation and sets 1-5) revealed no significant interactions, P > 0.05. The placebo vs creatine main effect was also nonsignificant, whereas the pre/post and set effects were significant (P < 0.05). Peak torque increased (approximately 3%) from pre- to post-testing, (P = 0.04), but the absolute magnitude of the differences is unlikely to be of any practical significance. Peak torque decreased from sets 1 to 4, whereas sets 4 and 5 were not different. A priori contrasts comparing the creatine group's performance pre vs post test for the fourth and fifth sets were nonsignificant (P > 0.05). CONCLUSIONS: Based on within and between group comparisons, we were unable to detect an ergogenic effect of oral creatine supplementation on the decline in peak torque during isokinetic exercise at 180 degrees x s(-1).     

Effects of high dose oral creatine supplementation on anaerobic capacity of elite wrestlers

AIM: The purpose of this study was to investigate the effect of high dose oral creatine supplementation on anaerobic capacity of elite wrestlers. METHODS: Experimental design: comparative randomized design. Setting: Wingate anaerobic tests of the participants were taken at the Human Performance Laboratory of the Department of Physical Education and Sports in The Middle East Technical University, Ankara, Turkey. Participant: 20 active international level wrestlers participated (22 to 27 years old). Interventions: the daily dosage of creatine or placebo was divided into 4 equal amounts (5 gx4 = 20 g). Every 5 g of supplement was dissolved in 250 ml water and it was given to participants 1 hour before breakfast, lunch, dinner, and workout session. Measures: subjects underwent a 30-s Wingate Anaerobic tests until exhaustion in pre- and post-tests. After the pretest measurements were completed, participants were classified as creatine (Cr., n=10) and placebo (Pl., n=10) groups with regard to their average anaerobic power scores obtained during the test. RESULTS: Results of paired "t"-test revealed that there was no significant change in placebo group between pre- and post-test in average and peak anaerobic power. However, average and peak power mean scores obtained from post-test (8.123+/-0.448 W/kg and 10.523 +/-1.004 W/kg) were significantly (p<0.01) higher than pretest (7.233+/-0.483 W/kg and 8.992+/- 0.665 W/kg) for creatine group. Results of the independent "t"-test also indicated that the mean gained scores of creatine group in average and peak power were significantly higher than placebo group (p<0.01). CONCLUSION: This study demonstrates that short-term high dose oral creatine supplementation has an ergogenic effect on anaerobic capacity of elite wrestlers.     

The effects of creatine supplementation on performance and hormonal response in amateur swimmers

Objectives

The purpose of this study was to determine the influence of short-term creatine supplementation on sprint swimming performance (50 and 100 m) and hormonal responses (growth hormone, testosterone and cortisol).

Methods

Twenty amateur male swimmers ingested creatine monohydrate (CR) or a matched placebo (PL) for 6 days. All subjects performed 6 days, swimming exercise. The subjects were tested for performance and hormonal responses the day before and after this creatine loading.

Results

The mean swimming time of CR group in 50 m was significantly decreased (Before-period: 53.1 ± 3.73 s, after-period: 50.7 ± 2.84 s). Growth hormone and cortisol were not affected by this creatine loading. But, testosterone concentration was significantly greater in CR compared to PL after supplementation period (P < 0.05).

Conclusions

Our data suggest that short-term creatine supplementation has improved 50 m sprint performance in amateur swimmer and it seems unlikely creatine loading is hormonally mediated.