Days Of Creatine Supplementation Research Articles

Effects of Low-Dose Creatine Monohydrate on Muscle Strength and Endurance

: To investigate the effect of low-dose supplementation of creatine monohydrate without the use of the saturation phase, 36 male university students engaged in resistance training (age 22.5 ± 4.3 years, height 1.76 ± 0.08 m, weight 77.0 ± 11.0 kg, and body mass index 24.6 ± 2.5 kg/m2) were randomly divided into three groups: group placebo (GP), group supplemented with creatine 3 g/day (3G), and group supplemented with 5 g/day creatine (5G). The subjects were tested for maximum muscle strength (1RM), upper body muscle endurance (MPU), and abdominal muscle endurance (MSU) before and after 7, 14, 21, 28, and 35 days of creatine supplementation or placebo and performing standardized resistance training. After 35 days of supplementation and training, all groups showed a significant improvement in the 1RM test; however, the percentages of strength increase were significantly higher (P 0.528; G3, P > 0.076; G5, P > 0.148). These results support a number of earlier studies that demonstrated that creatine supplementation at low doses and without the use of the loading phase are effective for increasing maximal strength and endurance of upper limbs.

Metabolic Responses to Weight Lifting

Metabolic Responses to Weight Lifting

Creatine Supplementation Increases Total Body Water in Soccer Players: a Deuterium Oxide Dilution Study

This study aimed to evaluate changes in total body water (TBW) in soccer athletes using a deuterium oxide dilution method and bioelectrical impedance (BIA) formulas after 7 days of creatine supplementation. In a double-blind controlled manner, 13 healthy (under-20) soccer players were divided randomly in 2 supplementation groups: Placebo (Pla, n=6) and creatine supplementation (CR, n=7). Before and after the supplementation period (0.3 g/kg/d during 7 days), TBW was determined by deuterium oxide dilution and BIA methods. 7 days of creatine supplementation lead to a large increase in TBW (2.3±1.0 L) determined by deuterium oxide dilution, and a small but significant increase in total body weight (1.0±0.4 kg) in Cr group compared to Pla. The Pla group did not experience any significant changes in TBW or body weight. Although 5 of 6 BIA equations were sensitive to determine TBW changes induced by creatine supplementation, the Kushner et al. 16 method presented the best concordance levels when compared to deuterium dilution method. In conclusion, 7-days of creatine supplementation increased TBW determined by deuterium oxide dilution or BIA formulas. BIA can be useful to determine TBW changes promoted by creatine supplementation in soccer athletes, with special concern for formula choice.

Study of renal and hepatic toxicity in rats supplemented with creatine

To evaluate the renal and hepatic function, through biochemical analysis after 14 days of creatine supplementation in physically inactive rats. Twenty four male, adult, Wistar rats were used which were kept in individual metabolic cages and were distributed into four groups, and received the following treatments by gavage:1) CONTROL: distilled water; 2)Creatine 0.5g/Kg/day; 3) Creatine 1g/Kg/day; 4) Creatine 2g/Kg/day. Their urinary outputs as well as food and water intake were daily measured. At the end of the experiment, the animals were euthanized and serum samples were stored for biochemical analysis. Creatine supplementation at the doses given produced no significant changes in plasma levels of aspartate aminotransferase, alanine aminotransferase, alkaline phosphatase, total protein, albumin, total cholesterol, HDL cholesterol, LDL cholesterol, VLDL cholesterol, triglycerides, glucose, creatinine, urea, and creatinine clearance, compared to control group (p> 0.05) Similarly, water and food intake, as well as urinary output, did not show significant changes among the four groups studied. At the doses used, oral creatine supplementation did not result in renal and/or hepatic toxicity.

Effects of short term creatine supplementation and resistance exercises on resting hormonal and cardiovascular responses

Summary Introduction The purpose of this study was to examine the effects of 3, 5 and 7 days of creatine loading coupled with resistance exercise on resting testosterone and cortisol concentrations, systolic blood pressure (SBP), diastolic blood pressure (DBP), mean arterial pressure (MAP), heart rate and rate pressure product (RPP). These measures were compared to those in placebo group. Summary of facts Twenty active males were randomly assigned to either a creatine group (Cr) or placebo group (Pl). Participants performed resistance exercises at day 3, 5, and 7; and also tested at day 4, 6, and 8. Subjects of the Cr group showed significant increases in testosterone concentrations and decreases in cortisol concentrations, in comparison with Pl and baseline, after 5 and 7 days of Cr loading (P 0.05). Conclusion Results of the present study suggest that more than 5 days of creatine supplementation, associated with resistance exercises is sufficient for increasing testosterone concentrations and decrement in cortisol concentrations.

The Effects of 3 versus 7 Days of Creatine Supplementation on Intramuscular Creatine and Thermoregulation in the Heat

The Effects of 3 versus 7 Days of Creatine Supplementation on Intramuscular Creatine and Thermoregulation in the Heat Many thermoregulation studies associated with creatine supplementation have utilized a pre/post-supplementation protocol. Additionally, investigations have not measured intramuscular creatine (MCR) levels to ensure increases in MCR while examining thermoregulation. The aim of this investigation was to determine the effects of 3 and 7 d of creatine supplementation (0.3 g.kg.d-1 total body weight) on MCR and thermoregulation while exercising in the heat. Ten subjects participated in two thermoregulation sessions following 3 and 7 d of creatine supplementation. Subjects ran for 60 min at 65-70% of VO2max in the heat (temp = 32.85 + 0.91°C; hum = 17.10 + 3.50%). Pre- and post-test exercise measures included nude body weight (NBW), urine specific gravity (USG), serum creatinine levels (SCR), and MCR. Total body water (TBW), extracellular water (ECW), and intracellular water (ICW) were measured preexercise. Core temperature (Tc) was assessed at 5 min intervals during exercise. Regardless of condition, Tc was not significantly different (p ≥ 0.05) from 0-5 min after which Tc increased throughout exercise. There was no significant difference or interaction (p ≥ 0.05) for TBW, ECW, and ICW. NBW was greater (p<0.05) preexercise versus post exercise for both conditions. There was no significant difference or interaction (p ≥ 0.05) between conditions for SCR.

Short-term creatine supplementation does not reduce increased homocysteine concentration induced by acute exercise in humans

The purpose of the study is to evaluate the effects of creatine supplementation on homocysteine (Hcy) plasma levels after acute exercise in humans. Twenty-three young (under-20) soccer players were divided into 2 groups: creatine (Cr)- and placebo (Pla)-supplemented groups. The supplementation was performed in double-blind controlled manner using creatine or placebo tablets with 0.3 g/kg during 7 days. Before and after 7 days of supplementation, the athletes performed an acute high-intensity sprint exercise (two consecutive running-based anaerobic sprint test protocol consisted in 6 × 35 m sprint with 10 s between them). Blood samples were collected before and after 7 days of supplementation as well as 0 and 1 h after exercise protocol. Homocysteine concentration significant increased (P < 0.05) 1 h after acute exercise (18%). Acute exercise also decreased red blood cell S-adenosylmethionine (SAM) 30% with no changes in SAM/SAH ratio. Seven days of creatine supplementation were able to increase (P < 0.05) plasma creatine concentration (Pla 130.1 ± 21.7 vs Cr 1,557.2 ± 220.3 μmol/L) as well as decrease (P < 0.05) plasma guanidinoacetic acid (33%). Controversially, creatine supplementation did not change Hcy plasma level after 7-day supplementation (Pla 6.9 ± 0.2 vs Cr 7.2 ± 0.2 μmol/L) or after acute exercise (Pla 8.2 ± 0.3 vs Cr 8.4 ± 0.3 μmol/L). No changes in plasma vitamin B12 and folate as well as cysteine and methionine were found. Seven days of creatine supplementation does not avoid increased plasma Hcy induced by acute sprint exercise in humans.

Contribution of creatine to protein homeostasis in athletes after endurance and sprint running

Few studies have focused on the metabolic changes induced by creatine supplementation. This study investigated the effects of creatine supplementation on plasma and urinary metabolite changes of athletes after endurance and sprint running. Twelve male athletes (20.3 ± 1.4 y) performed two identical (65-70 % maximum heart rate reserved) 60 min running exercises (endurance trial) before and after creatine supplementation (12 g creatine monohydrate/day for 15 days), followed by a 5-day washout period. Subsequently, they performed two identical 100 m sprint running exercises (power trial) before and after 15 days of creatine supplementation in accordance with the supplementary protocol of the endurance trial. Body composition measurements were performed during the entire study. Plasma samples were examined for the concentrations of glucose, lactate, branched-chain amino acids (BCAAs), free-tryptophan (f-TRP), glutamine, alanine, hypoxanthine, and uric acid. Urinary samples were examined for the concentrations of hydroxyproline, 3-methylhistidine, urea nitrogen, and creatinine. Creatine supplementation significantly increased body weights of the athletes of endurance trial. Plasma lactate concentration and ratio of f-TRP/BCAAs after recovery from endurance running were significantly decreased with creatine supplementation. Plasma purine metabolites (the sum of hypoxanthine and uric acid), glutamine, urinary 3-methylhistidine, and urea nitrogen concentrations tended to decrease before running in trials with creatine supplements. After running, urinary hydroxyproline concentration significantly increased in the power trial with creatine supplements. The findings suggest that creatine supplementation tended to decrease muscle glycogen and protein degradation, especially after endurance exercise. However, creatine supplementation might induce collagen proteolysis in athletes after sprint running.

Thermoregulatory Changes During 30 Days Of Creatine Supplementation While Exercising In The Heat

PURPOSE: The purpose of this investigation was to determine the effects of 30 d of creatine supplementation (20g/d for 7 d followed by 6g/d for 23 d) on thermoregulation in the heat (temp 33.06 + 0.58oC; hum 21.42 + 3.02%). Specifically the investigation determined thermoregulation in the heat at 7 d intervals while engaged in a common creatine supplementation protocol. METHODS: Twelve males (age = 21.13 + 1.54 yrs; ht = 172.92 + 8.43 cm; wt = 80.52 + 10.35 kg) participated in a total of 10 exercise sessions (5 Cr supplementation; 5 Pl). Exercise sessions consisted of running at 65-70% VO2max for 45 min in the heat at 7 d intervals over a 30 d supplementation period. Measures of thermoregulation, hydration, and body water were performed at each exercise session and included: pre-exercise total body water (TBW), extracellular water (ECW), and intracellular water (ICW); pre/post-exercise changes in nude body weight (NBW), and urine specific gravity (USG); during exercise changes in core temperature (Tc) and plasma volume (PV). The order of testing sessions were: day 0 baseline, test session 1; day 7 test session 2; day 14 test session 3; day 21 test session 4; day 28 test session 5. RESULTS: There were no significant differences in ECW and ICW between creatine and placebo over the 30 d supplementation. TBW resulted in a significant interaction. TBW for creatine was less at pre-supplementation versus days 14 and 21 (pre = 48.49 + 1.66 L; day 14 = 49.92 + 1.52 L; day 21 = 49.80 + 1.41 L) and day 7 TBW was less than day 21 (day 7 = 48.67 + 1.34 L; day 21 = 49.92 + 1.52 L). For placebo, day 14 TBW was greater than day 30 (day 14 = 48.99 + 1.43 L; day 30 = 48.13 + 1.39 L). Creatine had significantly lower USG versus placebo (Cr = 1.015 + 0.003; Pl = 1.020 + 0.002) at day 21. There were no differences between creatine and placebo for Tc and PV. Tc however resulted in a significant time effect with Tc increasing throughout the exercise session for both creatine and placebo. CONCLUSIONS: Creatine supplementation had no effect on thermoregulation versus placebo while exercising in the heat. The changes in TBW and USG at 21 days for the creatine condition suggest that TBW increases continue to appear with creatine supplementation and that those changes may not be of significant magnitude to positively affect thermoregulation while exercising in the heat.

The Effects of 3 Versus 7 Days of Creatine Supplementation on Thermoregulation in the Heat

PURPOSE. The purpose of this investigation was to determine the effects of 3 and 7-d of creatine supplementation (0.3 g/kg total body weight) and intramuscular levels of total creatine on thermoregulation in the heat during 60 min of submaximal aerobic activity. METHODS. 10 subjects participated in two thermoregulation exercise bouts following 3 and 7-d of creatine supplementation. Prior to the supplementation period, anthropometric measurements were obtained, with BF% measured via bioelectrical impedance assessment (BIA). For thermoregulation sessions subjects ran for 60 min at 60-65% of VO2max in the heat (32.93 + 0.87oC; 17.39 + 3.63%). Pre- and post-test exercise measures included nude body weight (NBW), urine specific gravity (USG), serum creatine levels (SCR), urinary creatinine levels (UCR) and intramuscular levels of total creatine (MCR). Total body water (TBW), extracellular water (ECW), and intracellular water (ICW) were measured pre-exercise via BIA. During the 60 min run, core temperature (Tr) was assessed in 5 min intervals. RESULTS. Regardless of condition, Tr was not significantly different (p >.05) from 0-5 min after which Tr increased throughout exercise. There was no significant difference or interaction (p >.05) for TBW, ECW, and ICW. NBW was greater pre-exercise versus post exercise for both conditions. There was no significant difference or interaction (p >.05) between conditions for UCR and SCR, however, each was significantly (p <.05) greater post-exercise versus pre-exercise. There was no significant difference (p >.05) in MCR between conditions. MCR was significantly (p <.05) lower at baseline versus pre- and post-exercise, and pre-exercise levels were significantly (p <.05) greater than post-exercise levels. 3-day USG was significantly (p <.05) lower pre-exercise versus post-exercise, while 7-day USG resulted in no significant difference (p >.05) pre- versus post-exercise. CONCLUSIONS. 3-d of creatine supplementation does not affect thermoregulation or dehydration during submaximal exercise in the heat. However, 7-d of supplementation may provide a potential defense against dehydration during submaximal exercise in the heat. Additionally, 3 and 7-d of supplementation at 0.3 g/kg of body weight are equally effective for increasing intramuscular creatine levels.

Effect of Short-term High-Dose Creatine Supplementation on Measured GFR in a Young Man With a Single Kidney

It currently is unknown whether creatine supplementation is safe for people with or at risk of kidney disease. We report on the short-term effects of creatine supplementation on kidney function in a young man with a single kidney and mildly decreased glomerular filtration rate (GFR). A 20-year-old man who had undergone unilateral nephrectomy and presented with mildly decreased GFR without kidney damage underwent a trial with 35 days of creatine supplementation (20 g/d for 5 days followed by 5 g/d for the next 30 days) and had his kidney function monitored. After the intervention, (51)Cr-EDTA clearance (pre, 81.6 mL/min/1.73 m(2); post, 82.0 mL/min/1.73 m(2)), proteinuria (protein excretion: pre, 130 mg/d; post, 120 mg/d), and electrolyte levels were unchanged. Albuminuria, serum urea level, and estimated creatinine clearance were decreased (pre, 4.6 mg/d; post, 2.9 mg/d; pre, 37 mg/d; post, 28 mg/dL; and pre, 88 mL/min/1.73 m(2); post, 71 mL/min/1.73 m(2), respectively), whereas serum creatinine level was slightly increased (pre, 1.03 mg/dL; post, 1.27 mg/dL), falsely suggesting kidney function impairment. This prospective report suggests that short-term creatine supplementation may not affect kidney function in an individual with a single kidney, mild decreased GFR, and ingesting a high-protein diet (ie, 2.8 g/kg/d). This finding has great relevance considering that creatine-induced kidney disease has been a growing concern, even for healthy people.

Creatine supplementation improves the anaerobic performance of elite junior fin swimmers

The objective of this study was to determine whether creatine supplementation (CrS) could improve mechanical power output, and swimming performance in highly trained junior competitive fin swimmers. Sixteen male fin swimmers (age:15.9+/-1.6 years) were randomly and evenly assigned to either a creatine (CR, 4x5 g/day creatine monohydrate for 5 days) or placebo group (P, same dose of a dextrose-ascorbic acid placebo) in a double-blind research. Before and after CrS the average power output was determined by a Bosco-test and the swimming time was measured in two maximal 100 m fin swims. After five days of CrS the average power of one minute continuous rebound jumps increased by 20.2%. The lactate concentration was significantly less after 5 minutes restitution at the second measurement in both groups. The swimming time was significantly reduced in both first (pre: 50.69+/-1.41 s; post: 48.86+/-1.34 s) and second (pre: 50.39+/-1.38 s; post: 48.53+/-1.35 s) sessions of swimming in CR group, but remained almost unchanged in the P group.The results of this study indicate that five day Cr supplementation enhances the dynamic strength and may increase anaerobic metabolism in the lower extremity muscles, and improves performance in consecutive maximal swims in highly trained adolescent fin swimmers.

Three Weeks of Creatine Monohydrate Supplementation Affects Dihydrotestosterone to Testosterone Ratio in College-Aged Rugby Players

This study investigated resting concentrations of selected androgens after 3 weeks of creatine supplementation in male rugby players. It was hypothesized that the ratio of dihydrotestosterone (DHT, a biologically more active androgen) to testosterone (T) would change with creatine supplementation. Double-blind placebo-controlled crossover study with a 6-week washout period. Rugby Institute in South Africa. College-aged rugby players (n = 20) volunteered for the study, which took place during the competitive season. Subjects loaded with creatine (25 g/day creatine with 25 g/day glucose) or placebo (50 g/day glucose) for 7 days followed by 14 days of maintenance (5 g/day creatine with 25 g/day glucose or 30 g/day glucose placebo). Serum T and DHT were measured and ratio calculated at baseline and after 7 days and 21 days of creatine supplementation (or placebo). Body composition measurements were taken at each time point. After 7 days of creatine loading, or a further 14 days of creatine maintenance dose, serum T levels did not change. However, levels of DHT increased by 56% after 7 days of creatine loading and remained 40% above baseline after 14 days maintenance (P < 0.001). The ratio of DHT:T also increased by 36% after 7 days creatine supplementation and remained elevated by 22% after the maintenance dose (P < 0.01). Creatine supplementation may, in part, act through an increased rate of conversion of T to DHT. Further investigation is warranted as a result of the high frequency of individuals using creatine supplementation and the long-term safety of alterations in circulating androgen composition. STATEMENT OF CLINICAL RELEVANCE: Although creatine is a widely used ergogenic aid, the mechanisms of action are incompletely understood, particularly in relation to dihydrotestosterone, and therefore the long-term clinical safety cannot be guaranteed.

Effect of Thirty Days of Creatine Supplementation with Phosphate Salts on Anaerobic Working Capacity and Body Weight in Men

The purpose of this study was to determine the effect of 30 days of single-dose creatine supplementation with phosphate salts (CPS) on body weight (BW) and anaerobic working capacity (AWC) in men. Using a double-blind design, 32 men randomly received 1 serving of either CPS (5 g Cr + 4 g phosphate) (n = 17) or 20 g of dextrose as placebo (PL) (n = 15) for 30 days. AWC determined from the Critical Power Test and BW were measured at baseline, 10 days, 20 days, 30 days, and 10 days post-supplementation. Results (2 x 5 ANOVA) showed no significant differences between groups for AWC at any time point; however, BW was significantly increased at 10 days in the CPS group (1.0 kg) vs. PL (0.0 kg), and remained elevated for the duration of the study. These findings suggest that a single 5 g x d(-1) dose of CPS for 30 days increases BW but is not effective for increasing AWC in men.

Effects of resistance exercise with and without creatine supplementation on gene expression and cell signaling in human skeletal muscle

To test the hypothesis that creatine supplementation would enhance the anabolic responses of muscle cell signaling and gene expression to exercise, we studied nine subjects who received either creatine or a placebo (maltodextrin) for 5 days in a double-blind fashion before undergoing muscle biopsies: at rest, immediately after exercise (10 x 10 repetitions of one-leg extension at 80% 1 repetition maximum), and 24 and 72 h later (all in the morning after fasting overnight). Creatine supplementation decreased the phosphorylation state of protein kinase B (PKB) on Thr308 at rest by 60% (P < 0.05) and that of eukaryotic initiation factor 4E-binding protein on Thr37/46 (4E-BP1) by 30% 24 h postexercise (P < 0.05). Creatine increased mRNA for collagen 1 (alpha(1)), glucose transporter-4 (GLUT-4), and myosin heavy chain I at rest by 250%, 45%, and 80%, respectively, and myosin heavy chain IIA (MHCIIA) mRNA immediately after exercise by 70% (all P < 0.05). Immediately after exercise, and independent of creatine, mRNA for muscle atrophy F-box (MAFbx), MHCIIA, peroxisome proliferator-activated receptor gamma coactivator-1alpha, and interleukin-6 were upregulated (60-350%; P < 0.05); the phosphorylation state of p38 both in the sarcoplasm and nucleus were increased (12- and 25-fold, respectively; both P < 0.05). Concurrently, the phosphorylation states of PKB (Thr308) and 4E-BP1 (Thr37/46) were decreased by 50% and 75%, respectively (P < 0.05). Twenty-four hours postexercise, MAFbx, myostatin, and GLUT-4 mRNA expression decreased below preexercise values (-35 to -50%; P < 0.05); calpain 1 mRNA increased 70% 72 h postexercise (P < 0.05) and at no other time. In conclusion, 5 days of creatine supplementation do not enhance anabolic signaling but increase the expression of certain targeted genes.

Creatine supplementation improves muscular performance in older women

Muscle power and strength decrease with age leading to reduced independence and increased health risk from falls. Creatine supplementation can increase muscle power and strength. The purpose of this study was to examine the effects of 7 days of creatine supplementation on body composition, muscular strength, and lower-body motor functional performance in older women. Thirty 58-71 year old women performed three test sessions (T1-T3) each separated by one week. Each session consisted of one repetition maximum tests for bench press and leg press, and isometric hand-grip, tandem gait, upper-body ergometer, and lower-body ergometer tests. Following T2, subjects were assigned to a creatine monohydrate (0.3 g kg body mass(-1) for 7 days) (CR: 63.31 +/- 1.22 year, 160.00 +/- 1.58 cm, 67.11 +/- 4.38 kg) or a placebo (PL: 62.98 +/- 1.11 year, 162.25 +/- 2.09 cm, 67.84 +/- 3.90 kg) supplementation group. CR significantly (P < 0.05) increased bench press (1.7 +/- 0.4 kg), leg press (5.2 +/- 1.8 kg), body mass (0.49 +/- 0.04 kg) and fat free mass (0.52 +/- 0.05) and decreased completion time on the functional tandem gait tests from T2-T3. No significant changes were found for PL on any of the measured variables. No adverse side-effects were reported by either group. Short-term creatine supplementation resulted in an increase in strength, power, and lower-body motor functional performance in older women without any adverse side effects.

Effects of Creatine Supplementation and Three Days of Resistance Training on Muscle Strength, Power Output, and Neuromuscular Function

Previous studies have demonstrated increases in peak torque (PT) and decreases in acceleration time (ACC) after only 2 days of resistance training, and other studies have reported improvements in isokinetic performance after 5 days of creatine supplementation. Consequently, there may be a combined benefit of creatine supplementation and short-term resistance training for eliciting rapid increases in muscle strength, which may be important for short-term rehabilitation and return-to-play for previously injured athletes. The purpose of this study, therefore, was to examine the effects of 3 days of isokinetic resistance training combined with 8 days of creatine monohydrate supplementation on PT, mean power output (MP), ACC, surface electromyography (EMG), and mechanomyography (MMG) of the vastus lateralis muscle during maximal concentric isokinetic leg extension muscle actions. Twenty-five men (mean age +/- SD = 21 +/- 3 years, stature = 177 +/- 6 cm, and body mass = 80 +/- 12 kg) volunteered to participate in this 9-day, double-blind, placebo-controlled study and were randomly assigned to either the creatine (CRE; n = 13) or placebo (PLA; n = 12) group. The CRE group ingested the treatment drink (280 kcal; 68 g carbohydrate; 10.5 g creatine), whereas the PLA group received an isocaloric placebo (70 g carbohydrate). Two servings per day (morning and afternoon) were administered in the laboratory on days 1-6, with only 1 serving on days 7-8. Before (pre; day 1) and after (post; day 9) the resistance training, maximal voluntary concentric isokinetic leg extensions at 30, 150, and 270 degrees x s(-1) were performed on a calibrated Biodex System 3 dynamometer. Three sets of 10 repetitions at 150 degrees x s(-1) were performed on days 3, 5, and 7. Peak torque increased (p = 0.005; eta(2) = 0.296), whereas ACC decreased (p < 0.001; eta(2) = 0.620), from pretraining to posttraining for both the CRE and PLA groups at each velocity (30, 150, and 270 degrees x s(-1)). Peak torque increased by 13% and 6%, whereas ACC decreased by 42% and 34% for the CRE and PLA groups, respectively, but these differences were not statistically significant (p > 0.05). There were no changes in MP, EMG, or MMG amplitude; however, EMG median frequency (MDF) increased, and MMG MDF increased at 30 degrees x s(-1), from pretraining to posttraining for both the CRE and PLA groups. These results indicated that 3 days of isokinetic resistance training was sufficient to elicit small, but significant, improvements in peak strength (PT) and ACC for both the CRE and PLA groups. Although the greater relative improvements in PT and ACC for the CRE group were not statistically significant, these findings may be useful for rehabilitation or strength and conditioning professionals who may need to rapidly increase the strength of a patient or athlete within 9 days.

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

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

The Effect of 7 Days of Creatine Supplementation on 24-Hour Urinary Creatine Excretion

Since the discovery that oral ingestion of creatine leads to an increase in intramuscular creatine, its supplementation has become widespread. However, the dosage necessary to maximize retention and create significant increases in intramuscular creatine is poorly understood. In this study, 24-hour urinary creatine and creatinine levels of 20 university men's football players and 20 university men's hockey players involved in a resistance-exercise program and supplementing with creatine were collected and analyzed. In a double-blind, randomized design, 10 football players and 10 hockey players were randomly assigned to either the supplement or placebo group. Subjects provided a 24-hour urine sample twice during the study: once prior to supplementation (baseline) and the second 7 days after daily supplementation and resistance exercise. Creatine dosage was 0.1 g·kg−1 lean body mass. The quantity of creatine ingested was compared with the amount excreted in the urine of those subjects supplementing with creatine and with placebo. Creatinine levels were compared between the first and second urine collection and between groups. Creatine and creatinine concentrations were determined using high-performance liquid chromatography. In 24-hours, 46% of the ingested creatine was excreted. There was no change in creatine levels for placebo subjects. Creatinine levels remained the same within groups at the first and second collection times (p < 0.05). Our findings indicate that when supplementing with dosages of 0.1 g·kg−1 lean body mass or between 6 and 8 g at a time, approximately half of the ingested creatine gets excreted. Because there was no change in urinary creatinine, it can be assumed that enhanced degradation of creatine did not occur.

The Effect of 7 Days of Creatine Supplementation on 24-Hour Urinary Creatine Excretion

Since the discovery that oral ingestion of creatine leads to an increase in intramuscular creatine, its supplementation has become widespread. However, the dosage necessary to maximize retention and create significant increases in intramuscular creatine is poorly understood. In this study, 24-hour urinary creatine and creatinine levels of 20 university men's football players and 20 university men's hockey players involved in a resistance-exercise program and supplementing with creatine were collected and analyzed. In a double-blind, randomized design, 10 football players and 10 hockey players were randomly assigned to either the supplement or placebo group. Subjects provided a 24-hour urine sample twice during the study: once prior to supplementation (baseline) and the second 7 days after daily supplementation and resistance exercise. Creatine dosage was 0.1 g x kg(-1) lean body mass. The quantity of creatine ingested was compared with the amount excreted in the urine of those subjects supplementing with creatine and with placebo. Creatinine levels were compared between the first and second urine collection and between groups. Creatine and creatinine concentrations were determined using high-performance liquid chromatography. In 24-hours, 46% of the ingested creatine was excreted. There was no change in creatine levels for placebo subjects. Creatinine levels remained the same within groups at the first and second collection times (p < 0.05). Our findings indicate that when supplementing with dosages of 0.1 g x kg(-1) lean body mass or between 6 and 8 g at a time, approximately half of the ingested creatine gets excreted. Because there was no change in urinary creatinine, it can be assumed that enhanced degradation of creatine did not occur.