Creatine is widely used by both elite and recreational athletes as an ergogenic aid to enhance anaerobic exercise performance. Older individuals also use creatine to prevent sarcopenia and, accordingly, may have therapeutic benefits for muscle wasting diseases. Although the effect of creatine on the musculoskeletal system has been extensively studied, less attention has been paid to its potential effects on other physiological systems. Because there is a significant pool of creatine in the brain, the utility of creatine supplementation has been examined in vitro as well as in vivo in both animal models of neurological disorders and in humans. While the data are preliminary, there is evidence to suggest that individuals with certain neurological conditions may benefit from exogenous creatine supplementation if treatment protocols can be optimized. A small number of studies that have examined the impact of creatine on the immune system have shown an alteration in soluble mediator production and the expression of molecules involved in recognizing infections, specifically toll-like receptors. Future investigations evaluating the total impact of creatine supplementation are required to better understand the benefits and risks of creatine use, particularly since there is increasing evidence that creatine may have a regulatory impact on the immune system.

The purpose of this study was to determine gastrointestinal (GI) permeability during prolonged treadmill running (60 min at 70 % V.O2max) with and without fluid intake (3 ml/kg body mass/10 min). Twenty runners (11 males, 9 females; age = 22 +/- 3 (SD) yrs; mean V.O2max = 55.7 +/- 5.0 ml/kg/min) completed four experiments: 1) rest, 2) running with no fluid (NF), 3) running with ingestion of a 4 % glucose solution (GLU), and 4) running with ingestion of a water placebo (PLA). To determine GI permeability, subjects also drank a solution containing 5 g sucrose (S), 5 g lactulose (L), and 2 g rhamnose (R) immediately prior to each trial. Gastroduodenal permeability was determined by urinary S excretion, while small intestinal permeability was determined by the L/R excretion ratio. Percent body mass loss (i.e., dehydration) was negligible during rest, GLU and PLA, while NF resulted in a 1.5 % loss of body mass (p < 0.05). Gastroduodenal and intestinal permeability were significantly (p < 0.008) increased in NF compared to rest. There were no other differences in GI permeability. These results indicate that fluid restriction during 1 h of steady-state running increases GI permeability above resting levels.

The purpose of the present study was to determine the validity of various laboratory methods for estimating percent body fat (%fat) in NCAA Division I college female athletes (n = 29; 20 +/- 1 year). Body composition was assessed via hydrostatic weighing (HW), air displacement plethysmography (ADP), and dual-energy X-ray absorptiometry (DXA), and estimates of %fat derived using 4-compartment (C), 3C, and 2C models were compared to a criterion 5C model that included bone mineral content, body volume (BV), total body water, and soft tissue mineral. The Wang-4C and the Siri-3C models produced nearly identical values compared to the 5C model (r > 0.99, total error (TE) < 0.40%fat). For the remaining laboratory methods, constant error values (CE) ranged from -0.04%fat (HW-Siri) to -3.71%fat (DXA); r values ranged from 0.89 (ADP-Siri, ADP-Brozek) to 0.93 (DXA); standard error of estimate values ranged from 1.78%fat (DXA) to 2.19%fat (ADP-Siri, ADP-Brozek); and TE values ranged from 2.22%fat (HW-Brozek) to 4.90%fat (DXA). The limits of agreement for DXA (-10.10 to 2.68%fat) were the largest with a significant trend of -0.43 (P < 0.05). With the exception of DXA, all of the equations resulted in acceptable TE values (<3.08%fat). However, the results for individual estimates of %fat using the Brozek equation indicated that the 2C models that derived BV from ADP and HW overestimated (5.38, 3.65%) and underestimated (5.19, 4.88%) %fat, respectively. The acceptable TE values for both HW and ADP suggest that these methods are valid for estimating %fat in college female athletes; however, the Wang-4C and Siri-3C models should be used to identify individual estimates of %fat in this population.

The purpose of this investigation was to determine the effect of creatine (Cr) loading on the onset of neuromuscular fatigue by monitoring electromyographic fatigue curves from the vastus lateralis muscle using the physical working capacity at the fatigue threshold (PWC(FT)) test. Using a double-blind random design, 15 women athletes [mean age 19.0 +/- 2.0 (SD) yr] from the university crew team received a placebo (n = 8; 20 g glucose) or Cr (n = 7; 5 g Cr monohydrate + 20 g glucose) four times per day for 5 consecutive days. Analysis of covariance was used to analyze the data (covaried for presupplementation PWC(FT) values). The adjusted mean postsupplementation PWC(FT) value for the Cr group (mean = 186 W) was significantly (P < 0.05) higher than that of the placebo group (mean = 155 W). These findings suggest that Cr loading may delay the onset of neuromuscular fatigue.

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This study assessed tolerance to fluid ingestion with repeated sessions of drinking while running. Runners (n = 7; age 22 +/- 2 yr; V O (2max) = 54.4 +/- 7.1 ml/kg/min) performed six 90-min runs (65 % V O (2max); separated by 7 - 11 days). During run 1, subjects drank a glucose-electrolyte solution AD LIBITUM for 1 min every 10 min. During runs 2 - 6, subjects drank a volume of the solution every 10 min equal to their sweat production over 10 min during run 1. Stomach comfort (1 - 4 scale) and gastrointestinal symptoms were also assessed every 10 min. Gastric emptying rate was determined in runs 2 and 6. Subjects consumed more (p < 0.05) fluid during runs 2 - 6 (mean +/- SD; 1247 +/- 162 ml), than during run 1 (508 +/- 476 ml). Stomach comfort improved (p < 0.05) on runs 5 and 6 (1.7 +/- 0.5 mean ranks) compared to run 2 (2.3 +/- 0.5 mean ranks). Gastric emptying rate was not different between runs 2 and 6 (12.0 +/- 1.9 ml/min vs. 12.3 +/- 2.3 ml/min, respectively). These results indicate repeated sessions of drinking at a rate matching sweat rate improves stomach comfort, however, gastric emptying rate does not change under such conditions.

Consumption of energy drinks by both recreational and competitive athletes has increased dramatically in recent years. The primary ingredients in many energy drinks include caffeine (CAF) in various forms and taurine. The purpose of this randomized, double-blind, crossover study was to examine the effect of sugar-free (SF) Red Bull (RB) containing CAF and taurine to a CAF only drink and a SF CAF-free placebo (PL) on 1 repetition maximum (1RM) bench press (BP) and the volume load (VL; repetitions × kg at 70% 1RM) during one BP set to failure in experienced lifters. Seventeen college-age men randomly received the following: (A) 500 mL of SF-RB containing CAF (160 mg) and taurine (2000 mg); (B) 500 mL of a SF drink containing CAF only (160 mg); or (C) a SF CAF-free 500 mL PL drink 60 minutes before testing on 3 separate occasions. After a standard warm-up, the 1RM was determined for each subject and, after 5 minutes rest, they completed repetitions to failure at 70% of their 1RM to assess VL. Differences between trials for 1RM BP and the VL were identified using repeated measures analysis of variance (p < 0.05). The results indicated that neither SF-RB nor the CAF drink had any effect on 1RM BP (115.13 ± 16.19 kg and 114.87 ± 16.16 kg, respectively) or VL (1173.08 ± 170.66 kg and 1164.14 ± 147.03 kg, respectively) compared with PL (1RM = 114.07 ± 16.09 kg; VL = 1141.46 ± 193.41 kg). Although the CAF content in the energy drinks used in the present study was low (∼2.0 mg/kg), the finding of no effect of the CAF containing energy drinks for 1RM BP are in agreement with previous studies using intakes up to 6.0 mg/kg. These findings suggest that SF-RB has no effect on upper body 1RM strength or VL in resistance trained men.

The purpose of this study was to examine the effects of fluid replacement on power output (PO), rating of perceived exertion (RPE), heart rate (HR), body weight (BW), urine osmolarity (Uosm), and urine electrolyte concentrations ([UNa+], [UK+], [UCl-]) in physically active men (n = 4) and women (n = 7). The participants were asked to generate their highest possible PO during 60 minutes of cycling under 3 randomized conditions: ingestion of (a) no fluid (trial 1); (b) 1200 ml of distilled water (trial 2); and (c) 1,200 ml of Gatorade (trial 3). BW and urine volume (Vu) were measured before and after the ride to determine sweat rate [(SR = deltaBW + Vfluid intake + Vu)/time]. The results indicated that there were no significant differences between trials for PO (123-127 W), RPE (14), HR (140-142 b x min(-1)), and SR (11.9-12.4 ml x min(-1)). However, [UNa+] was significantly (p < 0.05) lower postexercise for all 3 trials, and [UCl-] was significantly reduced following trials 2 and 3. There was a significant increase (p < 0.001) in BW postexercise for trials 2 and 3 when compared with the no-fluid trial; however, the effects of water and Gatorade were similar. These results suggest that fluid replacement during 1 hour of moderately intense cycling does not enhance performance in physically active men and women who are normally hydrated.