Search Results

The authors examined the effects of combined creatine (Cr) and glycerol (Gly) supplementation on responses to exercise in the heat. Subjects (N = 24) were matched for body mass and assigned to either a Cr or placebo (Pl) group. Twice daily during two 7-d supplementation regimens, the Cr group received 11.4 g of Cr·H₂O and the Pl group received 11.4 g of glucose. Subjects in both groups also ingested 1 g of Gly/kg body mass (twice daily) in either the first or the second supplementation regimen. This design allowed 4 possible combinations of supplements to be examined (Pl/Pl, Pl/Gly, Cr/Pl, and Cr/Gly). Exercise trials were conducted pre- and post supplementation at 30 °C and 70% relative humidity. In the Pl group, total body water (TBW) increased by 0.50 ± 0.28 L after Gly and in the Cr group by 0.63 ± 0.33 L after Pl and by 0.87 ± 0.21 L after Gly. Both Cr/Pl and Cr/Gly resulted in significantly attenuated heart rate, rectal temperature, and perceived effort during exercise, although no regimen had any effect on performance. The addition of Gly to Cr significantly increased TBW more than Cr alone (P = 0.02) but did not further enhance the attenuation in HR, T_re, and RPE during exercise. These data suggest that combined Cr and Gly is an effective method of hyper hydration capable of reducing thermal and cardiovascular responses.

Oral supplementation with glycine-arginine-α-ketoisocaproic acid (GAKIC) has previously been shown to improve exhaustive high-intensity exercise performance. There are no controlled studies involving GAKIC supplementation in well-trained subjects. The aim of the current study was to examine the effects of GAKIC supplementation on fatigue during high-intensity, repeated cycle sprints in trained cyclists. After at least 2 familiarization trials, 10 well-trained male cyclists completed 2 supramaximal sprint tests each involving 10 sprints of 10 s separated by 50-s rest intervals on an electrically braked cycle ergometer. Subjects ingested 11.2 g of GAKIC or placebo (Pl) during a period of 45 min before the 2 experimental trials, administered in a randomized and double-blind fashion. Peak power declined from the 1st sprint (M ± SD; Pl 1,332 ± 307 W, GAKIC 1,367 ± 342 W) to the 10th sprint (Pl 1,091 ± 229 W, GAKIC 1,061 ± 272 W) and did not differ between conditions (p = .88). Mean power declined from the 1st sprint (Pl 892 ± 151 W, GAKIC 892 ± 153 W) to the 10th sprint (Pl 766 ± 120 W, GAKIC 752 ± 138 W) and did not differ between conditions (p = .96). The fatigue index remained at ~38% throughout the series of sprints and did not differ between conditions (p = .99). Heart rate and ratings of perceived exertion increased from the 1st sprint to the 10th sprint and did not differ between conditions (p = .11 and p = .83, respectively). In contrast to previous studies in untrained individuals, these results suggest that GAKIC has no ergogenic effect on repeated bouts of high-intensity exercise in trained individuals.

This study examined the effects of Cr supplementation on muscle strength in conjunction with resistance training in nonresistance-trained males utilizing strategies previously reported in the literature to help optimize muscle Cr uptake. Nineteen nonresistance-trained males underwent 4 weeks of resistance training (3 days · week⁻¹) while assigned to Cr (20 g · d⁻¹ Cr + 140 g · d⁻¹ glucose) for 7 days (loading), followed by 5 g · d⁻¹ Cr + 35 g · d⁻¹ glucose for 21 days (maintenance; n = 9) or placebo (160 g · d⁻¹ glucose [loading] followed by 40 g · d⁻¹ [maintenance; n = 10]). In subjects classified as “responders” to Cr on the basis of body mass changes (n = 7), the magnitude of change in 180∞ · s⁻¹ isokinetic (p = .029) and isometric (p = .036) force was greater compared to the placebo group. A positive correlation was found between changes in body mass and 180º · s⁻¹ isokinetic (loading: r = 0.68, p = .04; maintenance: r = 0.70, p = .037) and isometric (loading: r = 0.82, p < .01) force. Estimated Cr uptake was also positively correlated with changes in 60º · s⁻¹ (r = 0.90, p < .01) and 180º · s⁻¹ (r = 0.68, p = .043) isokinetic force, and isometric force (r = 0.71, p = .033). These results indicate that Cr supplementation can increase muscle strength (allied with 4 weeks of strength training) but only in subjects whose estimated Cr uptake and body mass are significantly increased; the greater the Cr uptake and associated body mass changes, the greater the performance gains.