Consumption of sports drinks to enhance athletic performance has been the subject of extensive research. Critical areas of interest are the volume and timing of fluid ingestion, and the source and concentration of carbohydrate (Coombes and Hamilton, 2000). However, little research data are available comparing commercially available sports drinks, and the combined ergogenic effects of carbohydrate and caffeine. This study investigated the effects of pre- and post-exercise ingestion of caffeinated and non-caffeinated commercially available sports drinks on exercise performance and rehydration in male cyclists. Methods Following local ethics approval,10 elite male cyclists (mean ± SD, age 27± 6.6yr, mass 74.2 ± 5.2kg, VO2max 70.5 ± 7.5ml.kg-1.min-1) volunteered for this study. Initially, subjects undertook a maximal incremental test to exhaustion on a cycle ergometer to assess VO2max and determine workloads equivalent to 65, 85 and 95% VO2max. The sports drinks investigated in subsequent trials, in randomised order, were Lucozade Sport (LS), Red Bull (RB), and water (W) was used as a control. On arrival, an indwelling forearm catheter was inserted and subjects then ingested the test drink. Volumes ingested were equivalent in all trials, and were calculated relative to body mass, while ensuring a caffeine intake of 3mg.kg-1 when consuming RB. Subjects undertook a 10min warm-up (120W) 30min post-ingestion. Subjects then cycled for 60min at 65% VO2max, followed by 30min at 85% VO2max. Subsequent responses to high intensity exercise were investigated using alternating 1min elements at 95 and 65% VO2max to exhaustion. Following a warm down at 120W, non-hydrated recovery was monitored for 30min, after which a rehydration bolus equivalent to half the initial pre-exercise volume of test drink was ingested, subjects were monitored for a further 60min. Blood samples were collected to measure blood glucose, lactate, and non-esterified fatty acids. Haemoglobin and haematocrit were measured to calculate plasma volume changes across time. Heart rate (by radio telemetry, Cardiosport Ltd.) and breath-by-breath metabolic data (VO2, RER, Quark B2, Cosmed Ltd.) were recorded at regular intervals during the exercise phases. A repeated measures ANOVA and pairwise Tukey HSD post-hoc test was used to infer significant differences across drinks. For all statistical tests values of P<0.05 were considered significant. Results In all trials, subjects dehydrated to the same extent during the exercise period (~11% of plasma volume). Times to exhaustion data were similar for all test drinks (92.3±28.0, 83.5±11.3, 83.2±18.9min for LS, RB and W, respectively). Heart rate, metabolic data, plasma volume changes and urine output were not different across drinks. Pre-exercise blood glucose was significantly higher following ingestion of LS compared with W (6.1±1.0 and 4.1±0.5mmol.L-1, respectively). Also, 60min post-ingestion of the rehydration bolus, blood glucose for LS (5.7±0.5mmol.L-1) and RB (5.4±0.6mmol.L-1) was significantly higher than that for W (4.2±0.5mmol.L-1). Pre-exercise blood lactate was higher for RB (1.8±0.4mmol.L-1) when compared to W (1.1±0.4mmol.L-1). Following 60min of rehydration blood lactate was higher for RB (1.8±0.3mmol.L-1) when compared with both LS and W (1.2±0.3 and 1.3 ±0.3mmol.L-1, respectively). Discussion The results of this study revealed that pre-exercise ingestion of RB or LS relative to water did not limit dehydration at any time point during exercise, or indeed during rehydration following post-exercise ingestion. In addition exercise performance was unaffected by the composition of fluid ingestion prior to exercise in these male cyclists, and all markers of exercise metabolism showed little effect of the test drink throughout exercise and recovery. The available scientific data investigating the ergogenic effects of Red Bull have reported positive effects on exercise performance (Geiss et al., 1994, Alford et al., 1999). However, the present study failed to detect any significant ergogenic effect. Research data available regarding the effect of carbohydrate ingestion on exercise performance differ with respect to the exercise protocols used, and the timing and volume of fluid ingested. However, clear differences in performance are reported more consistently during constant load exercise to exhaustion. It appears likely, that any ergogenic effect of carbohydrate in the present study may be masked by the use of relatively intense workloads towards the end of the exercise trials. In conclusion, fluid ingestion prior to- and 30min post-exercise with LS, RB or W did not effect dehydration or rehydration, and thus performance and markers of metabolism were unchanged under these exercising conditions.
© Copyright 2004 Book of Abstracts - 9th Annual Congress European College of Sport Science, July 3-6, 2004, Clermont-Ferrand, France. Alle Rechte vorbehalten.