The influence of a 6.5% carbohydrate-electrolyte solution on performance of prolonged intermittent high-intensity running at 30°C

Nine male student games players consumed either flavoured water (0.1 g carbohydrate, Na+ 6 mmol (bullet) l^-1), a solution containing 6.5% carbohydrate-electrolytes (6.5 g carbohydrate, Na+ 21 mmol (bullet) l^-1) or a taste placebo (Na+ 2 mmol (bullet) l^-1) during an intermittent shuttle test performed on three separate occasions at an ambient temperature of 30°C (dry bulb). The test involved five 15 -min sets of repeated cycles of walking and variable speed running, each separated by a 4-min rest (part A of the test), followed by 60 s run/60 s rest until exhaustion (part B of the test). The participants drank 6.5 ml · kg-1 of fluid as a bolus just before exercise and thereafter 4.5 ml (bullet) kg-^1 during every exercise set and rest period (19 min). There was a trial order effect. The total distance completed by the participants was greater in trial 3 (8441 (plus-minus) 873 m) than in trial 1 (6839 (plus-minus) 512, P < 0.05). This represented a 19% improvement in exercise capacity. However, the trials were performed in a random counterbalanced order and the participants completed 8634 (plus-minus) 653 m, 7786 (plus-minus) 741 m and 7099 (plus-minus) 647 m in the flavoured water (FW), placebo (P) and carbohydrate-electrolyte (CE) trials, respectively (P = 0.08). Sprint performance was not different between the trials but was impaired over time (FW vs P vs CE: set 1, 2.41 (plus-minus) 0.02 vs 2.39 (plus-minus) 0.03 vs 2.39 (plus-minus) 0.03 s; end set, 2.46 (plus-minus) 0.03 vs 2.47 (plus-minus) 0.03 vs 2.47 (plus-minus) 0.02 s; main effect time, P < 0.01). The rate of rise in rectal temperature was greater in the carbohydrate-electrolyte trial (rise in rectal temperature/duration of trial, °C (bullet) h^-1; FW vs CE, P < 0.05; P vs CE, N.S.). Blood glucose concentrations were higher in the carbohydrate-electrolyte than in the other two trials (FW vs P vs CE: rest, 4.4 (plus-minus) 0.1 vs 4.3 (plus-minus) 0.1 vs 4.2 (plus-minus) 0.1 mmol (bullet) l^-1; end of exercise, 5.4 (plus-minus) 0.3 vs 6.4 (plus-minus) 0.6 vs 7.2 (plus-minus) 0.5 mmol (bullet) l^-1; main effect trial, P < 0.05; main effect time, P < 0.01). Plasma free fatty acid concentrations at the end of exercise were lower in the carbohydrate-electrolyte trial than in the other two trials (FW vs P vs CE: 0.57 (plus-minus) 0.08 vs 0.53 (plus-minus) 0.11 vs 0.29 (plus-minus) 0.04 mmol (bullet) l^-1; interaction, P < 0.01). The correlation between the rate of rise in rectal temperature (°C (bullet) h^-1) and the distance completed was -0.91, -0.92 and -0.96 in the flavoured water, placebo and carbohydrate-electrolyte conditions, respectively (P < 0.01). Heart rate, blood pressure, plasma ammonia, blood lactate, plasma volume and rate of perceived exertion were not different between the three fluid trials. Although drinking the carbohydrate-electrolyte solution induced greater metabolic changes than the flavoured water and placebo solutions, it is unlikely that in these unacclimated males carbohydrate availability was a limiting factor in the performance of intermittent running in hot environmental conditions.