The effects of carbohydrate-electrolyte sports drinks on performance and physiological function during an 8km cycle time trial

Jack Hornsby


Background: Supplementation in the form of sports drinks has in latter years become an integral part of professional and amateur exercise. Currently much of the research is directed at carbohydrate-electrolyte (CE) drink supplementation for exercises lasting one hour or above and has been shown to improve performance. However the effects of supplementation prior to and during intense, short term exercise on performance is less understood. Therefore the purpose of the present study was to investigate the effects of ingesting different CE drinks prior and during exercise on an 8km time trial (TT) performance against a placebo.

Methods: Fifteen male subjects were randomised in a balanced double-blinded repeated measures crossover manner to consume three drinks A (8% CHO), B (5% CHO) and C (placebo) 5min prior (4.0 and 1.0 at 3 and 6km during the 8km cycle TT. Tests were performed on standardised cycle ergonometers at room temperature (18-22°C) with seven days between trials.

Results: Time taken to complete the time trials were not significantly different between drink treatments A (11.43±1.31min), B (12.02±1.3min) and C (11.73±1.44). Mean heart rate for drink C (169±12.26bpm) and drinks B and A had slower heart rates of 1.7bpm and 3.7bpm respectively with no significant differences between drink treatments (p=0.388). No differences were found in physiological measurements of mean change in RPE, RPM, body weight and systolic and diastolic blood pressure, between drink treatments.

Conclusions: Performance and physiological function during a maximal cycling exercise lasting approximately 10min (8km) is not improved or limited by endogenous substrate availability prior and during the event.

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