Effects of a carbohydrate-electrolyte solution on cognitive performance following exercise-induced hyperthermia in humans

Abstract

Background

There is limited information on the effects of sports drinks on cognitive function after exercise in the heat. We aimed to investigate the effects of ingesting a commercially available carbohydrate-electrolyte (CHO) solution on cognitive performance following exercise-induced hyperthermia.

Methods

Twelve participants completed three practices of cognitive tests, one full familiarisation and two experimental trials in an environmental chamber (dry bulb temperature: 30.2 ± 0.3°C, relative humidity: 70 ± 3%). The experimental trials consisted of five cognitive tests (symbol digit matching, search and memory, digit span, choice reaction time and psychomotor vigilance test) performed before and after a 75-min run on a treadmill at 70% VO₂ max. One ml/kg body mass of a 6.8% CHO solution or placebo was consumed at the start, every 15 min during exercise and between cognitive tests after exercise. Core temperature, heart rate, blood glucose concentrations, subjective ratings and cognitive performance were assessed (symbol digit matching, search and memory, digit span, choice reaction time and psychomotor vigilance).

Results

Participants were hyperthermic at the end of the run (placebo: 39.5 ± 0.4°C, CHO: 39.6 ± 0.5°C; Mean ± SD; p = 0.37). The change in blood glucose was higher with CHO ingestion (1.6, 0.7 to 4.5 mmol/L) (median, range) than with placebo ingestion (0.9, -0.1 to 4.7 mmol/L; p < 0.05). CHO ingestion reduced the maximum span of digits memorized, in contrast to an increase in maximum span with placebo ingestion (p < 0.05). CHO solution had no effect on other cognitive tests (p > 0.05).

Conclusions

These results suggest that CHO solution ingestion may impair short-term memory following exertional heat stress.

Keywords:

• Glycemic Index
• Choice Reaction Time
• Sport Drink
• High Glycemic Index
• Psychomotor Vigilance Test

Electronic supplementary material

The online version of this article (doi:10.1186/s12970-014-0051-x) contains supplementary material, which is available to authorized users.

Electronic supplementary material

The online version of this article (doi:10.1186/s12970-014-0051-x) contains supplementary material, which is available to authorized users.

Acknowledgements

The authors expressed their gratitude to Ms. Lydia Law, Dr. Frederick Tey and Ms. Tan Ying Ying from DSO National Laboratories for their inputs on the selection of cognitive tests. We would also like to thank Mr. Glen Liu (from National University of Singapore), Ms. Jacinta Yeo and Mr. David Fun (from DSO National Laboratories) for their assistance during data collection. The authors would also like to thank all participants for their commitment to the study. The study was funded by DSO National Laboratories, Singapore and the National University of Singapore. All authors declared they had no conflict of interest.

Competing interests

The authors declare that they have no competing interests.