The city of Aberdeen is not normally associated with heat exhaustion - but that's where scientists chose to carry out a study aimed at establishing what fights exercise fatigue best in hot environments.

Six males cyclists exercised to exhaustion in artificially high temperatures on three different fluid replacement regimes: no drink; a 15% carbohydrate (glucose)-electrolyte drink and a 2% carbohydrate-electrolyte drink.
 

Skin and rectal temperature and heart rate were measured throughout the trials and venous blood samples were also taken to establish plasma volume changes, blood metabolites, serum electrolytes and osmolality.

Unsurprisingly, the cyclists reached exhaustion fastest on the no-drink trial - 70.9 minutes, compared with 84 minutes in the 15% carbohydrate trial. But the most dramatic finding was that the men on the more dilute drink regime took 118 minutes to reach exhaustion - 34 minutes than those taking the more concentrated drink.

The research team conclude that the onset of fatigue when exercising at a moderate intensity in a hot environment can be delayed by consuming a large volume of dilute glucose-electrolyte drink.

The success of this more dilute drink may be due to its effectiveness at restoring blood and plasma volume, reducing cardiac drift and maintaining blood glucose concentration.

Galloway SDR & Maughan RJ. The effects of substrate and fluid provision on ermoregulatory and metabolic responses to prolonged exercise in a hot environment. Journal of Sports Sciences, Vol 18, No 5, pp 339-351
 

Nick Grantham