Dehydrated athletes perform much slower when running than those who intake fluids before race in all conditions, study confirms

Dehydrated athletes run significantly slower than hydrated runners even in temperate conditions, according to a new study which shows the importance of drinking fluid before a race.

A loss of just 2 per cent body weight, excreted via sweat, can cause some runners to become up to 19 per cent slower.

The research, published in the Journal of Sports Sciences, concluded that athletes competing in longer races in hotter environments should “adopt fluid intake strategies with the aim to limit hypohydration to less than 2 per cent body mass if performance time or exercise intensity are of importance”.

People who took part in the study who completed a 3km treadmill time trial in a state of hypohydration – a decrease in body water – were 6 per cent slower on average. When they performed the same test with optimal body water content they ran faster.

The test, performed at the University of Loughborough, put runners through 72 minutes of moderate running first, at 65 per cent of VO2 max, before they attempted the time trial. This allowed researchers to give the athletes fluid to replace lost sweat or withhold it from them, causing a 2.2 per cent body weight loss.

They then had a 15-minute break before undertaking the time trial. All participants took part in both the hydrated and dehydrated tests in a randomised order so their performances could be compared.