Sweat rate & fuelling

A simple weigh-in test for your sweat rate, then fluid and carbohydrate targets per hour for your race.

1 · Sweat test

Weigh yourself without clothes before and after a training session at race effort, in similar weather to your race. Towel off before the second weigh-in.

Before (kg)

After (kg)

Drank during (ml)

Toilet stops (ml)

Session length (h:mm:ss)

2 · Your race

Expected race time (h:mm:ss)

Sweat rate (ml/h, optional)

Carbs per gel (g)

Your numbers

Sweat rate1300 ml/h

Weight change-1.1%

ResearchFluid for 5:30:00

Drink about 1040 ml–1300 ml per hour. That keeps your loss under 2% of body weight without drinking more than you sweat. Over the whole race that's 5710 ml–7150 ml.

ResearchCarbohydrate

Up to 90 g per hour beyond 2.5 hours, if your gut tolerates it. Above 60 g per hour use a glucose–fructose (or maltodextrin–fructose) mix.

That's 60–90 g per hour, or 330–495 g over the race (about 14–20 gels of 25 g, or the same carbs from drink mix and bars).

Coaching tipPractise your race fuelling in training. The gut adapts, and higher intakes are much easier to handle after practice.

General guidance for healthy adults, not medical advice. If you have a medical condition, or very high or salty sweat losses, talk to a sports dietitian or doctor.

Fluids

Sweat loss = weight before − weight after + fluid drunk − urine (1 kg ≈ 1 litre). The aim is to avoid losing more than about 2% of body weight, without drinking more than you sweat (ACSM 2007).

Carbohydrate

Recommended intake grows with duration: around 30 g/h for 1–2 hours, up to 60 g/h to 2.5 hours, and up to 90 g/h beyond that using glucose–fructose mixes (Jeukendrup 2014).

Good to know

General guidance for healthy adults, not medical advice. Sweat rates change with heat and intensity, so test in conditions like your race. More in the methodology.