The effect of dehydration on sporting performance

Anyone training for marathons, (or any performance goal) be mindful of hydration.

The effect of dehydration on sporting performance and physiological function is well documented. Dehydration of 2–3% body mass will significantly impair performance, and even smaller levels of dehydration have a measurable negative effect on the thermoregulatory response to exercise.

Dehydration in exercise


Muscles contract as we exercise, this increases heat production and as a result the body core temperature begins to rise.

The body ramps up sweat production to decrease temperature as the sweat evaporates from the skin. This will continue as long as we remain hydrated.

But if not hydrated, then as sweat is produced, over time blood volume will decrease as a result of a decrease in body fluids.

This is when we have a problem!

Decreased blood volume means a decreased ability to dissipate heat from the core via the circulation and also stroke volume (the amount of blood pumped by the heart in a contraction) is decreased. This will cause our heart rate to increase in order to compensate for the reduction of blood being pumped out of the heart during each contraction.

The result of dehydration in terms of performance is reduced muscular endurance and overall physical performance.

Check the colour of your urine. A pale straw colour would indicate you are fairly well hydrated. Anything darker and you need to have a look at your hydration strategies.

More Information

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Liam Leech, BSc (Hons) Sport and Exercise Science, MSc. ANutr.

Liam Leech

Liam Leech ANutr.
MSc. Human Nutrition, University of Ulster
BSc (Hons) Sport & Exercise Science, Loughborough University



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