Dehydration is when the water content in your body falls too low.
It can have a major effect on exercise performance.
It's important to start any exercise session well hydrated.
Aim to do this by drinking water regularly during the course of the day.
The amount you need to drink during exercise depends on the amount you sweat.
This varies from person to person and also depends on the intensity and length of time exercising, as well as environmental factors.
Water is usually enough for most forms of exercise up to about an hour.
For longer-duration exercise lasting several hours,
where energy and fluid needs may be greater,
a carbohydrate,
electrolyte-containing sports drink may benefit.
For athletes with a heavy training schedule each day,
the carbohydrates in a sports drink can help to maintain energy levels,
and the electrolytes can help to replace salt lost in sweat.