When should I have an isotonic drink?
Endurance sports, such as triathlon, involve a risk of dehydration through perspiration. Sweat is composed of water and minerals (mainly sodium, but also a little potassium). During effort, the body may lose over one and a half litres in perspiration an hour, and sometimes up to 3 litres an hour. So, unless this loss is balanced by drinking, the body becomes dehydrated. Moreover, we know that muscles use energy during effort, so regular carbohydrate intake enables us to make up for losses and maintain effort.
Isotonic drinks are the best solution, since they provide water, sodium and carbohydrates. They are 'all-in-one' drinks.
After an hour of effort, you will thus need to drink isotonic drinks regularly. The required dose is 1 mouthful every 10-15 minutes from the start of your effort.