To successfully replace electrolytes after heavy exercise and endurance events, an electrolyte drink must also be an isotonic solution.

A home-made electrolyte drink can be made by using water, sugar and salt in precise proportions.

Every 15 or so miles, rest stops offered mechanics, sparkling portable lavatories, a selection of energy bars, electrolyte drinks and more food (all free).

They drink their electrolyte drinks, but still they can't cope.

Four different carbohydrate and electrolyte drinks are used by the medical staff, who also employ cooling strategies such as ice baths and ice towels.