How much and what to sip during a run

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There is a reason trail runners carry cool back packs with so-called “bladders” in them…

When you exercise, total body metabolism is increased and a large amount of this energy is released as heat, which need to be dissipated to achieve body heat balance. In hot climates a large volume of body water can be lost via sweating to enable evaporative cooling. Some electrolytes are also lost through sweat.  Your running will be adversely affected by dehydration, even as little as 2% (that is 1.4L in a 70kg runner).

Dehydration can be prevented by consuming enough fluids during a race – here’s the basics!

How much?

General guidelines are not practical as each runner is different. It is however easy to estimate fluid requirements by weighing yourself before and after a training session.  Every 1kg weight lost equals 1L of fluid lost.  Divide the losses by the amount of hours trained to get L/hour.  This will give an estimate of how much is needed per hour. In many runners usually 600-800ml/hour.  Remember that in hot environments more is needed.

“Every 1kg weight lost equals 1L of fluid lost.”


For training sessions and races shorter than an hour, water is enough, but in hot climates or longer races, sports drinks are better options. These contain carbohydrate in the correct concentrations (4-8%) to allow refueling during exercise without gastro-intestinal discomfort. It also contains sodium and is flavoured which is proven to promote fluid intake. A cool drink will also promote fluid intake, so add some crushed ice in that “bladder” to keep your drink cooler for longer.

Remember to replace any residual fluid deficit after exercise by replacing 150% of lost fluids (that is 1.5L for every 1L lost). If rapid rehydration is needed, consider salty food or an oral rehydration solution e.g. Rehydrat to optimally replace sodium and retention of fluids.

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