1. Sweat Testing

Keeping hydrated is important in any endurance or ultra-endurance competition. Adequate hydration, known as euhydration, helps to support blood plasma levels and thermoregulation. Dehydration may lead to impairments in performance, lab studies have suggested that even a 2% loss in body weight due to dehydration may impair performance. However, this is a lab study and not the same as real world. Additionally, over-hydration can lead to hyponatremia. However, as a clinically dangerous level, this is rare, but over consumption of fluids can also cause uncomfortable feelings in the gut and a need to vomit.

Sounds confusing? It seems like a difficult balance between over and under-consumption, but the easiest way to plan for your fluid intake, and current recommendations for ultra-marathon, are to simply drink to thirst in order to regulate your fluid intake.

Understanding your sweat rate is very useful to provide an insight into your fluid needs per hour, allowing you to better regulate and understand you personal fluid needs. To do this you can do a simple sweat test.

Over time try to build up a spreadsheet of data, that provides an idea of your pace, the temperature, humidity and how you felt. This will help you gain a greater understanding of your fluid needs across a range of conditions. A sweat test at one intensity and one temperature will be useless at other intensities and temperatures.

As an example, on a race such as UTMB, during the day in a valley temperatures may be 34c, at the top of a mountain in the snow at night, temperatures may be near to 0c (I speak from experience). Therefore sweat rates and fluid intake would be different, so the plan would change dramatically.