Water: Too much is bad

2013-01-12 00:00

WATERLOGGED. This is the title of Professor Tim Noakes’s relatively new book, which looks at the advice that has been given to runners over the past three decades.

It describes the science, and commercial, reasoning that has resulted in runners being influenced to drinking substantially more than required.

The short message is that we were designed to run in the heat and need less to drink than we have been told, and that those who do best will finish the race slightly dehydrated.

Importantly, while being significantly dehydrated can cause a drop off in performance, it is not critical and easily attended to, whereas those who over-hydrate become “waterlogged” and present a considerably more critical situation with dilution of electrolytes and swelling of the brain.

In fact Noakes’s research suggests that runners do not die of dehydration, but there have been a number of deaths from over-hydration.

The London 2005 Marathon was held in “extreme” UK conditions of around 25°C. Runners were warned to drink more and had options on drinking 500 ml water every 1,5 km and 375 ml at six additional energy points.

The advice is to drink when thirsty and in South Africa with water every three kilometres this is rarely a problem. About 600 ml per hour is a reasonable guideline.

Of course humidity presents additional challenges as this prevents the cooling and induces greater sweating. (As high as 38 ml per hour per kilogram body weight).

High humidity increases the risk of heat exhaustion as the core temperature can’t be reduced, but again the brain acts as a safety valve forcing a reduction in pace/performance. Keep in mind the long easy events are less of a risk than the short intense efforts such as track training and 10 km races, as the heat build up is greater the faster the running.

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