Heat Stroke And Dehydration Are Not The Same

How people changed their minds regarding drinking water during exercise:

Adolph was the first to test the presumptions most people still have about what to do if forced to make any sort of effort in extreme heat. Most, he discovered, were myths. Stripping to T-shirt and shorts, for instance, is not the best way to cope with dehydrating conditions. Long sleeves and long trousers may feel hotter, but they'll slow the loss of water. Nor is there any point in rationing water when supplies are low. Putting off drinking it merely makes you unhappier sooner. "It is better," wrote Adolph, "to have the water inside you than to carry it."

The most important of Adolph's findings was the simplest: drinking during exercise improves performance. Today, we take this for granted, but generations of coaches and distance runners were taught that drinking during exercise was for wimps. It would only make you thirstier, some claimed. Others said it could even trigger a heart attack. ... Adolph tested the old assumptions by splitting his soldiers into two groups. Both marched through the desert for up to 8 hours during the time of year when the average afternoon high was 42 °C. The soldiers in one group were allowed to drink as much water as they wanted and the others weren't allowed any. The results were clear: the drinkers outperformed the non-drinkers, but the men in both groups gave up once they had sweated off 7 to 10 per cent of their body weight.

To Adolph, this made perfect sense. On days when the temperature is hotter than the average person's skin temperature - about 33 °C - the only way for the body to cool itself is by the evaporation of sweat, and he could calculate how much moisture that required. A brisk walk could easily require three-quarters of a litre or more of evaporative cooling each hour. Over an 8-hour stint, that's a lot of sweat.

Adolph's research was driven by the North Africa campaign, which ended in 1943. But he returned to the desert each summer during the war years and supplemented his experiments with tests in his heated lab. His findings stayed secret until 1947, when he was allowed to publish his pioneering Physiology of Man in the Desert. It went almost entirely unnoticed. In the late 1960s, marathon runners were still advised not to drink during races and until 1977, runners in international competitions were banned from taking water in the first 11 kilometres and after that were allowed water only every 5 kilometres.

Then there was a complete reversal of opinion. A trickle of studies began to warn of the dangers of running a marathon without enough water and suddenly runners were being told they must drink during a race - and if they didn't feel like it they should force themselves or risk heatstroke.

...Runners and coaches in the 1970s and 1980s presumed that collapsing athletes like Salazar were simply extreme cases of the same thing. Dehydration and heat collapse were virtually synonymous in many minds. "Drink early and often," athletes were told - and not just when thirsty.

Yet, as Noakes points out, none of Adolph's dehydrated soldiers suffered heatstroke. "They just got very angry and stopped walking." What's more, they recovered rapidly when allowed to rest and drink. "Able to walk almost immediately after taking water," Adolph wrote in one case. In another: "exhaustion relieved by water". Salazar's brush with death wasn't the result of drinking too little: he had simply tried to run a world-class race on a very hot day. Under those conditions heat is the enemy, not dehydration.