‘DEHYDRATION WON’T RESULT IN SPONTANEOUS COMBUSTION’

I’m just back from a two-hour run on Spanish soil. It was one of those follow-your-nose runs – you’re not entirely sure where you’re heading but you need to get the miles in. It was warm in the spring sunshine, and I ran out of water before I’d even reached double figures in mileage. Nonetheless, I continued; the sensation of thirst was uncomfortable but it didn’t really affect my running – my last mile was my fastest.

A few years ago, it would have been a very different story. I can picture myself, red-faced and parched by growing panic, pleading ‘agua, agua’ at random front doors and shop counters, fearing a dramatic collapse at any moment.

Since ‘drink to thirst’ became the preferred maxim for runners, I’ve developed a much more relaxed attitude to hydration. On shorter runs, I mostly don’t bother and if I forget, or run out, it doesn’t worry me.

This has come as a relief to my runner husband, who tried for years to prise from my hand the bottle that I stubbornly carried in every run or race. The fact that I got a PB the first time I raced a 10K without water on board helped me come around to his way of thinking.

There’s also reassuring evidence from the world of elite running that losing two per cent – or more – of your body weight through dehydration won’t result in spontaneous combustion and, in fact, may not hamper your performance at all. Haile Gebrselassie was reportedly more than nine per cent dehydrated when he set the marathon world record at Berlin in 2008, while a 2011 study of the nutrition and hydration practices of Ethiopian elites found that they drank no fluid either before or during their runs.

For many runners, the mere thought of leaving home without a bottle leaves them dry-mouthed. Thirst – and its satiation – fulfils a deep psychological need as much as it does a physical one and it can sometimes be difficult to distinguish between the two.

I believe there’s also a subtle difference between ‘ad libitum,’ the term used by scientists in hydration studies, and its common interpretation, ‘drink to thirst’. Ad libitum literally translates as ‘at your pleasure’ – an invitation to drink when you desire it rather than when you feel a need for it. In one instance, you’re quenching the mind, in the other, the body.

A Greek study found that when previously dehydrated athletes were given just 100ml of water during a subsequent 20-minute time trial they outperformed those who received no water. Given the limited hydration value of such a small volume of water, the researchers suggest that the sensation of swallowing it must have been the relevant factor in the superior performance.

In another recent study, runners who drank ad libitum fared just as well in a 20km race as runners who received a volume of fluid based on their own physiologically determined requirement, despite drinking half as much.

You could use this as a basis to argue it doesn’t matter how much or how little you drink on the run (with the exception of very long races or extreme heat). But one aspect of hydration that will affect your race times is having to stop for the loo. Many a runner has forfeited a PB, or at least added minutes to their race time, thanks to a midrace pit stop, the result, in almost every case, of over-hydrating before or during a run. One of my most enduring race memories is of being overtaken by a fit-looking guy wearing compression socks and carrying a Camelbak. ‘That’s a bit unnecessary for a half marathon,’ I thought. A couple of miles later I passed him as he queued outside a portable toilet. Now that must have been hard to swallow.