thirst for knowledge

I’m just back from a two-hour run on Spanish soil. It was one of those follow-your-nose runs where you’re not entirely sure where you’re heading but 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. I continued; the sensation of thirst was uncomfortable but it didn’t really affect my running - the last mile was my fastest.

A few years ago, it would have been a very different story. I can just see myself, red-faced and parched by panic, pleading ‘agua, agua’ at front doors and shop counters in full expectation of collapsing 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 the bottle that I stubbornly carried in every run or race out of my hand, arguing that it was excess baggage. The fact that the first time I raced a 10K without water on board I PB’d 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 affect 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, rehydrating over the course of the day.

For many runners, the mere thought of leaving home without a bottle leaves them dry-mouthed. Thirst – and its satiation - fulfils a psychological need as much as a physical one and it can 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 widely-used interpretation as ‘drink to thirst’. Ad libitum literally translates to ‘at your pleasure’ – which invites you 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 (approximately seven tablespoons) during a subsequent 20-minute time trial they outperformed those given no water at all. The researchers suggest that the sensation of cool, wet water flowing down your throat may be more important than the actual hydration value the water provides.

In other recent research, scientists compared two fluid replacement protocols during a simulated 20km race. In one condition, the runners were given fluid based on their own physiologically-determined requirement while in the other, they drank ad libitum. By the end of the run, those receiving tailored hydration had drunk twice as much as those drinking freely. So does this mean (as was once widely claimed) that thirst is a poor mechanism, leaving the ad libitum group woefully underhydrated? Or were those who were drinking to a set formula overhydrated and sloshing around with far more fluid than necessary? Well, while the ad libitum drinkers lost a greater percentage of body weight (remember Gebrselassie) and had more concentrated urine by the end of the run this had no effect on either their body temperature or race time. In other words, neither drinking pattern affected the end result.

You could use this as a basis to argue that it simply 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 most definitely 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 mid-race pitstop and in almost every case this is a result of overhydrating before or during a run. One of my most enduring race memories is of being overtaken by a fit-looking guy in compression socks carrying a Camelbak. ‘That’s a bit unnecessary for a half marathon,’ I thought grudgingly. A couple of miles later, I passed him as he queued outside a portaloo along the course. Now that must have been hard to swallow.