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The hydration myth


THINK BEFORE DRINKING A woman receiving a bottle of water from one of the volunteers 2016 Great Pink Run 10km marathon in Phoenix Park.

Physio Focus
Andrew O'Brien

‘Hot enough for ya, mate?’. In an Australian summer it’s one of those questions that old blokes ask out one corner of their mouth so flies can’t get in the other corner. It’s reserved for stinking hot days, the kind of weather that has bushfire services on red alert and sees retirees flocking to the cinema looking for the coolest place in town. There are two accepted answers: sarcasm (‘Just about, mate’) and swearing.
I recall one such day, when I was about 17 or 18. Over the summer holidays, my sisters and I often used to go cotton chipping to earn a few bob. ‘Chipping’ involves walking up and down the rows of a cotton crop with a hoe in hand and cutting out weeds. On a nice day it can be pleasant enough; you start at 6am and stroll up and down until 3pm, chipping the odd small weed out of the crop. On this particular day, I woke at about 4am and the thermometer hanging on our verandah told me it was 27 degrees.
There was barely a breath of wind, which was something of a relief, because that would have just made the oven into a fan-forced unit. Normally flies are more ‘friendly’ on a still day, but even they had quit by 8 or 9am, retiring to a shady spot to laugh at the fools out in the sun.
To make matters worse, the previous season the farmer had grown corn on the block, so we were regularly cutting our six-foot-tall woody corn plants. Our boss, the toughest woman I’ve ever met, decided at lunchtime that maybe it was a bit too warm and called it a day. At 6 that evening the temperature was still well over 40 degrees. Hot enough for ya, mate!
The last fortnight has been lovely, warm even, but not the kind of thing that dries out the mouth on every breath. In reality it’s never that hot here, and yet… I’m amazed by how often I’ve heard well meaning folk recommend drinking extra fluids because of the heat. I even know a couple of people who fainted during races last summer and were told it was due to dehydration from the heat. But is it really? Does it ever get hot enough in the west of Ireland to need to take on extra fluids as a precaution? Probably not.
The ‘science’ of hydration in sport is a bit vague. We’re bombarded by television ads for the ‘ades’, Lucozade, Powerade and Gatorade, telling us how they put back what the sweat takes out and how dehydration can impair sports performance. Conventional wisdom has it that a loss of 2 percent of body weight through dehydration impairs performance. But the problem with conventional wisdom is that it’s often not wisdom at all, and research has shown that a loss of up to 4 percent of body weight is still unlikely to impair exercise performance in a real world scenario.
Over the last 30 years or so, dehydration has been seen as so dangerous that people think they should drink 500ml every half hour when exercising. Assuming you’re a recreational runner doing a half marathon in two hours, that’s a full two litres. Given the weight of water, you would finish the race heavier than you started it!
The reality for many athletes is that over-drinking is more dangerous, and more likely, than dehydration, particularly in longer events like the marathon and long-course triathlons. Drinking too much can lead to a potentially fatal condition called hyponatraemia, where the body’s sodium concentration falls too low. Mild symptoms include a decreased ability to think, headaches, nausea and poor balance. Severe symptoms can include confusion, seizures and coma. None of which are uncommon sights at the end of a long event.
Sports drink manufacturers will tell you that they include sodium so as not to raise the risk of hyponatraemia, but there is an easier way to reduce your risk.
Over millennia, humans have evolved as very intelligent creatures, outwitting and outlasting all of our competitors, and if we really need anything, natural selection generally allows it to develop. Amazingly, we have an early warning system for dehydration. It’s commonly referred to as thirst. When you are exercising, drink if you’re thirsty. If it’s hot, you might sweat more and be more thirsty. If so, have a drink. If you’re not, don’t.
Whatever you do though, don’t try to tell me it’s hot enough for ya.

> Andrew O’Brien is a chartered physiotherapist and the owner of Wannarun Physiotherapy and Running Clinic at Westport Leisure Park. He can be contacted on 083 1593200 or at www.wannarun.ie.

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