Extract from the January 2012 issue of Runner's World
Running (and racing) in high temperatures means more than hydrating properly. Here’s a summertime survival guide
How much you sweat tells you how much to drink
PROPER HYDRATION requires replacing fluids-on the run-that you lose through sweat. Figure out your sweat rate so you know just how many liquid ounces you need.
1 Weigh yourself naked (with an empty bladder) before your run e.g. 65kg.
2 Run at or close to your race pace for one hour and keep track of how much you drink (in millilitres) during that time e.g. 400ml.
3 Weigh yourself naked after your run e.g. 64.7kg.
4 Subtract your post-run weight from your pre-run weight e.g. 65 - 64.7 = 0.3kg
5 Convert the difference into millilitres e.g. 03 x 1000 = 300ml
6 Add to that number the amount of fluid you consumed during your run e.g. 400ml + 300ml = 700ml.
7Divide your hourly fluid loss by four to determine how much to drink every 15 minutes. e.g. 700/4 = 175ml. In this example, you would need to drink 175ml every quarter-hour.
THE LATEST RESEARCH
Studies question hydration and salt intake
Nearly half of recreational runners might be drinking too much during races, say doctors from Loyola University Medical Center in Chicago. Of the 197 runners surveyed, 36.5 per cent drank at pre-scheduled intervals or to maintain body weight and 8.9 per cent drank as much as possible. Study author and Loyola sports medicine physician Dr James Winger said that the safest known way to hydrate during endurance exercise is to drink only when thirsty. Otherwise, you risk hyponatremia (over-hydrating) or low sodium levels.
Dr Tim Noakes, exercise physiologist and author of The Lore of Running, explained ‘the salty sweat myth’ (radio interview: www.bengreenfieldfitness.com). His team tested soldiers in South Africa, who exercised in the heat (43C), fully kitted and each carrying a 25 kilogram pack.
“They covered 25 kilometres comfortably in just over four hours. They each drank up to 1.2 litres per hour, but they needed it, that was the key. They drank to thirst and consumed no salt. They didn’t need to, as the human body is so well-designed to regulate its own sodium concentration, that the only thing that can affect your sodium level concentration is if you drink too much water.”
*Purchase the January issue of Runner's World *