Media Spr 08: Hydration in Athletics
FLUID LOSS & REPLACEMENT IN ATHLETICS
The Hows and Whys of Proper Hydration
By Dr. Christopher Woollam, Dip Sport Med
The human body is a very inefficient engine. It only converts, 25 per cent of its fuel into energy. The remainder is lost as heat. If we were light bulbs, we'd all be incandescent - to be tossed into the trash (or recycle bin) in place of new compact fluorescents and LEDs.
Fluid loss that occurs during activity is largely sweat (consisting of water and electrolytes - mostly sodium). Other fluid loss is through respiration. As we lose fluid we must replace it, whether active or not.
During activity our fluid loss may be very high especially in the heat. Sweating increases under these conditions in order to promote evaporation on the skin surface, hence cooling our bodies. In addition to water loss we lose electrolytes, notably sodium (note the salty taste of sweat).
Consequently, during exercise, we must attempt to replace not only the water but also the sodium. Very high sodium drinks are mostly not palatable and often very upsetting to the stomach. Consequently the common "sports drinks" are low in sodium and contain a little glucose along with water.
Water is usually adequate for activity which lasts one hour or less. Some prefer the sports drinks - and that is fine.
Beyond one hour, especially in the heat, sports drinks are preferred for their better absorption and small amounts of sugar and electrolytes. There is, as you know, a myriad of drinks available, each with a claim of superiority. Simply put, I have no preference as long as they include carbohydrates and elecrolytes. Be certain to read the label. Don't be fooled by claims of superiority based on "marginal" additives having no proven value.
The "new" kid on the block is a condition called hyponatremia (hypo=low, natremia=sodium in the blood stream). This condition has been recognized as a serious condition in long-distance, high-heat events. Due to low sodium (lots of sweating with its high salt loss) the blood becomes relatively "water logged" and translates this condition to the brain, which then swells, leading to catastrophic consequence.
It is almost implossible to replace all of our salt loss during and endurance event, hence we advise (to keep a balance) that you reduce the amount of drinking. We suggest you drink only according to thirst and not over-drink, as was once preached.
The other side of the equation is dehydration and overheating. The two must be balanced: It is sometimes difficult to be certain whether to drink or not. I have no hard and fast rule other than drink when thirsty. You should expect to lose weight during exercise - through fluid loss and your metabolic process.
At our marathons we suggest people weigh themselves pre- and post- run. They should lose, on average, one to two kilos and definitely NOT remain the same or gain weight.
If all this seems daunting and you're about to return to the couch; remember these simple steps:
1. Drink when thirsty.
2. Drink electrolyte/sugar drinks when exercising more than one hour.
3. Stop if you feel unwell.
These tips are simple but successful. So try them...And remember, don't return to the couch. That only guarantees an early demise.
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