Stay Ahead Of The Water Cycle
Sydney Morning Herald
Thursday November 20, 2003
As we slough off our winter woolies and emerge into the bright light of summer, many people are taking to the gyms, the pavements and the pools to shape up.
What many may not be aware of, however, are precautions that are needed to prevent dehydration and heat stress.
The body loses about 7 per cent of its mass each day without doing any exercise. Most of this is easily replaced by food and fluids but when you step up the pace, that loss can increase to 10 or even 15 per cent.
If lost fluid isn't replaced you could become severely dehydrated.
``Someone weighing about 70 kilograms should be drinking 1.7 litres a day just to maintain their base hydration," says Kenneth Graham, the manger of the sports science department at the NSW Institute of Sport. ``Once they start to exercise they should increase this amount to about a litre an hour. We know that athletes who are running or cycling outside in a Sydney summer can sweat about three litres of fluid an hour. Even swimmers in training can sweat two to 2.5 litres an hour."
This fluid loss can translate into 3 kilograms or more than a 2 per cent drop in body weight for a person under 100 kilos and will impair athletic performance. This is not so important for the average person out for a jog or doing a gym session, but for those seeking the competitive edge, particularly our elite athletes, it is critical.
``The effect of an extra kilogram of fluid is much more beneficial than being a kilogram lighter and reducing performance," Graham says.
Dr Nathan Gibbs, the sports physician for the South Sydney Orthopaedic Sports Medicine Centre, says the main effects of dehydration come from direct sunlight and he recommends exercising in the shade or indoors: ``When people exercise in hot weather, the body heats up and the main mechanism to control heat production is sweat which cools the body when it evaporates. If you keep sweating you are going to dehydrate because the body has only got so much water. Anything you can do to minimise heat production so you don't sweat as much will be beneficial."
Gibbs suggests that people exercise early or late in the day and be aware of the environmental temperature.
``The actual temperature on the day might register at 30 degrees but that is in the shade. If you are in the sun, that can be 40 degrees," he says.
``If you can't determine the time you exercise, you can determine the length and place. If you can only exercise at midday, you should do less or do it indoors."
Gibbs also warns people who have been ill with a fever, vomiting or diarrhoea not to exercise in hot weather. It's also essential to wear light-coloured clothing that reflects heat and absorbs moisture.
``If your clothing isn't permeable to water or sweat, it has a suffocating effect on the skin," he says. ``You also want as much body area as possible exposed because this promotes cooling by the air movement and helps with evaporation."
Of course, if the activity is in the direct sun, sunscreens and hats are essential.
Signs of dehydration include muscle cramps, lethargy, dizziness and, if quite advanced, fainting. Athletes who fail to recognise the signs, may be at risk of suffering from heat stroke and falling into a coma. This is the final stage of overheating and can be fatal. There are plenty of ways of checking your hydration level before these symptoms occur.
Nigel Taylor, an associate professor with the department of biomedical science at the University of Wollongong, says a simple way to test hydration is to check urine colour the darker the urine, the more concentrated and the less hydrated you are.
An alternative is by using a set of bathroom scales. ``Take note of your weight over the course of a week or two," Taylor says. ``At the end of the day, if you are a couple of kilograms lighter you can almost guarantee that it is fluid that has been lost."
He says that thirst is a poor indicator of hydration and recommends people ``keep ahead of your thirst", that is drink regularly and eat properly.
Before going on that run or working out, it's important to be in a normally hydrated state. Again the scales come in handy: ``If your weight doesn't vary over a week you can be sure you are maintaining a well-hydrated state," Taylor says.
At the other end of the spectrum are the problems caused by overhydration. This occurs when people working for many hours continually rehydrate with water but fail to replace the salt lost during exercise. ``This means they have overcorrected the water loss and reduced the concentration of sodium in the blood," Taylor says. ``This can also have serious health consequences."
With the 2004 Olympic Games scheduled to coincide with summer in Greece, the science of hydration is entering a new realm. Graham is working with Professor Martin Thompson at the University of Sydney to prepare athletes for the hot, dry conditions in Athens.
``We are training them to acclimatise so they can handle the heat," Graham says. ``We train the athletes in a hot environment [either outside or in a heat chamber] and as a natural adaptation the body starts to sweat earlier and more profusely to keep the body temperature down.
``At the same time, the sweat glands learn to hold back the salt so the athletes are just sweating water. The body effectively becomes conditioned to sweat at the start of exercise.
``The payback is the athletes need to take more fluids, but in a competitive situation it allows a better quality performance," says Graham.
Save money, drink straight from the tap
Sports drinks are not necessarily the magical elixirs that marketing companies would have us believe. In fact, such drinks offer little benefit over water, particularly when exercise lasts less than 90 minutes.
``Sports drinks are based on making money," says Nigel Taylor. ``They are designed to help with hydration before, during and after exercise. Unfortunately, when attempting to serve three functions, the end result is often inadequate.
``The average person has no real requirement for sports drinks providing they have a healthy diet of fresh fruit and vegetables and maintain hydration with water."
Taylor says that 99 per cent of sweat is water and the average person needs only to replace the water.
``Average workouts are only about 30 minutes and people are really not at risk of dehydration [during this time]. You see a lot of people walking around gymnasiums carrying bottles of water. This often reflects fashion trends in exercise, not science, as there is no pressing need for water replenishment during short periods."
However, he warns that if you are exercising or doing hard labour for more than 90 minutes, rehydration to replace the water and salt lost through any perspiration is essential.
``For these people, sports drinks do help but there are many cheaper ways of doing it; anyone can make up their own sports drink or tonic."
RECIPE FOR SURVIVAL
* 1 litre of water
* Add 40-80g of raw sugar
* Add .5g of table salt
* Add flavours to suit taste
© 2003 Sydney Morning Herald