With every glistening droplet of sweat that trickles down your face and falls to the ground, your body is losing nutrients, salt and most importantly, water.
Dehydration can cause headaches, poor concentration and cramp.
It can be caused by not drinking enough during exercise, or by lack of fluid intake while sitting at your desk.
If you don't drink throughout the day, you can spend most of your time dehydrated.
But how much water should you drink?
Under normal circumstances, you need between two and three litres of fluid per day
sports dietitian Lisa Sutherland says.
You reach this amount by the total amount of fluids you drink, plus the foods you eat. Water should make up a large proportion of total daily fluid intake as a low-calorie, low-sugar beverage.
For most people, eight 250ml glasses (1 Cup) will be sufficient, but if your'e hot and your'e exercising, you will need more.
People often wait until they feel thirst to act, but this is way too late.
Substantial amounts of water are lost through sweating when exercising vigorously. Exercise in hot or humid weather will result in additional fluid loss and increase the risk of dehydration.
What causes dehydration?
Dehydration during exercise occurs when the body is low in fluids because a person is not drinking enough to replace what is lost through sweat.
Warning signs of dehydration include thirst, headache, dizziness, weakness, irritability, fatigue and nausea.
Dehydration of even 1-2% could affect the performance by up to 10%. Dehydration leads to more extreme versions of heat illness such as heat cramps, exhaustion, stroke and even death.
Weight loss during exercise represents fluid loss, therefore if you lose 1kg during exercise, this equates to around 1 litre.
Excerpts courtesy of Herald Sun, December 15 2008