Stay hydrated during exercise by POON CHIAN HUI (in Mind Your Body of the Straits Times )

Drink before, during and after exercise to replenish fluids - or run the risk of dehydration. POON CHIAN HUI reports (in Mind Your Body of the Straits Times dated 10 September, brought to you by 100 PLUS)

People who are active in sports but pay little attention to fluid replacement run the risk of dehydration. The effects can be far-reaching.

Blood volume and pressure drops when there is too much fluid loss, said Dr Stanley Liew, an endocrinologist at Raffles Hospital.

The heart will try to rectify this by beating faster to pump more blood into the bloodstream.
But if this fails to compensate for the effects of fluid loss, vital organs will suffer from an inadequate supply of nutrients and a build-up of waste products, he added.

A chain of psychological and physical effects can follow, such as decreased concentration, poor judgment, clumsiness, decreased endurance, fatigue and headaches, said Dr Tan Jee Lim, a consultant orthopaedic sports surgeon at Gleneagles Medical Centre.

Water has another key role - to keep the body temperature normal at 37 deg C - to allow enzymes to function properly, he said. Enzymes drive numerous bodily functions, such as digestion, cell repair and the release of energy for movement.

Over-heating will affect enzyme functions as they work only within certain temperatures, he explained. Heat cramps, heat strokes and even death can result when our body temperature exceeds these limits.

Sports dietitian Fahma Sunarja of Sportsmed Central recommended that people drink up before, during and after exercise to avert dehydration.

The need to drink on schedule stems from the fact that estimating fluid losses can be tricky, even for very seasoned athletes.

A 2003 American study found that experienced runners grossly underestimated sweat loss and drank too little to stay well-hydrated.

Ms Sunarja said that generally, one should take 300ml to 500ml of low-fat drinks two hours before exercise; 500ml to 1 litre of sports drinks or water every hour during exercise, and 300ml to 500ml of low-fat drinks every hour after exercise until the next meal or snack.
However, the replenishment of fluid loss differs for every individual.

One way to gauge this variation is to measure and compare body weight before and after exercise, said Dr Liew. One should drink enough to ensure that one loses no more than 2 per cent of body weight, particularly during endurance sports like marathons.

As for sports drinks - which contain additional nutrients like carbohydrates and minerals - all three experts agree these are best suited for athletes who exercise for long periods or at high intensities.

People who exercise casually once or twice a week or who do light exercise for less than one hour are not likely to benefit from sports drinks. Neither are people who are trying to lose weight.