|
It is important to know how much and what to drink when you exercise
 FORMULA One drivers lose about three litres of fluids in every race, no thanks to the racing suits and helmets that they have to wear as well as their close proximity to fiery hot engines.
Which is why Mercedes GP Petronas driver Nico Rosberg sucks about 1.5 litres of electrolytes through a drinking tube attached to his helmet during his races.
Of course, you do not need to be behind the wheel of a million-dollar race-car to know the importance of hydration during any form of exercise.
A failure to replace the fluids lost during such exertions can lead to dehydration and in more serious cases, heat stroke.
In his book Run For Your Life, Dr Ben Tan, the head and senior consultant at Changi Sports Medicine Centre, said that runners can tolerate up to 2 per cent of dehydration without much consequences.
However, beyond that, performance can be impaired by up to 20 per cent.
But on the contrary, guzzling down too much liquids can cause hyponatraemia, a situation where the sodium level in the blood drops below normal. This may result in vomiting, cramps, seizures, and even coma and death.
So what is the right amount to drink, and how?
A commonly-used calculation by physicians and athletes is the weight-loss method which requires a person to weigh himself before and after an exercise session that lasts for at least an hour.
The loss in weight, plus any amount of fluid consumed during the exercise, equates to the amount of fluids lost for that bout of exercise.
Dr Stanley Liew, a specialist in endocrinology at Raffles Hospital, said: “The amount of fluid loss would depend on the speed and duration of the exercise, environmental temperature and humidity, as well as the body weight of the runner.
“In general, the runner should drink 1.5 litres of fluid for each kilogram of body weight lost. On average, approximately 400ml of fluid is lost during a 5km run.”
Drinking too much just before or during exercise may lead to stitches, so knowing when to hydrate is also important.
Dr Liew advised runners to ensure that they are well-hydrated at least four hours before their run, and to consume about 125ml of fluid for every 20 minutes of exercise.
In general, they should aim to drink between 300 to 800ml of fluids per hour. Faster and heavier runners competing in warm conditions should drink more (up to 800ml) while slower runners in cooler environments can drink less.
Athletes should therefore monitor their body weight changes during the exercise to estimate their fluid loss for that particular exercise, with respect to the environmental conditions. They can then customise their individual fluid replacement requirement for the duration of the run, or exercise.
This in turn prompts the next question: Should one drink plain water or isotonic drinks?
While medical experts say water is good enough for exercises of low intensity or short duration (less than 90 minutes), they recommend sports drinks for more intense or longer exercises.
“Research has shown that fluid intake is enhanced when the beverages are cool (about 15 deg C), flavoured and contain salt,” said Chenchill Kho, an accredited dietician from beverage company Fraser and Neave, which owns the 100Plus brand of isotonic drinks.
“Made up of a unique combination of carbohydrates and electrolytes, isotonic drinks help to promote absorption and retention of fluids in the body and facilitate the transportation of nutrients throughout the body.”
So while water can replace the fluids lost, isotonic drinks go a little further by helping to replace electrolytes and sugar.
But Dr Tan noted that soft drinks, fruit juices and cordials are not recommended as their high sugar content delays gastric emptying.
A high gastric emptying rate means ingested fluids will be better, and more quickly, absorbed.
Downing litres of water may not be an easy thing to do when you are huffing and puffing after a strenuous bout of exercise, and that, too, is when isotonic drinks have a slight edge over plain H2O.
“When you drink plain water, with no sodium, the desire to drink is often switched off before you consume enough fluid to match sweat loss,” said Kho.
“Therefore, it is easier to replace fluid via isotonic drinks as they are more palatable and do not switch off the desire to drink.”
|