Slim

nAmid the humid weather, you cross the marathon finish line, feeling dizzy and on the verge of collapsing. Instinctively, you blame it on the heat and assume that you must be dehydrated. The first-aid personnel mull over whether to put you on a drip to pump your body with more fluids.
But wait - that extra liquid might make things worse, especially if you're not suffering from dehydration, but over-hydration.
Drinking too much liquid before and during a race puts you at risk of hyponatremia, a condition where there is excessive fluid in your blood and diluting your body's sodium content. The disorder can cause your brain to swell, induce a coma and even cause death. Symptoms include bloating, nausea and headaches and in serious cases, athletes become confused or delirious as the brain swells from high water content.
Experts agree that this condition is more common to women as well as those who drink a lot during the race.
Another high-risk group are those who take a long time to complete their races.
If you have signed up for a long-distance run or a triathlon before, how many times have you heard someone telling you to keep drinking fluids before or during the event?
Sports doctors are now unsure if this advice is sound.
At the 2002 Boston marathon, 28-year-old Cynthia Lucero collapsed during the race and died in hospital from hyponatremia.
Before she collapsed, she told a friend that she felt "dehydrated and rubber-legged".
Hyponatremia can easily be mistaken for dehydration or heat stroke, both of which are even rarer. Their symptoms can overlap and the best way to distinguish hyponatremia is to put the patient through a blood test.
Despite several cases of hyponatremia-related deaths cited in medical literature, there is scepticism about its prevalence here.
Medical staff - and athletes - must stop assuming that in sunny Singapore, dehydration and heatstroke will be more common than hyponatremia. Long queues outside porta-loos before any race here suggest nervous athletes are drinking more than they should.
Experts also agree that the condition can hit athletes who take part in night races, like this week's adidas Sundown Marathon.
With more endurance races being held in Singapore and more people signing up for them, the number of people suffering from the condition could rise.
The good news is that some race organisers are aware of this problem and are taking it seriously. At last year's The North Face trail race, for example, participants had their weight taken before and after the race to determine sweat loss.
These numbers help doctors establish if the athlete had lost too much water (dehydration) or gained weight (hyponatremia).
Is it time for more race organisers to gather such data?
Then what can you do? It seems like athletes can't drink too much, or too little.
For a start, you should drink based on sweat rate. You should determine your sweat rate during training runs by measuring your body weight before and after. For example, if you lose 2kg from running for two hours, you have a sweat rate of one litre per hour.
It is not necessary to replace fully the body mass lost during the race because we can tolerate a dehydration of up to 2 per cent of our weight. Full replacement of fluid lost should only take place after the run.
If you weigh 70kg - and going by a weight loss threshold of 2 per cent - you can afford to lose 1.4kg of weight. This puts the deficit at 600g (2kg minus 1.4kg), meaning you need to drink at least 600ml during a two-hour run, or only 300ml every hour.
With overlapping syndromes, hyponatremia puts athletes - especially inexperienced ones - in a bind.
Some might not be used to running under the sun and they will feel dizzy during a race. Many will want to prevent dehydration and stop at every drink station.
Sometimes, you feel light-headed after a run simply because of postural hypotension - a common condition when blood pools around your legs due to prolonged running. A quick way to recover is to raise your legs against a wall and let blood flow back to your upper body.
If you know it is going to be hot on race day, heat acclimatisation - getting used to heat by training shorter distances in hot weather - can also make a difference between finishing the race with a smile, or ending up in the medical tent - or worse, getting the wrong type of diagnosis and treatment.