Runners are often told to drink and stay hydrated during a workout.
Some of them are even told to drink at every water station during a race.
Yet, few are aware that over-hydration could actually harm them.
One condition that could arise from the excessive water consumption is hyponatremia, or having low sodium levels in the blood.
This is becoming a big concern for medical professionals and runners alike.
It has reportedly led to deaths at marathon and triathlon events.
Sodium is an electrolyte that is crucial in our bodily functions, such as nerve conduction. Even as you are reading this article, sodium is used to fire up the nerves that connect your brain to your eye muscles to allow you to read smoothly.
RUN WITH MOK - WEEK 4
With more fitness under your belt, it is time to test yourself again. You can run this workout along your favourite route, preferably free from pedestrian traffic.
Start with a 10-minute easy jog and some stretching. Once ready, set your watch to a one-minute timer on repeat. Start your timer and run fast until the minute is up, then slow down gradually to a jog. Repeat eight times.
Finish with a 10-minute cool-down run and some light stretching.
You should now be very familiar with your race pace. This week we will begin cutting down the volume so you start to feel fresher on race day.
You will run 8km today. Feel free to join running groups such as Running Department, who run on Wednesdays at 7pm at UOB Plaza.
This is also a good time to try out the pair of shoes you intend to use for the ST Run.
This is an optional run for those who are fitter or keen to train more.
Do a 30-minute run as an easy effort. You may replace this with an easy 30-minute swim or cycle.
This active recovery will help your body get ready for Saturday's long run.
You will run 12km at an easy pace. Again, there is no need to run at race pace. Take it easy and enjoy it with your friends.
This is a good time to try out any energy gels if you plan to use them on race day.
Training effort description
Easy/long run: You should be able to hold a conversation comfortably during the run.
Moderate (race pace) run: You should be able to speak in phrases but not in full sentences.
Hard (fast) run: During these intervals, you should be able to speak only in a sporadic fashion.
Exercise-associated hyponatremia (EAH) was first reported in 1981.
It was first thought to be most common in ultra-endurance events such as ultra-marathons and ironman triathlons.
This made sense as these events take more than half a day to complete and the chances of excessive water consumption are much higher than in a marathon.
However, recent studies show that even half-marathon runners are not spared.
In a 2008 study done in Florida, it was found that four out of every 100 half-marathon runners were found to have low sodium levels.
You may even have experienced this. Have you ever felt bloated and swollen after a long run?
Symptoms such as nausea and light-headedness - which some may link to fatigue - could really be due to hyponatremia.
Truth is, runners' knowledge on hydration is not quite on a par with their enthusiasm to complete a race. In a survey of participants at the 2010 London Marathon, 12 per cent said they planned to drink more than 3.5 litres of fluids, a level found to be associated with higher incidence of EAH.
So how can you prevent this from happening? Agencies such as the American College of Sports Medicine (ACSM) have come up with several guidelines for hydration.
Drinking to satisfy thirst - and not the commonly-advocated "beyond the point of thirst" - is the best way to prevent overhydration and EAH.
Another way is to weigh yourself before and after a long run to find your fluid-replacement needs.
For instance, if you tend to lose 1kg after a run, you should drink a maximum of 1kg of water during the run.
However, if you do not want to go through this trouble, a good guide would be 400-800ml an hour.
The ACSM guidelines also recommend that isotonic drinks with electrolytes should be made available at races and training.
So, yes, do remember to hydrate yourself during your training and racing - but be wise about it.
•Have any questions for Mok? E-mail them to firstname.lastname@example.org with the subject "Run with Mok" and he will try to answer as many as he can in his weekly column