The human body is made up of 70 per cent water and it is essential for a wide range physiological functions in the body, such as sweating. Sweating is a mechanism to cool down our body during physical activity or when the body is overheated.
While it is an effective means by which the body counters heat stress, excessive sweating without proper replenishment can lead to repercussions.
Ninety per cent of our blood plasma consists of water. Excessive sweating will therefore reduce the blood volume we have in our bodies. Our blood flows in vessels, very much like the pipes that deliver water to our homes.
When a water shortage occurs, water has to be rationed and each household will receive less water. Similarly, when there is reduced blood volume, less blood is available to flow through the vessels and to supply the muscles.
Blood carries red blood cells which in turn carries oxygen to our muscles. A reduction in blood volume requires the heart to work harder to supply oxygen and nutrients to the exercising muscles.
This scenario is further complicated when there is also competition for blood supply to the skin to promote convective heat loss.
While severe clinical dehydration rarely occurs during exercise, a less hydrated body is nonetheless more susceptible to thermal strain during exercise. In other words, our bodies overheat faster when we are dehydrated.
Moreover, research has also shown that endurance performance is affected when athletes' fluid loss exceeds two per cent of their body weight.
Clearly, a good hydration strategy is critical for safe and successful endurance running.
Endurance runner and ONEathlete Banjamin Quek shared those sentiments. He said: "Our body loses water up to two per cent of our weight when we work out. Therefore, we need to hydrate in order to run over a long distance."
More is not always better when it comes to drinking. One of the important salts in our blood is sodium. Excessive water consumption may overly dilute the sodium concentration, a condition known as hyponatremia.
Hyponatremia can pose a serious threat with symptoms such as nausea, vomiting, headaches, confusion, muscle cramps, seizures and even the onset of coma.
It has been recommended by the American College of Sports Medicine that event organisers provide sodium-laden sports drinks as a strategy to reduce participants' risk of dilutional hyponatremia during long-distance endurance races such as marathons.
Sports drinks in the form of ice slushies can be a good alternative to boost heat tolerance during endurance races.
Research evidence from the Department of Physiology, National University of Singapore, has shown that ingesting ice slushies before exercise can lower pre-exercise core temperature and increase heat tolerance in hot and humid conditions.
Runners should never toe the starting line in an under-hydrated state.
Always ensure that the body is well (but not overly) hydrated before a race and avoid alcoholic beverages before training and races.
A well-crafted hydration plan is the first step towards a successful race. While we should always race hard, never forget to race smart too. It is always better to race smart than to race hard.
• Dr Ivan Low is a research fellow in the Department of Physiology, National University of Singapore. The exercise physiologist ran the Boston Marathon in 2015.