Proper hydration before you exercise, monitoring your hydration status during exercise, and replacing fluid losses post-exercise are vital to ensuring your body has the fluids it needs to perform.

Just a decade ago, recommendations emphasized drinking as much as one could handle during exercise, however it is now recommended to replace at least 75% but not more than 100% of sweat losses. But don’t depend on your thirst mechanism to tell you when and how much to drink. Thirst is a poor indicator of hydration status, as an athlete can lose over 1.5 L of body water before becoming thirsty.

Sweat rates vary among individuals, and sweat losses of 1-2% of body weight compromises physiologic function, and harms exercise performance. A loss of 3% of one’s body weight increases the risk of heat cramps and heat exhaustion, where losses of 5% or more of body weight can cause heat stroke and a trip to the medical tent or closest hospital.

Weigh yourself before and after exercise to monitor your fluid losses. As a guideline, the American Dietetic Association suggests 1 Litre/kg of body weight lost during exercise.


Hyponatremia is a potentially fatal condition of low blood sodium levels. This can happen during prolonged exercise if sodium levels are not properly replenished, with salty snacks or electrolyte sport drinks. It can also happen from drinking too much water, which effectively dilutes the sodium content of the blood. Sodium losses range from 2.25-3.4 g/L of sweat (which is equivalent to about ½ tsp of salt). Conditioned athletes may be more efficient with their sodium losses, however this varies from person to person.

Research indicates that ingesting 20 – 50 mEq (0.5-1.2 g) of sodium/L is effective in preventing hyponatremia. This is equivalent to less than ¼ tsp of salt per liter of water.
Some drugs such as NSAIDS (aspirin, ibuprofen) or diuretics have been shown to alter kidney function, which may exacerbate the risk of hyponatremia during long duration events. Athletes should be aware of this increased risk, know the signs and symptoms, ensure that they are not limiting dietary salt intake when in training, and ensure proper rehydration strategies are in place.

Signs and Symptoms

The signs and symptoms of dehydration and hyponatremia are very similar, and if incorrectly diagnosed can be detrimental, possibly even causing death. For example, an athlete suffering from hyponatremia can easily be mistaken as dehydrated, and drinking water, as one would do to treat dehydration, will only exacerbate the problem. Water will dilute the blood, thereby further decreasing its concentration of sodium, and worsening the symptoms of hyponatremia.















Loss of consciousness





Hydration Status and Sport Drinks for Athletes