Water is the largest component of the human body, making up around 60-65% of the total body mass, which is equal to around 36 – 39L of water in a 60kg person. The water in our body is not present as pure water though, but rather it contains various different electrolytes. Electrolytes are salts and minerals dissolved in our body that are essential to normal body function. The most common electrolytes in the human body are sodium, potassium and chloride.
Sweating, particularly during exercise, is one of the major ways in which the body loses water and essential electrolytes and not replacing them leads to dehydration. Signs of dehydration include thirst, cramps, fatigue and headaches, amongst many more. All of which negatively affect athletic performance and could be the difference between winning and losing. Various studies have found that high levels of dehydration have been linked to a decrease in both physical and cognitive performance by up to 60% in various sports from cycling and running to football and basketball (Maughan & Shirreffs, 2010; Harper, 2017). The effects of this are even greater in hot and humid conditions or in endurance type events lasting more than 90 minutes. Keeping hydrated is essential to reaching those tops speeds, maintaining that accuracy and keeping us on top of our game.
In order to prevent dehydration and improve performance any losses must be replaced through drinking fluids. However, contrary to the belief of many athletes, water alone is not an ideal rehydration fluid as it stimulates urine output and can lead to higher levels of dehydration. To prevent this, the fluid consumed must contain sufficient amounts of electrolytes (particularly sodium), and many popular sports drinks also contain carbohydrates for an extra energy boost.
An easy way to avoid dehydration and its negative effects on performance is to think about splitting it into three categories: pre-hydrate before, hydrate during and re-hydrate after.
The American College of Sports Medicine (2007) recommends:
Consuming fluids before exercise or a work out will ensure you begin the event in water balance and will reduce the risk of dehydration.
Gradually consume around 500mL of fluid 4 hours before exercise.
The amount of sweat an athlete produces varies from person to person (Shirreffs, 2007), meaning there is no set amount for how much to drink during events.
However, hydration should begin early and at regular intervals during exercise (where possible) in order to prevent more than a 2% loss in total body weight.
For events lasting more than 1 hour- drinks containing carbohydrates (30-60g) are recommended to ensure glycogen stores don’t become depleted.
While the amount that must be consumed after exercise will again vary amongst athletes and sports, it must exceed the amount that has been lost through sweat in order to hydrate the body (Shirreffs, 1996). Individual sweat rates can be calculated by weighing the athlete (fully clothed) before and after exercise to calculate the change in body weight. 150% of the amount lost must be replaced to prevent dehydration and replenish electrolytes.
Emmy Cambell, YSN® Research Assistant.
American College of Sports Medicine position stand (2007) ‘Exercise and fluid replacement’ Medicine and Science in Sports and Exercise 39(2) pp377-390
Harper, D.L et al (2017) ‘The influence of a 12% carbohydrate-electrolyte beverage on self-paced soccer-specific exercise performance’ Journal of Science and Medicine in Sport 20(12) pp1123-1129
Maughan, R.J & Shirreffs, S.M (2010) ‘Dehydration and rehydration in competitive sport’ Scandinavian Journal of Medicine & Science in Sports 20(3) pp40-47
Shirreffs, S.M et al (1996) ‘Post-exercise rehydration in man: effects of volume consumed and drink sodium content’ Medicine and Science in Sports and Exercise 28(10) pp1260-1271
Shirreffs, S.M et al (2007) ‘Fluid needs for training and competition in athletics’ Journal of Sports Science 25(1) pp83-91