In a physical activity such as running, replenishing water and electrolytes lost by sweating is essential for physical performance and for avoiding health problems.
When running, body temperature increases as a result of the functioning of your muscles; this temperature is regulated through sweat, which eliminates water and electrolytes, such as sodium. Any significant loss of liquids without proper replenishment, will lead to a decrease in blood volume, increasing cardiac output and decreasing performance. Additionally, in a hypohydration scenario, the body’s thermal regulation is altered, leading to cramps, fainting due to heatstroke, and even death.
It’s important not only to replenish the water lost during training or during a race, but also the lost electrolytes and carbohydrates. Electrolytes – such as sodium – are essential for retaining liquid in your body, and they participate in basic bodily functions, while carbohydrates maintain plasma osmolality and aid in the absorption of liquid at an intestinal level.
In this case, isotonic beverages are the best source of hydration, as they are prepared with the appropriate quantity of carbohydrates and sodium required to maintain the human body’s proper functioning.
During an average race, approximately 1.5 litres of water for each hour of running are eliminated through sweat. In turn, gastric clearance amounts to about 1 litre per hour and, consequently, the absorption of water is slower than the loss of water while you’re performing sports. For this reason, specialists recommend for you to hydrate before, during, and after your training or race and, for the same reason, if you drink too much liquid at once, you could overload your stomach with liquid and the liquid will take too long to reach the intestine to be absorbed by your body, causing your stomach to feel “heavy” and affecting your performance.
The advice is to drink 500ml of liquid 2 hours prior to training or racing, in order to be properly hydrated before the beginning of the athletic activity. This hydration can be checked by observing your urine: clear, almost transparent urine, means that you’re properly hydrated, while a yellowish, darker urine, can be interpreted to mean dehydration.
Since gastric clearance is slow, the recommendation is to drink between 150-250ml of an isotonic beverage which contains around 9% carbohydrates, and 0.7-1g/litre of sodium, every 10-20 minutes of the race. In addition, after the race, it is advisable to drink between 150% to 200% of the lost liquid; this quantity is easy to calculate, by measuring your body weight before and after the training/race, with 1kg. of lost weight = 1 litre of lost liquid.
To sum up, hydration in running is key to achieve an enhanced performance and to prevent health problems. The recommendation is to drink isotonic beverages which contain a concentration of electrolytes and carbohydrates that is similar to that of our body, in order for them to be easily absorbed and thus prevent an electrolytic imbalance which could directly affect our health. Since the absorption rate is slower than the elimination of liquids while running, it is very important to constantly hydrate in small doses, so as to avoid stomach heaviness and favour liquid absorption.