Hydration: What you need to know

By Sanford Sports Science Institute

Hydration during sports

How much fluid you should drink during physical activity is determined by several key factors. An appropriate rate of fluid intake depends on how much you sweat, which is primarily driven by how hard you are working and environmental conditions – temperature and humidity. It also depends on how long you exercise. Your body loses water throughout the day through breathing and going to the bathroom; but exercise- and heat-induced sweating prompt significant body water losses and hydration challenges. Just relying on your body to indicate that you “feel thirsty” is not always sufficient to stay well-hydrated during physical activity, especially when you sweat a lot. Being mindful of, and deliberate with, how much fluid you take in every day through beverages and food is crucial to prevent levels of dehydration that are severe enough to hurt your performance and increase your risk of exertional heat illness. This is especially during situations when there is limited recovery time such as tournament events and two-a-day practices.

014002-00299P-SSSI-Adam-Thielen-06-27-2017_RGBSweat electrolyte losses, particularly sodium and chloride, vary by individual. Muscle cramping due to exertional heat stress can be attributed to an electrolyte deficit caused by sweating, as the sodium and chloride lost through sweat are not matched sufficiently by dietary salt intake. Replacing sodium is crucial to enhancing body water retention and distribution. Some athletes are referred to as “salty sweaters”, because they have a relatively high concentration of sodium in their sweat and a high sweat rate. This combination puts these particular athletes at an elevated risk for developing muscle cramps. Knowing how much fluid and electrolytes your body loses through sweating helps you to properly rehydrate after training or competition.

Before training and competition

Your body only needs to be dehydrated slightly to have a negative impact on performance, especially in the heat. Side effects of significant dehydration during sport include: decreased performance, strained cardiovascular system, premature fatigue, and increased risk for heat illness. This highlights why being properly hydrated before beginning a training session or competition is crucial for your body to perform safely and at its best. A simple way you can determine if you are drinking enough is by looking at the color and volume of your urine. Urine that is darker in color and low in volume can be a sign of significant dehydration. The goal is to have regular urinations that are light yellow in color. If you are making frequent stops at the bathroom with perfectly clear urine, it is probably a sign that you are drinking too much water.

During training and competition

Fluid and electrolyte (primarily sodium) losses during exercise can vary tremendously per individual and are also heavily influenced by environmental conditions, intensity of the activity, age, and heat acclimatization state. Guidelines for fluid consumption during sport are as follows:

  • Adults and Older Adolescents – Drink about 6-12 fluid ounces of water or sports drink every 15-20 minutes to maintain optimal hydration during activity. Keep in mind that one medium mouthful of water is equal to about one ounce.
  • Youth – Supervisory staff, such as coaches, should advise and provide opportunities for young children between the ages of 9-12 years to drink 3-8 fluid ounces of water or sports drink every 20 minutes of activity.

A common question is whether you should choose water or a sports drink to rehydrate during exercise. Sports drinks provide not only water, but also electrolytes and carbohydrates, which are particularly desirable to athletes who train at higher intensities for longer than 60 minutes. Exercising at higher intensities or in the heat increases your body’s demand for carbohydrate as a fuel source to sustain activity and avert fatigue. Providing carbohydrate in the form of a sports drink is not only convenient, but may help increase daily caloric intake for athletes who struggle to get enough calories every day with meals alone. For these reasons, consuming a sports drink is often a good choice for rehydration during training or competition. If you are training at lower intensities for shorter durations, water is sufficient for rehydration.

After training and competition

After exercise, your body’s primary dietary needs are water, carbohydrate, electrolytes (primarily sodium and chloride – salt), and protein for complete rehydration and muscle recovery. Sufficiently replenishing water, electrolytes and other nutrients is crucial for recovery from exercise, as well as overall health. With a little planning, you can make sure you are drinking enough fluid to optimize recovery. Measure your weight before exercise and then again afterward (without wearing your sweaty clothes). This will let you know how much more fluid you lost during exercise than what you consumed. For every one pound lost through sweating that was not replaced during training or competition, drink 16-20 fluid ounces over the next several hours or more to make up for the remaining fluid deficit. Eating a salty snack or meal is also beneficial, because it will help you replace some of the sodium lost through sweating and will enhance fluid retention and distribution throughout your body – examples of appropriate foods include soup, vegetable juice, or pretzels.

It is possible to drink too much during exercise. If you gain weight by the end of a training session or competitive event, it is a sign you drank too much water or other fluid during your activity. Drinking too much could result in excess water in the blood and a dangerously low sodium concentration. This condition is known as hyponatremia. Although it is rare, hyponatremia can be fatal; reinforcing the importance of drinking proper amounts of fluid, as opposed to trying to drink as much as possible.

1. Policy Statement–Climatic Heat Stress and Exercising Children and Adolescents. Pediatrics. Aug 8 2011.
2. Bergeron MF. Muscle cramps during exercise – is it fatigue or electrolyte deficit? Curr Sports Med Rep. 2008;7(4):S50-S55.