Hydration and physical activity

Find out the recommended hydration practices for sport and recreational activities.

August 15, 2018

Aerial view of glass of clear water.
Dehydration is the process of losing water, while “hypohydration” is the actual state of being in a water deficit beyond what is normal.

We’ve all been there. The feeling of parched lips and excessive sweating after a workout, run, or even heavy gardening. These feelings are greater now in the summer, especially when we have temperatures in the 90’s and humidity over 90 percent. But what causes these feelings of dehydration, how can we lessen these symptoms, and are there any evidence-based recommendations for dealing with these feelings? 

Dehydration versus hypohydration

Before we answer these questions, we need to have a good understanding of what dehydration is. Dehydration is the process of losing water, while “hypohydration” is the actual state of being in a water deficit beyond what is normal. The key difference is that dehydration is the process and hypohydration is the outcome. 

Water lost during exercise

When we think of water loss during exercise, we commonly think of sweating. However, we also lose water through respiration, gastrointestinal function and renal functions. Not only do we lose water when sweating, but we also lose a number of other important things, such as electrolytes, which are important in maintaining numerous bodily functions including nervous system function and maintaining water balance. We sweat to help dissipate heat that is generated during any type of physical activity, however, this can be exacerbated by environmental factors such as the temperature, solar radiation, ground heat and humidity. Regardless, research reveals that a fluid deficit of greater than 2 percent leads to detriments in aerobic exercise performance and cognitive function. A fluid deficit of 3-5 percent can lead to detriments in high intensity exercise such as resistance training. Not to mention increasing one’s risk for a number of heat-related illnesses such as fainting, cramps and heat stroke.

How can we monitor hydration levels?

There are a number of different ways to monitor one’s hydration levels, although three are most commonly used:

  • Using thirst as a gauge
  • Measuring changes in body weight
  • Monitoring urine color

The easiest method is using thirst as a gauge. Typically, when we feel thirsty, we have already lost about 1-2 percent of our body mass. Another method is fluctuations in body weight. One would measure their body weight before and after activity. Any weight lost can be attributed to dehydration due to activity. Lastly, monitoring urine color is another simple method to assess hydration status. The darker the urine color, the more likely and/or degree of dehydration the individual has. Ideally, urine should be a pale, yellow color. When using these methods to assess hydration, the idea is if you have one of the above this may indicate dehydration; two indicates likely dehydration; and all three indicates very likely dehydration. 

What are the recommendations for hydration before, during, and after physical activity?

Before activity

Overall, the recommendation is for people to be properly hydrated prior to activity. This consists of consuming around 2-4 mL (0.07-0.14 oz) of water per pound of bodyweight 2-4 hours before activity. This equates to about 10.5-21 oz for a 150 pound individual. Additionally, be sure that your beverage provides some electrolytes, such as sodium.

During activity

Ideally, an individual should be consuming water periodically during any type of physical activity. The recommendation is about 0.4-0.8 L (13.5-27 oz) of fluid per hour. Intake should be varied according to the individual, type of activity, and environmental factors. One should consider consuming a beverage containing some carbohydrate and electrolytes for physical activity that extends beyond 45 minutes or during high heat/humidity. To reduce gastrointestinal side effects, it is recommended that only 5-10 percent of the beverage contains carbohydrates. There are numerous sports beverages which you can buy at any grocery or convenience store. If you wish to make your own, there are numerous recipes online. Refer to the 2016 Position of the Academy of Nutrition and Dietetics, Dieticians of Canada, and the American College of Sports Medicine: Nutrition and Athletic performance for further information about carbohydrate recommendations during physical activity. 

After activity

To replenish water lost during physical activity, the recommendation is to consume 1.25 to 1.5 L of fluid for every kilogram of bodyweight lost (~20-24 oz per pound of bodyweight lost). It is worth noting, that consuming too much fluid after exercise could potentially lead to negative side effects too, so use the recommendation as a starting point.

We lose water and electrolytes a multitude of ways during physical activity. Not being properly hydrated before, during, and after physical activity can lead not only to decreases in performance, but also increased risks for heat-related illnesses. Follow evidence-based hydration recommendations for better performance and safety this summer.

Do you want to learn more?

To help people be healthy at every stage of life, Michigan State University Extension delivers affordable, relevant, evidence-based education to serve the needs of adults, youth and families in urban and rural communities.

Our programs cover all areas of health, from buying and preparing nutritious, budget-friendly food to managing stress, preventing or living well with diabetes and optimal aging – MSU Extension has the information you need in a format you can use, in-person and online. Contact your local MSU Extension county office to find a class near you.

Tags: food & health, msu extension, physical activity

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