MSU Extension Physical Activity

We have all experienced the feeling of parched lips and excessive sweating after a workout, run or even heavy gardening. These feelings are greater in the summer, especially when temperatures are above 90 degrees Fahrenheit and humidity is over 90 percent.

What causes these feelings of dehydration? How can we lessen these symptoms? 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 two percent leads to detriments in aerobic exercise performance and cognitive function. A fluid deficit of three to five 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:

1. Using thirst as a gauge
2. Measuring changes in body weight
3. Monitoring urine color

The easiest method is using thirst as a gauge. Typically, when we feel thirsty, we have already lost about one to two percent of our body mass. Another method is fluctuations in body weight. One would measure their body weight before and after an activity. Any weight lost can be attributed to dehydration due to participating in the activity. Lastly, monitoring urine color is another simple method to assess hydration status. The darker the urine color, the more likely the individual is dehydrated. 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, having two indicates likely dehydration and all noticing 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 two to four mL (0.07-0.14 oz.) of water per pound of bodyweight two to four 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 varies according to the individual, type of activity and environmental factors. One should consider consuming a beverage containing some carbohydrates and electrolytes for physical activity that extends beyond 45 minutes or during high heat or humidity. To reduce gastrointestinal side effects, it is recommended that only five to ten percent of the beverage contain carbohydrates. Numerous sports beverages that fit these guidelines are available for purchase at any grocery or convenience store. If you wish to make your own, there are also many 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 the 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.