Hydration

Importance of consuming the appropriate amount of fluid during exercise 

Fluid imbalances are common in endurance sports, particularly distance running. Hypohydration/dehydration (low/inadequate body water) and hyperhydration (excessive body water) can both negatively impact performance. 

Dehydration can occur when body water losses are higher than fluid intake. During exercise, fluid loss not only occurs through sweat, but also from exhalation. Certain environments can increase dehydration risk, such as very hot and/or dry climates.

Hyperhydration is when fluid intake is much greater than losses. The concern with this is that blood sodium levels drop dangerously low, where it could become fatal if not quickly resolved. Hyperhydration usually only happens to athletes when excess fluid losses occur and high volumes of plain water (vs. sodium containing sports drink) is consumed. For that reason, it is wise to make sure your sodium is being replenished when your sweat losses are high.

Since fluid needs and losses vary widely from individual to individual, it is important to understand your individual needs for various conditions. This page will discuss tips to help you assess your fluids needs. 

First, Meet your baseline hydration needs (listed below) based on Adequate Intake (AI) Values, consume additional water based on exercise losses.

Average Sweat and Sodium Losses During Exercise

Sweat volume and the amount of sodium loss varies widely between individuals and also within one individual -depending on factors such as environment, running duration and intensity. For reference, consider the following average estimates of sodium and sweat excreted:

• Average sweat rates: ~1-2 L/hr

• Average sodium lost in sweat: ~360-1440 mg/L

• Aim to drink 400-800 ml (~14-28 oz) /hr, adjust based on water losses, and specifics of the event (intensity, environment, etc)

Considerations for determining a hydration plan for during exercise

Developing a personalized hydration plan involves 4 steps: 

1. Assessment: Assess current hydration and electrolyte status. Pay attention to thirst sensations, weight loss, and sodium losses during exercise. Are you losing more than 2-3 lb during exercise? Do you have salt crystals on your skin or clothes? See below for methods to calculate fluid and sodium needs during exercise. 

2. Goals: Consider the following when assessing your hydration goals. 

   • Do you need to improve your hydration status outside of exercise? If so, one of the goals should be to drink more water throughout the day so you start your run euhydrated. 

   • Is your run/ work out longer than ~45 minutes? If so, you may need carbohydrates. If they are not coming from another avenue (e.g. gels, energy blocks), choose a carbohydrate containing sports beverage (see table below for examples)

   • You will likely need sodium replenishment if you are: 

     • exercising for long durations 

     • exercising in hot environments

     • a heavy sweater  

     • a salty sweater 

   • What other foods and beverages will you be consuming during the event? What are your preferences? Do you prefer to just consume sports drinks to meet your fluid, carbohydrate, and sodium needs? Or do you like to consume mostly solid foods and plain water? 

3. Implementation: Account for carbohydrate and sodium content of all other foods and beverages that will be consumed. 

4. Reassessment: It’s important to reassess how your hydration plans are working. Did you meet your goals? Was hyper and hypohydration prevented? Was gastrointestinal distress present? How did the environment impact your hydration status? If there are any aspects about your current strategies that did not work, what needs to be adjusted to improve it in the future?

Tips For Monitoring Hydration Status 

• Sweat production- decreasing sweat production can be a sign of dehydration 

• Thirst sensations which may include dry mouth, headache and weakness. These signs can vary depending on the individual and the goal would be to prevent dehydration. 

• Body weight fluctuations can also be insightful when evaluating hydration status. During exercise, weight loss is indicative of inadequate fluid intake while weight gain is indicative of excessive fluid intake.

• Urine color can be used as one indicator of hydration status. “Normal” urine is the color of lemon juice. Dark yellow or golden colored urine can be a sign of dehydration. It should be noted that other things can affect urine color such as very high protein diets and certain vitamins (e.g., the B vitamin riboflavin).

Tips to Stay Hydrated

• Aim to prevent dehydration of >2% of body weight loss by starting your activity euhydrated, and bring along enough water to meet the majority of your losses. Consider a sports drink which may promote intake due to flavor and sugar and sodium content. 

• Have a hydration protocol in place (as discussed above), focusing on the amount and timing of fluid consumption

• Rehydrate post exercise. The goal is to consume 150-200% of fluid lost. Figure out how much water you lost by weighing yourself before and after the exercise bout then drink 24-32 oz for each pound lost. 

• Eat something salty or add salt to your post work-out meal to aid in water retention and replenish sodium losses 

• To remain hydrated; weight yourself before and after your run. Calculate the percent of loss. From that, you can calculate the amount you should consume during a similar event with similar conditions (i.e. similar distances and temps). 

Benefits of Consuming a Carbohydrate and Electrolyte Containing Beverage During Exercise:

• Promotes fluid intake due to the taste/palatability  helping to prevent negative outcomes of dehydration

• Helps to meet carbohydrate needs during the activity, enabling higher level and/ or longer duration performance

• Replaces electrolytes lost through sweat

• May be easier to tolerate for some athletes compared to other carbohydrate-containing sports foods (gummies, blocks, etc). 

• Fulfills fluid, carbohydrate, and electrolyte needs

  • preventing risk of dehydration, bonking, and hyponatremia (low serum sodium)

The ideal carbohydrate concentration of a sports beverage is 6-8%. Carbohydrate needs are individualized and can vary depending on the duration, intensity, and environment of the individual’s run. Some runners may have increased GI symptoms consuming drinks over the recommended CHO amount of 8%. If you can tolerate the highly concentrated carbohydrate beverages, that would be a good way to get carbohydrates and fluids in before and during exercise. Otherwise, they could be diluted to be closer to 8%. Likewise, CHO and electrolytes sports drinks that fall under the recommended 6% CHO will likely not meet the carbohydrate needs of the runner. These lower CHO drinks would be ideal for hydration when obtaining CHO needs through solid foods, gels or sports chews. They would also be appropriate for pre-run hydration and for runs of short duration (<45 minutes).

Reference

Dunford M & Doyle JA. Nutrition for Sport and Exercise 4th ed. Cengage. 2019.