Registered Dietitian's Guide to Hydration for Athletes
Staying hydrated is crucial for athletes to maintain performance, prevent dehydration, and ensure overall well-being. This blog will answer some key questions about hydration for athletes, the importance of electrolytes, and how to assess your hydration needs.
Why is it important for athletes to stay hydrated?
People who exercise regularly typically have increased fluid and sodium needs, especially those who exercise in the heat and sweat a lot of salt. Active individuals exercising in hot environments may also need more calcium, chloride, magnesium, and potassium. If you do not replenish your fluid and sodium losses, you risk dehydration and adverse symptoms that come with it. By understanding your fluid and sweat rate, you can experiment with your diet to ensure you replenish your fluid, sodium, and electrolyte needs. Fluid rate is different from the amount of salt in your sweat. Anyone can conduct a fluid rate test at home. It is harder to know exactly how much sodium is in your sweat, but there are ways to estimate. Keep reading to learn how to conduct a fluid test and estimate the amount of sodium in your sweat.
Why is sodium important for optimal hydration?
Before we dive into the fluid and sodium estimates, it’s important to know why sodium is crucial for optimal hydration. Sodium is a major player in euhydration. Sodium is the main driver for blood volume and a key player in mental focus, hand-eye coordination, reaction time, and awareness. By reducing the risk of dehydration, you also reduce the risk of heat illness, maintain cardiovascular and thermoregulatory function and improve performance during vigorous and/or long-duration physical activity. By staying adequately hydrated, you also lower your heart rate, core temperature, perceived exertion and increase your stroke volume, cardiac output, skin blood flow and sport performance. Learn more about the impact of dehydration on performance in this blog!
What are electrolytes? Why do athletes need them?
Electrolytes are minerals in your body that carry an electric charge. They are essential for various bodily functions, including maintaining fluid balance, transmitting nerve signals, and muscle contractions. Common electrolytes include sodium, chloride, potassium, calcium, and magnesium.
Athletes need electrolytes to replace those lost through sweat. Sweat is made up of 99% water and mostly salt, with a mix of other electrolytes. This is why replenishing electrolytes after sweating is crucial. Athletes tend to sweat more than the average person due to the nature of their physical activities. When athletes sweat more and do not properly replenish the lost electrolytes, they are at a higher risk of dehydration, muscle cramps, and decreased performance.
Knowing how much you sweat and what’s in your sweat can be the difference between coming in first or cramping at mile 10 and having to exit the race. Meeting with a Sports Dietitian Nutritionist can help you learn about your sweat and how to properly replenish it to avoid any negative effects from dehydration and loss of electrolytes.
What should athletes drink to stay hydrated and when?
Understanding what to drink and when is vital for maintaining hydration. Without adequate fluid-sodium balance, individuals can develop hyponatremia, a condition when sodium levels in your blood drop. This can lead to nausea, muscle cramps, weakness, fatigue, headaches, and swollen hands. Hyponatremia is more common in people who drink excessive plain water without sodium during prolonged exercise, especially in hot and humid environments.
The sodium drop in blood can be intensified by the loss of sodium in sweat from exercise, especially if you are a salty sweater. Think: marathon runner who is running at a slower pace and it may take 6 hours to complete the race, only drinking plain water puts this runner at risk of hyponatremia. Hikers in a hot, dry environment might not notice the sweat and salt leaving the body, if only drinking plain water with no salty food or beverage, this hiker is at risk of hyponatremia.
When engaging in exercise lasting longer than 60-90 minutes, it’s important to follow a hydration protocol to ensure you enter your activity hydrated, maintain hydration throughout, and properly rehydrate after. Below are current recommendations to guide your hydration and sodium intake (Adapted from American College of Sports Medicine Position Stand: Exercise and Fluid Replacement (2007) & American College of Sports Medicine Roundtable on Hydration and Physical Activity Consensus Statements (2005):
Before Exercise:
4 hours before: Consume 5-7 mL of fluid per kg of body weight (e.g., 350-490 mL (11-16.5 oz) for a 70 kg or 154 lbs person.
2 hours before: Consume 3-5 mL of fluid per kg of body weight (e.g., 210-350 mL for a 70 kg person). Avoid excessive fluid intake.
If consuming sodium before: 20-50mEq (460-1150 mg) per liter.
During Exercise:
Main goal is to prevent excessive dehydration (<2% body weight losses)
Consume 0.4-0.8 L/hour = 400-800 mL/h = 13.5-27 oz/hr. (Academy of Nutrition and Dietetics 2016)
After Exercise:
Consume 125-150% of lost weight within 6 hours after exercise
20-24 fl oz for every pound lost during training
How to assess your fluid and sodium losses in your sweat
Anyone can conduct a “fluid” loss test by weighing themselves minimally clothed (or nude) before and after exercise. (If you struggle with knowing your weight, you can ask for assistance from a friend to get a “blind weight” or tare the scale to a random number with a random object on top of the scale.)
To calculate net fluid loss during activity:
Weigh yourself before exercise.
Weigh yourself after exercise.
Track the amount of fluid consumed during exercise.
Example Calculation:
Pre-exercise weight: 152 lbs
Post-exercise weight: 150 lbs
Fluid consumed during exercise: 16 oz
Difference in weight: 152 lbs - 150 lbs = 2 lbs
Adjust for fluid consumed: 2 lbs + 1 lb (16 oz) = 3 lbs net fluid loss or 48 oz.
Divide by total time of activity to get fluid loss per minute or per hour. Aim to consume enough fluid during activity to minimize dehydration beyond 2% of your body weight loss.
After Exercise Fluid Replacement: To replace the fluids lost, consume 125-150% of the lost weight. For instance, if you need to replace 2 lbs or 32 oz of fluid, you should consume 40-48 oz of fluid after exercise.
Monitoring the saltiness of your sweat can provide insight on if you should consider consuming a higher level of sodium. Do you have visible salt stains on clothes or skin after exercise? Does your sweat taste really salty or sting your eyes/cuts? You may be a salty sweater and could benefit from a higher sodium intake. Here are common signs you are a salty sweater.
Common symptoms of high fluid/sodium loss:
Salt marks on skin/clothing
Salty tasting sweat/sweat stings eyes and cuts
Feel faint or get head rushes when standing up quickly after exercise
Muscle cramps during/after long periods of sweating
Feel terrible after exercise in heat
Crave salty foods after exercise
Headaches/ lightheadedness during or after exercise
If you commonly experience some or all of these signs, you are likely a salty sweater and should consider a higher sodium intake. In general, endurance athletes should aim to consume 300-1000+ mg sodium/hour to reduce risk for hyponatremia and support performance.
Final Thoughts on Hydration for Athletes
Understanding and maintaining proper hydration is essential for athletes to perform at their best and stay healthy. By knowing your sweat rate and electrolyte needs, you can tailor your hydration strategy to ensure optimal performance and recovery.
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