The human body is made up of 55 to 75% water which is an essential nutrient for survival. This is why we are going to learn more about hydration for athletes. To start off water helps your body:

• Regulate body temperature
• Lubricate and cushion joints
• Remove waste through urination, sweat, and bowel movements
• Protect your spinal cord and other sensitive tissue
• Digest food and transport nutrients to your cells

How Much Should You Be Drinking?

Well… it depends. Although there is no recommendation of how much plain water you need to consume daily, The National Academy of Sciences recommends men consume 3.7 liters and women 2.7 liters of fluids per day. This can come from plain water, decaffeinated beverages, and foods (soups, dairy, fruits, and veggies). It is important to note, however, this is not a one size fits all approach. Everyone’s fluid needs will vary based on your unique needs as an individual, your sweat rate, and your sweat concentration.

Points to consider when thinking about your fluid intake:

• Daily activity – movement for 60+ minutes per day is a reason to consider hydrating with carbohydrates and electrolytes
• Sweat rate can vary based on the individual as well as environmental factors. Drinking to thirst during exercise is an effective way to manage electrolyte balance and dehydration. I recommend drinking a beverage with some carbohydrates and sodium hydrate most efficiently. 
• Sweat sodium concentration
• Environmental conditions – heat, humidity, altitude
• Daily nutrition – consuming foods with higher water content is also hydrating
• Body size will determine the amount of fluid you need per day. A larger body will need additional fluid in relation to blood volume. 

Sweat Rate 

Sweat rate varies considerably from person to person as well as for the same individual in different environmental conditions, training intensity, equipment/ clothing, genetics, and heat acclimation. I recommend testing your sweat rate in a variety of conditions to help guide your hydration strategy in different scenarios.

Here is how to calculate your sweat rate:

1. pre-training weight – measure weight after using the restroom and dressing down to comfort. Nude will give the most accurate data as the clothes you weigh in will accumulate sweat as you train.
2. post weight – measure weight after session, toweling off all sweat and removing clothing down to comfort. Again, nude is best.
3. Change in body weight
4. The volume of fluids consumed during activity – you will weigh the bottle you use before adding fluids to it, zero out the scale, add fluids + electrolytes to it, and record the weight of fluids
5. Urine volume – you will need to measure any void done during the activity. For ease of measurement, try to use the restroom immediately before the session.
6. Sweat Losses 
7. Exercise time in hours
8. Sweat rate 

The next factor of sweat is that it is not just made up of water. Sweat is made up of water and electrolytes (sodium, chloride, magnesium, potassium, and calcium). The predominant electrolyte lost in sweat is sodium. An average sodium loss in sweat is 1000 mg per liter of fluids lost; however, it can range from 250 mg to 3000 mg per liter!

Factors that may influence sweat sodium concentration: 

• Sweat rate increases with increased intensity or energy expenditure as does the rate of sodium concentration in your sweat
• Heat acclimatization
• Genetics – there is a gene called CF1 that determines how much sodium you lose in your sweat

You may be able to tell if you are a salty sweater if:

• You have salt residue on your clothing, hat, or skin after a workout
• Your eyes or cuts sting when it gets in them
• Your dog or a friendly dog comes up to lick your legs after a training session
• You have a head rush or get dizzy when standing up quickly after exercise
• You crave salty foods during and/or after exercise
• You suffer from muscle cramps during and/or after long or hard training sessions

How Do I Know If I am Hydrated?

The simplest way to tell if you are hydrated is by looking at the color of your urine. You are aiming for a pale, light yellow (like the color of lemonade). Dark yellow urine is a sign of dehydration; for example, your first void in the morning is more concentrated from not having fluids through the evening. Brown-colored urine is a medical emergency and a reason to seek medical attention.

Can I Drink Too Much Water?

There is a risk of over-hydrating with plain water which causes the concentration of sodium in your blood to become diluted. This causes your cells to swell and cause 

As an endurance athlete, competing in marathons, ultramarathons, triathlons, and long-distance, high-intensity activities you are at higher risk for hyponatremia.

Premenopausal women are at the greatest risk of hyponatremia-related brain damage, which is thought to be in relation to female sex hormones’ role in balancing sodium. Understanding your sweat rate and concentration can help you develop a personalized hydration protocol during training; drinking to thirst is also a way to ensure you are not overhydrating. 

What Level of Dehydration Is Ok?

Dehydration is characterized as just 3% of body weight loss from fluid depletion. A  1-2% loss is associated with decreased cognitive function and psychomotor skills. A 3-4% loss decreases performance (muscle endurance and strength), increases respiration, and causes headaches, irritability, and sleepiness; it also increases basal temperature in children. A deficit of 8% or more can cause death; however, there is some research showing athletes tolerating a 10% deficit.

As an athlete, your ability to tolerate dehydration is highly variable on the individual and likely on different days in different climates. For premenopausal females, the level of dehydration tolerance can likely change throughout your menstrual cycle as well as basal body temperature increases during your luteal phase (second phase of your cycle). 

Menopausal females also have a higher incidence of dehydration as body water decreases by about 6 liters (or 15%) between the ages of 20 and 80 years old. Thirst sensation also decreases which can make it more difficult to stay on top of hydration using internal cues. This is why as you enter menopause, you may be less tolerant to heat.

The American College of Sports Medicine recommends drinking enough during exercise to prevent >2% body weight loss from water deficit rather than drinking to 100% replace fluid losses. This can be determined based on your individual sweat rate.

Tips for Staying Hydrated:

• Bring a reusable, insulated water bottle with you when you are out and about.
• Hydrate early and often. It is best to sip on fluids throughout the day versus guzzling down large amounts in one go.
• Drink 10-12 ounces of decaf fluids within the first 30 minutes of waking
• Have a glass of water with meals
• Add fruit such as berries, lime, lemon, or orange to the water to add some flavor
• Sip on herbal teas, sparkling or seltzer waters as a part of your hydration
• Add low-fat or fat-free milk; unsweetened, fortified milk alternatives, or 100% fruit or vegetable juice into the mix for your hydration plan
• Consume fruits and veggies as a part of a balanced diet
• During training, include fluids containing at least 800 mg of sodium per liter. Optimally, testing your sweat rate and sweat sodium concentration in different scenarios (environment, intensities) and replacing fluids lost based on your individual objective and subjective data (thirst, salt cravings, fatigue)

-Dana Eshelman, MS, RDN, CSSD, METS I

READ MORE: HYDRATION SYSTEMS FOR TRIATHLON BIKES