Remember that old adage of “drink 8 glasses per day”? Well, that’s not always the best way to hydrate, admits Natalie Rizzo, MS, RD, a plant-based sports dietitian with Greenletes in New York City and the author of Planted Performance.
“Fluid intake is highly individualized, based on a person’s size, activity level, sweat rate, and environmental conditions,” Rizzo says. If you work out, those factors become even more important in determining the best hydration practices for you.
Human bodies are, on average, 60 percent water, according to the United States Geological Survey. We can’t function without it, and it impacts nearly every system in our bodies, from our muscles to our cardiovascular system to our brain, says Roxana Ehsani, MS, RD, CSSD, a Miami-based board-certified sports dietitian.
“It's important to stay well hydrated to optimally support fluid balance and its functions, including transporting nutrients and oxygen around the body, regulating blood volume and blood pressure, protecting and lubricating our tissues and joints, and regulating body temperature,” explains Kelly Jones, MS, RD, CSSD, LDN, a Newton, Pennsylvania-based sports dietitian to pro athletes and everyday exercisers. “Water is also involved in energy metabolism, helping us convert the foods and nutrients we eat into usable energy for our cells.”
So how, exactly, will you know if you’re not hydrating properly? Watch out for signs of dehydration, Even when mild, these could keep you from feeling your best during your workout and hitting your goals.
Signs of Dehydration
Individual signs can vary, but the following are among the most common symptoms of dehydration, according to a December 2018 report in the journal BMC Public Medicine:
Dry mouth and/or tongue
Dark yellow urine
During severe hydration, individuals may experience low blood pressure, sunken eyes, a lack of tears or sweat, rapid heart rate, and in extreme cases, unconsciousness.
The Best Way to Hydrate for Every Stage of Exercise
Those all sound ideal to avoid, right? It’s possible to do so if you start to sip early and often.
“It's important to not just drink a cup of water right before activity and think that you’re adequately hydrated and will perform well during a workout,” Ehsani admits. “A lot of people, including elite athletes, are chronically dehydrated. It’s essential to focus on staying hydrated throughout the day to perform at your best during workout time.”
Since duration and intensity of workouts, fitness level, weather, apparel, and even altitude changes can impact how much you sweat, Jones says that these factors also impact how much fluid you need before, during, and after exercise. (And if you’re exercising in the heat, you’ll want to be particularly mindful of hydration.)
As a general rule, start with your weight in pounds (for example, 180 pounds), divide it by two (90) and that’s the minimum number of ounces of water you should shoot for each day if you’re not exercising, Jones says. In this example, that would work out to around 11 cups of water. From there, scale up using the guidance below for the best way to hydrate.
How to Hydrate Before a Workout
The experts we spoke to agree that you should start ramping things up two hours prior to your sweat session. Drink 16 to 24 ounces at that time, then 15 minutes before you clip in to your bike or start a workout, drink another 8 to 16 ounces.
“This isn't always realistic for morning exercisers however, so if that’s when you have time to train, hydrating well the day before is more important for you,” Jones says. “Including adequate carbohydrate and sodium to support your activity level can help you better absorb and use the fluid you're consuming, too.”
How to Stay Hydrated During Exercise
Whether you’re cycling, running, lifting, or otherwise, you’ll likely be sweating during the process. So to keep up with hydration, a good starting point is to drink about 16 to 32 ounces per 30 to 60 minutes. Err on the higher side if you’re a heavy sweater, are working out in more intense conditions, like heat or altitude, or if you’re going a longer workout.
“If you’re exercising for longer than an hour, it’s an intense activity or the weather is very hot or humid, you will also need electrolytes and a source of carbohydrates,” Ehsani adds. A sports drink or electrolyte packet in your water plus an energy gel or bar will do. (More on that later!)
How to Hydrate After a Workout
After a moderate sweat sesh of 30 to 60 minutes, simply get back into the flow of your usual daily eating and drinking patterns, Jones says.
For workouts over an hour, it’s a wise idea to plan to weigh yourself before and after without clothes on so you can track how many pounds you lost from sweat. Ideally, “you do not want to lose any body weight during activity. Research suggests that performance can be significantly impaired if more than 2 percent of body weight is lost through fluid,” Rizzo says.
If you did happen to fall behind on some hydration and sweated more than you consumed during the workout, for each pound lost, drink 24 ounces of water.
You don’t need to do this after each session, but Ehsani recommends doing so once or twice per training season to gauge how much sweat you typically lose amidst those conditions.
What About Electrolytes?
“Electrolytes are critical to performance,” Ehsani says. “These essential minerals work together to help regulate and maintain fluid balance, muscle function, and overall health of athletes. Sodium is the electrolyte we lose most in sweat, and needs to be replaced after workouts.”
Electrolytes, including sodium and potassium, are found in sports drinks or powdered hydration packets, as well as in food.
“When we add sodium to beverages, like with electrolyte packets or sports drinks, this stimulates us to drink more; helping you fully rehydrate,” Ehsani says.
While sodium might get a bad rap because 47 percent of Americans have hypertension (a condition that can be worsened by increased sodium consumption), rehydration "water weight" isn't a bad thing for the average active adult, Jones says.
“Replacing sodium specifically is important to hold on to enough of the fluid we drink to maintain blood volume and blood pressure and support our nerve impulses and muscle contractions. It’s recommended that the average person consume between 1,500 to 2,300 milligrams of sodium per day,” Jones says.
Since sweat is made up of 99 percent water and 1 percent salt and a few other trace compounds, it’s an important part of the equation to consider as well. Sweat loss can add up to 500 to 1,500 milligrams of sodium per hour, Jones says. (Remember that 10-pretzel portion of pre-workout fuel? It offers 760 milligrams of sodium.) Try to refresh your electrolyte stores within 60 minutes post-workout.
How to Hydrate Fast
If you’ve fallen behind on hydration, chugging massive amounts of water before your workout isn’t your best solution. That might lead to an uncomfortable sloshing feeling in your stomach. You’re better off starting at the time that aligns with the recommendations above, then sipping steadily every 5 to 10 minutes throughout your workout—and after, Rizzo recommends.
If you really overdo it on that not-recommended pre-workout water chugging, you can actually end up overshooting your hydration goals and may slip into hyperhydration territory. In serious cases, this can lead to coma, seizures, or death. In more moderate circumstances, this condition, also known as “water intoxication,” can result in symptoms like:
Hyponatremia, or severely low sodium levels
As you can tell, some of these symptoms overlap with those listed above as signs you’re dehydrated; making the situation even more complex to keep in check.
So no need to go wild with your water intake if you happen to be approaching a workout slightly dehydrated. Instead, stick to the best practices mentioned above and lean into the powers of electrolytes and carbohydrates.
“Two hours before your workout, try to drink at least 2 to 3 cups of fluid, which can be a mix of water and electrolytes, such as a sports drink,” Ehsani says.
As we mentioned, the extra sodium and carbohydrates in that sports drink help your body better utilize the fluid you are consuming.
On rest days, set a goal to drink half of your body weight in pounds in ounces. Then when you’re active, aim for this mark and add 16 to 24 ounces two hours before your workout, another 8 ounces 15 minutes before starting, and 16 to 32 ounces every 30 to 60 minutes during exercise, depending on your comfort level, the conditions, and your sweat rate. After you cool down, rehydrate with 24 ounces for every pound of fluid you lost, or sip until you’re urinating a liquid that looks like lemonade or lighter every 2 to 4 hours.
By keeping up with your hydration throughout the day, you can avoid the uncomfortable—and sometimes dangerous—symptoms of dehydration or hyper hydration, and can set yourself up for sweat success.
This content is for informational and educational purposes only and does not constitute individualized advice. It is not intended to replace professional medical evaluation, diagnosis, or treatment. Seek the advice of your physician for questions you may have regarding your health or a medical condition. If you are having a medical emergency, call your physician or 911 immediately.