How You Should Hydrate for Exercise

Hydration plays a vital role in exercise performance, body temperature regulation and recovery. Even small changes in your fluid balance can affect endurance, strength and perceived exertion, especially if you’re an athlete. 

Research shows that proper hydration isn’t just about drinking plenty of water. The frequency with which you drink and the types of fluids you consume are also important. You also must consider the intensity and duration of your workout, as well as weather conditions.  

Most of us can lose between 2% and 6% of our fluid volume when exercising in the heat, according to the American College of Sports Medicine (ACSM). Fortunately, most of us don’t exercise intensely enough (or for long enough) to worry about replacing every drop of sweat we lose during a workout, especially in normal weather conditions. But if you’re exercising outside in the heat,  or “going the distance,” knowing how to hydrate can improve your performance and keep you healthy.

Why Hydration Matters

Water makes up about 60% of body weight and is essential for maintaining our body’s core temperature, cardiovascular funtion and nutrient transport. However, exercise can disrupt the status quo.  For instance, sweating during a workout lowers blood plasma volume, raising heart rate and core temperature. In fact, a fluid loss of just 2 percent of your body mass (about three pounds of sweat for a 150-pound person) can impair aerobic performance—especially in hot or humid environments.

Dehydration above 2% can reduce endurance capacity, coordination and even cognitive function, but this varies by person and temperature.

Resistance exercise is somewhat less sensitive to dehydration, but studies indicate that strength and power output also decline when we don’t consume enough fluids, particularly across multiple sets. Dehydration increases perceived exertion and can amplify fatigue, even when what we’re actually doing hasn’t changed.

Proper hydration also helps: 

Muscle endurance. Proper hydration can prevent cramps and keep your muscles performing at their peak.

Flexibility and speed. Water helps cushion your joints, which can affect speed and flexibility. Your mood. Your noggin needs water to function properly. Dehydration can also dampen your mood and cause irritability.

Breathing. When you breathe, your body uses fluids to humidify the oxygen, making it easier for your lungs to absorb.

How Much Do I Need to Drink

There is no single “right” volume that fits everyone, because sweat rates and sodium losses vary widely. The best way to determine how much fluid you lost during a workout is to weigh yourself before and after your session. But even this method can be questionable, as it depends on how much fluid you drink while exercising and how well your body regulates your temperature during a workout. Keep in mind,  you’ll lose more fluid during hotter days.

However, there are practical research-based guidelines.

Before exercise

You should pre-hydrate. Why? It will help you normalize your electrolyte and fluid levels, according to the ACSM. The organization also recommends that most people drink about 17 ounces (two cups) of fluid a few hours before working out. This allows your body to absorb the fluid and excrete any extra.

Drinking more may improve some endurance exercise in hot environments by increasing blood volume and reducing heart rate, according to one 2023 study.

During exercise

Your goal during exercise is to replenish what you’re losing while you sweat. If you sweat a lot, you need to drink more. For every pound of sweat you lose, you’ll need to consume a pint of water or other liquid to replace it. 

For endurance exercise, start drinking early and at frequent intervals to replace what you’re losing. For intense exercise lasting longer than one hour, you’ll want to consume drinks that include carbohydrates and electrolytes to delay fatigue. 

For endurance exercise, research shows most people benefit from about 5 to 12 ounces of fluid every 15–20 minutes of activity, adjusted for temperature and intensity. For exercise lasting longer than an hour, you may also need more than just water – carbohydrates and electrolytes can delay fatigue. 

After Exercise

Once your workout is done, replacing the fluids you’ve lost is key. Most of us lose about 2 quarts of fluid during an hour of moderate to intense exercise. However, endurance activities such as running and cycling can increase fluid loss to about 3 quarts. Again, heat and intensity will determine how much fluid volume you’ve lost that needs to be replaced.

For example, if you lost five pounds of water during a long run or an intense tennis match, you probably need 2 or more quarts of water to replace it. 

Hydration is more than just quenching your thirst – and it’s critical when you’re exercising for performance and/or health. Replenishing what you’ve used can reduce your risk of muscle cramps, fatigue, headaches, heart strain and even cognitive isues. But there isn’t a one-size-fits-all approach to rehydration; it’s highly individualized. If you sweat heavily, you may need to replenish fluids and electrolytes constantly while working out. Following the guidelines above can help, but listening to your own body can help you customize your approach, improve your performance and protect your health.