This is general information, not medical advice or a training plan. Needs vary with the person, the activity and the weather. Check with a doctor before starting or increasing strenuous exercise, particularly if you have a heart, lung, kidney or other medical condition, or take medicine that affects fluids or heart rate.
Why exercise changes fluid needs
When you are active, your body warms up, and it cools itself largely by sweating. Sweat is mostly water, with some salts such as sodium. If you lose a lot of sweat and do not replace it, you can end up with less fluid than your body would like. Even modest shortfalls are associated with feeling more tired and finding effort harder, although how much this matters differs between people and activities.
For a gentle walk or a short stretching session, a normal day of drinking and eating usually covers it. Fluid planning matters more as sessions get longer, harder or hotter.
Before activity
A sensible aim is to start reasonably hydrated rather than trying to catch up afterward. A few common ideas:
- Drink regularly through the day, so you are not starting a workout already thirsty.
- Have a glass of water, or a drink and a small meal, in the hour or two before longer sessions.
- Notice your urine color. Pale yellow is commonly seen when fluid intake is adequate.
- Avoid drinking a very large amount right before you start, which can leave you uncomfortable.
If caffeine affects your stomach or heart rate, be mindful of coffee or pre-workout products before exercise. Check labels, and ask a professional if you are unsure.
During activity
For shorter sessions, usually under an hour at moderate effort, many people do well with water and sipping when thirsty. A few points:
- Drinking to thirst is a reasonable guide for most healthy people in ordinary exercise.
- Small, regular sips tend to be more comfortable than large gulps.
- In heat, take breaks in shade, wear light clothing and slow down if you feel unwell.
- Forcing fluids beyond thirst is not recommended. Drinking far more than you lose can dilute blood sodium, which can be dangerous and is a particular concern in long endurance events.
Your warm-up routine and an easy start can also help you gauge how you feel before things get hard.
After activity
Afterward, you can replace fluid by drinking over the next few hours, along with your normal meal. Foods that contain fluid, such as fruit, vegetables, yogurt or soup, add to the total, as described in our piece on hydrating foods. Milk is a popular choice after workouts for some people, and it provides fluid along with other nutrients.
If you have sweated a lot, your body also lost salt, which a regular meal typically helps replace. People who have been advised to limit sodium for health reasons should ask their clinician before adding extra salt or salty drinks.
Heat, humidity and altitude
Hot, humid conditions make sweating less effective at cooling, so the body may feel more strain at the same effort. Altitude and cold dry air can also increase fluid loss through breathing. Some practical habits:
- Exercise in cooler parts of the day when possible.
- Allow time to adjust if you are new to a hot climate.
- Wear breathable clothing and a hat outdoors.
- Slow down or stop if you feel dizzy, nauseous, confused or unusually weak.
More everyday precautions are covered under hot weather safety. Know the signs of dehydration, and treat confusion, fainting or a very high body temperature as an emergency.
Sports drinks, electrolytes and plain water
Plain water is generally sufficient for most casual workouts. Sports drinks supply fluid, sugar and salts, which some people find helpful during prolonged exercise, such as long runs or rides lasting more than an hour or so, or in very hot conditions. They also add sugar and calories, so they are not a good everyday beverage for most people. Check the nutrition facts label if you use them, and keep in mind that products vary.
Alcohol is not a helpful recovery drink, as it tends to increase fluid loss.
When to ask a professional
Longer or intense efforts, such as a marathon, a multi-hour hike or hard training in heat, call for more individual planning. Because sweat rates and salt losses vary widely, there is no single recommendation that works for everyone. A doctor, sports medicine clinician or registered dietitian can help, especially if you:
- Have a medical condition, such as heart, kidney or blood pressure issues, or diabetes
- Take medicines such as diuretics
- Are pregnant, older, or returning after illness
- Regularly feel faint, cramp badly or get headaches during exercise
If you are restarting exercise after a long break, build up gradually and be gentle with yourself. Rest days also matter, and drinking normally on days off helps your body keep its balance.
Keep it simple
Most people can keep their hydration on track with a few habits: start a session fairly well hydrated, sip when thirsty, take extra care in heat, and eat and drink normally afterward. If you are ever unsure, or things feel wrong during activity, stop and rest.