Hydration for Athletes: Before, During, After

Quick answer

Position stands advise starting exercise well hydrated, drinking during exercise to keep fluid losses under about 2% of body mass, and replacing losses afterward. Sweat rates differ several-fold, from about 0.5 to 2 liters an hour, so both major stands recommend measuring your own sweat rate.^1,2,3

Key facts

The ACSM position stand sets the goal of drinking during exercise as avoiding a water deficit of more than 2% of body mass, and says sweat rate can be estimated by weighing before and after exercise.¹
The National Athletic Trainers' Association stand says both too little fluid and too much can harm performance and health, and recommends quantifying sweat rates.²
Athletes typically sweat about 0.5 to 2 liters an hour, so needs differ widely from person to person.³
The U.S. adequate intake of total water, from drinks and food together, is 3.7 liters a day for men and 2.7 liters for women aged 19 to 30, and about 81% of it comes from drinks.⁴
NIH notes that athletes in endurance activity lasting over an hour, or in extreme heat or at altitude, might need to replace lost fluids and electrolytes.⁵

A hydration for athletes chart: before, during and after

What the ACSM and NATA position stands say about drinking around exercise^1,2
When	What the stands say	Source
Before	Start exercise well hydrated. If you need extra fluid, begin at least several hours ahead, so the body can absorb it and urine output can return to normal.	ACSM 2007
During	Drink enough to avoid losing more than 2% of body mass to a water deficit. Match drinking to your own sweat rate, not a fixed amount.	ACSM 2007, NATA 2017
During, drink choice	Drinks with electrolytes and carbohydrate can beat water in some situations.	ACSM 2007
After	Replace the fluid and electrolyte deficit. How aggressive to be depends on how fast you need to rehydrate and how large the deficit is.	ACSM 2007
Throughout	Aim for enough, not too much. Overdrinking carries its own risks.	NATA 2017

That table is the chart. The two stands agree on the shape of the advice and decline to give one number, because sweat rates and sweat sodium vary so widely between people.^1,2,3

How to work out your sweat rate

The ACSM stand says individual sweat rates can be estimated by measuring body weight before and after exercise. Weigh yourself before and after the session and note how much you drank. Weight lost plus fluid drunk is roughly what you sweated out.¹

A worked example with invented numbers¹
Step	Example
Weight before	70.0 kg
Weight after one hour	69.0 kg, so 1.0 kg lost
Fluid drunk during the hour	0.5 liter
Sweat lost, roughly	1.5 liters in the hour
Body mass lost	1.0 kg, about 1.4% of body mass. The 2% line for 70 kg is 1.4 kg

Athletes typically sweat about 0.5 to 2 liters an hour, and whole-body sweat holds roughly 230 to 1,600 mg of sodium per liter, so losses differ several-fold from person to person.³

Hydration recommendations for athletes: the details

Position stands advise starting exercise well hydrated. When extra drinking is needed, it should begin at least several hours before, so the body can absorb the fluid and urine output can settle back to normal.¹

During exercise, drinks with electrolytes and carbohydrate can do better than water alone in some situations. Because sweat rates and sweat sodium vary so much, the advice is a plan matched to your own losses rather than a set amount.^1,2

After exercise the goal is to replace the fluid and sodium lost. In a lab study, people who drank 1.5 times the weight they had lost in sweat passed less urine over the next 6 hours the more sodium the drink contained.^1,6

Water you drink starts to reach the blood within about 5 minutes and is fully absorbed in roughly 75 to 120 minutes.⁷

NIH notes that athletes in endurance activities lasting more than an hour, or in very hot conditions or at high altitude, might need to replace lost fluids and electrolytes.⁵

The daily baseline: how much water in a day

Training hydration sits on top of an ordinary day. The National Academies set an adequate intake of total water, counting drinking water, other drinks and the water in food, at 3.7 liters for men and 2.7 liters for women aged 19 to 30. About 81% of intake came from drinks and the rest from food. No upper limit was set, and the report notes the kidneys of a healthy person can clear roughly 0.7 liter an hour.⁴

The adequate intake is set from what healthy Americans typically drink and eat, so it describes the general population, not athletes in particular. It does not replace a plan built around your own sweat losses.^1,4

Checking hydration: urine color and thirst

MedlinePlus says light or very pale yellow urine means you are getting enough fluid. A systematic review of 10 studies found urine color tracked other hydration measures with correlations from 0.40 to 0.93 and was good at flagging low hydration, but the match was weaker in adults over 60.^8,9

Thirst is the other signal, and the sources do not agree on how far to trust it. MedlinePlus advises drinking before, during and after a workout even if you do not feel thirsty. A 2017 review tied drinking beyond thirst to the main hazard from overdrinking, which we describe in the safety section below. Both ACSM and NATA point to knowing your own losses and planning to them.^1,2,8,10

Some people lose their sense of thirst as they age, so they may not drink enough.¹¹

Best hydration for athletes: water or a sports drink

For less intense workouts MedlinePlus says water is your best choice, and for sessions of a couple of hours it suggests a sports drink, which replaces salts and minerals as well as fluid. ACSM's wording is similar: drinks with electrolytes and carbohydrate can beat water alone in certain circumstances. Our homemade electrolyte drink guide gives a recipe, and the electrolytes page covers sodium amounts.^1,8

Stop and ask a doctor if

Heat and sweat bring real risks. MedlinePlus describes heat cramps, heat exhaustion and heatstroke. Early signs of heat exhaustion include heavy sweating, tiredness, thirst and muscle cramps, and later signs include weakness, dizziness, headache, nausea and dark urine. Call emergency services for signs of heatstroke, such as a fever over 104°F, hot dry skin, confusion, a seizure or loss of consciousness.⁸

Contact a provider if signs of heat exhaustion do not get better an hour after you are out of the heat and drinking fluids. Children, older adults, people taking certain medicines and people with heart disease have a higher risk of heat illness.⁸
You are tempted to take salt tablets. MedlinePlus advises against them because they can raise the risk of dehydration. Ask a doctor about sodium if you sweat heavily for hours.⁸
You drink a lot during long events. Overdrinking, beyond thirst, is the most common reason blood sodium falls in exercisers, and in 488 Boston Marathon finishers 13% tested low. MedlinePlus says a large drop in blood sodium is an emergency.^10,12,13
You have heart disease, take water pills or other medicines, or have a medical reason to limit fluids or salt. Ask your doctor how much to drink, because the general amounts above may not apply.^8,13

Questions people ask

What is a hydration for athletes chart?

The table on this page sets out the ACSM and NATA advice by phase: start well hydrated, drink during exercise to avoid losing more than 2% of body mass, then replace the deficit afterward.^1,2

Is there a hydration for athletes pdf or infographic?

We have not built a printable infographic. You can print the table here, or read the NATA position statement, which lists a free copy on PubMed Central.²

Which hydration for athletes studies are on PubMed?

The main ones are the ACSM position stand on exercise and fluid replacement (2007), the NATA position statement on fluid replacement (2017), a systematic review of urine color as a hydration measure (2021) and a review of the risks of overdrinking during exercise (2017).^1,2,9,10

What is the best hydration for athletes?

Water for shorter and easier sessions. For about two hours or more, or heavy sweating, MedlinePlus suggests a sports drink, and ACSM says drinks with electrolytes and carbohydrate can beat water in some situations.^1,8

What are the hydration recommendations for athletes in one line?

Start hydrated, avoid losing more than 2% of body mass during exercise, replace losses afterward, and tailor the amounts to your own sweat rate.^1,2

Can athletes drink too much water?

Yes. Overdrinking beyond thirst is the most common reason blood sodium falls during exercise, and 13% of 488 Boston Marathon finishers tested low. A large drop is an emergency, so ask a doctor about a drinking plan for long events.^10,12,13

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Sources

This page is information, not medical advice. Talk to your doctor or pharmacist about your own situation.