Hydration and Exercise: How Much to Drink Before, During and After Training

Good hydration and exercise go together when you start training well hydrated, drink during longer or hotter sessions to avoid losing more than about 2% of your body weight, and replace what you lost afterwards. The simplest way to know how much you need is a sweat test: weigh yourself before and after training. Overdrinking is also risky, so drink to a plan, not to a fixed number of litres.

“Drink three litres a day.” “Drink before you feel thirsty.” “Drink a gallon to build muscle.” Hydration advice is everywhere, often contradictory, and rarely tailored to the person reading it. A 55 kg woman lifting weights in an air-conditioned gym and an 85 kg man playing football outdoors in August are not going to need the same amount of water.

This guide shows you how to work out your own needs, how dehydration actually affects strength and endurance, when sports drinks make sense, and how to avoid the less-known danger of drinking too much.

How Dehydration Affects Performance

When you sweat more than you drink, your blood volume falls, your heart has to work harder and your body struggles to get rid of heat. A comprehensive review of the dehydration literature concluded that losing about 2% or more of body weight through dehydration is a threshold for impaired endurance performance. For strength and power, the review found smaller, less consistent effects, and the impact on thinking appears small and mostly related to discomfort.

In practical terms, a 70 kg person who loses 1.4 kg of sweat during a long run or football match without drinking is likely to see their endurance suffer. The same person doing a 45-minute strength session in an air-conditioned gym is unlikely to lose that much, and even a small deficit will affect their lifting much less.

Find Your Sweat Rate in Four Steps

The American College of Sports Medicine recommends customised fluid plans because sweat rates vary so much between people, and suggests estimating sweat rate by weighing before and after exercise. Here is how:

1. Use the toilet, then weigh yourself in minimal clothing just before training.
2. Train as normal and note how much you drink in millilitres.
3. After training, towel off and weigh yourself again in the same clothing.
4. Calculate: weight lost in kilograms plus fluid drunk in litres equals sweat loss in litres. Divide by the hours of training for your hourly sweat rate.

Repeat the test in different conditions, such as indoor and outdoor, summer and winter, because your sweat rate changes with heat, humidity and intensity.

Before, During and After Training

After exercise, a common practical guideline is to drink roughly 1.25–1.5 litres for every kilogram of body weight lost, spread over the following hours, because you keep losing some fluid through urine as you rehydrate. Eating a meal at the same time helps, as food provides sodium that helps your body hold on to the fluid.

If You Are New to Training

Beginners often worry about hydration more than they need to, carrying litres of water into a 40-minute gym session. If you are just starting out, keep hydration and exercise simple: arrive having drunk normally through the day, take a bottle with you, sip when you feel like it, and drink a glass or two with your next meal. Save sweat tests and electrolytes for when your sessions become longer, hotter or more intense. Your attention is better spent on learning good technique and turning up consistently.

Urine Colour: A Simple Daily Check

A classic study found that urine colour correlates well with laboratory measures of hydration such as urine specific gravity. It is not perfect, but it is free and quick. Pale straw-coloured urine usually suggests good hydration, while dark yellow or amber urine suggests you need more fluid. Note that some vitamins, especially B vitamins, can turn urine bright yellow regardless of hydration, and the first urine of the morning is often darker.

Electrolytes and Sports Drinks

Sweat contains sodium and smaller amounts of potassium and other minerals. The ACSM position stand notes that drinks containing electrolytes and carbohydrate can provide benefits over water alone in certain situations. Those situations usually include:

• Sessions longer than 60–90 minutes.
• Training in heat and humidity, common across the Gulf for much of the year.
• Very heavy sweaters or “salty sweaters” who see white salt marks on clothing.
• Multiple sessions in one day or tournaments.

For a typical one-hour gym session, water and a normal meal afterwards are enough. Sugary sports drinks add calories you may not need if your goal is fat loss.

The Hidden Risk: Drinking Too Much

The National Athletic Trainers’ Association position statement warns that both underdrinking and overdrinking can harm performance and health. Drinking far more than you sweat, especially plain water during long events, can dilute blood sodium, a condition called exercise-associated hyponatraemia. Symptoms include headache, nausea, confusion and swelling, and severe cases are a medical emergency.

The warning sign is simple: if you weigh more after exercise than before, you drank too much. That is why your sweat test is useful in both directions. Drink to replace losses, not to “flush” your system.

Hydration in the Heat

Training in hot climates raises sweat rates and the risk of heat illness. Schedule outdoor sessions for early morning or evening, acclimatise gradually over one to two weeks, wear light clothing and take breaks in the shade. Our guide on training in hot weather covers heat illness warning signs in detail. If you fast during Ramadan, the challenge changes completely; see our guide to hydration during Ramadan.

Dehydration or Heat Illness? Know the Difference

Dehydration and heat illness often occur together, but heat illness is more dangerous. Stop exercising, move to a cool place and drink if you notice heavy sweating, cold and clammy skin, dizziness, nausea, headache or muscle cramps; these can signal heat exhaustion. Confusion, collapse, very hot skin, or a person who stops making sense are signs of possible heat stroke, a medical emergency that needs immediate cooling and urgent medical help. Hydration alone does not prevent heat illness; heat, intensity and acclimatisation all matter.

Hydration and Exercise for Women

The principles are the same for women, but a few details are worth knowing. Body weight can shift by a kilo or more across the menstrual cycle because of fluid retention, so a sweat test is more accurate when you compare sessions at a similar point in your cycle. Women are often smaller than men and may sweat less in absolute terms, so copying a male training partner’s drinking plan can lead to overdrinking. During pregnancy and breastfeeding, fluid needs rise, and heat tolerance can change, so follow your doctor’s guidance on hydration and exercise during these stages.

Older Adults and Teenagers

With age, the sense of thirst tends to become less sensitive, so older adults may not feel thirsty even when they need fluid. Some medications, such as diuretics, also affect fluid balance. A drinking routine with meals and around exercise is more reliable than waiting for thirst. Teenagers and children, on the other hand, are often so absorbed in play or sport that they forget to drink, and they can be more vulnerable in heat. Supervised water breaks during outdoor activity in hot weather are a simple safeguard.

Building a Daily Hydration Routine

Most people do not need complex calculations for everyday life. A few simple habits cover the basics and leave sweat testing for long or hot sessions:

• Keep a refillable bottle on your desk and in your gym bag.
• Drink a glass of water with each meal and when you wake up.
• Link drinking to existing habits, such as after each prayer or each work meeting.
• Eat water-rich foods such as fruit, vegetables, soups and yogurt.
• Check your urine colour in the afternoon rather than first thing in the morning.

These habits take care of daily needs, so your hydration and exercise plan only has to deal with what you lose during training.

Hydration, Muscle and Recovery

Muscle is roughly three-quarters water, and good hydration supports normal training quality and recovery. That does not mean extra water builds extra muscle. Drinking beyond your needs simply leads to more trips to the toilet. For muscle growth, the priorities remain progressive training, enough protein and good sleep; see our guide on sleep and muscle recovery. Hydration supports those processes; it does not replace them.

Different Sessions, Different Needs

Hydration by Type of Training

What to Keep in Your Gym Bag

A little preparation removes most hydration problems: a large refillable bottle, a small pack of electrolyte tablets or powder for hot or long days, a salty snack for after long sessions, and a towel to wipe off sweat before your post-training weigh-in. If you train outdoors, a bottle that keeps water cold makes it much more likely you will actually drink.

Common Hydration Myths

Hydration and Exercise: Checklist

Where MOVIN Fits

Hydration is easier when it is part of a plan rather than an afterthought. In MOVIN, your coach can schedule sessions around the heat, include hydration in your nutrition plan, and use your logged sessions and connected device data to adjust guidance as conditions change. The app’s daily water intake calculator gives you a personal starting point that you can refine with your own sweat tests.

Hydration and Exercise: Frequently Asked Questions