Sports Hydration: How Much Water to Drink Before, During and After

Dehydration, even at mild levels (as little as a 2% loss of body weight), can sharply reduce athletic performance, cutting strength, endurance and cognitive function by up to 20%. Staying properly hydrated is therefore a cornerstone for any athlete who wants to get the most out of their physical and mental capacity during training or competition.

Why water matters for athletic performance

Water is not just a liquid to quench thirst. It is an essential component involved in vital body functions, especially during exercise. It acts as a regulator of body temperature, dissipating the heat generated by muscle activity through sweat.

It also helps carry nutrients and oxygen to the muscles, lubricates the joints and helps remove metabolic waste products. Insufficient hydration compromises all of these functions, leading to lower performance and a higher risk of injury.

Signs and consequences of dehydration

Recognizing the first signs of dehydration is crucial to acting in time. Thirst is the most obvious indicator, but it often appears when some level of dehydration has already set in. Other symptoms include early fatigue, muscle cramps, dizziness, headache and a noticeable drop in urine output, with urine that is also darker than usual.

• Premature fatigue: The heart works harder to pump blood, increasing the feeling of tiredness.
• Muscle cramps: Imbalance of electrolytes such as sodium, potassium and magnesium, which are essential for muscle function.
• Reduced strength and endurance: Lower blood volume and poorer oxygen delivery to the muscles.
• Dizziness and confusion: The brain is very sensitive to lack of hydration, which affects concentration and coordination.
• Rising body temperature: A reduced ability to sweat and dissipate heat, leading to overheating.

Key factors that shape your fluid needs

The amount of fluid you need during exercise is not a universal figure. It varies significantly depending on multiple individual and environmental factors. Knowing them will help you personalize your strategy.

• Exercise intensity and duration: The higher the intensity and the longer the session, the more you sweat and, therefore, the more fluid you need.
• Ambient temperature and humidity: Heat and humidity raise the sweat rate to regulate body temperature.
• Level of heat acclimatization: Acclimatized athletes sweat more efficiently and in greater volume, but they also need to replace more fluid.
• Individual sweat rate: Everyone sweats differently. Some people are "heavy sweaters" and others not so much.
• Type of clothing: Clothing that does not allow adequate breathability can increase fluid loss.

You can use the PesaFit water calculator to estimate your baseline daily needs, and then adjust for exercise from there.

How much to drink before, during and after: the ACSM protocol

The American College of Sports Medicine (2007 position stand) gives starting guidelines for anyone who hasn't done the sweat test yet. Adjust them afterward with your own number.

• Before (2-3 h prior): 5-7 ml/kg, which is 400-560 ml for 80 kg.
• Before (10-20 min prior): an extra 200-300 ml.
• During (sessions longer than 1 h): 150-250 ml every 15-20 min.
• After: 1.25-1.5 L for every kg lost on the scale after the session.

How to calculate your hydration needs during exercise

The most accurate method for determining how much fluid you should drink during exercise is the sweat rate test. This test lets you quantify how much fluid you lose per hour under your usual training conditions.

1. Weigh yourself before training: Do it naked and after urinating to get the most accurate weight possible (Starting Weight).
2. Train as usual: Do a 60-minute exercise session at your usual intensity and in your usual environment. Drink a controlled amount of fluid during the workout (record how much).
3. Weigh yourself after training: Again, naked and after urinating (Final Weight).
4. Measure the fluid you drank: Write down the exact amount of fluid you drank during exercise in milliliters (Fluid Intake).

The formula to calculate your sweat rate is as follows:

Since 1 gram of body weight lost is roughly equivalent to 1 ml of fluid, this formula gives you a direct estimate of your sweat loss. If your session is longer or shorter, adjust the duration in the formula.

This result (1.3 liters/hour in the example) is the amount of fluid you should aim to replace for every hour of exercise in similar conditions to avoid significant dehydration. Split this amount into frequent drinks of 150-250 ml every 15-20 minutes.

Hydration strategies by type of training

Your hydration strategy should be adapted to the type, intensity and duration of your physical activity. Not every session requires the same attention.

• Strength training (< 60 min): Water is generally enough. Drink 200-300 ml before starting and small sips (100-150 ml) between sets or exercises, for a total of 500-700 ml per hour.
• Moderate-to-intense cardio (60-90 min): In addition to water, if you sweat a lot or the environment is warm, you can consider a drink with electrolytes to replace lost sodium and prevent cramps. Aim for 600-1000 ml per hour.
• Long endurance (> 90 min): In activities such as marathons or long-distance cycling, isotonic drinks are key. They provide electrolytes and carbohydrates (30-60 g/hour) to maintain blood glucose levels and delay fatigue. Intake can be 800-1200 ml per hour, depending on your sweat rate.
• HIIT/CrossFit training: Because of the high intensity and short rests, hydration should be constant, with frequent sips of water. In very long sessions or with heavy sweating, electrolytes can be beneficial for recovery and cramp prevention.

Sports drinks and electrolytes: when are they necessary?

Water is the foundation of hydration, but in certain circumstances, sports drinks and electrolyte supplementation offer significant advantages. These drinks are designed to replace not only fluids but also the key electrolytes (sodium, potassium, magnesium, calcium) and carbohydrates lost through sweat.

• Exercise duration > 60-90 minutes: In prolonged activities, the risk of electrolyte imbalance and muscle glycogen depletion is higher.
• High sweat rate: If you are a "heavy sweater", you lose more sodium and other minerals, making electrolytes more necessary.
• Hot or humid weather: These conditions increase sweating and the need to replace electrolytes.
• Preventing cramps: An electrolyte imbalance, especially of sodium and magnesium, is a common cause of cramps.

Sports drinks should contain between 6% and 8% carbohydrates for optimal absorption and a sodium concentration of 400-800 mg per liter. For very long workouts, some may include protein to aid muscle recovery.

If you prefer to make it at home, a simple isotonic drink takes 1 L of water, 30 g of sugar, 1 g of salt and the juice of half a lemon. It provides about 400 mg of sodium per liter, within the recommended range.

Monitoring and adjusting your hydration plan

Hydration is a dynamic process. What works one day may not be optimal the next, because of changes in weather, training intensity or your physiological state. Constant monitoring will let you adjust your plan.

• Urine color: A simple indicator. Light yellow or almost clear urine indicates good hydration; dark yellow suggests dehydration.
• Body weight: Weigh yourself before and after exercise. A weight loss of more than 2% indicates significant dehydration that should be corrected.
• Feeling of thirst: Although it is a late indicator, it should not be ignored. If you are thirsty, you already need to drink.
• Performance: An unexplained drop in your performance (early fatigue, lower power) can be a sign of insufficient hydration.

Using a sports watch or heart rate monitor can help you track the duration and intensity of your exercise, which directly affects how much you sweat and, therefore, your fluid needs. In addition, our heart rate calculator lets you define training zones to optimize your effort and adjust your hydration strategy.

Frequently asked questions

Is it bad to drink too much water during exercise?

Yes, drinking excess water without replacing electrolytes can lead to hyponatremia (low blood sodium levels), a dangerous condition that causes bloating, nausea, confusion and even seizures. It is essential to drink to thirst and according to guidelines for replacing fluids and electrolytes, especially in very long endurance events.

What temperature should the water be when drinking during exercise?

Cool water, between 10 and 15 °C, is recommended. At this temperature, the body absorbs it more quickly and it helps cool the body, which is beneficial for thermoregulation and comfort when exercising in warm environments.

Are energy drinks good for hydrating during exercise?

No, energy drinks are not formulated for sports hydration. They tend to be high in sugar and caffeine, which can be diuretic and cause gastrointestinal discomfort. They are different from isotonic or sports drinks, which are designed with a specific balance of carbohydrates and electrolytes for fluid and energy replacement.

How do I know if I'm heat acclimatized enough to train safely?

Heat acclimatization is a physiological process that takes 7 to 14 days of gradual exposure to a warm environment. Signs of acclimatization include a lower heart rate at the same intensity, a lower core body temperature, an earlier onset and higher rate of sweating, and a lower sodium concentration in sweat. If you are not acclimatized, reduce the intensity and duration of your sessions in the heat.