Hydration is one of the simplest ways to support better sports performance, yet it is often ignored until fatigue, cramps, dizziness, or a drop in concentration appears. Whether you are running, cycling, training in the gym, playing football, or taking part in longer endurance events, your body relies on fluid balance to regulate temperature, transport nutrients, maintain blood volume, and support normal muscle and nerve function.

Evidence from Susan M. Shirreffs’ review in Nutrition Bulletin shows that exercise induced dehydration can have a negative impact on performance and that restoring fluid balance after exercise is essential. The review also explains that while plain water is helpful, a properly formulated carbohydrate electrolyte sports drink may support performance even more effectively in some situations.

In simple terms, hydration is not just about drinking when you feel thirsty. It is about helping your body perform, recover, and stay safe during exercise.

Why hydration matters for athletic performance

When you exercise, your body produces heat. To cool itself, it sweats. That cooling process is vital, but it also means you lose fluid and electrolytes. According to the review, sweat rates can reach around 2 to 3 litres per hour in some situations, which means noticeable losses in body mass can happen surprisingly quickly during training or competition

Those losses matter because dehydration affects more than thirst. The review reports that body mass losses of around 3 to 4% can reduce strength, power, and high-intensity endurance, while losses of 2 to 7% can significantly reduce endurance performance, especially in hotter environments.

Hydration is only one part of the picture in hot conditions

When exercising in hot conditions, hydration is only one part of the performance picture. Evidence from the BASES expert statement suggests that heat can impair exercise performance even in relatively modest temperatures, depending on humidity, airflow, and exercise intensity. Athletes should aim to begin exercise well hydrated and avoid losing more than 2% of bodyweight through fluid loss, but they should also avoid over drinking, as this can increase the risk of hyponatraemia. Practical strategies such as heat acclimation, cold drinks, ice slurry, and pre-cooling may also help improve tolerance and performance in the heat when used appropriately.

What happens when you become dehydrated during sport

Even mild dehydration can start to affect how you feel and how you perform. As fluid levels fall, blood volume can decrease, body temperature can rise, and your heart may have to work harder to deliver oxygen and nutrients where they are needed. That can lead to earlier fatigue, poorer endurance, reduced concentration, and a greater sense of effort.

The evidence reviewed suggests that drinking during exercise can improve performance, provided the activity is long enough for the fluid to be emptied from the stomach and absorbed in the intestine.

Water or sports drinks: what is best?

For many shorter or lower intensity sessions, plain water is a sensible option. Drinking water is generally better than drinking nothing at all. However, for longer, harder, or hotter sessions, sports drinks can offer added benefits because they provide fluid, carbohydrate, and sodium in one convenient format.

The review explains that most mainstream sports drinks are built around three key ingredients: water, carbohydrate, and sodium. These ingredients matter because they can support fluid absorption, provide fuel during exercise, and help with recovery afterwards.

When water is usually enough

·        Your session lasts under about 60 minutes

·        The intensity is moderate rather than very high

·        Conditions are cool or temperate

·        You are not losing large amounts of sweat

When an electrolyte or sports drink may help more

·        Your training lasts longer than about 60 to 90 minutes

·        You are exercising in the heat

·        You sweat heavily

·        You have more than one demanding session in a day

·        You need both hydration and carbohydrate support during exercise

How to hydrate before, during and after exercise

Before exercise, the goal is to start well hydrated. During exercise, the aim is to reduce excessive fluid loss without over drinking. After exercise, the goal is to replace both the water and the sodium lost in sweat so recovery is more complete.

Before exercise

Try to begin exercise in a well hydrated state. Practical signs such as urine colour and how thirsty you feel can be useful everyday checks.

During exercise

Drink enough to support performance and limit large fluid losses, but avoid drinking so much that you gain weight during exercise. The International Olympic Committee guidance quoted in the review recommends limiting dehydration to less than about 2% of body mass during exercise and including sodium when sweat losses are high, especially if exercise lasts more than about two hours.

After exercise

Recovery hydration is often where athletes make the biggest mistake. Sweat is not just water. It also contains sodium. The review states that until electrolytes, particularly sodium, are replaced after exercise, water balance will not be effectively restored and maintained. That is why rehydration after exercise should include both fluid and salts, not plain water alone when sweat losses have been high.

The review also notes that the amount you drink after exercise should be greater than the net volume of sweat lost, because the body will continue to lose some fluid through urine.

Why sodium matters

Sodium is the main electrolyte lost in sweat and the most important one to consider in hydration drinks. Sodium helps stimulate water and sugar uptake in the small intestine, supports extracellular fluid balance, and helps maintain the drive to drink. In practical terms, that makes sodium especially important for longer sessions, hotter conditions, and post-exercise rehydration.

Common hydration mistakes to avoid

·        Waiting until you feel very thirsty before you drink

·        Using only plain water after a long, sweaty session

·        Drinking too much fluid during very prolonged exercise

·        Following the same hydration plan regardless of weather, duration, or sweat rate

A simple takeaway

Hydration supports temperature control, circulation, muscle function, endurance, and recovery. Dehydration can reduce strength, power, and performance, especially during longer sessions and in hot conditions. For shorter sessions, water is often enough. For longer, harder, or hotter sessions, drinks containing sodium and carbohydrate can be more effective. After exercise, replacing both fluid and sodium is a key part of proper recovery.

Frequently asked questions

Does dehydration really affect sports performance?

Yes. The evidence summarised in the review shows that dehydration can impair several aspects of exercise performance, especially endurance performance and high-intensity efforts.

Are sports drinks necessary for everyone?

No. Plain water is often enough for shorter or lighter sessions. Sports drinks are more useful during longer, more intense, or hotter exercise where fluid, sodium, and carbohydrate needs are greater.

Why is sodium important after exercise?

Because sweat contains sodium as well as water. Replacing water alone may not restore fluid balance effectively after heavy sweating.

How can I make hydration more personal?

Tracking your sweat rate can help. Weigh yourself before and after training, note how much you drank, and use the difference to estimate how much fluid you typically lose.

Sources

1. Shirreffs, S. M. Hydration in sport and exercise: water, sports drinks and other drinks. Nutrition Bulletin, 34, 374 to 379. Read the full review. 

2. Webber Nutrition. Hydration Effects on Sports Performance

3. The BASES Expert Statement on Interventions for Improving Performance in the Heat