Hydration and Exercise

Why water is fuel too

When people think about fuelling for sport, they usually picture food. But there is another fuel that is just as important and easy to forget: water. Your body is roughly 60 percent water, and that water does an astonishing amount of work, especially when you exercise. Get your hydration right, and you feel strong and focused. Get it wrong, and your performance drops long before you even feel thirsty.

This lesson explains what water actually does in your body, how sweating keeps you safe, how to spot dehydration, and how to drink smartly around sport.

What water does in your body

Water is involved in almost everything your body does. During exercise, three of its jobs really stand out:

• Transport. Your blood is mostly water. It carries oxygen and nutrients to your working muscles and removes waste products like carbon dioxide. When you are well hydrated, this delivery system runs smoothly.
• Cooling. Exercise generates a lot of heat. Water, through sweat, is your body's main cooling system.
• Cushioning and function. Water lubricates your joints and is essential for countless chemical reactions, including the ones that release energy in your muscles.

Because water touches so many systems, even a small shortage affects the whole body. You can see how oxygen delivery connects to fitness in How the Heart and Lungs Work in Exercise.

The science of sweating

When you exercise, your muscles produce heat, a lot of it. If that heat built up unchecked, your core temperature would climb to dangerous levels. So your body cools itself, mainly by sweating.

Here is the clever part. Sweat sitting on your skin does not cool you much by itself. The cooling comes from evaporation. Turning liquid sweat into vapour takes energy, and that energy comes as heat drawn from your skin. As the sweat evaporates, it carries heat away, lowering your skin and body temperature. This is the same physics that makes you feel cold stepping out of a swimming pool.

This explains a few real-world facts. On a humid day, the air is already full of water vapour, so sweat evaporates slowly and you feel hotter and stickier. And every drop of sweat you lose is water leaving your body, water that must be replaced, or dehydration sets in.

What dehydration does to performance

Dehydration means your body has lost more water than it has taken in. You might assume it takes a lot to matter, but the opposite is true. Research suggests that losing even around 2 percent of your body weight in water can measurably reduce endurance, strength, and concentration.

That is striking, because by the time you feel genuinely thirsty, you may already be mildly dehydrated. Thirst is a useful signal, but it is a slightly late one. The effects of dehydration include:

• Feeling tired and finding exercise harder than usual.
• Slower, weaker muscles and reduced endurance.
• Poorer focus and slower decisions, which matters in skill sports.
• Headache, dizziness, and cramping as it worsens.

In hot conditions, severe dehydration combined with overheating can lead to heat illness, which is a medical emergency. This is why coaches take hydration and heat seriously.

Spotting the warning signs

You do not need fancy equipment to monitor your hydration. A few simple checks work well:

Check	Well hydrated	Watch out
Thirst	Not very thirsty	Strong, persistent thirst
Urine colour	Pale, like light straw	Dark yellow, small amount
Energy	Steady	Unusually tired or sluggish
Head	Clear	Headache, dizziness

The urine colour check is one of the most reliable everyday guides: pale and plentiful is a good sign, while dark and scant suggests you need more fluid.

How to drink smart: before, during, and after

Good hydration is not about gulping a huge amount at one moment. It is about steady drinking spread across the day and around your activity.

Before exercise. Arrive already hydrated. Drink normally through the day and have some water in the hour or two beforehand, so you start topped up rather than playing catch-up.

During exercise. Take regular sips rather than waiting until you are desperate. For most sessions under about an hour, plain water is perfect. Longer or very intense sessions, particularly in heat, may benefit from a drink containing electrolytes, the mineral salts (like sodium) you lose in sweat that help your body hold onto fluid and keep muscles and nerves working.

After exercise. Rehydrate to replace what you lost. A simple habit is to keep drinking water with your post-exercise meal or snack. Hydration teams up with good food to help you recover, see Nutrition for Young Athletes for the bigger picture.

Sports drinks, electrolytes, and common myths

Sports drinks contain water, sugar (for energy), and electrolytes. They have their place during long, sweaty endurance efforts, but for everyday exercise they are usually unnecessary, and the extra sugar adds up. For most young athletes, water is the default choice.

A couple of myths are worth clearing up. First, you cannot rely on thirst alone, since it lags behind your actual needs, especially during intense exercise. Second, more is not always better: drinking enormous amounts of plain water very fast can dangerously dilute your body's salts, a rare but serious condition called hyponatraemia. The goal is balance, replace roughly what you sweat out, no more and no less.

Quick recap

• Water powers transport, cooling, and joint function, so even mild shortage hurts performance.
• Sweating cools you by evaporation, drawing heat from your skin; humidity makes it less effective.
• Losing even a small percentage of body water reduces strength, endurance, and focus.
• Watch for thirst, dark urine, tiredness, and headache as early dehydration signs.
• Drink before, during, and after exercise; plain water suits most activity, with electrolytes for long, hot sessions.

Make hydration a habit, not an afterthought. A water bottle by your side and a few regular sips can be the difference between a great session and a sluggish one.