Hydration and sports: the complete guide

Updated: September 10, 2026

You spend time calculating your protein intake, picking the right program, making sure you never skip a session. But are you drinking enough water? Spoiler alert: probably not. And it's a bigger deal than you might think, because even mild dehydration can wreck your performance and recovery, no matter how solid your training or diet is.

Why water matters just as much as your macros

Your body is roughly 60% water. Your muscles? Closer to 75%. Water isn't some minor detail — it's involved in almost every function that lets you perform at your best.

Nutrient transport: blood, which is 90% water, carries glucose, amino acids, and oxygen to your muscles.
Thermoregulation: you release heat produced during exercise through sweat. Without enough water, your body overheats faster and your performance drops.
Joint lubrication: synovial fluid protects your joints during repetitive movements.
Waste removal: your kidneys and liver need water to flush out metabolic byproducts created during exercise.

Bottom line: you can have the best program and perfectly dialed-in macros, but if you're dehydrated, part of that effort goes to waste.

What actually happens when you're dehydrated

Studies on the topic are pretty clear: losing just 2% of your body weight in water is enough to noticeably hurt your performance. For someone weighing 165 lbs, that's barely 1.5 liters of unreplaced sweat.

Strength and endurance drop: your ability to sustain effort falls by 10 to 20% once you hit 2% dehydration.
Heart rate spikes: your heart has to work harder to compensate for reduced blood volume, so you tire faster for the same effort.
Higher risk of cramps and injuries: less hydrated muscles are less elastic and more prone to strains.
Reduced focus: dehydration also affects your brain, which impacts your technique and alertness during exercise.

And here's a classic trap: hunger is often mistaken for thirst. If you feel a little hungry 30 minutes after your workout even though you just ate, try a big glass of water before reaching for more food.

How much to drink, in practice

Daily, outside of workouts

The general recommendation is around 30 to 35 ml per kilogram of body weight (roughly half an ounce per pound). For someone weighing 154 lbs, that's about 2.1 to 2.4 liters a day, including water from food (soup, fruits, veggies).

During exercise

Here, you need to adjust based on duration and intensity:

Sessions under 45 minutes: a bit of water is enough — no need to chug liters at every break.
Sessions of 45 to 90 minutes: aim for 500 to 750 ml per hour of exercise, sipped regularly rather than gulped all at once.
Sessions over 90 minutes, or intense heat: at this point, water alone isn't enough — you need to think about electrolytes too (more on that below).

A simple trick to find out your sweat rate

Weigh yourself naked before and after a one-hour session, without eating or drinking in between. Each pound lost roughly equals 16 oz of sweat (or each kilo lost equals about 1 liter). If you lose 1.75 lbs over an hour of running, you know you need to replace about that much water during similar workouts going forward.

Before, during, after: getting the timing right

2 to 3 hours before training: drink 400 to 600 ml so you show up hydrated without feeling bloated.
During: take small, regular sips every 15-20 minutes instead of gulping a large amount at once that just sits in your stomach.
After exercise: this is often the part people neglect. To recover properly, aim for about 1.5 liters for every kilogram lost through sweat. Yes, more than what you lost, since some of it will be eliminated before it's fully absorbed.

Muscle recovery, protein synthesis, clearing lactic acid — all of it works better when you're properly rehydrated in the hours after your workout.

Electrolytes: the game-changing detail in hot weather

Drinking plain water during a long, intense workout, with nothing else, can sometimes throw things out of balance. When you sweat, you also lose sodium, potassium, and magnesium. If you don't replace them during long sessions (over 90 minutes) or in hot weather, you risk:

Muscle cramps despite being well hydrated with water
A feeling of fatigue that seems way out of proportion to the effort you put in
In extreme cases, hyponatremia (too much water, not enough sodium)

For these types of sessions, a homemade isotonic drink works great: 1 liter of water, a pinch of salt (1-2 g), a splash of lemon juice, and a spoonful of honey for carbs if you want. No need for overpriced sports drinks.

How to tell if you're properly hydrated

You don't need a fancy app — two simple indicators do the trick:

The color of your urine: pale yellow means you're good. Dark yellow means it's time to drink up. Completely clear all the time might mean you're overdoing it — that's not the goal either.
Your weight before and after exercise: as mentioned earlier, this gives you an accurate measure of your actual fluid loss, more reliable than thirst alone.

Speaking of which, thirst is actually a poor indicator during exercise: by the time you feel thirsty, you're often already slightly dehydrated. The goal is to stay ahead of it instead of reacting to it.

Hydration: a pillar that's too often overlooked in training plans

At Kaizmax, we calculate your calories and macros using the Mifflin-St Jeor formula, tailor your workouts to your equipment and sport, and recalculate everything as you progress. But no algorithm can drink water for you. It's the one variable that's 100% in your hands, and it's often what separates a workout where you keep your pace from one where you crash after 20 minutes.

Here's the key takeaway: drink regularly throughout the day, adjust based on how much you sweat, don't rely solely on thirst during exercise, and think electrolytes once things get long or intense. It's free, it's simple, and it has a direct impact on your results.

This article is informational and not a substitute for medical advice. In case of a health condition, pregnancy or doubt, consult a healthcare professional.

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