Hydration: The Quiet Foundation of Performance and Health

Most people don’t think about water until they’re thirsty. In the gym, it’s often overlooked entirely — not because lifters don’t care, but because it’s rarely discussed in the same breath as macros, programming, or recovery strategies. Yet, if you strip things back, hydration underpins everything your body does — from blood flow to brain function to bar speed. Without it, nothing works well, and some things don’t work at all.

Hydration doesn’t shout for your attention like a torn hamstring or a missed rep. It’s quiet — until it isn’t. And once you understand how important it is, you start to realise how often you’re asking your body to perform without the conditions for good performance in place. That’s what this article is about.

You’re Mostly Water — and That’s Not Just Trivia

The average man is about 60% water. For women, it’s closer to 50% — slightly lower due to higher body fat percentages, which hold less water than muscle. But this isn’t just an abstract fact for pub quizzes. That water isn’t sitting in a big tank somewhere in your belly. It’s in your blood, your muscles, your brain, your joints, and even the spaces between your cells. Every signal your nerves send, every muscle that contracts, every breath you take — it all happens in that watery medium.

You don’t think about it because it’s automatic. But the body’s systems rely on having the right balance of water and electrolytes in the right places, all the time. If that balance shifts — even slightly — everything starts to feel just a bit off. And if it drifts further, you’ll know about it.

The Role of Hydration in Performance

When you train, your body is doing three things at once:

• Cooling via sweating to shed the heat produced by movement and energy turnover.

• Circulating blood to deliver oxygen, nutrients and hormones, and to clear waste.

• Transmitting signals between brain and muscles so contractions are timely and coordinated.

Every one of those processes relies on fluid.

1) Cooling

Exercise is inefficient by design. Only part of the energy you produce becomes movement; the rest becomes heat. To prevent overheating, your body increases blood flow to the skin and produces sweat. The cooling comes from evaporation: when sweat evaporates, it carries heat away.

If you’re short on water, sweat output falls and blood volume (aka plasma volume) shrinks. You might not notice it on a single set, but across a session the effort of thermoregulation (controlling core temperature) starts to bite, even with mild dehydration. Recovery between sets slows, effort feels higher for the same work, and the session drags. This isn’t mindset; it’s physiology operating at a disadvantage.

2) Circulation

Blood is mostly water. When you’re well hydrated, it flows easily, delivering fuel and oxygen and removing waste. If plasma volume drops, your heart must beat faster to move the same amount of blood. That higher heart rate isn’t because you’re pushing harder; it’s compensation for having less circulating fluid to work with.

The result is predictable: delivery becomes less efficient, clearance slows, and set-to-set recovery is blunted. Muscular performance fades earlier than it should, coordination slips, and the session feels unnecessarily hard — not because anything “broke”, but because the system is under-supplied.

3. Neuromuscular Control

Sodium, potassium, calcium, and magnesium — the core electrolytes — regulate how nerves signal and how muscles contract. These minerals move in and out of cells along fluid gradients. If you’re low on fluid or low on sodium, those gradients shift, signals slow down, and coordination suffers. That’s why dehydration doesn’t just make you tired — it makes you clumsy. Reps feel awkward, grip weakens, and bar speed drops.

In short: if your muscles are the engine, water is the oil. You can run without it — briefly. But the friction mounts, and something always gives.

What Dehydration Feels Like

The signs of dehydration aren’t always obvious, especially in the early stages where performance begins to suffer. As a genral guidline you can expect the following symptoms to occure for the % of body weight you loose through water loss (excluding urination).

• ~1% down: warm‑up feels heavier than usual; concentration fades; mild thirst.

• ~2% down: endurance and repeat efforts fall off; technique drifts sooner; higher heart rate for the same workload; hotter for the same session.

• ~3% down: clear drop in performance; clumsier reps; rising risk of cramp and heat illness; slower decisions.

• ~4–5% down: dizziness, nausea, and poor training quality — time to stop, cool down, and rehydrate with electrolytes.

• ~6–7% down: severe dehydration — pounding heart, rapid breathing, very hot, light‑headed on standing, headache, nausea/vomiting, cramps; coordination and attention are poor. Stop immediately, cool actively, and rehydrate with electrolytes. If symptoms don’t improve within 30 minutes, seek medical advice.

• ~8–9% down: danger zone — high risk of heat illness progressing to heat stroke; confusion, disorientation, stumbling or fainting, hot skin, minimal urine. Begin aggressive cooling (shade, cool water/ice, airflow) and oral fluids if fully conscious. Call emergency services if there’s altered mental state or vomiting prevents drinking.

• At 10%, you’re in serious trouble, and likely to need medical assistance to avoid death.

Even at a 1–2% loss — common within an hour of hard training — thirst may not kick in despite already being a bit dehydrated — especially in cool conditions or when you’re focused on what you are doing — so don’t rely on thirst alone.

Thirst: a useful signal, not the whole plan

Thirst keeps humans alive, but it isn’t an early-warning system. Physiologically, the thirst signal is triggered mainly by rising blood osmolality (more salts relative to water) and, to a lesser extent, by a drop in circulating volume (plasma volume). Both of those changes take time to develop. In cool conditions, when you’re focused, or as we get older, that signal often turns up later than is ideal for performance.

So use thirst — but don’t outsource the job to it. A better approach is proactive: begin the day with some fluid on board, keep a steady drip through meals, and arrive at training already comfortable rather than playing catch‑up. During sessions, sip according to heat, duration and how you personally sweat; on hotter, longer or sweatier days, add some sodium in (more on this later) so what you drink actually stays in circulation. Between sessions use simple checks that your adiquitly hydrated: urine that stays a pale-straw colour and a post pee morning weight that stays within ~2% of normal; drift outside that and nudge fluid intake up (and a little salt if you’re lighter).

Put simply: thirst confirms you’re behind; routine prevents you from getting there. Which brings us to the numbers most people find workable in day‑to‑day life.

How Much Do You Need?

Most active adults do well with around 30 to 35 millilitres of fluid per kilogram of bodyweight per day.

For a 100kg lifter, that’s roughly three to three and a half litres across the day. Spread it out. If you cram it in late, you’ll spend the night getting up to pee and not much of it will be retained. Aim to start the day with a glass or two and keep a steady pace through meals and between sessions. Pale straw‑coloured urine is a fair cue you’re about right; apple‑juice shades suggest you’re behind.

In the gym, sip water as needed. If the session is long, hot, or high‑intensity, include some sodium. If you’re regularly finishing significantly lighter than you started, you’re under‑drinking. If you’re finishing heavier, you’re probably overdoing plain water.

Visual cue: use the urine‑colour scale below as a quick check. Aim for pale straw most of the day; darker, amber‑to‑brown shades signal you need to top up. (Bright yellow after a B‑vitamin or certain medicines doesn’t necessarily mean you’re dehydrated.)

Sources of Hydration (And What About Caffeine and Alcohol?)

It doesn’t have to be plain water. Herbal teas, squash, milk, and even coffee all count toward hydration. For habitual caffeine users, moderate intake isn’t meaningfully dehydrating. Alcohol, on the other hand, is a diuretic. It increases urine output and slows rehydration. If you’re having a drink post-training, match each alcoholic drink with water and ideally a salty snack.

Food helps too. Vegetables, fruits, yoghurt, and soups bring water with them. So do cooked grains and pulses. A diet rich in whole foods makes staying hydrated much easier than a dry, packaged one.

Most people don’t get dehydrated from doing nothing. It’s the quiet slide of under-drinking through the day, sweating hard in the gym, and not replacing it after. The body adapts for a while. But that doesn’t mean it’s working well.

Good hydration habits are built on convenience and consistency. Keep a bottle in sight. Pair your drinks with meals, transitions, or regular tasks. Use taste and temperature to your advantage. Don’t aim for perfection; aim for rhythm. And in hot spells or busy training blocks, add a pinch of salt when you know you’ll sweat.

Why Sodium Matters

You’ve seen sodium come up repeatedly for a reason. Sodium is the main electrolyte in the fluid outside your cells; it sets the concentration gradient that holds water in your bloodstream, helps nerves fire on time, and supports muscle contraction. When you sweat you lose mostly water and sodium; potassium, magnesium, and calcium are lost in much smaller amounts. If you only replace water (hypotonic more on this later) after a sweaty session, blood sodium can drift lower, you retain fluid less well, and performance — and how you feel — slides. In long endurance or very hot workouts this can tip into hyponatraemia, where blood sodium becomes too diluted after heavy sweating and large intakes of plain water. Adding a sensible amount of salt on sweaty days is protective.

That said, you don’t need sodium in every drink. As a workable starting range, 500–700 mg sodium per litre suits many lifters (isotonic territory) in warm conditions. if you sweat heavily or see salt rings on clothing, 1,000–1,500 mg/L on hot or long days is often more comfortable (toward the higher end of isotonic or even hypertonic if carbohydrate is added). Taste is a good governor; if the drink tastes uncomfortably salty, you’ve probably gone a bit far. And remember diet counts — if you’ve just eaten a salty meal, you can be more conservative with what you add to your bottle.

One caution worth stating. If you’ve been advised to restrict sodium for medical reasons (e.g., hypertension, kidney or heart disease), follow that advice and keep your training drinks simple; food-first sodium will usually be enough.

It’s at this point people often ask about cramps. While low sodium can contribute, cramps are multi-factorial — fatigue, pacing, heat, and overall workload are at least as important as minerals. Think of sodium as one piece of the puzzle, not a magic fix.

A word on the other electrolytes. Potassium lives mostly inside the cell and is key for nerve and muscle function. Sweat losses are modest; a normal diet with fruit, vegetables, pulses and dairy usually covers it. Magnesium and calcium support contraction and relaxation, heart rhythm and bone health; sweat losses are small, and deficits are more often dietary than exercise-induced. Chloride partners sodium to maintain fluid balance.

Sports Drinks Demystified

In the section above you probably noticed the terms hypotonic, isotonic, and hypertonic. These describe how concentrated a drink is compared to your blood — in other words, how much “stuff” (sugar, salt, and other solutes) is dissolved in it. That concentration determines how quickly the fluid moves from your gut into your bloodstream, and whether it pulls water with it or slows things down.

A hypotonic drink is more dilute than blood. Because the fluid gradient favours rapid absorption, it gets into circulation quickly. Plain water, water with a pinch of salt, weak squash, or electrolyte tablets like ZERO all fall into this category. These are the best option when hydration is the main goal. For most strength trainees — especially in shorter, gym-based sessions — hypotonic fluids are usually enough. They replace what’s lost in sweat without adding unnecessary sugar or calories.

An isotonic drink is about the same concentration as blood. Sports drinks with a modest amount of sugar and sodium fit here. They deliver water, electrolytes, and carbohydrate at a rate your body can comfortably handle. This is where the classic bottles of Lucozade Sport, Gatorade, or Powerade sit. They work well in longer or hotter sessions, or when hydration and fuel are needed together. But they’re nothing mystical: sugar, salt, and water in the right proportions. If you’d rather not buy them, you can easily make an isotonic drink yourself with water, a little sugar, a pinch of salt, and something for flavour.

A hypertonic drink is more concentrated than blood. Fruit juice, cola, and carbohydrate gels are good examples. These are useful when fuelling is the main priority, but because they’re denser than blood they can pull water into the gut and slow absorption, sometimes causing stomach upset if taken alone. Endurance athletes training for more than an hour often use hypertonic fuels alongside water and sodium. For strength athletes, they’re usually unnecessary — but there are exceptions. Dieting lifters who are very low on carbs sometimes find that sipping a small glass of juice in the gym stabilises energy and prevents that light-headed, “flat” feeling when glycogen is low.

In practice: when you need fluid quickly, go hypotonic with some electrolytes; when you need fluid and fuel together, go isotonic; and when you need extra carbohydrate, go hypertonic — but always balance the latter with water and salt.

Or more simply: strength + short = hypotonic; long or hot = isotonic; endurance or low-carb = hypertonic support.

The Bottom Line

Hydration isn’t glamorous. It doesn’t get a line in your spreadsheet or a post on social media. But it’s the quiet discipline that keeps the machine running.

Stay hydrated and your lifts feel snappier, your head stays clearer, and your recovery improves. Ignore it, and you’ll pay with slow sessions, fuzzy thinking, and the creeping sense that something just isn’t clicking.

Water is the medium in which strength lives. Keep it in balance, and everything you care about — strength, energy, recovery, consistency — stands on firmer ground.