What to drink during training: water, sports drink or nothing

You are standing by the rack with a water bottle in one hand and a brightly coloured sports drink in the other, wondering whether the second one does anything. For most gym sessions it does very little, but there are situations where the difference is obvious. Here is how to tell them apart without guessing.

What you actually lose when you sweat

Sweat is mostly water plus electrolytes, and of the electrolytes it is mainly sodium. Sweat rates run roughly from 0.5 to 2 litres an hour depending on intensity, room temperature and how heavily you happen to sweat. In an air-conditioned gym, over 45 minutes of lifting, most people lose somewhere between 300 and 600 ml.

Sodium concentration varies enormously between people — very roughly 0.5 to 1.5 grams per litre of sweat. That is why two lifters doing the same session can have quite different needs: one dries off clean, the other ends up with white salt marks on a black shirt.

What you do not lose through sweat is fuel. Muscle glycogen is spent by work, not by sweating. That matters, because it explains why carbohydrate in the bottle only starts to help once the work goes on long enough.

The evidence is strongest for one threshold: once you are down about 2 per cent of body mass in fluid, performance starts to slip. In long endurance work and in heat the drop is plain. For sets of five to eight reps the effect on raw strength is smaller, but concentration fades and perceived effort climbs — the session feels harder than it is.

Water covers most of what you do in a gym

A typical strength session runs 45 to 75 minutes, rest periods are 90 to 180 seconds, and the room sits at 20 to 24 degrees. Under those conditions neither your fluid nor your sodium falls far enough for anything beyond water to matter.

The fuel for that session came from the meals you ate earlier in the day, and muscle glycogen comfortably covers an hour under the bar. A half-litre bottle and a few mouthfuls between sets sorts it out. There is more on what your total daily intake should look like, not just the training hour, in the piece on hydration and training.

A refillable bottle counts as basic kit — if you are just starting, have a look at what to bring to your first session and how the hour actually unfolds.

When a sports drink earns its place

Isotonic means the concentration of dissolved particles is close to that of blood, so the drink leaves the stomach quickly instead of sitting there. A standard mix is 6 to 8 grams of carbohydrate per 100 ml plus sodium. Nothing mysterious about it: water, sugar and salt in a ratio the body absorbs fast.

It makes sense in these cases:

• Work lasting longer than 60 to 90 minutes without a real break — long combined sessions, longer runs, team sports.
• Summer heat or a gym with no air conditioning, where your shirt is soaked inside 20 minutes.
• Two sessions in one day with less than six hours between them.
• Early morning training in a fasted state, if your energy visibly drops in the second half.

For longer work the usual target is 30 to 60 grams of carbohydrate per hour, which is roughly 500 to 800 ml of a standard sports drink. If you combine lifting and a long cardio block into one 90-minute session, that is where a sports drink genuinely does something — how to order those two is covered in the piece on cardio before or after weights.

When nothing at all is fine

A 30 to 40 minute session, decent fluid intake across the day, no thirst — you do not need to force anything down. The idea that you must be sipping constantly is overstated. For most gym-goers, thirst is a good enough guide.

There is a practical reason too. A stomach full of liquid before a heavy squat or deadlift is uncomfortable, and combined with a belt and hard bracing it can bring on reflux. Mouthfuls of 100 to 150 ml beat half a litre in one go.

But nothing during training must not turn into nothing all day. If you walk in already short on fluid, one hour of sipping will not fix it. If your throat is dry on the first working set, take a few mouthfuls during your warm-up and the problem is gone before it starts.

How much to drink: numbers instead of guesswork

As a starting point: 400 to 600 ml in the two hours before training, then 150 to 250 ml every 15 to 20 minutes if you are visibly sweating. That comes to roughly half a litre per hour of work.

If you want your own number, weigh yourself before and after a session, dry and in the same clothes. Every kilogram lost is about a litre of fluid. Replace 1.25 to 1.5 litres per kilogram over the next two to four hours, and next time you know exactly what your rate is.

Urine colour is a crude but useful check: pale straw is fine, dark means you are behind. If white salt marks dry onto your shirt and cramps keep showing up, you are probably one of the saltier sweaters — a pinch of salt in the bottle or a sports drink handles that more cheaply than anything else on the shelf.

Two common mistakes. First, energy drinks instead of water: those are caffeine and sugar, not a hydration strategy. Second, a sports drink on a 45-minute session. That is 120 to 140 calories you did not need, and if you are trying to lose weight it is half your daily deficit drunk for no reason.

When to see a doctor

See a doctor if dizziness, nausea or headaches keep recurring in training despite sensible drinking, if cramps show up away from the gym as well, or if you gain weight suddenly with swelling in the legs.

It is an emergency if someone in the heat stops sweating, becomes confused or feels hot to the touch — those are signs of heatstroke and a bottle of water will not fix them. Confusion, nausea and headache after several hours of work washed down with large amounts of plain water also need urgent help, because sodium can fall dangerously low.

If you take diuretics or blood pressure medication, or you have kidney disease, heart disease or diabetes, the rules on salt and fluid are different for you. Ask your own doctor before you start adding electrolytes on your own initiative.

The short version

• For a strength session up to an hour in normal conditions, water is enough and you are missing nothing.
• A sports drink earns its place beyond 60 to 90 minutes of continuous work, in heat, and with two sessions a day — 30 to 60 g of carbohydrate per hour.
• Half a litre per hour is a fair default, taken in 150 to 250 ml mouthfuls, with 400 to 600 ml beforehand.
• The scales give you your real number: every kilogram lost is about a litre, replaced with 1.25 to 1.5 litres.
• Energy drinks are not a substitute for water, and a sports drink on a short session is just another 130 calories.