Sweat rate and what you lose.
The human body sweats between 500ml and 2.5 litres per hour depending on intensity, heat, body mass, and training status. Those numbers hide a lot of detail. Elite runners in heat can push 3 litres an hour. A gym session in a cool room might only cost you 700ml.
Sweat is not pure water. Every litre of sweat takes roughly 900mg of sodium, 150 to 300mg of potassium, and only a few to about 30mg of magnesium with it. Heavy sweaters can lose more; light sweaters lose less. Those are the losses a hydration plan is replacing.
How to test your own rate
- Weigh yourself before a 60-minute session, unclothed, dry.
- Train normally. Track any fluid you drink during (in ml).
- Towel off, weigh again.
- Weight lost (kg) + fluid drunk (L) = sweat rate per hour.
Most people are surprised by the number. A 75kg runner losing 1.2kg in an hour is sweating 1,200ml plus whatever they drank.
Pre, during, post. A practical protocol.
The pre-during-post framework covers 90% of athletic hydration needs. The other 10% is heat and duration edge cases covered below.
Hot weather training.
Every 1°C rise above 20°C ambient adds roughly 10% to your sweat rate if intensity is held constant. British summer training at 28°C pushes most athletes into a 1.5 to 2L per hour range where plain water becomes actively risky over long sessions due to hyponatremiai.
The recovery window.
There is a narrow window, roughly 30 to 60 minutes post-session, where muscle glycogen replenishment and fluid uptake are both at their highest. Getting fluid plus electrolytes in during that window sets up the next day's training.
A simple recovery protocol
- First 15 min: 300ml water + one sachet
- 15 to 60 min: protein + carb snack, another 300ml water
- 60 to 120 min: second sachet with next meal
- Evening: magnesium serving before bed for sleep + muscle
Creatine and electrolytes.
Creatine pulls water into muscle cells, which is part of why it supports strength adaptations. That extra intracellular water has to come from somewhere. Hydration becomes more important, not less, when you are taking creatine.
A useful rule: if you are supplementing creatine, add 500ml to your daily fluid target and include one electrolyte sachet a day on top of your training-day hydration. The potassium-forward Recuperol profile is particularly useful here because intracellular hydration is potassium-led.
Creatine moves water into the cell. Potassium keeps it there. Sodium outside, potassium inside, the same pattern the body uses naturally.
The Recuperol approach.
For training, the practical answer for most people is one sachet pre, one sachet during long or hot sessions, one sachet post. That is usually three sachets on a heavy training day, one to two on a rest day. Magnesium 3-in-1 sits alongside as a daily baseline.
The hypotonic formula makes Recuperol easier on the gut during running and cycling than a sugary isotonic drink. The potassium ratio replaces what is actually lost rather than piling on sodium you likely already have enough of from diet.