Lose two per cent of your body weight in sweat and endurance, output and concentration measurably drop off. For a 75 kg athlete that is a litre and a half of fluid.

A hard hour in a heated room will do it without you noticing.

The average adult here puts away around 8 g of salt a day against a 6 g guideline. Almost nobody walking into a gym has a sodium deficit.

So a brand telling you to load up on sodium all day is not solving your problem. It is selling you one.

Salt in last night's dinner does nothing for the session you finished at seven this morning. What counts is replacing what you actually lost, close to when you lost it.

Not a gram a serving because a label said so. The right amount, at the right time, for the session you actually did.