An isotonic sports drink carries roughly 6 g of carbohydrate and a little sodium per 100 ml — the concentration that empties from the stomach fastest while still delivering fuel. That combination earns its place during efforts longer than about an hour, in heat, or in repeated sessions on the same day. For a 40-minute gym session it is sugar water: water and a normal meal do the same job. The sodium is the point, not an additive to be avoided — it is what lets the fluid stay in the body.