Does cardio deplete muscle? I've heard it depletes the water in it, which comes back after a while.

Aerobic exercise in the beginning of the sugar consumed, about twenty minutes later began to consume more fat

But to duration after an hour, the three main functional systems began to function simultaneously

It will consume part of the muscle, that is, protein,

So you have to perform aerobic exercise to reduce fat

The best duration is between 30 and 60 minutes