Simply sending nerve signals to the brain to the muscles, resulting in muscle contraction, the movement is real or not.
These exercises were originally designed for sports people and locked to prevent muscle wasting. The imaginary work is effective on all the muscles, because "picturing" exercises that we used to do, the body knows where to direct nerve impulses and already knows the feeling.
The advantage is that with a little training, these are exercises that can be done anywhere, without equipment, without sportswear. And above all, they require zero motion, so no joint strain or pain.
Good news in just 3 weeks for 15 min / day, studies show an increase in muscle size (and its tone).
You have 3 minutes?