I lost a lot of muscles and gain fats how could i rebuild my muscles?

Work muscles harder: If muscles are used repeatedly until they tire, but are not injured, then they will grow bigger and stronger! if one does not eat or drink more calories than he uses during exercise, then his body will burn up fat for fuel. However, if he drinks a big orange juice (about 300 calories) while exercising, and exercises away only 200 calories, he will still get fatter even though he is exercising.