You can practice, but the effect is very, very limited and almost negligible. Muscle will not grow much without load. Muscle growth means destroying muscle fibers first and then repairing them. The muscles are getting thicker and thicker. When you stretch your arm horizontally, your muscles only bear the weight of your arm, and will not destroy the muscle fibers at all, so it is impossible to strengthen your muscles. If you persist for a few minutes and feel sour, it is because your muscles produce too much creatine. Don't think it's muscle gain. Think too much.