I can't train my chest muscles. You don't have to do it lying down. Which muscle can be exercised mainly depends on whether this muscle is exerting strength. If there is no pressure, there will be no exercise effect Standing horizontal chest expansion exercise mainly exercises the anterior middle bundle of deltoid muscle, without relying on the strength of pectoral muscle. You don't have to lie down as long as you can make your chest muscles work. For example, pushing a heavy object horizontally and clamping the chest with equipment all practice chest muscles horizontally. It's just that the common way to exercise chest muscles is to lie down and practice. For example: bench press, dumbbell bird.