All movements are coordinated by many muscles. When practicing large muscle groups, small muscle groups should also participate in the effort. For example, when practicing chest, shoulders, arms, waist and abdomen are actually involved. If you practice your shoulders or arms, you are already very weak after practicing your shoulders or arms. At this time, if you practice chest again, because of the weakness of small muscle groups, you will not be able to fully stimulate the chest muscles, and the chest muscles will naturally not grow. Therefore, it is necessary to practice large muscle groups first, and then practice small muscle groups after the large muscle groups are fully stimulated.