The popular science frequency of fitness and muscle enhancement is as follows: pectoral muscle, back muscle, leg muscle and deltoid muscle are all large muscle groups, and it is best to exercise once every three days; Rest parts such as biceps brachii are small muscle groups, and it is best to exercise once every two days. You can choose a large muscle group with 1-2 small muscle groups every day, and make a fitness plan for exercising four days a week according to your own situation. The daily exercise should be controlled within 90- 120 minutes to ensure that every muscle is fully exercised and given enough rest time, so as not to tear muscles during exercise.