The external cause is exercise, not the first day and the second day you said. It should be Monday, March 5, and exercise every other day. The reason is that muscles need rest, and when they rest, they gain weight. The detailed plan is as follows
Monday
Chest, triceps brachii, abdomen
Chest:? Barbell bench press? 3/ group? 12/ time? Dumbbell bird? 3/ group? 12/ time?
Push-ups? 3/ group? 12/ time?
Triceps brachii: Sit-ups? 3/ group? 12/ time? Dumbbell neck and arm flexion? 3/ group? 12/ time?
Heavy hammer down? 3/ group? 12/ time?
Abdomen:? Sit-ups? 3/ group? Twenty times? Lift your legs on your back? 3/ group? 20/ time
Tuesday
Back, biceps brachii, abdomen
Back: Pull-ups? 3/ group? Eight times? Neck to pull down? 3/ group? 12/ time?
Row in a sitting position? 3/ group? 12/ time?
Biceps brachii:? Barbell bending? 3/ group? 12/ time? Oblique bend? 3/ group? 12/ time?
Dumbbell forehand? 3/ group? 12/ time?
Abdomen:? Sit-ups? 3/ group? Twenty times? Lift your legs on your back? 3/ group? 20/ time
Friday
Legs, shoulders, abdomen
Leg:? Barbell squat? 3/ group? 12/ time? Bend over and bend your legs? 3/ group? 12/ time?
Sit and cross your legs? 3/ group? 12/ time?
Shoulder:? Dumbbell bench press? 3/ group? 12/ time? Barbell neck pressure? 3/ group? 12/ time? Dumbbell side lift? 3/ group? 12/ time?
Abdomen:? Sit-ups? 3/ group? Twenty times? Abdomen? Lift your legs on your back? 3/ group? 20/ time
Few people can stick to this plan. Just stick to it once a week.