First lie on your back, with your feet tightly together, and lift 10 cm, keep this action for about 10 second, then put your feet down and repeat this action 50 times, preferably 100 times.
Second, lie flat with your feet together, bend your knees, put your hands behind your head, raise your head slightly, look at your knees, and do sit-ups 50- 100 times.
3. Sit in the chair face forward, with the upper body straight, twist the two ends of the chair tightly with both hands, put your feet together, then lift it, hold it for 10-20 seconds, then put it down and repeat 100 times.