The correct posture is: lie on your back, put your legs together, raise your hands, use abdominal muscles to contract, swing your arms forward, and quickly become a sitting position. Your upper body continues to bend forward, and your hands touch your feet and bow your head. Then return to the sitting position. So continuous. Lie on your back on the mat with your knees bent about 90 degrees and your feet flat on the ground. Don't fix your feet on the flat ground (for example, your partner presses your ankles with his hands), otherwise the flexors of thighs and buttocks will also join the work, thus reducing the workload of abdominal muscles.
Practice sit-ups, the speed varies from person to person. You can try to do it five times a minute at first, and then slowly increase it until it reaches about 50 times.
Extended data:
Sit-ups, a form of exercise. For a participant who has just started to train abdominal muscles with sit-ups, the number of sit-ups should not exceed 10 repetitions (train your abdominal muscles first). After each sit-up, stand up or lie down to rest and let the abdominal muscles relax 10 minutes or more.
References:
Baidu encyclopedia-sit-ups