Lie on the ground with your legs together, with your body straight forward, your arms bent and your hands behind your head. Then bend your right leg properly with your knees, and bend your left leg upward with your knees so that your calves, thighs and thighs are perpendicular to the ground respectively. While lifting the leg, lift the right upper body to the left front, so that the right shoulder is off the ground, the right elbow is as close to the left knee as possible, and the abdomen is compressed. Do it again after changing sides.

Put your knees together, lie flat on the ground, fully stretch your back on the ground, bend your elbows, put your hands on your head, and tilt your shoulder blades backwards so that your arms can lean on the ground as much as possible. While exhaling, push your abdomen and lift your upper body. When lifting, the chin is retracted, the arm swings forward slightly, so that the elbow touches the knee and the feet keep on the ground. Then lie down slowly, regain your posture and do it back and forth several times.

Similarly, the preparation posture of sit-ups should also lie down, knees together, legs at about 90 degrees, hands on your head, shoulders off the ground when exhaling, chin closed, but don't lift your upper body too much, let alone do it. Try to keep your lower back, including your lower back and hips, and keep your feet off the ground. Use the muscles of your upper abdomen to complete the lifting action.

Lying on the ground, knees together, left arm bent, left hand holding the back of the head, right arm straight, right shoulder pulled up from the ground by the two forces of right hand stretching forward and abdominal pressure, right hand touching the outside of left knee, arm straight, right abdomen especially compressed, which can strengthen the muscle strength of oblique muscles inside and outside abdomen.