1. Kneel and abdomen (exercise the lower part of rectus abdominis). Hold the horizontal bar with both hands, the grip distance is slightly wider than the shoulder, the legs are straight, the knees are slightly bent, and the toes point down to the ground. Tilt the pelvis upward, and then slowly lift your legs to the highest point. Don't arch your back during exercise, but keep it natural. Hold for 1 sec, then slowly lower your legs and repeat this action. Rest 10 seconds, and then immediately start the next action: supine leg stretching. 2. Lie on your back, straighten your legs (exercise the lower part of rectus abdominis), put your arms at your sides and put your palms under your hips (this will keep your lower back straight during the whole exercise). Put your legs together so that they are perpendicular to the ground and your knees are slightly bent. Lift your head and shoulders off the mat, pull your pelvis towards your ribs, and slowly lift your legs towards your torso until your feet are just above your hips. Straighten your legs and stretch your pelvis as if your feet have reached the ceiling. Lower your legs to the starting position and repeat this action. 3. Turn to sit-ups (exercise the upper part of rectus abdominis), lie on your back, bend your knees, step on the ground with your feet, and gently put your hands on your sides. Stretch your legs while your feet are shoulder width apart, slowly lift your head and shoulders off the ground, and bend your torso to the left at a 45-seat angle. Return to the original position, and then bend the torso to the right at a 45-degree angle in the same way. Repeat this action. When you feel tired, please start the next action immediately: sit-ups with bent legs. 4. Sit-ups with leg flexion (exercise the upper part of rectus abdominis) lie on your back, gently hold the sides of your head with your hands, with your thighs perpendicular to the ground and your thighs at a 90-degree angle. Keep your thighs vertical to the ground and lift your head and shoulders off the ground as soon as possible. Return to the starting position and repeat this action.