I just want you to lie on the floor and pretend to step on an imaginary bike. The correct action is to press the floor with your back down and put your hands behind your head. Lift the knee at a 45-degree angle, and use the pedal. The left ankle should touch the right knee, and then touch the left knee with the right ankle.

Knee lift:

Find a sturdy chair and sit on the edge of the chair with your knees bent and your feet flat on the ground. Tighten your abdomen, lean back slightly, and keep your feet a few centimeters off the ground. Keep a steady movement, pull your knees towards your chest, and bend your upper body forward at the same time. Then put your feet back in place. Repeat.

Arm sit-ups:

Lie down, bend your knees, and hook the bed with your feet together. Wrap a towel around your neck from behind and pull one end with each hand. Tuck in your abdomen, lift your shoulders, slowly roll up your back, then slowly lean back, and continue to get up when you touch the ground. Repeat. If you find it too difficult, lift your upper body off the floor.

Ball lift:

Lie on your back with a tennis ball in your hand, raise your hands to the ceiling, straighten your legs together and hook your feet. Tighten the abdominal and hip muscles and lift the shoulders and head a few centimeters off the ground. Make sure the ball always goes up to the roof instead of forward.