Lie down on a mat, bend your knees and press your feet (at shoulder width) against the mat. Bend your knee joints at an angle of about 90˚ and keep them and your feet apart at the width of your shoulders. Lay your hands behind your head on the mat.
From the starting position lift your hands and your chest up from the mat and simultaneously lift your legs toward your chest, without changing the angle of your knees. In the upper position detach your shoulder blades completely from the mat while contracting your abdominal muscles. Your knees are directed at your chest and your pelvis is slightly lifted. Follow the movement with your arms and move them from the stretched position, bending your elbows so your arms to end up beside your body at the contraction. Exhale while lifting up from the mat.
Make sure your feet are in the right position and your knee joints are at the correct angle.
Pay attention to your breathing and maintain a neutral pelvic position to prevent lordotic spine curvature (bending your lower back) especially when you are returning to the starting position.
Concentrate on diaphragmatic breathing!
Execute the movement by pulling (concentrate on correct engagement of abdominal muscles), not by jerking.
To restrict over-bending your lower back, you need to have your pelvis in a neutral position and seek to push your lower back against the mat by engaging the “abdominal press” (adequate contraction of the abdominal muscles).