Begin sitting at the edge of a chair/ bench with knees bent to 90 degrees.
Bring arms straight up in front. Gently tighten your abdominal muscles and hold as you lean your upper body back without arching your back. Come back up to sitting and relax abdominals. Repeat.
Take note if you see or feel any doming (Diastasis Recti) of your abdomen. Avoid leaning so far back to avoid this or choose a different exercise if it cannot be avoided.