The correct way to do sit-ups is to lie on your back on the mat, with your legs bent 90 degrees and your feet flat on the ground. Hands can be placed behind your head or at your sides. Use the strength of abdominal muscles to slowly pull your body up and exhale when you pay attention. When your body rises to about 10-20 cm from the ground, tighten your abdominal muscles and pause for a while, then slowly lower your body back to its original position.