Abdominal crunch:
Lie down, plant your feet on the floor, hip-width apart. Bend your knees and place your arms across your chest. Contract your abs and inhale.
Lie down on the floor and bend your knees at right angles. Do not cross your legs. Make sure that the lower back is pressed to the floor. Exhale and lift your upper body, keeping your head and neck relaxed. Inhale and return to the starting position.
Recommendations: Do not lift your upper body too high. Exercise slowly.
Mistakes: You lift your upper body too high. You're working too fast. You do not relax your neck and/or help yourself with your hands. You relax your muscles after every repeat. You're holding your breath.

Abdominal crunch.