Lie supine (on your back) on the floor with your hands either lightly behind your head, touching your temple, crossed over your chest or resting on your abdomen.
Flex your knees and position the soles of your feet together so that your legs are wide open and your knees are pointing out to the sides.
Allow your legs to relax in this position.
To protect your lower back, press it down against the floor.
Keeping your lower back pressed against the floor and your legs relaxed in the frog position, exhale as you raise your head and shoulders off the floor by flexing your waist/abdomen.
Hold this position for a count of two.
Inhale as you lower your head and shoulders to the starting position.
Repeat for the prescribed number of repetitions.
Comments and tips
Keep your legs relaxed and your lower back pressed against the floor.
Keep your neck neutral. The same amount of space between your chin and sternum should remain throughout the movement.
Keep the movement slow and under control. Avoid using momentum.
The point of the frog crunch is that by keeping your legs relaxed in the frog position, you reduce the extent to which your hip-flexing muscles, such as your rectus femoris and iliopsoas, can contribute to the exercise. In so doing, you help to isolate your rectus abdominis and obliques.