Synergists: Internal and External Obliques, Rectus Femoris, Sartorius
Lie supine (on your back) on the floor with your hands behind your head, your knees bent, and the soles of your feet together.
Raise your feet a little off the floor.
To protect your lower back, press it against the floor.
Keeping your hands behind your head and the soles of your feet together, exhale as you simultaneously flex your abdomen and hips until you touch your elbows onto your thighs.
Hold for a count of two.
Inhale as you reverse the movement and lower your upper body and legs back to the starting position.
Repeat for the prescribed number of repetitions.
Comments and tips
Keep your feet off the floor and your lower back pressed against the floor.
Keep your neck neutral; there should be space between your chin and sternum.
The point of the frog crunch without leg raise is that by keeping your legs in the frog position (legs opened up and relaxed) you reduce the extent to which your rectus femoris, iliopsoas, and other hip flexors can contribute to the crunch and you therefore help to isolate your rectus abdominis and obliques. In the case of the frog crunch with leg raise, you are of course doing no such thing because you are actively flexing your hips. Therefore, the point of maintaining the frog position with this exercise is simply to increase the range of motion for both waist and hip flexion. The frog position also completely eliminates the contribution of some hip flexors, including the pectineus, adductor brevis, adductor longus, and tensor fasciae latae, which allows you to emphasize the remaining hip flexors, which are the iliopsoas, rectus femoris, and sartorius.
Make the frog crunch with leg raise more difficult by straightening your legs before each crunch.
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