Crunch (exercise)

Form

The biomechanics professor Stuart McGill was quoted in The New York Times Health blog as stating:

An approved crunch begins with you lying down, one knee bent, and hands positioned beneath your lower back for support. "Do not hollow your stomach or press your back against the floor", McGill says. Gently lift your head and shoulders, hold briefly and relax back down.

Research has shown that both sit-ups and crunches are mediocre strength-building exercises and have injured many people.

In a crunch, unlike a sit-up, the lower back stays on the floor. This is said to eliminate any involvement by the hip flexors, and make the crunch an effective isolation exercise for the abdominals.