With this exercise, we're looking to work the rectus abdominis (that six pack). The main function of this muscle is to create flexion in the spine or control extension of the spine. Here's the incorrect, but very common, way to do it:
And here's the right way:
To do a cable crunch properly, consider three things:
- Hip Position. The hips need to be kept high and locked in place throughout the entire set to avoid using the hip flexors and allow a full range of motion. Dropping the hips too low won't allow you to do a full crunch. Moving the hips during the reps means you're using your bodyweight and hip flexors to do the movement. Keep those hips high and still so the movement comes only from the spine.
- Hand Position. Hand position also determines the range of motion and the lever length used to perform the exercise. A rope attachment works best. Hold the rope, but instead of pulling it over your shoulders with your hands on your upper pecs, position your hands together with your thumb knuckles at the top of your forehead.
Tuck your chin into your chest, about two inches apart, and maintain this position to stabilize your neck. Doing this not only gets your hands and arms out of the way of the crunch, but it extends the lever length and allows you to get more stimulation with less weight.
- Range of Motion. With an ab crunch, focus on getting a deep contraction (as much flexion in the spine as possible). The setup is crucial. We want the spine to get to at least neutral at the top and to full flexion at the bottom, while maintaining control throughout. To make this movement quantifiable, try and get your elbows rolled as far into your lap as possible (far up your thighs).
- If you have a hard time maintaining the right hip position, use a big medicine ball or wall ball under your butt and on top of your calves. Don't sit on it, just keep contact with the ball with your butt and/or hams. This will give you positive feedback on your position during execution.
- You can also use a tennis ball and place it between your chin and chest to ensure stability during the set.