Click on the video box above to watch the exercise demonstration for a cable crunch. Equipment used in this video are a Hammer Strength Smith Machine and 2 Bosu Sport Balance Balls and a Bar Pad. Make sure the bar is stable on the upper part of your back, just behind your shoulders. On your first squat, make sure your knees do not go out past your toes! This will isolate the upper quads and hamstrings. Continue to do this exercise in a constant and fluid motion. If you feel pain in your knees or lower back, discontinue immediately!