Ab crunches increase the strength and function of the Rectus Abdominus muscle group, the largest and most visible ab muscles. Learn how to safely build your “6-pack” with your spine safely supported on the floor. Crunches required no equipment and can be performed at home or at the gym. This is a 10 rep set exercise demonstration. This exercise is part of a full length workout video from the mypypeline.com advanced fitness program, STX Strength Training Extreme Series, Volume 1, Session 7.