Alternating Moon Crunch is like a normal ab sit up but it is a way to strengthen the abs using dynamic movements that go beyond the normal sit up or crunch. By adding weight using the medicine ball and by raising the ball above your head, you are engaging more oblique muscle groups while you sit up which give you the striated side ab muscles when you take off your shirt.
How to do it:
Lay on the ground with your knees up in the air and your feet planted firmly on the ground. Grab a medicine ball and place it above your head. Sit up using your ab muscles while bringing the medicine ball above your head all the way until it touches one knee. Lower your body and the medicine ball all the way to the ground. Then raise yourself up again following the same movement but touch the medicine ball to the other knee. Repeat.
Muscle group worked:
Target Repetitions for Muscle Growth:
Target Repetitions for Muscle Tone/Endurance:
Why it works:
Since you are using a medicine ball, you are engaging more muscle fibers in your abs while you sit up. Since your arms are above your head for part of the movement, it lengthens the muscle fibers while also contracting them which causes tears in the muscle. When it heals, you have stronger, ripped side muscles.
Keep your abs tight throughout the entire movement. To increase the difficulty of the movement, you can either get a heavier medicine ball (I use 10-12lbs) or press against the medicine ball as you sit up. This will engage your chest muscles as well.
Make sure to breathe out as you sit up and breath in as you lay back down.
Disclaimer: Talk to your primary care physician before beginning any exercise regimen.