You can do this exercise either at the gym or at home. If you prefer to do them at home, you may be more comfortable performing this exercise on a yoga mat, towel or any other soft surface you can put between you and the floor. You will also need either a medicine ball or volleyball for this exercise.

This exercise works your rectus abdominis muscles, which are the major muscle group in your core and the muscles responsible for the six-pack look.c 

1. Lie flat on your back with your legs extended flat on the the floor and your arms raised above your head.
2. Simultaneously, lift your arms and legs, contracting your abs as you reach your arms towards your legs.
3. Lower yourself back to starting position. For an added challenge, don't touch the ground with your feet or arms between reps.
4. Once you've mastered this version, grab a medicine ball or volleyball and start with it in your hands. Transfer it to between your legs on the upward crunch. Go all the way down, then grab the ball on your next rep and repeat.