This move requires a Physio Ball or Stability Ball and is great for training your core and adding upper body strength.
Begin by laying on the ball and walking out onto your hands until the ball is on your thighs. To make it more advanced, walk the ball out until it's on your shins.
Once in this plank or pushup hold position, engage your abs and bring your knees in towards chest exhaling as you crunch.
Extend your legs back out keeping your core engaged, and repeat.
This exercise is great for working on your core and strengthening your shoulder girdle.
Important to keep your core engaged throughout the move and maintaining a neutral spine.