The exercise ball knee roll-in is an abdominal exercise that involves supporting yourself with your hands in a plank or push-up position and drawing the knees in toward the chest. This is a fairly advanced abdominal move requiring a fair amount of core strength.
Hits every part of the core, including the rectus abdominis or "six-pack" muscles and the deep core
Excellent way to build up to the full exercise ball pike
Get in the push-up position with your hands shoulder-width apart, securing a large stability ball under your lower quads. Your body should be almost straight with your feet together off the floor. This is your start position.
Contract your lower abs to raise your hips as high as you can, allowing the ball to roll down to your shins under control and bringing your knees into your chest.
Push your knees back out and allow your abs to relax to roll the ball back in the reverse direction.
Repeat for the required number of reps.
Alternative Exercises for Exercise ball knee roll-in