Crunches on floor:

Face up on the floor with knees bent, feet flat, and hands behind head. Careful not to pull the head forward and jamming the chin into the chest, crunch the abdominal muscles just below the ribs, raising the shoulder blades slightly off the floor while keeping the low back flat. Hold for a second, squeezing the abs, return and repeat.
Alternately: If crunches are too difficult with the hands behind the head, place them forward over your hips to reduce tension to the abs.

Crunches on ball:

Face up with the back over a ball, feet flat on the floor, and hands behind the head. Careful not to pull the head forward and jamming the chin into the chest, crunch the abdominal muscles just below the ribs, raising the shoulder blades slightly off the ball while keeping the low back flat. Hold for a second, squeezing the abs, return and repeat.
Alternately: If crunches are too difficult with the hands behind the head, place them forward over your hips to reduce tension to the abs.

Roll Outs:

Face down with elbows and forearms resting on the ball, abs tight, body in a plank position, and toes on the ground.
With the arms, slowly roll the ball forward, and then back. Repeat.

Roll Out Planks:

Face down with the front of the thighs on the ball and the hands on the ground holding the upper body up. Keeping the abs tight and the body in a plank position, roll slowly forward over the ball until the knees and then shins cross over it. Slowly roll back to the starting position. Repeat.

Abs Core Strength PDF

Roll Out Planks