Keep lower back pressed to the floor, hands gently cradling head

Don't strain the neck

Flatten abs at top of movement by exhaling and contracting the muscles--imagine creating a canoe-shape between your hips and ribs 

Don't use momentum--go slowly and take your time

Keep your lower back on the floor 

Use your abs to lift your hips straight up, just a few inches off the floor.

Flatten the abs at the top of the movement as described above

Focus on bringing your shoulder towards your hip, rather than bringing your elbow to your knee.  

Lift your shoulders off the floor and twist, feeling a squeeze in the opposite side of the waist

Flatten the abs at the top of the movement as described above 

Keep torso parallel to the floor (ball centered under mid-back or lower-back)

Place hands behind head or across chest.

Curl your abs by pulling the bottom of your ribcage down toward your hips. Avoid pulling on the head or neck.

Flatten the abs throughout movement

Lower Back flat on floor

Upper body relaxed

Use lower abs to lift hips off floor

Flatten the abs at the top of the movement and exhale

Lift shoulders off ball and twist, bring shoulder towards hip

Flatten the abs at the top of the movement and exhale

Start in plank (push up) position with stomach in and back flat (don't 'sag' in the middle)

Hold this position for as long as you can, relax and repeat

To add challenge, roll the ball towards you with your feet, tightening the abs and crunching at the end of the movement, but keeping your back as straight as you can (don't collapse).

Keep back flat and chest up, balancing on your tailbone with legs straight

Hold this in an isolation or lower your legs a few inches and bring them back up, repeating for a very advanced 'crunch'!

Flatten the abs at the top of the movement and exhale