When looking for abs exercise options, consider using a Swiss Ball for something a little different. Working other core muscles as well as the abs, this is a great all round option even for beginners.
A variation of Swiss ball sizes can be used for this exercise, which will place your spine in either a declined (small ball) - neutral (your back parallel to the floor) - inclined (large ball).
This exercise will mainly work the muscles of the lower abs and also hip flexor muscles, whilst upper-body strength will be required to hold the position. Beginners or persons with insufficient upper-body strength / rehab, may want to perform the exercise whilst resting on their forearms, using a large ball.
Mount the ball from a standing position, taking your arms over the ball onto the floor, whilst rolling over your abs, until your forefoot and shinbone are in contact with the ball, with your legs straight.
There are many variations of the hand positions that you can adopt, in order to work both the upper-body, and core stability muscles. Intermediates and advanced may want to try placing their hands in a wide - close (thumb and index finger touching) - staggered (one hand forward - one hand back) - on a wobble board or Bosu.
Keeping your upper-body firm, aiming to have little movement in your arms and chest muscles, slowly pull the ball towards you by bending at the knees, concentrating on a straight spine throughout.
Aim to bring your knees in-line with the floor, prior to extending the ball out again. The slower the movement in and out, the more benefit you will receive from this exercise, likewise aim to hold the knees bent position for a few seconds, with your abs contracted prior to exhaling and straightening your legs for the next repetition.
As with the arms, advanced athletes may want to adopt a different leg position, this could be having one foot on the ball, whilst the other foot is raised in the air, or slightly harder, out to the side. Resistance bands / ankle weights can also be utilized to add an extra level of difficulty, however this should only be performed once all other methods have been mastered.
Beginners aim for 6 - 10 smooth slow roll outs.
Intermediates aim to work for 10 - 15 roll outs.
Advanced work for 15+ reps for 2 sets.