Step into any gym at any given time and you'll most likely find someone doing crunches on the ball. And for good reason as crunches on the ball has been found to make the abs work 24 to 38 percent more than traditional crunches. The problem is, like all good things, they can get boring and become less challenging. If this is the case for you then don't stop crunching on the ball, just switch it up. Here are a few ideas for a more challenging crunch on the ball:

1. Bring your legs together. The closer your legs are together the harder it is to keep balance on the ball, which means the better the ab/core workout.
2. Try to slow it down to really challenge your abs — count 1-2-3 up, 1-2-3 down.
3. Try adding a light weight by holding a light dumbbell in your hands in front of your chest. This will provide added resistance and further challenge your abs.
4. Try placing the ball under your lower back, instead of under the upper or middle portion of your back, this will give you a tough ab workout.
5. Try adding a twist (twist to try and touch your elbow to the opposite knee — this is great for the obliques (aka love handles).

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