What you'll need: floor space, a pull-up bar, and a medicine ball 20 scissor abs 20 diamond sit-ups 20 knees-to-chest hanging from a pull-up bar 20 double crunches with a medicine ball 20 reverse ...

A personal trainer shares the "tuck crunch" exercise as an alternative to planks if you want to build a strong and stable core while remaining low impact on joints.

If the seated ab crunch as described is too difficult, instead of placing the fingertips behind the neck, fold the arms across the chest. On the other hand, if not challenging enough, hold a ...