I spent many years in the gym as an athlete performing hundreds & hundreds of crunchies & ab curls. They were hard so must have been good for you. Right?
How wrong. These last few years I have spent much more time performing planks, mountain climbers & functional exercises with medicine balls, bands & dumbbells. As a result I have a much stronger & well defined core than I did when I was competing.
During most everyday activities the primary role of the abdominal muscles is to support the trunk and control rotation of the spine. In order to train the abdominal muscles to provide this isometric support, we need to do exercises where the trunk is stabilised. These include Planks & variations that involve movements of the arms, legs as well as twisting. It is also important to use standing exercises as this is where we do most of our movements from. Standing whilst moving the arms & legs through all planes of motion).
Advantages of the Plank over Ab Curls
Improves posture (shoulder stability) rather than reinforce a curved back posture.
Trains more than just the upper abs. Trains the lower abs & obliques (side abs) for balanced strength development.
Easier to increase the intensity (level of difficulty is increased by moving the arms & legs in simple movements).