The problem with most of the ab work people do, is that it involves abdominal stabilization with hip flexor shortening. This goes for most crunches, sit ups, leg raises, bicycles, etc. So in turn, you may actually be weakening the abdominals by causing anterior pelvic tilt (rectus abs being in a perpetual state of stretch).
Planks/bridges are a better way to isometrically work the abdominals.
If you want to dynamically work the abs, then you need to de activate the hip flexors. This involves contracting the glutes. So, get a medicine ball, perform a supine bridge and really focus on contracting the glutes. Now, squeeze your ribs into your hips - a very short range of motion - using the abdominals. When you get good at this, you can start adding in resistance via exercise bands or cables.