How to improve on abdominal exercises?
Sounds to me like you have a common problem which occurs to people that train but lack a fundamental scientific background. First of all, the exercises you mention you have trouble with involve your lower abdominals so focus of those that involve hip flexion such has a reverse crunch. Also the problem with your back aching maybe do to a weak transverse abdominis, so make sure you do exercises which targets that muscle such as a prone plank. When working your transverse abdominis make sure you draw your stomach in and contract your abdominals. If you have a strong transverse abdominis you will have an easier time performing the exercises you mention becuase those exercises involve activating and maintaining the transverse abdominis. Also you must work your lower back more. Trying doing these exercises, fish flops, supermans, and opposite arm/leg raises. Try working more stabilization muscles opposed to movement muscles to improve on overall abdominal performance and apperance. Trust me.
