Most people find it easier to exercise their upper abs than their lower abs, because these muscles require greater core strength to work out properly without injuring yourself or straining other muscles in the body.
Before starting to exercise, here are a few things to keep in mind:
If it burns, you’re doing it right. If it hurts, you’re doing it wrong. This is especially true of stomach exercises, where it is very easy to put the strain on your lower back.
If you feel like some other muscles are doing the work, rather than the ones you’re trying to exercise, that’s probably happening. Take a break, and work on building your core strength.
If one exercise isn’t working for you, try something different. Sometimes exercises require muscles you just don’t have yet, or are difficult for someone who isn’t very flexible.