For years I have trained my abs like they are a different kind of muscle and this is not true. Although they have more slow twitch muscle fibres for endurance doesn't mean you need to do 50 reps per exercise. My current routine consists of 15 crunches (on the floor with a 20kg plate on my chest), 15 hanging knee raises, 15 hanging parallel leg raises x2, 15 hanging full leg raises. Each done with 1 min rest inbetween. Try it out, it tough but good. You have to make sure that you are tensing your abs during each rep by pulling your abs towards your lower back. Also activating that muscle that you use to stop urine flow whist doing a rep engages more of the smaller muscle behind the abs that you see which in turn will give you flatter and more defined abs.
Also there is an exercise called a 'vacuum'. This is good one to keep your stomach flat rather than bulge out and have a six pack beer belly! just standing up, hands on your hips, breath out fully and then pull your belly button towards your lower back as much as you can whilst puffing your chest out. Making sure you are holding your abs tight at the same time. Hold for 30 seconds and your done. do that once a day and you shall get much flater abs.
