One of the biggest myths about ab work is that you should be doing ab work everyday. This could not be farther from the truth! Abs are a muscle group and just like every other muscle in your body after a workout your abs need a few days of rest. Exercising breaks down your muscles and tissues so that proteins in your body will repair and rebuild the muscles to make you bigger and stronger. The process of rebuilding muscles only happens during the days of rest where you are not exercising that specific muscle group. If you continue to work the same muscle group everyday you are not giving your muscles any time to repair and rebuild. This will actually have the opposite of your desired affect on the muscle. One sign that your muscles need rest is if you become sore after a workout. This is your body's way of telling you, "give this muscle group a break while it grows." You should never exercise a muscle group that is sore!
To maximize your ab training you want to make sure you hit all the parts of your core muscles. A strong core is important to developing overall body strength and balance. Test show that athletes with a strong core are less likely to have injuries. The core muscle groups are the pelvic floor muscles, transversus abdominus(front abs inside the obliques), multifidus(Deep muscles in the back), internal and external obliques(outside abs above hips), rectus abdominus(front ab muscles), erector spinae (sacrospinalis) especially the longissimus thoracis, and the diaphragm. There are many exercises to work all parts of your core. Remember to train hard and rest so your muscles will rebuild and become stronger!