It takes training to increase strength, build endurance and DEVELOP the abdominals, but to SEE the definition in your abdominals – or any other muscle group for that matter – is almost entirely the result of low body fat levels.
This may sound counter-intuitive, but if you can’t see your abs, it’s not an issue of “muscle development” at all. You simply have too much body fat covering up the ab muscles. The lower abdominal area also happens to be the one place that most people – especially men – store the body fat first.
A great article from Muscle and Strength. Follow link below for full article.