What Causes Occurrence Of Red Lines After Exercising?

I keep on getting red lines that look like the outline of my ABS after exercise! What are the red lines? How come I keep on getting them and they stay there for a while! I started eating healthy and exercising more often! Could that be why? I eat healthy all the time and exercise all the time too! Please E-mail me the answer at YYYY@YYYY ! Thank You for your time and patience!