Whenever I do cardio (primarily walking/jogging), I get a very noticeable lump on the front/outside of my right shin. If I flex my muscle, the lump goes away. If I don't do cardio for a few hours, it will go away. However, if I start doing cardio every day, the lump will stay around. I am 26 now, and have noticed it since I was like 17-18, right after my first time on a treadmill.