I've been doing martial arts for about 5 years now (I'm 19), but never did much in terms of running. I weight lifted, trained (obviously), and did stuff like burpees and sprints for conditioning. Yesterday I ran long distance for practically the first time ever, and did 2.25 very hilly miles in 19 minutes with relative ease. I kindda enjoyed it and figured I would pick up running 3 days a week to add to my conditioning. My question is, can I work up to running, let's say, a half marathon without having to worry about loosing muscle, or is there a distance I should restrict myself too? I will keep weightlifting and fighting. I'm 19, 6'3" and 210lbs.