I don't know if what I've been doing is a good idea and if I should keep doing it or do something else. The route I do is 5 miles. I run the first 2 miles without stopping then for the other 3 miles do about 1 min of walking then 4 mins of running. It takes me about 50 mins to get around. Is it ok to stick with his or should I do shorter runs then slowly build up?