So i run on a regular basis (4-5 times a week) and do somewhere between 15-25 miles a week , nothing big usually under 6 miles a run. Now i have done some reading on running, and treadmills have gotten a split review by most authors. some say its fine, but its a little easier because it pulls u (which is 100% true) but u can cancel that out by making the incline 1 others dont use treadmills or recomend them, except in severe weather conditions. now i was wondering, what would the problem be if i run 3 times a week on a treamill and then the other 2 days a week i run outside. I therefore dont get only acustomed to something pulling me while running, and am comftorble running outside. So will that be bad for me, how will that effect my running? what are the problems with treadmills?