Walking Sideways Down The Stairs

I think I have found the solution to my over training issues.  I have been running on a treadmill for the past week and am having absolutely no leg fatigue. Normally as I get back into my mileage of 30 plus I start to get tired pretty quickly and am always walking sideways down the stairs.  I am thinking that in March when I return to the great outdoors I am going to continue to run about 30 of my miles indoor on a treadmill.  My biggest fear for this training year is over doing it.  I think that if I keep my outdoor / indoor ratio at around 50/50 peaking at 80 miles per week in September should not be a problem.  Okay, fingers crossed.