I read an interesting and well researched article about treadmill running vs. outdoor running… The 1% Incline Treadmill Myth, and I certainly agree with the conclusion that air resistance has little or no effect on a runner at relatively low speeds (compared to world-class runners that is). I do find running outside harder though, for a few reasons… one is that the ground is generally less forgiving than the treadmills I use at the Pro Club, and two is that in my part of the world… there is really no such thing as a ‘flat’ course. Even the simplest 3 mile loop around my area generally has about 150 ft down and 150 ft up …. and that is on roads that barely seem to be inclined at all to the eye.
For me, I normally have been running at 0%, but lately I’ve been experimenting with a variety of paces and inclines, I ran two miles last week at 5% for example… I feel it will do nothing but help my speed/endurance on relatively flat courses.