I have no idea about that, but I always run on an incline of at least 2 b/c I find that I have better technique (not right word but right one totally escaping me right now) when I do. I struggle with my form (that's the right word) on the treadmill and find that I start running incorrectly like striding really far out unless I use the incline. My thighs have thinned out and I find that I am able to run a lot faster. I feel stronger. Just my opinion though.