September has always meant one thing for me: hay fever. I can barely set foot outside without sneezing—which is an especially big problem for me this year since my favorite running path takes me through four miles of pollen. So I've had to move inside and run on a treadmill. When I did it the first time, I was surprised at how easy it felt to finish my workout. Had my performance radically improved overnight? Sadly, no. My trainer, Lauren Kern, explained that when you run outside, you deal with uneven terrain and hills, so the same distance takes more effort. She suggested I put my treadmill on a 2 percent incline. Now my indoor routine is just as tough as my outdoor one—and I don't suffer through a single ah-choo.