Most of us have a love-hate relationship with the treadmill. On a gorgeous fall day when you can run outside, it's the last thing on your mind. But when it's rainy or you're training for a marathon, it can quickly become your fitness BFF. So here is a quick, 30-minute treadmill workout anyone can do. Feel free to modify the speed to a pace that feels comfortable (yet still challenging) for you — and enjoy!