Running on the tread for a long time is mentally taxing and tortuous. Especially if you're doing serious milage because you're training for a big race like a marathon (or you just have tons of energy to burn). It can feel like you're sprinting on a hamster wheel of doom to nowhere — seemingly until you die. Although the act of running isn't physically harder on a treadmill, this stagnant form of training can take a toll on your motivation and mentality, John Honerkamp, an NYC running coach and the founder and CEO of Run Kamp