If your goal is to eventually compete/run races outdoors, you won't be used to the conditions. Running on a treadmill is easier because the ground is essentially being pulled underneath your feet. There's also no wind resistance, not to mention the monotony of running in one place for more than an hour and a half.Why..? Can you explain?
Physically yes, sure, you can do it, but I'm a keen proponent of outdoor running for the reasons mentioned above. I can only think of the treadmill as a tool for cardio (and anything above 30 minutes is really just pushing it). Personally, I'll be out running whether it's raining, snowing, hailing, ...



