On treadmills

I'm on a budget, so I don't spend money on gym memberships, not when I can get the benefit of treadmills by going across the street to the park and running uphill. Though I have to admit that the weather is not always conducive to this. But people don't use gyms very often either, most people anyway. Plus, I've been reading John Peterson's Push Yourself to Power, and it makes sense to me to use your own body weight to gain strength and build muscle rather than lift weights or use machines. This is in line with some other fitness experts, such as Matt Furey.