Jim, thought you may find this really cool. I'm fortunate to get to train on the very few that are available of these. It's called a shredmill its powered completely by the runner. Whether you hold on an do pushes from 0-500 pounds resistance or take the hill to a 20-25 percent incline an test top speed, stride length, and knee drive.
We do a variety of things an it kicks our asses. Have gotten way stronger in the legs an in fantastic shape. We have the only one in Ohio , an some players in the NFL have put them in their houses(mark Ingram for example) https://instagram.com/p/zihoR1JkT3g5Xup7OZRXl7Mzb85jQTctNoQCw0/