. . . guess it's called a treadmill.
qjs
I have spent a lot of time on treadmills, and noticed something about them---it seems that you go faster on a treadmill than you can actually do on even flat streets. I noticed that in the gym, I could do 4 MPH for at least a half hour, according to the machine speed setting, but in fact on flat terrain outside, the best I could sustain for the same length of time was about 3.7 MPH. The cardio effort seemed roughly equal to me.
I realize there are dozens of variables, but IMO, take the treadmill numbers with a grain of salt, as, when outdoors, truely, YMMV.