When keeping speed, incline, etc equal, I find some treadmills harder to run on than others. Why?
Theres going to be several reasons that is the case.
First and most obvious is the caliberation aspect. The machines are not going to be perfect, and such things as the belt stretching with age means older machines will be less acurate, and depending on the technology cost etc. all machines will read slightly differently.
Second is the conditions of the room your working in. Hotter conditions will work you harded; dry air, humid air etc. All will make a difference to your percieved exertion and how quickly you are tiring.
Another factor is the surface, run a mile on flat concrete, a mile on flat asphalt; and feel the difference. The concrete is much harder and less forgiving, and so will tire your leg muscles quicker as they cope with the additional shock. The same occurs on treadmills, less shock absorbtion in the surface will mean your legs tire quicker.
There are other factors that can make a difference as well, such as the way the display is set up, which can mentally motivate you more or less depending on how its laid out, what it shows etc.
Its not in your head though, but there are many reasons; one gym and machine will not be the same as another. Read More At : TF3i Folding Treadmill...