First, let me saw that as far as exercise/sports science goes I’m a complete novice and have learned everything I know from here and the books. That said, as a scientist I believe this statement is misleading:
“All these machines move under you, as opposed to you having to lift your body vertically against gravity. It is true that you do have to lift yourself with each step on the Stairmaster of pull yourself up on the Versa climber or treadwall. But the vertical distance you need to raise your body mass is much smaller than on real ground because the ground is moving under you with these devices.”
There is a lot of wrong information about this on the internet. While all these machines are going to be different in the their mechanics and the way they work your body, I think saying that because you aren’t “lifting your body vertically against gravity” means you aren’t doing as much work is misleading. All velocity is relative, and your velocity relative to the surface that is supporting you is the velocity you are moving at. The fact that your body isn’t moving up relative to the floor the machine is sitting on doesn’t matter.
Consider a tall elevator with a ladder in it. Climb up the ladder with the elevator stationary. Now send the elevator downwards and climb up the ladder at the same velocity it is moving downwards. In the second scenario your body isn’t moving up relative to the ground floor, but you did the same amount of work as you did in the first. Does driving east take less gas than driving west because of Earth’s rotation? Of course not; all velocity is relative.
Anyway, I’m not saying the training load is going to be the same when using these machines vs. training outside, but the differences do not come because you aren’t moving your body vertically relative to the gym floor. The differences are going to come from things like terrain, wind, non-uniformity of gait/stride, etc. As far as the physics are concerned, you’re doing just as much work on a pack to haul it up 100 steps on a stair treadmill as you are hauling it up an equivalent 100 step staircase. Maybe that’s what Scott was saying initially and I misunderstand, but felt like I wanted to clarify that for posterity. I’m certainly not in a position to dispute his experience and advice, so it’s probably just for academic’s sake in the end.
