B Is the Stairmaster a Valuable Exercise Tool Despite Physics Misconceptions?

[PeroK]

I was taking the more normal scenario of going up the up escalator. So whe the pedestrian pauses on the escalator, they are still going up. And when the resume, they are restarting from upward vertical velocity - not from stationary.

That makes no difference. That's just a constant upwards velocity relative to the Earth. You know enough physics to see that you simply have two inertial reference frames there: the surface of the Earth and the moving escalator. Newton's laws apply identically in both.

 

[russ_watters]

I was taking the more normal scenario of going up the up escalator. So whe the pedestrian pauses on the escalator, they are still going up. And when the resume, they are restarting from upward vertical velocity - not from stationary.

Ok, but that scenario isn't on the table so I'm not sure why bring it up or what you are trying to say about it...but it doesn't feel right.

Specifically, stationary is stationary. What matters is if the person is stationary or moving with respect to the steps. Whether the steps are moving up, down, left or right with respect to Earth makes no difference.

 

[.Scott]

That makes no difference. That's just a constant upwards velocity relative to the Earth. You know enough physics to see that you simply have two inertial reference frames there: the surface of the Earth and the moving escalator. Newton's laws apply identically in both.

Yes. I understand that - and it was my point. I was addressing remarks by @Dullard. I was trying to describe this in the same terms that he was using.

Ok, but that scenario isn't on the table so I'm not sure why bring it up or what you are trying to say about it...but it doesn't feel right.

Specifically, stationary is stationary. What matters is if the person is stationary or moving with respect to the steps. Whether the steps are moving up, down, left or right with respect to Earth makes no difference.

I believe that if @Dullard understands what I posted, he would also understand the other scenarios.

 

[Tom Hammer]

Let us consider climbing an incline on Earth that is the same angle as the stair climber and is parallel to the Earth's motion through space around the sun. Obviously relative to the sun the incline is moving. Let us approximate that the velocity is constant. The hill climber does not notice the motion and we calculate his work done relative to the center of the earth. The athlete on the stairmaster is analogous. The confusion results from the motion being obvious in the case of the stairmaster.

 

[votingmachine]

However, use of any external aids that are not moving down (e.g. the hand holds) does make a difference. To get the full value you mustn't pull on anything that is not descending. The people you see on the treadmill holding the bars, or pushing down on the handholds on the stairmaster are significantly reducing the work done. That's similar to being pulled uphill by a ski-tow.

Hanging on the bars is a HUGE difference. I see people locking their arms and bearing a significant amount of weight, reducing the work compared to a the same number of steps on real stairs.

The treadmill discussion brought up two differences between the treadmill and a track that seemed important: elastic rebound from the rubber tread stretch, and elastic bounce from the treadmill suspension. If there is a rebound or a lift provided, that will reduce the work. I don't know the mechanism and there are many different "stair" machines. There are differences in stairs themselves, say between a bouncy bleacher, and a concrete stair. I assume people adapt their gait and timing to take advantage of natural rebounds.

I run stairs in a ski conditioning class every fall. I don't currently run stair machines, but years ago, when I tried them, they seemed clunky and a bit odd.

An even larger difference is that in my fall conditioning class, there is an instructor and other people running. I have never pushed with the same intensity as when I am in that group, with those instructors. There is some human psychological benefit to being in a group that is told to do something intense for the next two minutes. You just don't quit. Bottom line: we are all a bit lazy, and it does not surprise me that stair machines get used at less than the maximal work, which would probably be as good as real stairs.

Air resistance seems like it would be a negligible difference between stair machines and stairs. No one is THAT fast on stairs.

 

[russ_watters]

Hanging on the bars is a HUGE difference. I see people locking their arms and bearing a significant amount of weight, reducing the work compared to a the same number of steps on real stairs.

The treadmill discussion brought up two differences between the treadmill and a track that seemed important: elastic rebound from the rubber tread stretch, and elastic bounce from the treadmill suspension. If there is a rebound or a lift provided, that will reduce the work. I don't know the mechanism and there are many different "stair" machines. There are differences in stairs themselves, say between a bouncy bleacher, and a concrete stair. I assume people adapt their gait and timing to take advantage of natural rebounds.

I run stairs in a ski conditioning class every fall. I don't currently run stair machines, but years ago, when I tried them, they seemed clunky and a bit odd.

An even larger difference is that in my fall conditioning class, there is an instructor and other people running. I have never pushed with the same intensity as when I am in that group, with those instructors. There is some human psychological benefit to being in a group that is told to do something intense for the next two minutes. You just don't quit. Bottom line: we are all a bit lazy, and it does not surprise me that stair machines get used at less than the maximal work, which would probably be as good as real stairs.

Yes, if we want to get into the weeds (and maybe we do, for the sake of completeness), the "same gait" assumption isn't necessarily true and almost certainly explains the differences in actual energy use. To address (agree with) a couple of your examples:

I have a treadmill that claims shock absorption. I don't know if that helps (elastic) or hurts (inelastic), but clearly different surfaces (asphalt, grass, sand) have an impact on running energy consumption.

I don't use a stairmaster, but I have tried an elliptical machine a couple of times and I really hate it. My feet are spaced too far apart and I think the stride length isn't optimized for my height (I'm 5'7") and as a result, I feel myself leaning back and straining to stay upright on it. I would think this would not apply to the stair-stepper style, but the steps need to be the exact right depth and height to compare with real stairs.

And not for nothing, but I wear a heart rate monitor while I exercise and find that my heart rate on a real bike vastly exceeds that on a stationary bike. It will be something like 150 on a stationary for half an hour to an hour and 170 on a real bike, for 2-4 hours. I think most of this is explainable as my body's attempt to keep cool when biking outside when it is warmer, but I really can't be sure. I also tend to have too regular of a pace on a stationary, when variability is said to help.

Regarding classes, I've never done one so I'm not sure I should comment, but a buddy of mine told me once he couldn't believe how much he would sweat in a spinning class vs biking on his own. This confuses me; I feel that if you aren't destroying yourself you aren't working hard enough, and a person should be able to make that happen on their own. But he was never an athlete whereas I did a lot of athletics in high school (not to mention the Navy), so I've learned what it feels like to push myself. Perhaps he didn't know - until someone beat it out of him - that he could be working harder.

 

[A.T.]

I've requested a copy of the full paper to check the methodology.

Looks like the numbers are from different papers, by different authors, with different subjects and likely different step heights (if they even used the stair version of the stairmaster, not the pedal one).

 

[OldYat47]

... which is false. It doesn't matter whether you employ a funny walk, you cannot cheat gravity.

"Funny walks" aside, the definition of work is force X distance. So repeatedly moving one's center of gravity up and down is more work per the technical definition. Stepping to match the machine's speed so your center of mass remains at the same elevation is less work per the technical definition. Whether or not that's more exercise (say, burning more calories or putting more stress on muscles) is another question. For me it's more difficult physically to do the latter.

 

[jbriggs444]

"Funny walks" aside, the definition of work is force X distance. So repeatedly moving one's center of gravity up and down is more work per the technical definition

It is the dot product of vector force times vector distance. It can be negative. If you bounce up and down, you do zero net work (albeit expending much effort).

 

[russ_watters]

"Funny walks" aside, the definition of work is force X distance. So repeatedly moving one's center of gravity up and down is more work per the technical definition.

Obviously, if you have a different gait you may use more or less energy. The question can't even be addressed without the assumption of a common gait.

 

[A.T.]

"Funny walks" aside, the definition of work is force X distance. So repeatedly moving one's center of gravity up and down is more work per the technical definition. Stepping to match the machine's speed so your center of mass remains at the same elevation is less work per the technical definition.

In the inertial rest frame of the support surface the center of mass is moving in the same way in both cases (assuming same same gait style), thus the work done is the same in both cases.

This has been explained ad nauseam in the other threads:
https://www.physicsforums.com/threads/fitness-treadmill-incline.937725/
https://www.physicsforums.com/threads/work-done-running-on-an-inclined-treadmill.927825

 

[OldYat47]

Shouldn't the inertial reference frame be the ground? The work isn't relative to the steps since gravity comes from the Earth. The work is the relationship between the Earth and the center of mass. Try changing the speed of the step and how quickly the stepping leg is extended. And again, this does not necessarily reflect the amount of exercise being done.

 

[PeroK]

Shouldn't the inertial reference frame be the ground? The work isn't relative to the steps since gravity comes from the Earth. The work is the relationship between the Earth and the center of mass. Try changing the speed of the step and how quickly the stepping leg is extended. And again, this does not necessarily reflect the amount of exercise being done.

That's valid on a large scale. But on the scale of a stairmaster the gravitational field is constant. Again think about an elevator moving at constant speed. You can't tell the velocity by dropping an object inside the elevator.

 

[jbriggs444]

work is the relationship between the Earth and the center of mass

The work done by what on what? In the case of a stairmaster, the device is absorbing work energy from the user and dissipating that energy internally. In the case of a stairs, gravitational potential energy of the climber is increasing. Either way, the muscles in the person's body have done the same amount of work.

 

[A.T.]

Shouldn't the inertial reference frame be the ground?

The motion relative to the Earth as such is irrelevant (assuming a uniform gravitational field for this small region). Only the relative motions between the human and support surface matter.

 

[russ_watters]

Shouldn't the inertial reference frame be the ground? The work isn't relative to the steps since gravity comes from the Earth. The work is the relationship between the Earth and the center of mass. Try changing the speed of the step and how quickly the stepping leg is extended. And again, this does not necessarily reflect the amount of exercise being done.

The reference frame can be whatever you want, as long as you do the calculation right(and relevant to what you want to know). But since we're trying to find the energy expenditure of the person, the easiest frame to deal with is the frame in which they are moving relative to what they are pushing against.

 

[MasterTheStairs]

a buddy of mine told me once he couldn't believe how much he would sweat in a spinning class vs biking on his own. This confuses me; I feel that if you aren't destroying yourself you aren't working hard enough, and a person should be able to make that happen on their own. But he was never an athlete whereas I did a lot of athletics in high school (not to mention the Navy), so I've learned what it feels like to push myself. Perhaps he didn't know - until someone beat it out of him - that he could be working harder.

I'm going off-topic in my own thread, but if you mean biking outside, he's probably sweating exactly the same amount per effort, or at least very close, but the passage of air on a bike would mean the sweat evaporates faster so you simply don't notice it. On a spin bike, no air movement, usually higher humidity, particularly in a group, would just mean the sweat isn't going anywhere. Even further off-topic, depending on what you're training for, high intensity all the time is not a good idea, it's becoming a discredited model as you need an aerobic base for long-term improvement, so a roughly 80/20 low/high intensity regime is far more use, depending on exactly what you're aiming for. On topic, you're right about the machine I was referring to, I should have said stepmill rather than Stairmaster, to distinguish it from the paddle-stepper type.

Folks, thank you all so much again for the replies, they really are appreciated, interesting and useful. I'm also delighted with myself for being able to understand so many of them