Does a StairMaster actually simulate climbing stairs?

Factual Questions
61

Of course you can create the hypothetical arbitrary circumstance, heck easy enough just to posit that the specific user makes sure to shift all of his/her weight immediately totally lifting the other foot up from the other pedal as soon as the top foot begins to bear down … the point of contention is whether or not it is necessarily so.

Anyway it is a good work out that uses many of the same muscles as climbing real stairs in patterns not completely dissimilar and is more than capable of providing a fine work out.

One part of real stair climbing that it does not do by the way is the back down part. I do stair intervals sometimes … both as part of my runs (there are some good outdoor stairs on two of my routes) and in my home, in my basement going up and down carrying dumbbells a few times as part of a circuit. The descents are also exercise, not just active recovery, primarilyeccentric in nature, and not reproduced on machines at all.

62

The simplest way to analyze an escalator is just to change reference frames. The reference frame where the ground is at rest is no more nor less valid than the reference frame where the steps of the escalator are at rest. In the reference frame where the escalator steps are at rest, what you’re doing is like climbing stairs, because that’s exactly what you’re doing. Therefore, it’s like climbing stairs in any other reference frame, too.

Note that this only applies to escalators. I make no statement about Stairmaster machines, since I don’t know how closely those emulate escalators.

63

So Chronos you’d contend that if I am on an escalator and I raise one foot and place it on the higher step, gradually shift my weight over to that step completing putting all my weight on to it as it has lowered itself to the midpoint at which time I begin to transfer weight over to the foot that is now in the higher position, I have done as much powered by my muscles as if I walked up the stairs?

Really?

It is not exactly climbing stairs because I am not overcoming gravity as much.

Imagine being on a ladder vs on a ladder that is moving past you with you just keeping up moving your hands and feet into the new positions. Do really believe that the person who has actually pulled their body up a 100 rungs of a ladder is only doing the same work as someone who just moved their hands and feet into the new positions as the ladder moved 100 rungs?

64

Yes, absolutely, a thousand times yes. If an escalator moves downward 1 foot and you step up so that your center of mass ends up at the same altitude as when you started, then you did the same amount of mechanical work as if you had climbed 1 foot up a concrete staircase. Your leg muscles don’t know the difference, and if you closed your eyes, your brain wouldn’t know the difference, either.

This is the part you’re not getting. Concrete stairs? You’re pushing yourself up with 160 pounds of force through a given distance. Down-moving escalator? You’re pushing the escalator tread down with 160 pounds of force through that same distance. Your muscles have done the same amount of work either way.

Yes, absolutely the same in terms of work being done. Close your eyes, your brain won’t know the difference; you’ll be just as exhausted either way.

65

But I am not pushing the escalator down. It is moving down powered by a motor and I am just placing my feet in different positions at the same center of gravity, moving my center of gravity up and down wee bits each time. Even if those are a thousand times.

Even it was self powered what would matter is the force I need to exert to move the steps; it is not the same as my body weight just because it moves under my feet and me staying in place with my arms and legs moving is not me lifting my body weight.

I don’t have to imagine the ladder scenario. It is not too different from a Versaclimber. I could do (have done) a Versaclimber for 45 minutes plus at a moderately low resistance setting easily. Climbing up a ladder that long same pace? No way.

66

Gravity is pulling you down at all times. If nothing is resisting that, then you accelerate downward at 32 feet per second squared. If you are stationary, or moving upward or downward at a steady speed, then something is pushing up on you with 160 pounds of force, and you are pushing down on that thing with 160 pounds of force.

In other words, yes, your weight is pushing the escalator down. If you believe it is not, then you will have to explain why your body isn’t accelerating downward at 32 feet per second squared.

When no one’s on it, the motor draws electrical power to overcome friction and keep the steps moving, but if you put 20 people on it - 3200 pounds of meat - friction won’t be enough to keep the speed down. The motor will be operating as an electric brake, generating electrical power and shoving it back into the grid. If the motor wee suddenly disconnected, then the escalator tread would accelerate downhill and violently dump its passengers in a heap at the bottom.

Again, if you believe the force on the steps is not exactly equal to your weight, you will need to explain why you are not accelerating up or down.

67

The force on the step is equal to my weight when I am standing still, so? Am I doing the same amount of muscle work (related to the physics definition but not quite the same) standing still as running up steps or climbing a ladder? The question is how much force did my muscles need to exert over what distance.

Your explanation should tell you what is wrong with your argument. Standing still and pushing on the ground with 160 pounds (offset by the ground pushing back with the same force) is not the same as lifting yourself a foot off the ground.

Standing still I am doing no physics work despite the fact that I am exerting my 150ish pounds of force against the ground (and the ground for its part is exerting 150ish pounds of “normal” force against me). I am doing some muscle work because various muscles are contracting and lengthening every second to balance me there. (Unless I am laying there dead, and then I am still exerting that same force, not dropping down accelerating at g, without doing any muscular work at all.) Most of my muscle work going up stairs is required to move my center of mass up a distance against gravity, more than required standing still. Maintaining my center of gravity’s position with just a little variation in its vertical location up and down (which is what you generally do in the escalator and stair stepper conditions) requires much less muscular work than moving it against gravity a greater distance.

68

This statement is confusing. are you saying that:

A) when you are standing still, the force on the step is equal to your weight,

or

B) when you are walking up/down steps at a steady speed, the force on the steps is equal to (your weight when you’re standing still)?

If you are saying B), then we’re making progress. If you believe B is false, then you’ll have to explain why your center of mass doesn’t accelerate upward or downward under the influence of mismatched forces (gravity versus whatever force you are applying to the steps).

We’re not talking about standing still, we’re talking about walking up a down-moving escalator at offsetting speeds such that your center of mass is at constant altitude. Your legs are pushing down on the steps with 160 pounds of force, and the steps are moving away. Mechanical work is being imparted to the steps by your muscles. If the step moves downward 12 inches while it is subjected to 160 pounds of force from your feet, then it has received 160 pound-feet of work. If that work did not come from your muscles, you will have to explain where it did come from.

:confused: Who said anything about standing still?

To the rest of you dopers on the sidelines: am I the only engineer/physicist on the site? This is Physics 101 material. Can someone else explain it more clearly than me?

69

You did.

(Bolding mine.)

It was sort of your point. I need to explain why I do not fall accelerating at g when standing still. It seemed very trite to me.

  1. This is the escalator we are now talking about. I could be stationary on the escalator, dead on it, and it is moving down. Am I performing work?

  2. And more to the point of disagreement - the physics work involved is moving the body’s center of gravity a certain distance. Walking up real stairs each step moves the body’s center of gravity up the complete height of the tread. I believe such is not the case walking up an escalator attempting to maintain your position as the steps come to you. I believe that the total distance my center of gravity would have moved upwards in the work phase over 100 steps up a moving escalator maintaining my position as steps lowered to me is less than the vertical work done walking up the same number of steps. (Again the work the muscles do is different but for this analysis that difference is immaterial.)

70

You are wrong. It is exactly the same. An escalator is “real” steps they just happen to be moving with reference to the earth. Your body doesn’t know that, your body is not connected to the earth in any way. All your body knows is that it is on a set of stairs, they could be doing all sorts of things with reference to the earth, moving up, sideways, down etc. Your body is on a set of stairs and, in the reference frame of the stairs, which is all that matters, you are moving your centre of gravity up the stairs.

The steps are not “lowered to you”, you are not hovering in space with these things coming towards you, the steps are moving and you are moving with them, in order to stop moving with them you have to climb them.

Any possible difference there may be in perceived effort from moving up an escalator that is stopped and remaining stationary on a moving escalator is that you would probably climb a stationary escalator faster than the escalator moves when it is running. That means you use more energy per unit of time, but that is entirely self inflicted and is akin to saying it’s harder work running at 10 kph compared with 8 kph.

71

No, this is wrong, I think. My body is too connected directly to the earth, bypassing the escalator, by the force of earth’s gravity pulling on me.

(This GQ thread [del]is turning[/del] has turned into a GD thread! Whoda thunk? :slight_smile:

Case A: If I climb a set of stationary stairs, I am raising my body relative to the earth, against earth’s gravity, and that is where the hill-climbing exercise comes from. This is (substantially) Scenario A, above, and also substantially equivalent to DSeid’s scenario of climbing a stationary ladder.

Case B: If I walk up the down escalator, keeping my COG stationary, then yes, I’m making the same movement relative to the steps as in Case A. But that’s not where the exercise in Case A came from. In Case B, I am stationary relative to earth, and relative to earth’s gravity, and thus NOT getting the hill-climbing exercise of lifting myself upward. This is (substantially) Scenario B, above, and also substantially equivalent to DSeid’s scenario of climbing the descending ladder.

Granted, my 160 lbs. is still pushing down 160 lbs on the steps in any case. And, depending on the mechanism of the escalator (or Stairmaster), that may or may not be what’s driving the steps downward. But that’s going to happen just the same, whether I climb the steps or just stand still on the steps. That is not where the hill-climbing exercise comes from.

72

ETA: (Missed edit window): Okay, I [del]might have gotten[/del] got Machine Elf’s Scenarios A and B switched in the above post, relative to my “Case A” and “Case B”. Deal with it.

73

This isn’t scientific or anything, but I’ve walked up 15 flights of stairs before (took me about 5 minutes) and I’ve done 5 minutes on the stairmaster. It is not the same thing, the stairmaster was far less intensity.

74

Machine Elf and Richard Pearse are arguing that as I walk up the down escalator (or Stairmaster), I’m pushing “down” with all my weight on the steps, and this is driving the steps down against the resistance of the eddy brake – thus equal exercise to walking up some stationary stairs. And they are arguing: If that’s not the case, then what force is driving the steps down against the resistance of the eddy brake? Whereas DSeid and I are saying that’s going to happen even if just park my 160 pounds on one step and stay there.

So where is the discrepancy? Do we have a paradox here? Cognitive dissonance much? :slight_smile:

I spent all last night thinking about this. And recall, I’ve never used a Stairmaster nor any similar device, nor ever even seen one in action but briefly (but I do climb up fixed stairs from time to time). So I’m doing some guesswork here.

One of the scenarios is that of a user continuously walking up while the machine continuously moves down, at equal but opposing rates, such that the user remains vertically stationary. This is the case that we haven’t settled yet. Recall that a few posts up, I questioned whether this scenario actually ever happens.

Here is my speculation:

We’ve established that the Stairmaster has a control to set the resistance of the eddy brake. I’m guessing here that if the resistance is set higher, then when the user steps up to the next step and straightens his leg, the step will descend slowly, taking longer than the time it took for the user to straighten his leg. Thus, the user goes up, then down. When he goes up, he gets up-hill exercise. When he goes back down, that energy is transferred to the brake. The constant-COG-position scenario does not happen here.

If the resistance is set lower, then when the user steps up to the next step and puts his weight on it, the step descends faster. In this case, the user rises less than in the high-resistance case, or possibly not at all, before the machine lowers him. By rising less (in the intermediate case) or not at all (in the lowest-resistance setting), the user gets less up-hill exercise with each step. And, correspondingly, because the brake resistance is set lower, less energy is taken to drive the step downward against the brake. In the limiting case, the user gets NO up-hill exercise, and the energy transferred to the brake is minimized. I think this case must approach the situation of walking on level ground, as I have suggested earlier.

75

Senegoid, I’m not going to throw more math at you, but I want to point out the major conceptual flaw you keep demonstrating. You think it’s easy to lift your foot to the next step. It isn’t. Your weight is on your back foot, pinning it to the lower step. In order to lift it, you need to transfer it to your front foot and then straighten that leg. That requires lifting your entire body weight up one step.

As you do that, both feet are being pushed (err…“allowed to fall”) to the ground. Both feet. Before you can take the next step, you need to get the weight from the lower foot to the higher foot. That’s where the work comes in.
What you’re imagining is more akin to a stairclimber in a sling, suspended from the ceiling. They’re roped to the roof, so they don’t support their weight, and so their feet are free to move lazily up the moving stairs. That’s not the case here.

Try this. Stand up in your living room. Now lift one foot off the carpet. Now stay like that and lift the other up, too. Can’t do it? When you understand why, you’ll understand why climbing moving stairs takes work.

76

You are no more connected to the earth by its gravity than you are to the sun by its gravity.

You are not getting the hill climbing exercise of lifting yourself upward but you are getting the hill climbing exercise of keeping yourself stationary on a piece of equipment that is actively trying to drag you down. These two things are identical.

I’m curious how you perceive the physics of walking down the up escalator. Do you think it would be harder, easier, or the same as walking down stationary stairs?

77

No. It does not. It requires you shifting enough of your body mass to the upper pedal to overcome the resistance of the flywheel … which I have been told is only a couple of pounds … no more is required to make it start to lower. That is the key difference here that you are missing. Walking up steps in contrast does require that higher leg lifting the entire body weight.

No one says there is no work involved. But do this: raise one foot, hold it up a second, lower it, raise the other foot, hold it and lower it. Your legs have gone through the same motions as a the StairMaster allows. Have you done the same work as walking up stairs?

78

No, that is not equivalent. The stair master forces you to push down with the down going foot, the steps are not just things for your feet to rest on, they provide resistance. I haven’t used a stairmaster, but if designed properly the up going step should just be following your up going foot rather than providing it with any support, in this case your full body weight is transferred to the down going foot and it is equivalent to climbing stairs.

This whole thing is confused a bit by the different types of stairmaster. If you’re using the one that is essentially a mini escalator then there is no question that it is identical to climbing stationary steps of the same size at the same speed. If it’s one where the steps move up and down with your feet then depending on how well designed it is it may be possible to cheat in the same way you can cheat on a treadmill by supporting your body weight with your arms.

79

Walking down is not at all the symmetric reverse of walking up. As DSeid noted in Post #61, walking down (a hill or stairs or whatever) is an eccentric exercise, which has very different dynamics.

If walking up a hill requires me to exert a lot of energy to overcome gravity, then I should recover that energy while walking downhill, right? All I would need would be some good regenerative braking design work in my muscles.

Instead, when walking down a hill, I must exert positive effort with my legs muscles to control my descent (kind of like a returning space capsule firing its retro-rockets).

My semi-WAG guess: Assuming we can disregard a bunch of extraneous factors (and assuming we can even agree on what factors are extraneous): Walking down a hill or stairs, I’d be likely to descend with increasing velocity, unless I fought overtly to contain that. (Witness the tendency of down-hill hikers to fall forward, outrunning their feet.) Walking down the up escalator, keeping my COG stationary, I guess that factor would be absent: Hence, no overt effort on my part to keep from accelerating forward; hence, easier.

80

If the step would only go down with your full body weight against the resistance then you’d have a point. It is indeed more resistance than just raising and lowering your foot. And less resistance than your complete body weight. Again, it has been claimed only a couple of pounds of resistance will cause it to go down. Walking up stairs is your complete body weight being lifted by a single leg at a time.