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I had this discussion with my relatives about the reason why it feels like you spend less energy on a step machine in the gym (basically an escalator that goes down), than it is to move up some stairs. They agreed that the former takes less energy than the latter, but we had different reasons for why.

My reasoning was that on real stairs you walk up against gravity. This means that you have to convert kinetic energy from your moving legs into potential energy ($m\cdot g \cdot h$). While on step machine (or downwards escalator) you only have to keep yourself in one place, so $h = 0$.

However my relatives argued that it had nothing to do with physical laws, but rather a combination of these factors:

  • The handles on the step machine allow you to carry less weight.
  • I move at an irregular pace up actual stairs.
  • I don't walk with the same velocity up the stairs as the step machine goes down.
  • Air resistance.

While I agree that these factors will cost additional energy on the stairs compared to the step machine, I doubt that it's enough to explain my personal experience with the two. When I walk four floors up the stairs at my office I have to catch my breath a bit. However when I walk against the step machine I can keep up for like 20 minutes. I did notice though it was a bit harder when I released the handles, but I could still keep up a solid 10 minutes in one go.

Their counterargument against my reasoning is that I would need to use the same amount of energy to push myself against a step that is moving down to keep myself in place as it is to go up a stationary step, because it's all just relative.

However my countercounterargument would be that since you are walking against gravity, that the relativity argument does not hold up. Relativity is for when you are in a inertial frame of reference and when gravity is involved there is no inertial frame of reference anymore (unless maybe when you are in freefall, but then walking stairs becomes impossible).

Who's right here?

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    $\begingroup$ You are at least partially correct - in an escalator, you could in principle move only your legs to go with the movement of the steps while keeping the rest of your body stationary, so that your center of mass barely moves at all. You would be doing work only on your legs. I'm posting this as a comment because a full answer would need to take into account all the other factors. $\endgroup$
    – Javier
    Commented Jun 14, 2022 at 13:47
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    $\begingroup$ You aren't performing work on your COG. It's like doing squats holding dumbells except you bend your arms so the dumbells remain stationary in space. Your legs are a lot less tired because they aren't actually moving the dumbells. This is why treadmills are also easier. $\endgroup$
    – DKNguyen
    Commented Jun 14, 2022 at 13:51
  • $\begingroup$ Do you walk up the steps in your office at the same speed? Are the step sizes the same size? $\endgroup$
    – Jbag1212
    Commented Jun 14, 2022 at 13:54
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    $\begingroup$ @Javier, The pedals of a stair climber support the full weight of your body, and they move. Force times distance equals work. The same work that your legs would do to raise your body by the same distance on fixed stairs. The difference is where that energy goes. On fixed stairs, The work that your legs do raises your body mass against Earth's gravitational field. It's converted to gravitational potential energy. On the stair climber the work that your legs do is converted to heat in the brake* that allows the pedals to slowly descend. $\endgroup$
    – Solomon Slow
    Commented Jun 14, 2022 at 15:01
  • $\begingroup$ * brake or other mechanism. A stair climber could, in principle, use an electric motor and regenerative braking, and it could feed the energy into the power grid. $\endgroup$
    – Solomon Slow
    Commented Jun 14, 2022 at 15:02

3 Answers 3

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The Galilean relativity principle is old physics but still more than correct enough for use in this type of situation. This states that the laws of physics are the same in in all inertial frames of reference.

So there is no fundamental physical difference between maintaining a position on an escalator that moves steadily downwards, and climbing stairs at a steady pace. The mechanical work you have to do is exactly the same.

Imagine you were walking up the stairs in a narrow stairway with smooth walls. And imagine there are walls behind you and in front of you that always stay at the same distance. There is no experiment you could do to tell the difference between a stationary staircase with motorized walls in front and behind, and a moving staircase with stationary walls.

To deal with your question about energy - you are converting your internal energy into potential energy in either case, in the same quantity. It's just that on fixed stairs the potential energy builds up in your body. On moving stairs the potential energy is removed by the device at the same rate that you add it. In the latter case the energy could in principle be used to power a machine attached to the stairs.

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  • $\begingroup$ Imagine if the set of the Virtual Insanity music video had had stairs. $\endgroup$
    – bdsl
    Commented Sep 12, 2022 at 10:25
  • $\begingroup$ Don't inertial frames of reference require that there is no gravity? $\endgroup$
    – user3635700
    Commented Feb 18, 2023 at 15:15
  • $\begingroup$ @user3635700 Not in newtonian physics they don't. Newtonian physics is more than accurate enough for this sort of question. You're introducing general relativity which would just make this more complicated without changing the answer. $\endgroup$
    – bdsl
    Commented Feb 19, 2023 at 17:07
  • $\begingroup$ In addition to what this answer describes, I think it's true that the stationary handles on step machines make you use less energy if you use them (on real stars, they would be essentially pulling you up), and that there is a difference in air resistance (though I expect that this would be negligible). $\endgroup$
    – a3nm
    Commented Feb 22 at 21:04
  • $\begingroup$ @a3nm Right, if you put any weight on the handles then you don't have to do so much work with your legs. $\endgroup$
    – bdsl
    Commented Feb 22 at 21:28
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You don't use the same force for pushing down your leg on the step machine as compared to a real staircase.

On a staircase, you have your full weight on one leg while the other is up in the air on its way to the next step.

On a typical step machine, the other foot is still in contact with the pedal, taking up some of your weight. And if you use the handles, you'll probably also take up some of your weight with the arms. And both, the other foot and the arms, don't do any work. They are either steady or even gaining energy.

If everything else is identical (step height and stepping speed), you do less physical work because of the lower force that you apply with your "working" leg.

To create a comparable experience, refrain from taking up any weight with either your arms or the "other" leg (and adjust the machine accordingly to provide enough resistance).

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    $\begingroup$ I think you're imagining a different, simpler form of step machine that has pedals. The OP describes a step machine that's basically a very small escalator that moves down as the user stays in place. Something like this fitkituk.com/images/products/medium/1574440013-49232600.jpg $\endgroup$
    – bdsl
    Commented Sep 12, 2022 at 10:15
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    $\begingroup$ @bdsl You're right. I've never seen a step machine like the one you linked. That matches OP's description perfectly, and then most of my answer doesn't fit. $\endgroup$
    – Ralf Kleberhoff
    Commented Sep 15, 2022 at 10:22
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The escalator effort depends on whether you are maintaining position or drifting. Even maintaining position requires less effort than walking up stairs, because your mean "step up" distance is half a step. The "stair" is dropping as you step up to the next level, so to speak.

I can't comment on a "step machine" without knowing whether the machine is motorized, whether it has adjustable friction resistance, etc.

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  • $\begingroup$ The step machine is motorized and can be set to your preferred speed. I don't know what adjustable friction resistance is. $\endgroup$
    – user3635700
    Commented Jun 16, 2022 at 8:10

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