Does a StairMaster actually simulate climbing stairs?

Factual Questions
41

That will depend on how sophisticated the machine is. An eddy current brake produces increasing resistance torque as RPM increases. A given configuration of the magnets in an eddy current brake results in a particular torque-versus-RPM curve, and when you change the resistance setting on the control panel, the Stairmaster is repositioning those magnets to change the torque-versus-RPM characteristic. If it’s dead simple, then whenever the operator selects (for example) “5” on the control panel, the magnets will move to the same position every time, regardless of how much the operator weighs; a heavy person will make the pedals move faster than a light person. If the mechanism is more sophisticated, then pressing “5” on the control panel means the machine will move the magnets to wherever it has to in order to achieve the RPM that it associates with “5”, regardless of how much the operator weighs.

It’s been years since I touched a stairmaster, so I don’t know which is the case.

The resistance force at the pedals must exactly equal the operator’s weight. If the resistance is greater, the pedals won’t move down; if the resistance is less, then they will slam to the floor when the operator steps on them, with the speed of that slam mitigated only by the inertia of the flywheel. The fact that eddy current brake torque increases with RPM assures that there will be some speed at which the resistance exactly offsets the operator’s weight.

See above: I don’t think it is sensitive to weight, but it may be sensitive to RPM at any given resistance setting. Finding out for sure would require a heavy person and a light person to use the machine on the same setting, and observe whether the pedals move faster for the heavy person. If not, then the system has been designed to compensate (albeit indirectly, by watching RPM) for operator weight.

In terms of work delivered to the machine, yes, your CanoeMaster is identical to the Stairmaster. And both are identical to climbing stairs, at least in terms of what happens when you push on the pedal/step.

Yep, the total downforce on the step is your weight plus however hard you’re pushing up on the ceiling.

Because if the step/pedal is stationary, the eddy current brake is also stationary, and it offers zero resistance. As soon as you start pressing down on it with enough force to overcome the pedal return spring (I’m guessing that’s maybe just a couple of pounds), it’s going to start moving down.

If you step onto the pedal and quickly straighten your leg before the pedal has a chance to descend, you will lift your center of mass up, increasing your gravitational potential energy - and then as the pedal sinks, your body also sinks, and your GPE gets converted to heat in the eddy current brake.

A step forward on level ground theoretically doesn’t require any work to be done. If you’re starting from a dead stop you may have to do a bit of work to accelerate yourself (and absorb some work to stop yourself afterward), but if the step forward is arbitrarily slow, then the force is arbitrarily small, and work approaches zero. Zero force multiplied by any distance equals zero work.

[url=http://www.youtube.com/watch?v=Z_4djaNyKEE]The Stairmaster
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allows you to choose any range of motion you want, up to the maximum range of motion of the machine, which might be something like 18 inches. You can take extremely short steps if you prefer.

42

Oh, one of those. Too many people in the way, blocking traffic. I was hoping to do it without the obstructions.

Portland. It doesn’t have any real tall buildings, although one of the taller ones may have one of them. But it wouldn’t be the same as the CN Tower, which as every Canadian knows, is the tallest freestanding structure in the observable universe.

43

I primarily do my cardio on home machines these days and don’t even believe the gym I go to has a stairmaster, but the last time I used one it was a very different machine then what is being described here. You guys are describing machines that are like treadmills, in that an electric motor is continuously moving something.

The few times I’ve used a StairMaster, it was a purely mechanical device. Depending on the resistance settings, myself at 250 lb could “stand” on the machine with one of the legs fully raised and the other fully depressed. To depress the other one, I had to use some force to push it down and that force was adjustable based on the resistance setting you chose. Obviously just like a leg press machine where you can do very little actual lifting but instead play games with leverage and press huge amounts of weight (while doing little to build muscle), I could have just alternated putting my full body weight on one of the StairMaster legs at a time and let gravity and my weight push it down. But if I wanted to do a fluid motion I absolutely had to use my leg muscles to alternate pushing down on the alternating legs (so when my right leg is pushing down–aided obviously by some of my body weight, my left leg is not working, and vice versa.)

44

Aha. This gets to the core of my question. As I envision it, that brief moment while you lift your body (center of mass, as you put it), is the part of the stepping cycle where the Real Work™ gets done; this is what must happen if the Stairmaster is to give a good simulation of real stairs.

You seem to be describing a stepping cycle in which, at a certain phase, the user raises his body, and at another phase of the stepping cycle, the Stairmaster lowers the user back down; user works up a lather, rinse, and repeat alternately with left and right feet. This alternating up-and-down movement is what makes the staircase simulation a staircase simulation: Each time the user raises his body is when the Real Work™ is getting done.

If this is actually how a Stairmaster (or similar device) works, then that substantially answers the question I was asking in the OP. And I was also asking, implicitly, what kind of mechanism in the machine would make this work; your explanation about the eddy brakes and magnets, etc., covers that. (I was envisioning that the machine simply was full of sensors that tracked your exact motions, and controlled by a computer that simply operated a motor to drive the steps in such a way as to accomplish that.)

The contrasting paradigms that I was hoping to rule out (and I think you’ve finally done so here), are:
(a) The steps move in a steady-state way, such that the user doesn’t have that up-and-down motion, thus no phase where he raises his CoG, thus no exercise other than overcoming friction (i.e., equivalent to walking on level ground), or
(b) The movement of the steps, being simply unsynchronized with the user’s movements in any way, just produces a haphazard up-and-down movement, if any, resulting in haphazard exercise.

Am I getting closer to understanding how this all works?

45

Not particularly. Again, your muscles don’t care whether they’re lifting you up or pushing something else down while you remain at constant altitude. All your muscles know is that they are exerting 160 pounds of force, and they are straightening your leg. In other words, all they know is that they are doing real mechanical work; they have no idea whether it goes into increasing your GPE or heating up a brake.

I’m describing that, and I’m also describing a stepping cycle in which the operator remains at constant altitude while the pedals move downward under the influence of the operator’s feet. From the perspective of your quads, glutes and calves, and your cardiovascular system, it’s exactly the same thing.

The part of your statement that I have bolded is incorrect. Again, your muscles don’t care who or what is moving; all they know is they have exerted 160 pounds of force while your leg straightened.

Not at all. It doesn’t matter whether you take big or small strokes on the Stairmaster pedals. You can take 10 12-inch steps, or 20 6-inch steps, and either way, the work you deliver to that eddy current brake will be exactly equal to the amount by which you raise your GPE when you climb a ten-foot concrete staircase.

46

FWIW a biomechanical comparative analysis.

Machine Elf I am pretty sure you are wrong, you are not automatically delivering the same work by pushing a pedal down. Imagine the one extreme of no resistance against the pedals. Essentially that is the work of marching up and down in place. Not the same as climbing stairs.

47

This study answers the question “is working on out a Stairmaster kinematically identical to climbing real stairs?” They are kinematically different, since climbing real stairs requires in a more or less diagonal path from below/behind you to above/in-front of you, and the Stairmaster makes your feet move mostly up and down. Clearly your ankle, knee, and hip joints experience different ranges of motion in the two scenarios. But that wasn’t the question currently under discussion, which is this:

Does moving a Stairmaster pedal downward through a given distance with your weight require as much mechanical work as raising your center of mass upward through the same distance?

Again, if there is no resistance to the pedal, it will slam to the ground as soon as you try to step on it. Have you actually used a Stairmaster?

In reviewing the OP, I think I see where Senegoid may be confused:

Ah. If you’ve never actually used a Stairmaster, then I can understand why you might be puzzled about its workings. The pedals of a Stairmaster aren’t like the pedals of an exercise bike (or an elliptical trainer) that move through a range of motion entirely determined by the length of the cranks. There is a ratchet mechanism that allows each pedal to move upward whenever the operator transfers his weight to the other pedal. It’s a bit like a Salad Spinner, if you’ve ever used one of those. This reversal of movement can happen at any point in the stroke of the pedal, which allows the operator to select whatever step size he wants, up to the mechanical stroke limits of the machine, which (IIRC) is something like 18 inches. This video illustrates the behavior of the pedals nicely:

-at 0:38, he’s actually got both pedals moving down together, and his hands aren’t on the rails. His center of mass slowly lowers to the floor at a steady rate. His hands aren’t on the rails during this event, which means all of his weight is being borne by the pedals. If the pedals did not offer resistance equal to his weight, he would slam to the floor rather violently.

-at 1:10, he’s taking very short steps, letting each fall maybe six inches before transferring his weight to the other pedal.

-at 1:54, he demonstrates that it’s possible to take longer strokes. Hopefully this demonstrates that the machine isn’t particularly “in synch” with your steps; you can step up or down whenever you want to (subject to the stroke limits of the machine).

The three important facts about the Stairmaster:

  1. At all times, your entire weight is on one pedal or the other (or distributed between both pedals), resulting in a particular torque delivered the flywheel (and countered by the eddy current brake). note: this assumes you aren’t cheating by supporting your weight via the handrails.

  2. Whenever your weight is on a pedal, it moves downward at a speed proportional to the workout intensity selected on the control panel.

  3. Whenever a pedal (or both pedals together) move downward under the influence of the operator’s weight, they are providing resistance equal to the operator’s weight. If they did not, they would slam to the floor as soon as you tried to transfer your weight from one pedal to the other.

Anyone who does not believe any of these three points is encouraged to visit a fitness equipment store or gym and try out a Stairmaster. Point #3 can be dramatically demonstrated by having an overweight friend ride piggyback while you use the Stairmaster; you will soon see that it takes a lot more force (equal to your weight plus your overweight friend’s weight) to push each pedal down.

48

It was the extreme example merely to serve to illustrate why the work is not the same necessarily as clmbing up stairs. Moving the distance with your weight pushing the pedal down is not the same as lifting your weight up that distance.

I watched the video clip. The drop down of the step under his body weight is occurring under gravity as he transfers weight from the lower leg to the leg now at the top. He does not push it down all that much, gravity acts on his mass and down it drops against the resistance slowing its descent. His work is raising his legs alternately, transfering weight from one foot to the other, and balancing to some degree during the descent. Some of that transfer from one foot to the other is his body mass being raised by his power, but not necesarily all of it.

49

This study noted that on the Stairmaster, the leg being raised was partially pushed up by the paddle. But note that the machine they are talking about is not the “moving escalator” Stairmaster but the paddle-style machine, clearly visible in the photo on the linked page. The extreme of no resistance against the *pedals *is exactly like marching in place, I will agree.

However, most of the discussion in this thread is about the moving-stair machine. With a moving-stair machine, the force needed to push down to maintain your center of gravity in the same position while the stair drops away is the same force needed to raise your center of gravity by the same distance above a fixed stair step.

50

Scenario A: You are keeping your center of mass at a constant altitude while the pedal slowing sinks beneath you, and you are moving your leg at the slow rate necessary to make that happen. You are doing work during this time (160 pounds times 12 inches of pedal movement), but since your center of mass is at a constant altitude, all of that work goes into the eddy current brake.

Scenario B: You quickly straighten your leg so that your center of mass rises up 12 inches before the pedal has a chance to sink. You are doing work during this time (160 pounds times 12 inches of increased altitude), and it goes into increasing your gravitational potential energy. Then you stand straight-legged as the pedal sinks, converting your GPE into heat in the eddy current brake.

In either case, the amount of work done by your muscles is the same.

You’re describing scenario B, but after transferring his weight over to the higher pedal, the operator could also straighten his leg more slowly if he chose to. In fact, he could straighten his leg slowly enough so that it just offsets the pedal sink rate, keeping his center of mass at a constant altitude. This is scenario A. Again, as far as the total work done by your leg muscles, no difference from scenario B.

You could also do the same two types of motion (slow straightening of the leg, or rapid straightening followed by a pause) on a Stepmill or on a set of concrete stairs. Same deal: total work per step is the same in all cases.

There’s been plenty of discussion of both. It doesn’t help that Stairmaster Inc. makes both types of machines, so there may have been confusion about which type of machine is being referred to by the term “Stairmaster.” The discussion lately has focused on the Stairclimber type of machine (this is what I’ve been referring to when I say “Stairmaster”), which has foot pedals that move up and down in a more or less vertical motion, as opposed to the Stepmill, which is like walking up a down-moving escalator.

This is a complicating factor, but not by much. There is indeed a return spring to bring each pedal up when you transfer your weight to the other pedal. However, IIRC, the force isn’t much; it’s just enough to get the pedal back up to the top of its range of motion while you’re pushing down on the other one. Going from memory, I think this is not more than a few pounds of force. In an idealized machine, the pedal would have no mass or weight of its own, and so could be raised back up to the top of its stroke instantly with a vanishingly weak spring.

51

Okay, this discussion continues to move onward and upward, one “step” at a time. Your Scenario A, clearly, is the one I’m having a hard time wrapping my mind around.

What happens if I simply place a 160-lb brick on the step? It sinks, but the brick isn’t doing any work. It’s merely releasing all that potential energy that it has. Or, if you call that “work” according to the formal definition of “work”, okay, but that’s not where any “exercise” is happening. It could only have acquired that potential energy at some earlier time, when I lifted the brick up off the floor onto the step; that’s where the “exercise” happened.

52

Let me try it this way:

Suppose we start with Machine Elf’s Scenario B. I step up 12 inches, then hold still while the machine lowers me down 12 inches. Then I step up 12 inches again, then the machine lowers me again. Repeat. Each time I step up, I’m doing the Real Work and getting the Real Exercise. Each time I pause while the machine lowers me back down, the potential energy I’ve acquired gets transferred to the brake, escaping forever as entropy. But that’s not where I’m getting any exercise. The exercise I’m getting happens every time I step up, lifting my body.

Now, let’s reduce the vertical step increment to 6 inches. The same applies, but at 6-inch increments, and with 6-inch “restores” when the machine lowers me back down 6 inches.

Now, let’s reduce the vertical step increment to 3 inches. The same applies, but at 3-inch increments.

See where I’m going with this?

Now, let the vertical step increment approach zero. What happens? As long as there’s some alternating up-and-down movement, with the UP movement powered by my legs, I’m getting a full quota of up-stairs climbing during the UP movements, alternating with equal downward restorations, during which all my efforts are shuttled into the brake.

But what happens when the alternating up-and-down movement increment goes to zero? This becomes Scenario A. Now you have continuous work of the user’s legs going directly to the work of the eddy brake instead of discrete up and down movements; with the intermediate potential energy (the rise against gravity) now out of the picture. (The question may be only theoretical. Can a human user actually do this?)

What if, instead of a brake adjusted to a certain resistance, you have an electric motor in the machine that is driving the steps, but making the same movement. The user steps on the next step; it sinks under his foot as he straightens his leg, but this is driven by the motor that has been adjusted to lower the step at just that speed. Now it’s the electricity that’s driving the motor that’s driving the step, not the user’s leg-power. Does the user feel this differently than a machine operating in Scenario A mode by resistance of the eddy brake?

53

The brick is not extending its “leg” to maintain itself in one position, it is allowing itself to sink. This would be the same as you not moving your legs and allowing yourself to sink down the step. In both cases you are correct that neither you nor the brick is “doing” anything. However, moving your leg so that your body maintains its position on a downward moving step is the same as moving your leg so your body gets higher on a static step.

54

What happens is you’ve reduced the movement to zero so again you end up not “doing” anything. But that is not scenario A, scenario A is continuous movement instead of discrete movement. To turn scenario B into scenario A you need to remove any pauses from the movement so that it is continuous. This doesn’t mean the steps stop moving, it means they are always moving down and you are always climbing them. Instead of climbing stopping moving down climbing stopping etc.

55

Well, that is what I thought I was trying to say. The user has an interval when he steps up; then an interval when he stands still while the machine moves him back down. Now make ALL those intervals shorter, and let them approach zero. Then you have the user continuously going up and continuously going down, simultaneously. (Which is what I think you are saying in the sentence I bolded above.)

I still need to think more about this . . .

56

OK, consider this:

From a standing position on the floor, you hop up rapidly on a pedal, raising your center of mass 12 inches. The pedal then moves down 12 inches. Your center of mass sinks, and all 160 foot-pounds of gravitational energy is delivered to the pedal as mechanical work, and pissed away in the EC brake. It sounds like you fully understand and agree with this scenario.

Now let us suppose that from a standing position on the floor, you get onto the pedal with your knee bent, so that your center of mass does not raise up any higher than when you were standing on the floor, i.e. your gravitational potential energy remains unchanged. The pedal begins sinking, but you straighten your leg so as to keep your COM at the same altitude. All of your weight is on this pedal, and it moves down 12 inches. Note that from the perspective of the pedal, this is the same as the previous paragraph: it has felt 160 pounds of downforce during the entire event, and it has moved downward 12 inches, so it has received 160 pound-feet of work and pissed it away in the EC brake, just as in the previous paragraph . Clearly this work did not result from a change in gravitational potential energy. The only remaining possible source of this work is your leg muscles; the work was done as you slowly straightened your leg.

Can you point to which part of that paragraph you disagree with or don’t understand?

57

In scenario A there is not necessarily 160 pounds each of the 12 inches. I am just needing to shift enough of my weight over to that leg to make it descend against whatever resitance is set. It is a fraction of my body weight per inch moved.

Lifting my body up real stairs however requires moving my complete body weight the whole distance.

58

To review, you’re talking about this scenario I mentioned earlier:

Gravity does not take a break; it’s pulling down on you with 160 pounds of force at all times. If that force is not exactly matched at all times by some other force, then your body will accelerate either up or down. This means that:

If the operator is transferring only some of his weight to the higher pedal (or gradually transferring all of his weight), then the lower pedal is bearing the remainder of his weight. As was noted earlier, if you step on a pedal with enough force to overcome the return spring (i.e. more than just a couple of pounds), it will descend. If the operator’s weight is distributed between the two pedals, then both pedals will are engaged with the flywheel/brake mechanism; they will both descend at the same speed, and the sum of the force on both pedals equals 160 pounds.

I’ll ask again: have you actually used a Stairmaster? Either the Stepmill or the Stairclimber (the latter being the current focus of discussion)?

59

Not in many years.

From your description some fraction less than 50% (and not necessarilly 100%) of body weight needs to be on a pedal to make it descend. A weight less than that minimum must be on a pedal to allow it to rise. The weight is shifted keeping that balance such that there is above that minimum on the descending pedal and below that minimum on the ascending pedal. Not putting 100% on either pedal other than at the bottom of the descent.

The sum is 160 but the ascending foot is not providing muscle power providing its fraction, the return tension is.

Go to your gym and test at the resistance level you use for a good work out and see how much weight (grab some free weight plates) you need to place on a pedal to cause it to descend. That is how much lthe ascending leg is supporting of your body weight as you shift and how much less force you have effectively lifted. You say it is just “a couple” of pounds; I suspect it is more than you suspect.

60

A good idea for gathering objective data, but unfortunately I’m not a member of a gym; like you, it’s been a while since I touched a Stairmaster. We’ll have to rely on someone reading this thread who is a gym member to go and check this out, and estimate how much force is required to hold one of the pedals stationary at mid-stroke.

Having said that, no matter what the return spring force is, I can posit an arbitrarily heavy operator such that the spring force X is a tiny fraction of his weight Y, and then the fraction of his weight borne by the flywheel/brake mechanism approaches 100%.