Work done running on an inclined treadmill

[votingmachine]

You are going to have to make this argument more detailed. As it stands, it is not even wrong.

Let me see if I can fill in the blanks where the details should be.

During the downstroke on a moving treadmill, your muscles are contracting and your leg is extending. The "just rides down" verbiage suggests that you believe that no effort is expended and no work is being done.

Please clarify.

Edit: found it.The word obvious is the clue that this is the error.

I should have used the word PERCEIVABLE, rather than obvious. I can add my voice to the chorus that says "it really is easier on a treadmill". How that difference in observed effort is reconciled with the physics of motion is not clear. I think it is partly in the "ride" effect.

People who have the experience of the two exercises know that the treadmill is not as much physical effort. That difference is real, even if the physics of the masses tells you that the same work is done on the system. Perhaps you need to calculate heat loss, which is not included in your mass-of-the-body calculation. I can say that the motion of my leg on the treadmill is perceptibly less effort than the motion of my leg on the ground. It may be that the explanation is entirely in the inefficiencies of physiology. Or balance differences between running between two guard-rails and running without them.

The temptation is to say that the effort has to be from a reduced work. You are clearly arguing that the work has to be the same, on an ideal treadmill, as on an ideal hill. That seems right, but I am still tempted to say that there is some work difference. It really does just seem more different than ordinary changes to gait and posture would account for.

 

[jbriggs444]

I think it is partly in the "ride" effect.

That effect appears to be a figment of the imagination. It has no basis in physical reality. There is no magical "I can stop running and let gravity do part of the work" mechanism in action.

 

[A.T.]

You are clearly arguing that the work has to be the same, on an ideal treadmill, as on an ideal hill.

With a human, nothing has to be the same. But there is no mechanical reason for it to be different.

 

[votingmachine]

That effect appears to be a figment of the imagination. It has no basis in physical reality. There is no magical "I can stop running and let gravity do part of the work" mechanism in action.

Yet when you run up a hill, you cannot separate the leg movement from the center of mass movement. On a treadmill you can. My movement is different. I think the legs that support my immobile upper body are moving in a way that is different from the way my legs move when they are forced to move my upper body up a hill.

The ideal movement on a treadmill would be to keep a transient support structure in place under the upper body. The ideal movement on a hill is to keep the upper body moving upward. Yes the treadmill is moving, and yes I use a running stride (more or less). But I think there is a difference in where the weight is, that does feel like I let the treadmill move my foot, rather than moving forward on the treadmill in a natural stride.

It could be a figment of my imagination. I might be imagining a different stride feel. I don't think I am though. I don't think I am calling upon anything magical. I am calling for a more complete description than the one that describes a 60 kg mass moved upwards 10 meters in a stationary frame, compared to the same 60 kg mass moved up 10 meters in a moving frame. Which you keep effectively saying is the same.

Where you make your mistake is in saying that therefore, any perception of a difference is a figment of imagination.

There are lots of differences between physics and physiology. I can bench press 60 kg 10 times. I can't bench press 600 kg once. The work is the same. The power differences matter to the individual. Sometimes incorrectly called work ... if I add a little weight, I struggle disproportionately and work harder. The effort and inefficiencies are getting tangled with the ideal work. Your rebuttal that it is a figment of imagination doesn't hold up to the reality of exercise.

 

[A.T.]

I am calling for a more complete description than the one that describes a 60 kg mass moved upwards 10 meters in a stationary frame, compared to the same 60 kg mass moved up 10 meters in a moving frame.

https://en.wikipedia.org/wiki/Galilean_invariance

 

[Grinkle]

Yet when you run up a hill, you cannot separate the leg movement from the center of mass movement. On a treadmill you can. My movement is different. I think the legs that support my immobile upper body are moving in a way that is different from the way my legs move when they are forced to move my upper body up a hill.

Your rebuttal that it is a figment of imagination doesn't hold up to the reality of exercise.

You are making this more of an either / or than it really is. Your running efficiency may be different on a treadmill than on a stationary surface. There are many reasons this may be the case. The physics of how gravity operates on mass that is on an inclined surface is NOT one of these reasons. Read post #65 by @A.T. Its a better / simpler visual than my post #63, I think. If you are inside such a box that moves at a fixed rate and you really don't want the back edge of the box to hit you, just like you don't want to fall off the back of a treadmill, your running efficiency may well change, but it won't be because gravity is now somehow behaving differently. Neither will your modified gait be a figment of your imagination. In fact, you couldn't tell if you were on a treadmill and the box were stationary or if you were on a long still belt and the box were moving. If you think you could tell the difference, explain how.

Your movement may be different. I think I run differently on a treadmill. I think its the pace-enforcement that changes my gait.

There are studies that show runners are less efficient on a treadmill than running outdoors, so it is not a universal conclusion that everyone find a treadmill easier than outdoors. I would say anecdotally most runners say the treadmill is easier, just noting that real studies don't bear that out. Here is one -

https://www.active.com/running/articles/equating-treadmill-and-outdoor-running?page=2

Snip:

Why is perceived effort higher, and performance consequently reduced, on the treadmill? Samuele Marcora, an exercise physiologist at the University of Kent who studies the relationship between perceived effort and endurance performance, says that running outdoors...

1. Produces more airflow against the body
2. Involves a visual perception of movement that is lacking indoors, and
3. Promotes more dissociative thinking through greater overall visual stimulation

All of these factors have been shown to reduce perceived effort.

 

[jbriggs444]

Yet when you run up a hill, you cannot separate the leg movement from the center of mass movement. On a treadmill you can.

That is not correct. You can separate leg movement from center of mass movement regardless. Stop and think.

Edit: You may be trying to suggest that how you move your center of mass depends on how you move your legs. That's true on both hillside and treadmill.

 

[russ_watters]

I should have used the word PERCEIVABLE, rather than obvious. I can add my voice to the chorus that says "it really is easier on a treadmill". How that difference in observed effort is reconciled with the physics of motion is not clear. I think it is partly in the "ride" effect.

Sorry, but this isn't correct.

The "ride" down is indeed free, but that is just what makes a treadmill a treadmill (keeps you stationary) and doesn't have any impact on the energy expenditure compared to walking up a hill. To see this more clearly, let's make the treadmill start and stop:

1. Treadmill is stationary and you take a step forward/upward. Then you stop.
2. Treadmill moves backwards to where you started and it stops.
--Repeat as desired.

It should be obvious that step 1 is exactly identical to walking up a hill -- because with the treadmill stopped it is just walking up a hill. Step 2 is the "free" (to you) ride down to reset for the next step.

 

[votingmachine]

Your movement may be different. I think I run differently on a treadmill. I think its the pace-enforcement that changes my gait.

There are studies that show runners are less efficient on a treadmill than running outdoors, so it is not a universal conclusion that everyone find a treadmill easier than outdoors. I would say anecdotally most runners say the treadmill is easier, just noting that real studies don't bear that out. Here is one -

https://www.active.com/running/articles/equating-treadmill-and-outdoor-running?page=2

Snip:

Why is perceived effort higher, and performance consequently reduced, on the treadmill? Samuele Marcora, an exercise physiologist at the University of Kent who studies the relationship between perceived effort and endurance performance, says that running outdoors...

1. Produces more airflow against the body
2. Involves a visual perception of movement that is lacking indoors, and
3. Promotes more dissociative thinking through greater overall visual stimulation

All of these factors have been shown to reduce perceived effort.

That link opens:

Given the fact that the energy cost of running on a treadmill is slightly lower than the energy cost of running outdoors, at least at faster speeds ...

I did not know that it was not universal. I thought everyone found a treadmill easier. That link says that runners perform better outside, even though it is harder. Perceived effort being inaccurate could be more important than actual differences in effort.

 

[votingmachine]

Here is a link I found that may more accurately portray what I feel as a "ride":
https://www.active.com/running/arti...gs-to-know-about-treadmill-training?cmp=23-69

Hamstrings: Because a machine powers the treadmill belt, the mechanics of your running stride differ when you run outside. When running on the treadmill, you use your quads to push off. But, unlike outdoor running, where you would typically rely on your hamstrings to finish the stride cycle and lift your leg behind you, the propulsion of the belt does much of that work for you. This means your hamstrings aren't firing as much and don't get worked running inside as they would outside.

Maybe it is that free finish to the stride cycle that feels like a ride.

 

[A.T.]

Here is a link I found that may more accurately portray what I feel as a "ride":
https://www.active.com/running/arti...gs-to-know-about-treadmill-training?cmp=23-69

Hamstrings: Because a machine powers the treadmill belt, the mechanics of your running stride differ when you run outside. When running on the treadmill, you use your quads to push off. But, unlike outdoor running, where you would typically rely on your hamstrings to finish the stride cycle and lift your leg behind you, the propulsion of the belt does much of that work for you. This means your hamstrings aren't firing as much and don't get worked running inside as they would outside.

Nonsense.

 

[Grinkle]

Perceived effort being inaccurate could be more important than actual differences in effort.

Especially when there are no actual differences in effort.

 

[votingmachine]

Nonsense.

Why is that nonsense? I see the same thing repeated in other links.

http://www.realclearscience.com/quick_and_clear_science/2017/05/30/you_may_need_to_run_15_faster_on_a_treadmill_to_equal_running_outside.html

In 1996, University of Brighton exercise scientists Jonathan Doust and Andrew Jones measured the energy use of nine trained male runners as they ran outdoors on a flat surface and on a treadmill. They found that running on a treadmill at consistent speeds between 6.7 and 11.1 miles per hour was less energetically demanding compared to running outside

...

researchers found that subjects exerted themselves to a greater extent on the track compared to the treadmill, despite running at the same speed.

...

As to why the treadmill was easier, the researchers speculated that the flimsy board of most treadmills upon which the belt runs could return elastic energy to the runner with every step, literally putting a spring in their stride.

I would think that the question is one amenable to study, and studies have indeed been done. The question appears to be incompletely answered. But that does not make it nonsense, but a physiological effect that is still poorly understood.

 

[A.T.]

Why is that nonsense?

The explanation of the difference ("because the belt is powered") is wrong, for the reasons stated many times in the thread.

I see the same thing repeated in other links.

http://www.realclearscience.com/quick_and_clear_science/2017/05/30/you_may_need_to_run_15_faster_on_a_treadmill_to_equal_running_outside.html
As to why the treadmill was easier, the researchers speculated that the flimsy board of most treadmills upon which the belt runs could return elastic energy to the runner with every step, literally putting a spring in their stride.

That is not the same explanation as the previous link. An elastic board is obviously not equivalent to a non-elastic road. Have you now moved from arguing about ideal treadmills to the imperfections of real ones?

 

[votingmachine]

The explanation of the difference ("because the belt is powered") is wrong, for the reasons stated many times in the thread.That is not the same explanation as the previous link. An elastic board is obviously not equivalent to a non-elastic road. Have you now moved from arguing about ideal treadmills to the imperfections of real ones?

No I have not. I'm not really interested in arguing at all. I was trying to add information about why treadmill running is WIDELY regarded (myself included) as easier.

The answer MUST be physiological, IF the physics of the two systems are the same. OR it lies in differences between the systems. OR there is no difference and the effect is entirely in the mind of runners. All of these are valid beginning hypothesis. If you want to argue with the researchers speculations, then contact them.

Treadmills seem easier. And researchers have seen a difference. I'm not sure why that difference exists, given that an ideal treadmill would be the same as an ideal track. The treadmill rubber definitely stretches on contact and release, and runners feel that, and change stride. The foot contact position was shown to be different in high speed video of treadmill and track runners and researchers have speculated about that. I think the foot release feels different, and again, that could again be the elasticity of the rubber (or spring in the platform) ... to me it feels like a free push on the back end of the stride.

The subject is interesting and far more complex than saying that there are two equivalent reference frames. Perhaps the elastic rubber stores and returns energy. Or the bouncy platform stores and releases energy. Or the gait differences matter. Certainly it is WELL understood that outdoor running has air resistance, and treadmill running has none.

If you are waiting for me to say that two ideal moving reference frames are the same physics ... I said that many posts ago. And I said there are perceived differences in effort. And I see research that says there is also a measurable difference in metabolic effort. So again, speculation about why is relevant. I did not read the "belt is powered" part carefully. More likely the "belt is elastic" is more relevant. Aid in finishing the stride cycle was the part I was calling attention to.

Be sure to recognize that running outdoors, you run against air resistance. And running on a treadmill, your body remains fixed relative to the air (very little air resistance). There are differences in the actual physics.

 

[A.T.]

If you want to argue with the researchers speculations...

What? I just wrote that an elastic board is obviously not equivalent to a non-elastic road.

Be sure to recognize that running outdoors, you run against air resistance.

Mentioned many times already.

Everything has already been said, but not yet by everyone. -Karl Valentin

 

[votingmachine]

You keep responding like you are trying to clear things up with a 5 year old. I am sure that is not your intention. Nor am I trying to pull a childish trick ... and if it appears I am, my apologies.

 

[Mister T]

If you ignore the energy losses due to heat transfer (from your body to the surroundings) and the moving of the arms and legs (since I'm assuming these to be about the same in climbing a hill as they are in running on an inclined treadmill) the chemical energy generated by your body's biological processes is equal to the gain in potential and kinetic energy of the center of mass of your body. Thus when you climb a hill you generate more chemical energy because you are raising the center of mass of your body, and increasing its kinetic energy.

A lot of the confusion in these types of discussions arises from a fundamental error made in introductory textbooks in the way work is introduced, an error that you see being corrected in many of the newer editions. The best way to start to understand this confusion is to look at the work done that's associated with a dissipative friction force. For example pulling a block at a steady speed across a level table top. The force you apply does, say, 100 J of work on the block. If you then say that the friction force does -100 J of work, the net work done is zero and the change in kinetic energy of the block is also zero. But how then do you account for the fact that the block and table top got warmer? The issue here is how to generalize the concept of work that's introduced in the study of dynamics to the concept of work that's introduced in the study of thermodynamics. The physics education literature has a vast discussion of this issue. The 100 J of work done by you produces an increase of 100 J in the internal energy of the block and the table, there is in the thermodynamic sense no work done by the friction force.

 

[jbriggs444]

Thus when you climb a hill you generate more chemical energy because you are raising the center of mass of your body, and increasing its kinetic energy.

This has been discussed to death in this thread already. When you run on a treadmill, the chemical energy (that is not wasted on biological or mechanical inefficiency) goes into work done on the treadmill. When you climb a hill, it goes into work done raising the center of mass of your body.

Six of one, half dozen of the other. To a first approximation, the same amount of chemical energy is used either way. [With apologies to those arguing about the second approximation]

 

[votingmachine]

That effect appears to be a figment of the imagination. It has no basis in physical reality. There is no magical "I can stop running and let gravity do part of the work" mechanism in action.

One other thing that occurs to me is that there has to be a speed micro-variation in the treadmill. The motor powering the treadmill has a response curve. The stride may be such that both legs are airborne, and no load is on the motor. The front foot strikes, and drives. Finally it lifts and both feet are airborne again, with the other foot the lead for the next stride. The load profile would be a crazy one. Combine that with the stretch of the treadmill rubber, and it could deliver a boost to different people who have different cadences, depending on how they synchronize with the load response. If there is a power return from elasticity, and from motor load response times, that would also make treadmills easier.

The motor is generally software controlled, with the target speed selected. I have no idea if the software tries to predict the jerks in the load that accompany running. It would make sense to have a flywheel. I've never thought about it much, but people jump onto the siderails, play with their phone, and then jump back onto the belt ... that has to be awful for motor life.

I'm not questioning the concept that the running motionless on the ideal treadmill simulates moving in the real world. Just pondering where the real treadmill is different.

 

[Grinkle]

I have no idea if the software tries to predict the jerks in the load that accompany running.

I don't think they do - they have closed loop velocity controllers that react to the varying load, but as far as I know they don't have any type of feed-forward to predict a variance.

Combine that with the stretch of the treadmill rubber,

Running surface definitely matters. My high school cross country coach credited the reduction of the 4 minute mile to a common place achievement to artificial track surfaces (as opposed to old school dirt tracks).

 

[A.T.]

Thus when you climb a hill you generate more chemical energy because you are raising the center of mass of your body, and increasing its kinetic energy.

This argument was debunked all over this thread. Did you read any of it?

Analyse an ideal inclined treadmill from the inertial frame, where the upper belt surface is at rest. Here you continuously move upwards and gain energy, just as you would on a real hill.

 

[votingmachine]

This argument was debunked all over this thread. Did you read any of it?

Analyse an ideal inclined treadmill from the inertial frame, where the upper belt surface is at rest. Here you continuously move upwards and gain energy, just as you would on a real hill.

I read that the same way as in post #124:

When you run on a treadmill, the chemical energy (that is not wasted on biological or mechanical inefficiency) goes into work done on the treadmill. When you climb a hill, it goes into work done raising the center of mass of your body.

Six of one, half dozen of the other. To a first approximation, the same amount of chemical energy is used either way. [With apologies to those arguing about the second approximation]

On the hill your chemical engine pushes thru the legs and lifts the body. On a treadmill, your chemical engine pushes against the band and puts a load on the treadmill system. I read that as calling attention to the work done thru the treadmill friction, when you look at it from the "rest" frame next to the treadmill.

Perhaps I misread, but I think it was the same argument made all thru the thread, but with a clarification about friction dissipating heat energy.

(since I'm assuming these to be about the same in climbing a hill as they are in running on an inclined treadmill)

 

[jbriggs444]

Thus when you climb a hill you generate more chemical energy because you are raising the center of mass of your body, and increasing its kinetic energy.

Perhaps I misread, but I think it was the same argument made all thru the thread, but with a clarification about friction dissipating heat energy.

I am not certain what argument you refer to. If it is the one above by @Mister T then I see no mention of friction.

 

[votingmachine]

I am not certain what argument you refer to. If it is the one above by @Mister T then I see no mention of friction.

Perhaps you are right. I might have misread. I just looked carefully, and there is a gap in the dots I connected. I read your post immediately after/simultaneously and put the friction he mentioned into your "work done on the treadmill" context.

... and I've just gone back and re-read again. Now I'm puzzled by the post. As I said, I checked the thread AFTER your response and read them back to back. I thought they were saying the same thing, with an aside about heat.

 

[Mister T]

This argument was debunked all over this thread. Did you read any of it?

Some of it.

In the second paragraph of Post #123, the work done by friction that I mention there is sometimes called pseudo-work, or whatever name you want to call it, to distinguish it from work that is thermodynamically valid (that is, able to be used in the 1st Law of Thermodynamics). I was thinking that the work done on the treadmill was of this type, but then I re-thought things when I saw what @jbriggs444 wrote in Post #124.

 

[fresh_42]

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