Hi, this is may be trivial but i am confused anyway, i want to ask about the force we exert or calorie we spend on a treadmil is same with outside running. I mean in treadmill the running belt somehow propels us? By the way i neglect the surface effect of the treadmill.

rcgldr
Homework Helper
Unless there's a high powered fan in front of the treadmill, there's no aerodynamic drag factor. Running on a typical treadmill means you have to keep a very steady speed to stay within the bounds of the tread mill, which could be more tiring that running outdoors with some variation in speed would not be an issue.

I think I am right in saying there is no universal state of rest.
So imagine a treadmill a mile long. If you sat down, then you could be said to be at a state of rest (after all we are travelling around the sun at thousands of miles an hour but I am at a state of rest on my armchair).
If I got up from the long long treadmill and started to run against it, I don't see any difference to getting up and running down the road in terms of energy required to go a certain speed relative to the ground.

I think I am right in saying there is no universal state of rest.
So imagine a treadmill a mile long. If you sat down, then you could be said to be at a state of rest (after all we are travelling around the sun at thousands of miles an hour but I am at a state of rest on my armchair).
If I got up from the long long treadmill and started to run against it, I don't see any difference to getting up and running down the road in terms of energy required to go a certain speed relative to the ground.

yeah that's a good point of view, but last night i try to compare treadmill and outside running by drawing some simplified free body diagram, and i kinda stuck in the point of finding the force we apply to the treadmill, anyone may have an idea how to figure this out?

EDIT: Not so sure, just thought about it and you're not moving the mass are you.

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Borek
Mentor
Treadmill is never flat, it is always slightly inclined. It is walking up this incline that requires the energy.

That's not an exact model, but it should serve the purpose as an approximation. Imagine you do a step up the incline, then you wait till treadmill moves you down. Now you have to do a step up again. When you run you don't move horizontally, but you do the same - feet position in front is a little bit higher than feet position behind your back.

I doubt aerodynamic drag plays any significant role at the speeds involved in running.

The treadmill is self powered, you put your foot on the front and it's going to force it back (try standing still). The only work I see you doing is to move your foot from the rear to the front.

On a hill, as you step forward up the incline you are moving your mass (lifting it up the hill). On a treadmill you'd simply be moving your foot forward on to the treadmill, which then pulls it back for you. You aren't lifting your mass.

(I've only used a treadmill a few times, it always felt the same as actually being outside. It's just that thinking about this has got me wondering why.)

Borek
Mentor
Body mass does move - mass center oscillates up and down. Treadmill is responsible for the down part, your muscles are responsible for the up part. Sure, it is not 100%, just the fraction of the oscillation, but this fraction is high enough to make you sweat

That's why you can regulate angle of the incline - that changes the effort required.

Spinnor
Gold Member
Body mass does move - mass center oscillates up and down. Treadmill is responsible for the down part, your muscles are responsible for the up part. Sure, it is not 100%, just the fraction of the oscillation, but this fraction is high enough to make you sweat

That's why you can regulate angle of the incline - that changes the effort required.

Even if the treadmill were perfectly level your center of mass would still be going up and down as I'm sure you know, and in addition you are accelerating pushing off the back foot and decelerating when the front foot hits the ground (or treadmill). Running is work!

See:

The use of a treadmill inside can be compared to running outside by using a Galilean Transformation. It is the same as running on a very straight very level street, or a street of constant slope, with the wind at your back exactly matching your running speed. Come on, this is nowhere near rocket science guys. It is merely an application of the fact that all velocities are relative.

Let me forget about Physics for a moment.
Whenever possible, don't use a treadmill and run outside.
You may see nice, towering trees, pristine creeks and gorgeous girls (or boys).
Running indoor might be healthy but I don't enjoy crowded rooms

The use of a treadmill inside can be compared to running outside by using a Galilean Transformation. It is the same as running on a very straight very level street, or a street of constant slope, with the wind at your back exactly matching your running speed. Come on, this is nowhere near rocket science guys. It is merely an application of the fact that all velocities are relative.

i know it's trivial but i just want some kind of equationwise proof that two things are identical.

i know it's trivial but i just want some kind of equationwise proof that two things are identical.

Then do a Galilean Transformation yourself. All you have to do is to make sure that you add the same velocity to everything in the system, this includes the air that surrounds you as you run.