# Walker question

1. Nov 27, 2005

### yetar

Hello

I had a debate on comparing walking on the ground with velocity V and wlaking on an electrical walker with the same velocity V.
My claim is that there is no difference between walking on the ground in velocity V and walking on an electrical walker with the same velocity V, in terms of the forces that the person muscles do.
To further "proof" it, I brought an example of escalator. I said that going up 10 stairs on the escalator requires the same effort as going up the same 10 stairs on the escalator if it hasnt moved at all.

What do you think?

2. Nov 27, 2005

### FredGarvin

That's not true. There has been discussion of this before. Treadmills do not provide the same resistance that walking or running on regular ground does. The main reason is that motorized treadmills provide your propulsive force. Any runner will tell you that it is much easier to run on a treadmill than on a track or a street even if it is perfectly flat and with no wind. Granted, you do get a workout on a treadmill, don't get me wrong. There is a difference between keeping up and actually running though.

The only way a treadmill can simulate the outdoors effectively is if it is a freewheeling type that can provide resistance via friction or incline. Much like a stationary bike does.

Last edited: Nov 27, 2005
3. Nov 27, 2005

### yetar

I don't understand what do you mean by resistance?
If the track of the treadmil is always moving on the same velocity and your weight or you walking on it does not change the velocity of the track, why it is any different then simply a ground with a constant velocity?
In two systems which one moves in a constant velocity compared to another, there should not be any difference in the forces operating in them.
If you take the example of the escelator, is it easier to climb ten stairs in a moving escelator compared to climbing ten steps on a stopped (not moving) escelator?

Last edited: Nov 27, 2005
4. Nov 28, 2005

### FredGarvin

Resistance in the form of friction between the rollers and the belt. That way your legs have to provide some sort of propulsive force to keep the belt moving. If that resistance is not there, then one is simply keeping up with the treadmill. One is simply lifting a leg and moving a foot. They are not pushing off or moving their body weight. You are not providing the same amount of work. That is the main difference between outdoors and the treadmill.

5. Nov 28, 2005

### jonathanku

Not sure I subscibe to the friction explanation above. The differences that I see are:
+ on a treadmill, you are not doing any work to accelarate your body mass, but that normally only takes a second or two in real life, so isn't significant.
+ on a treadmill, you will not experience any wind resistance that your legs need to get you through, unless your treadmill is positioned in front of a big fan. Not sure how significant this might be.
+ a treadmill might have a springy feel under-foot; this might make running a little easier.
I would guess that most of the effort in running is the up/down motion your legs have to maintain.
As for the escalator, it's an accelaration thing again. If you are standing on a moving escalator before you start climbing the 10 steps, then it will be identical to climbing the steps is the escalator is stopped. If you start climbing as soon as you get on it (while it's moving) you will do more work with your legs because you're working against it's "push" upwards as it accelarates you vertically.

p.s. take my words with a pinch of salt if you wish ---me being a newby!

Last edited: Nov 28, 2005
6. Nov 28, 2005

### Staff: Mentor

But Fred, with constant speed, the only thing your legs are really doing is making you bounce up and down. If there was a net forward force (neglecting wind, as you said), you'd accelerate.

Most runners I know find treadmills more difficult to run on than roads/tracks. I personally run much faster on a road than I can on a treadmill. The only reasons why that I can think of is actually having a momentum helps - on a treadmill, you are surging forward and falling back as you push off with one foot and absorb that push with the other. That, plus...
I have a longer stride than average, but for me, the treadmill's springy-ness is a bad thing. Besides absorbing impact, it also absorbs the push-off. Yeah, it's easier on your feet that way, but just like running on sand, it is tougher on your legs because you have to work harder to push off. Most treadmills absorb impact by flexing, and the flex frequency is far too low to effectively absorb impact, but it does absorb the effort from your legs. They need to be very rigid, but padded instead.

Last edited: Nov 28, 2005
7. Nov 28, 2005

### FredGarvin

The mechanics behind running are much more complex than one force. Your legs are creating forces and accelerations because of the starting and stopping of the motions of each leg individually. Think of the force vs. time plot of a piston. It is essentially a sine wave. Same thing here. If you don't provide a force forward, you will not move. Every stride one takes involves accelerations. Your body's overall speed may be constant, but your legs are a different story.

I know a lot of people who don't like running on treadmills because of either the mental issues of staying still (boredom) or the stride issue and not being able to go full stride because the machine is too small. If you can get over those hurdles you'll find it is easier to run the same distance on a treadmill than outdoors.

8. Nov 29, 2005

### PerennialII

Would think that if a runner has his/her technique in order and really "coasts" as one is supposed to any 'propulsive' effect is pretty much negligible due to the flow of the movement.

However, one thing do see the movement of the belt affecting really much (and really bad) is like Russ said :
the way I see it in addition to the springy-ness is that the time in contact gets shorter (or that you don't have a constant ("rigid") surface from which to push), which makes the 'efficiency' of running go down, you don't have that much time to "produce the force" which as such makes your stride inefficient compared to what one can come up with for example on track (and limits your elasticity, length of stride etc. in the process). And the springy-ness is a separate problem as well, for myself personally when starting to go down from 4 mins/km, near 3 mins/km even though have as sturdy of a treadmill as they come it pretty much deteriorates the running as a whole (just like it wasn't difficult enough even without).

Do think there is a sort of a consensus that treadmills are more difficult than running 'in nature', at least the runners do know tend to do systematically shorter exercises on treadmills due to it resulting to 'wearing one out' sooner.

Last edited: Nov 29, 2005
9. Dec 1, 2005

### yetar

Lets assume that the springiness is equal to that of a running track.
Would then the running be almost identical to running on a track?
I didn't understand the explaination about the shorter contact time, why does that happen?

10. Dec 1, 2005

### PerennialII

Equal springiness (& damping) and will have a hard time finding sources making things differ.

About the contact time .... I thought about it in a sense that the velocity profile of a runners leg is not constant during the effort, and as such if the 'boundary condition' of foot differs (constant velocity of the treadmill) it will affect the time & exertion during the time of contact, and if it is shorter (which seems reasonable) it will be more difficult for the runner - as such decreasing efficiency (muscles unable to do the same amount of work in a shorter duration and contraction)(usually the runner controls the velocity, in a treadmill that is not the case). Should see some measurements in order to be able to say what phenomenon is relevant (quantitatively relative to each other), but on the basis of doing lots of miles on treadmills have come to that sort of a 'conclusion' (also, not something you experience when "just running", need to have some speed to become prominent).