Physics Question - Hills on Treadmill

Some idiot once said to me "its easier running on a treadmill because the treadmill does all the work for you".

I avoid them anyway. Run outside and you won't have to worry.

gbgurt wrote:

After all this thread I didn't see anyone who actually WENT OUT AND TRIED IT. Thats what I just did I went outside theres a hill near my house thats at an 8% grade and 427m long I went out and ran up it in 98 sec so thats 9.74 mph so I rounded to 9.8mph and hit my treadmill at 8% incline and did the same thing and RUNNING UPHILL WAS HARDER. A lot harder actually and I know why.

What many of you are missing is that IT TAKES ENERGY TO LIFT AN OBJECT. The basic fact remains that the force due to gravity is overcome completely and then some to accelerate you upwards when you are on a real hill but the normal force of the treadmill overcomes some of the gravitational force and you only match it so it takes far less energy

I am going to give you the benefit of the doubt and assume that you are trying to be funny.

Newton wrote:

Where did I say you still thought you were right about the physics? My point was you were trying to show that you were right in the fact that there is a difference between the two scenarios(not necessarily the physics) which was never being debated. No one ever refuted that claim.

Thank you for the good example of a "tu quoque" argument as well.

I took people saying that there waas "no difference" and things of that sort to mean exactly that: no difference (apart from stated assumptions like lack of wind resistance).

Not really trying to argue, saying "you're wrong" in that case. Just observing the irony of you bringing up ad hominem arguments. :)

You still there Mr. Newton?

Can't really disagree with what is pointed out here:

"Or how about if the treadmill was truly stationary (in the sense that most folks here think) but the earth magically started moving backward at 8 mph (with the treadmill NOT moving backward at 8 mph). Is there any conceivable way to distinguish this scenario from the 8 mph treadmill and the non-moving earth? So there you are running on a completely stationary surface but your biomechanics are going to differ relative to running on a (wait for it) completely stationary surface?!?!?"

can you?

Don't feel bad. That's because THERE IS NO DIFFERENCE.

And if any of my students would ever come to my physics class and claim that an appeal to some study by some expert negates basic physics...well let's just say that is not the way to pass the exam.

Vegan Physicist wrote:

At it's core, the study only shows a difference in biomechanics when running at the same pace with different stride frequency / length combinations. I'm not sure why the author goes on to speculate that these difference originate from having a moving belt vs. a moving runner, but it is speculation. I'd be more inclined to attribute these to the physical nature of a treadmill and the variations inherent of such (i.e. flywheel effect of motor, flexation of surface, air resistance, etc.)

Also, as mentioned, the item you quoted is someone's facebook entry.

Right, I completely agree with you. I started writing this same basic response to Yuppers but you beat me to it. I do not attribute the bio-mechanic alterations to the fact that the treadmill is "moving" but to the variation you listed.

Scherbatsky wrote:

I took people saying that there waas "no difference" and things of that sort to mean exactly that: no difference (apart from stated assumptions like lack of wind resistance).

Not really trying to argue, saying "you're wrong" in that case. Just observing the irony of you bringing up ad hominem arguments. :)

I never claimed I wasn't a hypocrite.

Also, I believe the 1983 Frischberg study was for 100 meter sprints, not steady state running.

What the heck wrote:

And to all those folks who think that treadmill running is magically different than "real" running, please go back to physics class. The only differences are the lack of wind resistance and the cushioning of the treadmill. The fact that you are not going anywhere and that you have no gain in elevation is completely irrelevant.

This has been a public service provided by physicists anonymous and will be completely wasted on the Letsrun crowd.

What in the world are you folks still talking about? I gave you everything you need to know right up front.

What the Heck?

Newton wrote:

Vegan Physicist wrote:

At it's core, the study only shows a difference in biomechanics when running at the same pace with different stride frequency / length combinations. I'm not sure why the author goes on to speculate that these difference originate from having a moving belt vs. a moving runner, but it is speculation. I'd be more inclined to attribute these to the physical nature of a treadmill and the variations inherent of such (i.e. flywheel effect of motor, flexation of surface, air resistance, etc.)

Also, as mentioned, the item you quoted is someone's facebook entry.

Right, I completely agree with you. I started writing this same basic response to Yuppers but you beat me to it. I do not attribute the bio-mechanic alterations to the fact that the treadmill is "moving" but to the variation you listed.

I agree with Vegan Physicist and Newton, this makes sense to me.

Roommate out.

What's so comical about these threads trying to substantiate minute differences between running on a treadmill and running outside is that virtually every single run you do outside is different in some way depending on how many hills, the wind, and the temps.

Why does it even make a difference?

How do you know it's an 8% grade? Is it a steady 8% grade? Does it average out to 8%? Did you measure it with a transit? Did you calibrate the speed and incline of your treadmill? Is the belt tight on your treadmill? This was hardly a controlled experiment.

For the benefit of making it a reasonably approachable problem, the physics analyses in this thread have mad some assumptions, mainly:

-The motor holds the speed of the treadmill perfectly constant, regardless of required torque.

-The belt is inextensible.

Neither of these is true, particularly for crappy treadmills, but they are reasonable approximations. These assumptions make the treadmill an ideal machine for conceptual purposes. Things in reality are more complicated, but the core fundamentals remain the same. Examining the details for better understanding requires research and controlled experiments.

This has already been covered on the second page. The answer has to do with the ideal machine assumption of the treadmill. Go back and read.

Newton, I agree with most of what you've been posting and with Vegan's comment on the study you cited, but I have to bring this up:

Newton wrote:

"As the tread belt rolls backward it drags the foot backwards, eliminating the need for the Gluteals and Hamstrings to pull the upper body forward thus making the movement easier; hence its potential lower energy cost (Frishberg, 1983)."

This. Is. Completely. Wrong. If the treadmill is dragging your foot back through the entire step, then it is dragging you back off of the treadmill. Assuming you're not holding onto anything and there is no wind, then the friction between the belt and your shoe is the only external lateral force on your body. That means it must average to zero over each step, and if it doesn't, you will have accelerated in the direction of that friction force.

Now, perhaps they mean that initially the foot is being dragged backward until some point in the swing phase where the frictional force would change direction. This is possible and many people do this to a great extent, despite the inefficiency (basically either planting or dragging your foot at footstrike; I know someone who slides his heel a bit at every heel strike, you can hear it). However, even if this is what was meant in the above quote, the conclusion is still completely wrong. If indeed someone's stride is such that the belt will initially "pull" their foot backward, then the ground will do the same thing in a moving reference frame if that person runs the same way on the ground. If you wish to say that the treadmill is "eliminating the need for gluteals and hamstrings to pull the upper body forward" for a specific person's stride, then you have to say the ground is doing the same thing.

The only way I can imagine the treadmill "helping" you pull your foot through is if the belt is flexible enough to store energy upon planting your foot, which is recovered in the swing phase. This would still be inefficient since your pushoff would still have to be appropriately harder.

write up the problem. show formulas. perform experiments. fit curves. correct your formulas. be an engineer.

Reading this thread I can't escape the conclusion that the people who think running on a treadmill is different are holding onto the handles.

to be an engineer wrote:

write up the problem. show formulas. perform experiments. fit curves. correct your formulas. be an engineer.

I have done most of that, although thorough experiments can be expensive. And I am an engineer.

There are no puddles on treadmills.

The problem with your argument is that the force to gravity ratio is inversely proportional.

to be an engineer wrote:

write up the problem. show formulas. perform experiments. fit curves. correct your formulas. be an engineer.

Like we have time and budget to do that kind of stuff . . .

There are treadmills without motors. They just don't regulate your speed for you.

----------------------------------------------------

So are you saying that running a given speed on motorless treadmill takes the same effort as running the same speed on one with a motor ?