Running on a treadmill - Question for you physics people

LionelNashe

Hi folks,

I was just watching this vid about how to run on a treadmill, and one of the opening statements just struck me as plain wrong.

"While running on solid ground generally requires you to push off your back foot in order to propel yourself forward, running on a treadmill does most of that work for you."

Unless I am missing something, this guy in the video is fooling himself into thinking that treadmills require a different kind of running than the ordinary running. Surely movement relative to a treadmill is not different from movement relative to the ground? i.e it shouldn't matter if you are moving or if the 'ground' is moving.

Morbert

LionelNashe wrote: »

Hi folks,

I was just watching this vid about how to run on a treadmill, and one of the opening statements just struck me as plain wrong.

"While running on solid ground generally requires you to push off your back foot in order to propel yourself forward, running on a treadmill does most of that work for you."

Unless I am missing something, this guy in the video is fooling himself into thinking that treadmills require a different kind of running than the ordinary running. Surely movement relative to a treadmill is not different from movement relative to the ground? i.e it shouldn't matter if you are moving or if the 'ground' is moving.

Hmmm... I'm not sure if they are actually equivalent, even though I would have assumed they were.

http://www.posetech.com/training/archives/000188.html

"Sure the ground reaction will be the same because the transmitter of gravity to the ground is the same, which is the body weight. But which force is working to change the support or to move the body weight from one leg to the other? In overground run it is gravity, on the treadmill it is the belt, moved by an electric engine."

calahans

To understand it we would need to look at a force diagram.

With regular running you need to move up and forward a kind of 45degree acceleration. With running on a treadmill there is really only the up and down motion (possibly some forward) which I would think is less overall.

LionelNashe

calahans wrote: »

With regular running you need to move up and forward a kind of 45degree acceleration. With running on a treadmill there is really only the up and down motion (possibly some forward) which I would think is less overall.

But if there was a mark on the treadmill surface, say a drop of sweat, your motion relative to the drop of sweat would be forwards and upwards as well as the belt carried it backwards.

Thinking about it further: If running on the ground is different to running on a treadmill, then it should also be different to running on a train that's moving at a constant speed. But I can't imagine that it is. And as the earth is spinning, isn't it one big treadmill anyway?

Triangle

You can't use the train analogy as it's different from a threadmill.

On a train - you and the train are moving at the same speed. when you start running you acelerate and are moving faster than the train.

the threadmill is not moving forward and therefore is different.
Basically, if you just jump up and down on the threadmill then the belt still moves. Does this mean you're running?

When you foot drops onto the belt, the motor is drawing it back and doing some of the 'work' for you.
Unlike running on land, when your foot falls on the ground you need to expend energy to push yourself forward.

not sure if this makes sense to you.

LionelNashe

Triangle wrote: »

You can't use the train analogy as it's different from a threadmill.

On a train - you and the train are moving at the same speed. when you start running you acelerate and are moving faster than the train.

Yeah, but say the train is moving at a constant 10kph. You are in the train, running towards the back of the train at 10kph, relative to the train. So you are stationary relative to the ground beneath the train. This seems to me to be identical to running on a treadmill.

Triangle wrote: »

the threadmill is not moving forward and therefore is different.
Basically, if you just jump up and down on the threadmill then the belt still moves. Does this mean you're running?

No, you're not running, and not moving horizontally relative to the surface of treadmill in this situation, so you would fall off the back. Like if I was on standing on a train that was travelling at 200 mph and I leaped 3 feet straight up in the air, I wouldn't move horizontally, relative to the train. I would land on the same bit of carpet that I was standing on.

Triangle wrote: »

When you foot drops onto the belt, the motor is drawing it back and doing some of the 'work' for you.
Unlike running on land, when your foot falls on the ground you need to expend energy to push yourself forward.

not sure if this makes sense to you.

Surely the energy exerted to resist the backward movement on a treadmill should be equivalent to the energy used for forward movement on the road.

Bodicea

At the risk of being distateful and getting my wrists slapped..... Instead of thinking about it in terms of jumping..think of it in terms of going to the toilet...

If you pee in a toilet, on a train travelling 200mph....where does the pee go? Into the toilet of course....so why would the laws of physics change if you were to jump. Your pee is just as detached from the toilet (and you) , as you are from the train when you jump...

Most people 'have' used the toilet on a train....very few have tried jumping though

Bet ye will all check it out next time yer on a train

Bodicea

Oh, sorry, meant to add, that running on a tread mill and running on the road, are not really any different. If the treadmill were to stop dead under your feet, and there was nothing to block your forward movement..then you would keep running at the same pace, assuming you were prepared for the stop or else your balance would be affected, hence the wobble and legs in air. It happened to me once...Not nice!

calahans

As I have said to run on a road you need both forward an upward acceleration. When you run in a gym there is probably less upward acceleration required as there is almost a mini spring force in hitting the treadmill (more bounce than hitting the road).

With regard to the forward motion you need to expend to move it is less in a treadmill as the road is moving back effectively using energy supplied by the treadmill motor.

I know this empirically as being someone who has being running in parks and gyms for ten years, it is harder to run the roads after a couple of months running in the gyms!

LionelNashe

calahans wrote: »

As I have said to run on a road you need both forward an upward acceleration. When you run in a gym there is probably less upward acceleration required as there is almost a mini spring force in hitting the treadmill (more bounce than hitting the road).

I'd agree that this seems possible.

calahans wrote: »

With regard to the forward motion you need to expend to move it is less in a treadmill as the road is moving back effectively using energy supplied by the treadmill motor.

I think that this is possibly true for the first step, or half a step, on the treadmill, as your leg is drawn back and your body's inertia keeps it in the one place, but it makes no sense to me to say that it might be true once the treadmill is going. I have tried to say why in my response to Triangle's post, above. I found a paragraph elsewhere though that expresses it nicely:
The relative motion between runner and running surface is exactly the same as in the case when the runner is running on the road. Standing next to the runner on the treadmill and watching her motion is exactly the same as riding beside her in a cart as she runs down the road such that the speed of the cart is the same as the speed at which she is running. In both cases you are sitting in a nice inertial reference frame and the laws of physics will be exactly the same.

Professor_Fink

LionelNashe wrote: »

I think that this is possibly true for the first step, or half a step, on the treadmill, as your leg is drawn back and your body's inertia keeps it in the one place, but it makes no sense to me to say that it might be true once the treadmill is going.

That's because it's not true.

calahans

LionelNashe wrote: »

The relative motion between runner and running surface is exactly the same as in the case when the runner is running on the road. Standing next to the runner on the treadmill and watching her motion is exactly the same as riding beside her in a cart as she runs down the road such that the speed of the cart is the same as the speed at which she is running. In both cases you are sitting in a nice inertial reference frame and the laws of physics will be exactly the same.

You are right in this idealised case. The real world wont match the model and therein lies the difference. Without doing research I would think that you even hold yourself different when you run outside (more forward) than on the treadmill (more erect) and unevenness of the terrain. Because of these things the forces will be different.

To sum up I think that it would be harder to run outside because of the spring effect of the treadmill, wind resistance outside and the different terrain/body positioning outside.

krd

When you're on the thread mill, to stop from falling off, or running off the other end, your forward velocity must equal the velocity of the thread mills backward motion.

(Your forward velocity being the velocity you would be travelling at if you were running on flat ground that wasn't moving - on the thread mill you have a zero velocity because you're running on the spot)

So if the thread mill is spinning backwards at 20 Km/h - you have to run a precisely 20 Km/h otherwise you'll fall off - you need to run at a velocity of 20 Km/h.

The thread mill always feels weird because it's so flat and there's vibrations passing through it, you wouldn't have if you were running on normal ground. And you have to maintain a constant velocity or you'll fall off.

Capt'n Midnight

"Running very fast is leaning forward without falling over"

Try it if you don't believe me


try to figure out how having your centre of gravity ahead of your feet affects the amount of force you need to use to keep upright

then compare to how a thread mill works,


can you lean forward on a treadmill ?

LionelNashe

Capt'n Midnight wrote: »

can you lean forward on a treadmill ?

Yes:)
Or maybe not.
I'm not sure.

FISMA

You feel forces ON you not BY you.

My hand hurts not because I hit the wall, but because the wall hit my hand. The wall hurts because I hit it with my hand.

You run not because you pushed the ground, but because the ground pushed you. If you don't believe me, try running on ice. You can push all you like, but you'll get nowhere are the ice will not push you.

Also, Newton's Third, often called an action-reaction pair is a misnomer. It is not as if you pushed the ground and then the ground reacted by pushing you back. No - both occurred at the same time.

mikhail

calahans wrote: »

To sum up I think that it would be harder to run outside because of the spring effect of the treadmill, wind resistance outside and the different terrain/body positioning outside.

Your gym operates in a vacuum?

del88

If i go for a 3 mile run on the road then i'm moving up and plus moving my weight foward 3 miles.....if i run for 3 miles on a treadmill i'm still moving up and down but i don't have to carry my wight foward for 3 miles...so i use less energy....

Capt'n Midnight

del88 wrote: »

If i go for a 3 mile run on the road then i'm moving up and plus moving my weight foward 3 miles.....if i run for 3 miles on a treadmill i'm still moving up and down but i don't have to carry my wight foward for 3 miles...so i use less energy....

If you are in moving air then you can cool down better and so probably run faster before you overhead , another reason why you would use more energy outside

also unless you live on Lake Bonnerville it's difficult to find a perfectly flat solid area outside where you can run 3 miles in one direction

del88

Capt'n Midnight wrote: »

If you are in moving air then you can cool down better and so probably run faster before you overhead , another reason why you would use more energy outside

also unless you live on Lake Bonnerville it's difficult to find a perfectly flat solid area outside where you can run 3 miles in one direction

True but nothing to do with the different physics involved in running on a treadmill and running normally..the main difference between the two is having to move your own weight forward 3 miles and not having to on a treadmill.:p