Is a person running at 5 MPH on a flat treadmill spending the same effort as a person running 5 MPH on the street?
I don’t think so, but I need a good argument/explanation to demonstrate it to someone else. My argument is thus:
Let’s say a person weighs 200 lbs, 100 upper body and 100 for the legs (this is just for math. I don’t know the exact proportions.) If you’re running down the street, you’re pushing 200 pounds along. 100 above and 100 below. But if you’re on the treadmill, only the 100 below is being “moved.” The top 100 is not going anywhere relative to the earth and inertia is helping it to stay in place.
The top half of a running body (on the street) doesn’t require any pushing to stay at speed; it has its own forward inertia in the same way that a still body on a treadmill has “static” inertia. Now, it will take more energy to accelerate an entire body to running speed, which doesn’t occur on a treadmill. There will also some small amount of wind resistance on the outdoor runner. My guess is that these will be pretty insignificant at slow speeds and long distances.
No. The man is still pushing himself against the treadmill’s motion. Your concept would only work if the man was just hopping. As long as he has friction against the surface of the treadmill, it’s pushing him along, and he has to fight it.
Edit: yes, there are environmental factors too as lazybratche points out. Hills will affect this. However, given equal alternative conditions, the force of motion itself is the same.
This is a bit like walking up a down escalator and going nowhere which is the same as walking up stationary stairs.
You have to consider that if you don’t run/walk then the treadmill will physically move you backward, therefore, by holding position you are moving forward in a very real way and using the same energy as if you were on the street (ignoring the bounce and lack of wind etc.)
I may be wrong because I don’t fully comprehend the machanics of human locomotion once we step out of the car, but:
When running on the street, you have to kick forward, push against the ground and pull your leg back in order to maintain forward motion. So you have to push your body up and you have to push it forward.
When running on a treadmill, the “ground” is already moving backward relative to you because of the motor working the belt. You don’t have to push your incedibly fatty mass forward, you only have to move it up. Your legs have to kick forward, of course, but you don’t have to pull yourself forward from there.
For sake of argument, let’s say I had a 20 foot stride. If I’m on a tread mill I have to expend energy for the entire 20 feet. But if I’m on a treadmill I only have to put one foot out front and let the treadmill “bring it back” to me.
I guess I’m not in the mood for theory on this one — If I run 10mi on a treadmill it is way different from running the same 10mi on the towpath along the canal. No question whatsoever. I can almost always get better times on the treadmill.
I’m certain that anyone could run their maximum comfortable distance on dirt and then try a treadmill and see a significant improvement in either distance or time.
I guess that doesn’t really help with the “demonstrate it to someone else” bit though.
No, because your other foot is on the treadmill, heading backwards. You have to move your front foot forward, same as if running on the ground.
Forget the rest of the world: when you are on the treadmill and only touching the treadmill, you are running on it the same as you would on the ground. The only difference is that because the treadmill is moving backwards relative to the world, you don’t move relative to the world. That doesn’t affect your movement vis a vis the only thing you are touching: the treadmill.
Another way to think about it: imagine you are running on a smooth black plain. All the usual effort of running is involved. Now imagine your mind’s eye zooming out, till eventually you can see that you were running not on an ordinary plain, but a treadmill so huge you couldn’t see the edges of it.
Better still, consider that if you run due east, you are already running on a treadmill. It’s called the Earth. If you run at the right speed, you will go nowhere. It will just appear that you are going somewhere because the Earth (which is all you can see) is revolving underneath you.
Yeah, treadmills do seem a lot easier, but then again I tend to run much faster than 5 mph on them. There’s a few factors: wind resistance, hills, running surface, posture, and psychology.
But, I think you can make a much better fundamental case with the other popular kind of equipment: stairmasters. Oh, they’re such bs especially if you’re not trying to get a good workout. No wonder they’re popular.
To elaborate: wind resistance is VERY important, at least if you’re running instead of just jogging. Even if you’re jogging, wind gusts take a significant toll on your stamina. Hills are obviously also very important, even if they have a very slight slope. The springy running surface of a treadmill again makes a big difference.
You can isolate those three factors and compare running outdoors to running on an indoor track.
The other two factors are less concrete, but I think they play a part. Posture is more important than most people realize. If you lean forward, you’ll automatically walk or run faster because of how the pendulum-like motion of your body works. Just try to lean forward when walking, and you won’t be able not to go faster. There may be something about not having to see where you’re going or the handlebars at your sides that changes your posture and lets you assume the more ‘optimal’ stance. This, in fact, would be responsible for the illusion that the treadmill is pulling back your feet. Try that lean-forward walk and you’ll feel the same effect!
For those of you who think that running on a treadmill would involve not having to move “forward,” let me suggest you read up on the concept that motion is “relative.”
There are two kinds of wind when you run: your motion relative to static air, which feels like wind, and then any actual wind that changes the velocity of the air. On a treadmill you get neither of these, but when running you feel a wind which is the difference of your velocity from the wind’s velocity (I was going to say the sum, but if you and the wind are both going north at 5mph, you feel no wind, so there’s obviously a sign change at work).
For a completely calm day, your air resistance is your velocity squared multiplied by your frontal area multiplied by the density of air and your coefficient of drag, all divided by two.
From Wikipedia, and extrapolating backward to low velocity, the CdA of a 60kg human is about 3.5, and 5mph squared is almost exactly 5.0 m2/s2 (weird!). Dry air density is 1.2kg / m3, so at 5mph you feel a drag force of about 10.5 Newtons. That’s a non-trivial amount, and it quadruples going into a 5mph head-wind. Alex Dubinsky is right – it’s a lot of extra effort. Of course, I always preferred running in a headwind because it cooled me down and allowed me to run for longer. In a tailwind that was about the same as my speed I felt like my own exhaust was forming a muggy bubble of hot CO2-saturated air around me that actually hurt my efficiency.
Jurph has it right. (The wind you experience is the vector sum of your motion and the air’s motion.)
Some treadmills can simulate hills by tilting; very few include a wind tunnel, so they can’t introduce aerodynamic drag, which is a meaningful factor. But the physics of running on a treadmill are not fundamentally different from the real thing.
if your 100-lb butt is moving, and your 100-lb top is not moving, then your body would be torn in half (like being pulled apart on the “rack” in a medieval torture chamber.
I don’t think it’s that simple due to the motion of the human body (an airplane yes, but human is more complex).
When the treadmill brings my front foot back towards me (the only one touching at this point in time), the backward force on my upper body is dependent on the angle of my leg, which becomes a smaller force as my foot gets closer to my body.
In addition, I can reduce the effect of that force by not remaining rigid, flexing my knee, hips, allowing my body to rise/drop etc. thus reducing the backward effect on my upper body and isolating a portion of the effect in my foot and leg.
When you are running forward, you must provide enough energy to propel your upper body, you can’t reduce this requirement.
I think I should clarify an assumption of the OP. In my scenario, the treadmill is of the motorized type. Not one the user has to keep moving with his own effort. This is why I supposed that it is easier on the treadmill than the road. The legs aren’t really propelling the upper body. They’re simply counteracting the movement of the treadmill. And that movement is being powered by a motor.
To me, that’s a big difference. On the street, ALL of the energy involved is being supplied by my muscles. The motor is providing much of the energy for the treadmill.
I don’t think the up-the-down-escalator thing works. Once you start getting changes in altitude involved, then relativity no longer applies in the same way. For the treadmill relativity is fine, but for the escalator, you don’t have to use force to physically raise your mass against gravity, as you would have to if climbing stairs. You’ll burn more energy on the stairs.
