I was having a discussion with some of my co-workers and we’re stumped. Discounting wind resistance and a curvey path of a track, would you expend the same amount of energy running on a treadmill as on a track?
Thinking about this for a while, we thought about the momentum of the upper body, and feet being off the ground, but can’t come to any solid conclusion either way. To me it seems basic relativistic frames apply. Exerting energy to move across the top of the surface is the same as having the surface move under you and exerting energy to stay in the same place. Some argued that you’re not pushing the upper body forward, but I would think even running your upper body has moment and you’re not really “pushing” beyond the inital acceleration.
If anyone can help sort this mess out, I’d be eternally greatful!
This site says that treadmill takes less energy and less oxygen consumption, particularly at higher speeds. The difference appears to be too great to be accounted for by air resistance and is probably due to kinematic differences in the style of running required. (Track is propulsive, treadmill is mostly moving the legs to maintain your center of balance.)
My physical therapist told me that running on a treadmill is like running on a very slight downhill grade, which requires less energy than running on a level surface or incline. Also, constantly running downhill may make your lower back ache after a while. My physical therapist also informed me that, if I must use a treadmill, I should run at no less than a 1% incline to more accurately simulate running outside.
From a quick, naive, physics-based look at it, I would say that running on a treadmill takes the same energy as running on a track at a perfectly constant speed, where the only acceleration is to the legs as they move back and forth, and perhaps a little up and down movement of the torso.
However, accelerating on a track will take more energy than accelerating on a treadmill, as you need to bring your torso up to speed. And since you can’t run at a perfectly constant speed, you will always be accelerating or decellerating your torso to some extent, thereby using more energy.
There are undoubtedly also some effects based on how the human body moves differently on a treadmill versus track, but I’m too dumb to know about them.
The treadmill also burns less because you’re significantly more limited in your range of motion on a machine than you would be on a track. If you’re on a track or path, you can pump your arms and extend your legs as much as you like. On a treadmill, you can’t.
The major difference between outdoor and treadmill running is air resistance, but even discounting air resistance, you are likely to expend less energy on the treadmill.
One reason is that with certain running styles, the treadmill may overread. As your feet leave the treadmill surface, the belt will tend to speed up. If your running style is especially bounding, this transient speeding-up may become significant. Ah, I see that the PPOnline link provided by Finagle already makes this point, and others relating to changes in running biomechanics on the treadmill vs. Great Outdoors.
Treadmills are also quite bouncy, I have always felt that this makes it easier to run on them as each impact is absorbed and then some of the energy given back to you. Running on the track there is no such assistance.