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A bit of an unusual study from Brazil just published online in Medicine & Science in Sports & Exercise. Basically they asked 34 young adults to go for a 20-minute walk either on a treadmill or outdoors on a 400-metre track, at whatever pace they would “feel happy to do regularly.” The results: they chose to walk significantly faster on the track than on the treadmill — but their percent of VO2max and their perceived exertion was higher on the treadmill, despite the slower speed. In addition, their “affective valence was more positive” (i.e. they were happier) on the track.
The goal of the study was to figure how to convince more people to exercise (and in that sense, it was somewhat unsuccessful because the volunteers chose paces that were too slow to elicit significant fitness gains), and to figure out whether recommendations formulated in the lab can be applied to normal outdoor conditions.
Leaving aside the psychology (which is certainly interesting — I know I’m happier outside than on a treadmill!), the fact that people walked more slowly but worked harder on the treadmill is odd. This wasn’t a biomechanics study, but it seems like more ammunition for those who say that movement on a treadmill is fundamentally different from overground — a debate that’s been dragging on for a long time now. I still don’t really understand why it should be different (other than wind resistance, which wouldn’t explain the current results), but apparently this is one of those deep mysteries…
Ignoring potential temperature differences between the lab and the outdoors track (in Brazil!) the study’s summary claiming the subjects’ percent of VO2 Max measured higher walking slower on a treadmill than the track might only be possible if the track were highly elastic and rebounding, thereby permitting a greater stride energy recovery versus the utilized treadmill. I find this conclusion highly unlikely since as you noted the wind resistance would cause the opposite result; consequently, unless the track surface were extremely rebounding versus the treadmill it is hard to imagine this could more than fully offset the wind resistance drag effect.
Conversely, the study’s measurements of track subjects’ comparatively improved happiness seems entirely entirely logical and consistent with my own experience running in both settings. It would be interesting to measure the happiness gradient between subjects on the track versus the open road; my speculation based upon the Hawthorne Effect and the psychological ease of measuring progress would be that the track would score highest.
I think it might be the cushioning or suspension.
When I watch my wife (who is only 100 pounds) on our treadmill there is quite a bit of deflection with each step.
I am thinking that absorbs a lot of energy.
The other possibility is body temperature. Indoor room temp is usually too warm for comfortable exercise.
Interesting comments — thanks, guys. I’d never heard of the Hawthorne Effect — cool stuff, and worth bearing in mind especially when trying to apply these results to the real world. The softness of the treadmill could definitely account for some of these effects. The temperature of the outdoor trials averaged 20 C (and they postponed trials when the temperature deviated too far from that). For some reason, I can’t find where they say the temperature of the lab. I’d assume they controlled for it, but on the other hand, a difference between 20 and 25 C (which is a reasonably common room temperature) would also have a significant effect.
I agree with the psych angle. When I use a treadmill, I never compare data to that of outdoor runs. For me the major benefit of TM running is training the central governor. If I can run well and fast on a TM, missing the positive feedback from outdoor surroundings, my brain will allow me to run at a faster pace outdoors.
I recently did a fitness test on a treadmill. I hate them and I normally train in a 400mts track. However the treadmill felt hard. In my opinion this is due to the fact that in most treadmilss, to shorten the stride and avoid high speeds, a slope is added. I was running at 80% max BPM and the speed was very slow, but the operator would keep adding slope to the machine. I guess this should be factored in.
Regards!
Right now in Montreal, it’s -6 and has been snowing all day. I have a treadmill in my bedroom which I use. Walking outside in this climate between mid-November and mid-March is just not reliable or workable.
Andrea — definitely! Depending on the speed, about a 1% grade on the treadmill is equivalent to “flat ground” outside, because of the lack of wind resistance. Anything higher than that makes the treadmill feel much harder!
I am never able to keep the same average speed on a treadmill and outside. I consistently run slower on the treadmill, even if I push harder; the cardio meter confirms it. It’s not because I am not “happy” inside since the speed is fixed, it is not like the study you post where they may be walking slower on the treadmill just out of lesser motivation. And I’m running at 0º incline! so I don’t believe that “1% for the wind resistance” thing at all. I ran in cool temperatures as well on the treadmill and it just doesn’t work. I think “ac” has got it right, it must be the cushionning of the treadmill that absorbs a lot of the energy spent, unlike the concrete. I believe this has a much more significant effect than the “wind resistance effect”. (of course I’m talking about the wind created by the movement of the body; actual wind does have a very significant effect).
I also notice slower times on unpaved roads versus paved roads, it may be due to some slippage, but maybe not; again, I’m thinking less hard surface, more cushion, more energy lost. And yes, the treadmill is still slower than unpaved roads. Maybe I ought to find myself a harder treadmill… There must have been good studies on this somewhere…
This is something cyclists are very familiar with, as well, when comparing stationary vs. outdoor cycling. Trainer sessions almost invariably feel harder and less motivating; I know my heart rates (not that I use them much for training these days) are much lower indoors, but the RPE is higher. You’re really missing a lot of stimulus from not moving through space the way you would outdoors. Cooling is even more critical to a cyclist, as you’re essentially used to a constant 20mph wind blowing over you.
Concerning TM incline: I would bet that gait mechanics are altered and less efficient when walking uphill. You’re talking about more deceleration from gravity, leading to altered energy conservation mechanisms. Looking at the inverted pendulum (walking) and spring-point mass (running) models, one can see energy could be transmitted into the inclined surface (increased GRF) and increased braking forces could be present. As someone else mentioned, the decks of most treadmills are also designed to flex and lessen the impact of running (a questionable aim, IMO).
Obviously should have said “more work against gravity…”