wphamilton

A couple of things you can learn pretty quickly from casual searching on the internet are

1. Set the incline to 1% or 2% to make the treadmill run equal to outside, because of air resistance, and
2. The bio-mechanical differences of stride on the treadmill are factors making a significant difference

I have come to conclude that these are both likely urban myths. You can disagree which is one reason I'm posting - to hear the counter arguments.

In the first, I've looked at various calculators and calculations, some from pretty old literature, and there is so much variance that I'm more comfortable with the simple calculation from base principles and best available estimates. The familiar old drag equation and taking the more or less consensus estimate of Cd as 1, frontal area of the runner as .45 meters squared. I did find one reference to wind tunnel testing of a standing body, Cd of 1.1-1.2 and area .5, and reasonably the runner is slightly lower or leaning so area is smaller. I'm not sure why the drag coefficient would be less, but "around 1" appears to be generally accepted so I go with that.

So with those estimations, for various paces I come up with these watts spent for drag
6 min/mile 24 watts ranging to 10 min/mile, 5 watts (see chart)


So it's a pretty small amount at paces 8-10, and offset at those speeds by cooling air flow if you compare outside. That comports with some studies of oxygen intake comparisons, which found them pretty much equal on the treadmill and outside, at the slower paces. But it's WAY more than some claims I've seen, such as 3% of someone's effort "at a marathon pace" of 5.5 minutes per mile!

Bio-mechanically I know that it's less impact on the joints particularly, but beyond that I think that most (all?) of the claims are vapor. Other than psychological pressures to change the stride, and uneven ground outside, I just don't see any valid reason why the stride mechanics necessarily changes. Particularly the claim that the moving belt throws your foot up at the back of the stride - I'm calling urban myth on that one. And true to confirmation bias inclination I've found a study that agrees with me ... and some that don't ...

But I'm going to submit that there isn't any difference in effort or technique in an 8 minute pace on the treadmill or running outside! Feel free to dispute ...

FrenchFit 

I read these myths were recently debunked by an actual study by some fitness PhDs.Sorry, I don't have a link to the article. In sum, not much difference between road running and treadmill until you get up to the elite athlete level.

However, from personal experience, I'll add the absolute level and sameness of the treadmill track creates artificial impact/hot spots...the nice thing about outside running is the terrain changes, even slightly, which I think builds strong stabilizing muscles and spreads the impact around. Just my h.o.

wphamilton

For sure, the absolute level and sameness are both the reason I often use the treadmill and also why it's in some ways harder. I don't hurt myself as easily and can keep the pace steady which I can't outside, but outside the variety seems to make the same performance easier. I'm just postulating that using the same pace, either way, validly gives the same intensity of effort at these levels.

GailT

Christine Clark, the 2000 U.S. women's marathon champion, who was from Alaska, did most of her training on a treadmill. They mention the indoor heat, 70 F in her house, as one advantage of the treadmill. In some ways I think I get a harder workout on the treadmill because I set a target slope and pace and will work harder to maintain that setting, whereas outdoors I might slow down more when tired. It's also easier to maintain good form and avoid injuries on the treadmill. I think the major problem is that if I train mostly on the treadmill and then run outdoors, I'm more likely to get injured on the outdoor run (perhaps because of weaker stabilizing muscles as FrenchFit mentioned), so it's good to include some outdoor runs in the training.

wphamilton

It looks like no one is going to make a stand on my two "myths" but what about my wind drag numbers? In terms of "watts" out of habit and because that's how we're used to thinking, but around 10 watts at 8 minute pace is honestly more than I had expected. Getting more in the range of 6 or 7 minutes, the drag is a significant portion of the total (total power numbers more or less what we're accustomed to, according to internet "wisdom" and "smart" treadmills).

So I'm thinking, next time I race I'm going to wear a tighter shirt and shorts, maybe cycling jersey, and probably run behind some big guy for the draft! 20 or 30 watts drag (depending on which area and drag estimates), taking a third off that for drafting, that starts to add up.

jadocs

I do have a question (not related to wind resistance), I know nothing about treadmills, but I do ride rollers. If I could set my roller drums to spin to replicate a desired speed, would I not be putting less watts (less effort) when I pedaled to maintain that speed? Wouldn't that almost simulate going down a hill? Does this translate to treadmills as well when you run? Is that where the myth came from?

wphamilton

The treadmill surface moving at a constant speed, it wouldn't be different whether the treadmill is moving under our feet, or we're moving over the surface. Because physics, non-accelerating frame of reference. But where's the work go is your question I think, since our body isn't really moving forward? I haven't really studied it other than noticing "non-accelerating reference frame" but it looks to me:


1. We're leaping in the air, our center of mass going up and down (same on treadmill and road)

2. Air resistance (not on the treadmill)

3. From running form, the foot strike may slow us down a tiny bit especially if we over-stride, and we have to make that up on the push-off. (same on treadmill and road)

4. Running up/downhill, not getting into that here since we can keep the incline at zero.


The treadmill is usually softer and springier which makes the landing softer, and might spring back more than just the "spring loading" of our tendons. But that would be a very minor difference in the work, and mainly helps to make treadmilling easier on the joints. From the 3 above, only the air resistance is much different from running outside. Most of the work comes from #1 , and there is a little extra work outside getting up to speed to begin with.


On the bike we don't have anything analogous to #1 since the bike supports our weight.

jadocs

Thanks for the explanation. With respect to #1 , would there not also be an element of pushing forward (when running on a real road) that is not replicated on a treadmill? or is the difference so minute that it doesn't make a difference?

wphamilton

No, and that's probably the most confusing part about it. When you're moving at say 6 mph, it doesn't take anything more to continue moving at 6 mph (Newton's laws). Except for air and other external factors I attempted to account for in 2,3, and 4.

Initially getting up to the 6 mph does take more and isn't replicated on the treadmill, because the momentum changes from zero to whatever at 6 mph. But steady pace running at 6 is the same in that respect, treadmill or road. On the treadmill you have zero momentum all the time. Running across ground you have 6 mph times mass momentum, that's not changing if the speed is steady. It's the momentum change that we push against.

jadocs

Interesting thank you.

rumrunn6

fwiw, in real life, we have to propel ourselves forward. but on a treadmill, we only have to stay above the moving belt

Carbonfiberboy 

It's just Einstein. Frame of reference. We do propel ourselves forward in the "stationary" machine frame of reference, otherwise we accelerate backwards into another frame of reference with accompanying pain. We really are doing 6 mph though from another frame of reference we appear stationary. HR is about the same as it would be at the same speed off-machine, therefore we are doing the work of propelling ourselves forward.