Running Shod More Efficient

Discussion in 'Front Page News' started by Barefoot TJ, Mar 30, 2012.

  1. Barefoot TJ

    Barefoot TJ
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    Mar 5, 2010
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    Running Shod More Efficient
    Parts 1 & 2
    By Ahcuah

    Part 1:

    There’s been quite a bit of talk lately about a new study that came out early in the month, Metabolic Cost of Running Barefoot versus Shod: Is Lighter Better?, by Jason R. Franz, Corbyn M. Wierzbinski, and Rodger Kram. You can see one of the stories at Barefoot Running Less Efficient.

    I’ve taken a bit of a look at the study.

    The way these studies work is that they put special masks on their runners that measure both oxygen used and carbon dioxide produced. From those levels you can tell how much energy the body burned, and then comparisons can be made.

    It is already generally acknowledged in the literature that for about every 100 grams of extra weight on the foot, you burn about 1% more energy. Thus, most folks thought that removing the shoe entirely would be the most efficient.

    This study seems to show otherwise, and my big question was, why?

    The study itself notes that there have been seven previous studies. Five of those found NO difference in oxygen burned. Two of the studies did find a difference, with one in particular, Oxygen Cost of Running Barefoot vs. Running Shod, by N. J. Hanson, et al. finding a 5.7% difference, with barefoot running being more efficient.

    This latest study notes, however, that the previous studies did not control for a lot of factors, such as foot-strike pattern, barefoot running experience, and shoe construction). So they tried to do so as much as possible. They made sure that all their runners they tested had barefoot running experience. They made sure that all their runners used a mid-foot strike. When they wore footwear, they all wore Nike Mayflies, very lightweight shoes. When I first read the study, I figured they were something like a Vibram with an extremely flexible sole, since they had no arch support or any motion control features. But that was not the case. Here’s a picture of the Nike Mayfly:
    The Nike Mayfly

    Those are pretty thick soles: 14 mm.

    And then they compared it to barefoot running. OK, I guess I should have said “barefoot” running, because the subjects were not really barefoot. As the study says:

    For the duration of the experiment, subjects wore very thin, slip-resistant yoga socks for safety and hygienic purposes.​

    Huh? Geez, I hate those sorts of comments and hidden (wrong) assumptions. First, exactly what hygienic purpose is needed. Yes, they were running on a treadmill, but exactly how is hygiene implicated. And how do they provide safety? Were they afraid people were going to be strewing nails on their treadmill?

    But there’s more. They were also wearing a foot harness. They actually cut down the uppers of a running shoe to have a place to attach their weights. Here’s what the “barefoot” runners were really wearing:
    The "Barefoot" Apparatus

    As their description says:

    To add mass to each foot during barefoot trials, we modified the uppers of a running shoe to allow for easy attachment of small lead strips while still simulating barefoot running. We removed the outsole, midsole, and the entire front portion of the shoe upper, anterior to the midshaft of the fifth metatarsal, leaving only the heel counter, thin fabric arch section, tongue and laces.​


    So, what was going on? I suppose it is possible that the “barefoot” contraption was causing problems and that led to the “barefoot” running being less efficient. But there is also something else in the study.

    They took careful pictures and noted that the “barefoot” runners stride was about 3% shorter than the shod stride. That could account for the efficiency difference. But as I already pointed out, we don’t really know why the stride was shorter. Maybe the socks, even though “slip-resistant” didn’t feel slip-resistant, so the runners took shorter steps. Or, it could be that the heavy cushioning in the shoe allowed them to slap down their feet harder, as one is forced to do with a longer stride. One also has to consider the idea that this longer stride, and slap-down, might be generating increased stresses on the joints.

    Oh, and what about that other study (the Hanson study) that showed barefoot running to be more efficient? Let me say a couple of things about that. That study actually had their runners run outdoors (“overground” is the term used). That 5.7% difference is overground. On treadmills, the Hanson study found only a 2% gain in barefoot running over shod. I can see how there really might be a difference under real, outdoors running conditions.

    But not so fast. As Franz pointed out, Hanson’s study may have been flawed in the way they measured speed, particularly outdoors. They did so with a very fancy pedometer, but one that would have missed differences in speed due to stride-length. See Is Barefoot Running More Economical? It’s hard to believe, though, that they wouldn’t have checked their speed results more closely, and in the end, while they calibrated their device, nobody really knows just what those devices do.

    I’d say that the answer is still in doubt. From this study, it is plausible that barefoot running without the cushioning of the shoe, even if both are mid-foot striking, is less efficient due to a shorted stride length. But I don’t think they are there yet. I’d like to see more studies that forced even more uniformity and eliminated (and isolated) these other factors.

    But there is one more thing I’d like to point out.

    If I’m going for efficiency, I’m going to put on my inline skates. If I’m not out to win a marathon (or am on the edge of collapse from trying to win one), the efficiency difference probably doesn’t make a difference.

    Otherwise, I’m going for tactile sensations and fun.

    [Note: There's another good write-up on the study at Runner's World.]


    Part 2 (Follow-up):

    I got asked a number of questions about my previous look at the Running Shod More Efficient study, so I thought I’d answer them here.

    I also took another look at the study itself, and managed to ask myself a question that I sure couldn’t answer.

    Why did they control for factors that aren’t controlled in the real world?

    As noted in the study, there have been seven previous studies, and five of those showed no difference between energy use while shod or barefoot. What these folks tried to do is tease out if there were any differences. They really wanted to ask the question about whether running barefoot made a difference, not whether, for instance, running with a midfoot-strike versus running with a heel-strike made a difference.

    In any good study, you try to keep as much the same as possible.

    Why run on a treadmill instead of normal running conditions?

    It’s easier to control the speed.

    I do agree that there might be conditions “overground” that could make a difference, but this study just didn’t test that. On the other hand, there have been other studies that compare running on treadmills with running overground. It turns out that those studies find that they are pretty much equivalent (at least for the conditions of those tests) if you tilt the treadmill to a 1% incline (to compensate for lack of wind resistance).

    The previous overground study (the one by Hanson) probably screwed that up by relying on a speed measuring device that did not adjust to the difference in stride length between running barefoot and running shod.

    I still would have liked to have seen a decent test overground. I think they could have collected the data they needed by filming it and analyzing those pictures.

    What about that stupid yoga sock?

    My suspicion is that it really didn’t make a difference. It may have—we just don’t know.
    I do think it is a flaw in their design, though.

    Why use all the different weights? Why not just test barefoot versus shod?

    Here’s the data of simply barefoot versus shod with that very lightweight shoe. (From what I can tell, the shoe they used weighs about half the weight of a typical running shoe.)
    The "Pure" "Barefoot" versus Shod Graph

    There really is no significant difference there. And even their conclusion (where they compared shod with the light-weight shoes with weighted “bare” feet) had overlapping error bars, which tells me that the results really aren’t significant. Yet, they claim a (p<0.05) significance to that.

    I still think that the difference seen is completely related to the difference in stride lengths between their shod and "barefoot" runners. Remember, the barefoot runners used a 3% shorter stride.

    Using the different weights actually allowed a check with previous studies, which had found about a 1% increase in metabolic effort with each 100 grams of weight. These folks found the same thing, which leads credence to their results.
    Why would a shorter stride length lead to higher effort? Look at cyclists. They have an incredibly high turnover and that’s considered efficient.

    To go the same speed with a shorter stride requires a higher cadence. With cycling you have gears to compensate for and take advantage of that higher cadence, keeping your body’s efficiency in that “sweet spot”. I don’t think the same applies with running (but I could be wrong).

    As an extreme example, if you run in place, you’re still expending about the same energy but with zero speed. Most of the energy is expended during landing and take-off phase, so if you do that more often (in order to maintain a higher speed with a shorter stride), you will probably burn more energy.

    And here’s my question: what were the stride lengths, and do they make any sense?

    According to the data in the study, the stride length when “barefoot” was 2.18 meters (7ft, 1.8in), and 2.24 meters (7ft 4.2in) when shod. (Don’t forget that a “stride” is the distance from one foot hitting to when the same foot hits again, so the respective step lengths were 3ft 6.9in and 3ft 8.1in.)

    This could still implicate those stupid yoga socks. We don’t know if the “barefoot” runners had a shorter stride because of running without a sole, or because there was some effect due to slippage of the yoga socks on the windmill.

    But what about my unanswered question?

    The paper reports the stride length as 2.18 meters with a standard deviation of 0.59 meters (“barefoot”) and 2.24 meters with a standard deviation of 0.55 meters. Those are huge standard deviations, nearly 22 inches for the stride length (11 inches step length).

    Now, the way a standard deviation works 68% of the sample should fall within one standard deviation (and 95% within two standard deviations). Going with just one standard deviation, that means that they had people with step lengths of 2ft 7in and 4ft 6in. And if you go to two standard deviations, . . ., wow. They must have been testing giants and dwarfs.

    How the heck did they get these results? I have no idea.

    The more I think about it, the more I think they combined their data incorrectly. Instead of just combining the results from all their participants, they should have measured and analyzed the results for each individual separately, and then figured out how to combine the data. This way, we have no idea how each individual performed—all we see is the mash-up.

    This also makes their other results suspect, and now that I look at it, I am even more confused about what they are claiming. The error bars on a plot are supposed to show one standard deviation. If you look at the “barefoot” point above (no weight), that looks like a value of 40.3 with an error bar of about 1.

    What’s the value in their paper?

    40.28 with a standard deviation of 3.05.

    Here’s the screen capture of their table:
    The Data Values Table (click for readable version)

    I don’t see how these results can be significant at all!

    End of questions; back to commentary.

    But let’s suppose that the results really are significant. What does it mean to us?

    As I mentioned before, it probably only makes a difference if you are an elite athlete really trying to shave off that last millisecond. Otherwise (and as others have pointed out) all the other variables will totally overwhelm this particular point.

    There is something else going on here: many of us are indignant that bare feet might be worse, and we are working to find any reason to doubt the study. I feel the lure myself.

    We want to think that bare feet are the greatest thing since sliced bread! We’ve found the cure! It’s amazing! It slices, it dices . . .

    Seriously, going barefoot doesn’t have to be best in everything. It just has to be best for us.

    One more point.

    When driving above 40 miles per hour, closing your car windows and using the air conditioner gives better gas mileage. But if it is the first gorgeous spring day after a hard winter, and the temperature is 75°, you’re going to drive around with your windows open. The heck with efficiency.

    And when you are barefoot, it is always a beautiful spring day . . .
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  2. scedastic

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    Oct 7, 2011
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    +1, especially your last point.
    And to emphasize your earlier point about a small difference in the percentages; in statistical studies there should always be made a distinction between clinical significance and practical significance, in which case one considers for whom a slight difference in performance may be important. It ain't me one way or another, that's for sure.
  3. Barefusser

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    1. Denmark

    Apr 4, 2010
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    Nice review. I did not read the paper but I wonder to things after reading your review.
    1. Did they remember to take the weight of their 'barefoot' device into account when doing calculations? It might, combined with the sock, weigh more than 50 g.
    2. It is funny that the slope graf over efficience of the shod runners with increased weight is greater than for "barefoot" runners.
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  4. Ahcuah

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    Mar 13, 2011
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    Let me add that Ken Bob Saxton added some very insightful comments to the original version on my blog, here:

    That also prompted me to take another look at just how they picked the runners that they used, who supposedly had barefoot running experience. Here's what they say:

  5. Ahcuah

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    Mar 13, 2011
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    Regarding the weight of the "barefoot" device, they said nothing about it. In fact, it isn't even mentioned in the text of the article, but only shows up in one of the figures.

    Regarding the slope of the graph, they error bars are so large that the difference really is insignificant.

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