The big news in the world of running science over the past week was the release of a study from a locomotion lab at the University of Colorado. The study, titled “The metabolic cost of running barefoot vs. shod: is lighter better?”, was headed up by Jason Franz, and was co-authored by Corbyn Wierzbinski and Rodger Kram.
I received a press release about the study from one of the co-authors last week, and the quote in the title of my post is taken directly from the first paragraph of the release (I have now also read the full text). In the press release they describe their experiment as follows:
“In the study, 12 subjects with substantial barefoot running experience ran at 7.5 MPH with a mid-foot strike pattern on a motorized treadmill, both barefoot and in lightweight cushioned shoes (~150 g/shoe, 5.4 oz). In additional trials, they attached small lead strips to each foot/shoe (~150, ~300, ~450 g). For each condition, they measured the subjects’ rates of oxygen consumption and carbon dioxide production as an index of metabolic cost.”
Here is their report of the key findings:
1. For every 100g (3.5oz) (the average weight of a deck of playing cards) added per foot, energy cost increases by approximately 1% whether running barefoot or shod.
2. Running barefoot and in lightweight shoes do not significantly differ in energy cost.
3. When controlling for shoe/foot mass, running in lightweight shoes requires ~3-4% less energy than running barefoot.
And here is the graph depicting their results (via Alex Hutchinson of Sweat Science):
What you’ll notice in the above graph is that all of the shod datapoints (dark circles) fall on the bottom line, whereas all of the “barefoot” data points fall on the upper line, indicating greater oxygen consumption and thus lower economy when “barefoot.” However, the stars indicate that the only significant differences were when the lightweight 150g shoe (Nike Mayfly, photo at top of post) was compared to a “bare” foot with an equal amount of weight attached, and when the weight-matched “bare” foot with 300g attached was compared to the shoe with 150g attached.
When I read a study like this, I tend to think immediately in terms of what these results might mean from a practical standpoint to runners. What can we learn and apply from this?
I see two major take-home messages:
1. Adding weight to the foot reduces economy at a rate of roughly a 1% increase in energy cost per 3.5 oz added. This means that trading your 12 oz trainers for an ultra-light flat like the sub 4 oz Mizuno Universe on race day could improve your economy quite a bit. But, presumably you’d have to also be adapted enough to run the race distance in the ultra-light flats (i.e., you should probably do some amount of training in the shoes you plan to race in so that you are used to them).
2. The study shows that if you are already a regular barefoot or minimalist runner and are not a heel-striker (the authors specifically controlled for footstrike to avoid comparing heel striking in shoes to midfoot/forefoot when barefoot), running in a lightweight racing flat will probably not significantly change your economy (of the 12 runners, 8 were more economical in the shoe, 4 were more economical “barefoot,” and when pooled there was no significant difference economy between when the runners were shod vs. unshod). Thus, if you feel that lightweight shoes are desirable in a race situation, go for it – they might even improve your economy a bit.
Both of these findings are interesting and of practical value, and the study raises a ton of questions that will likely be examined in future research. Running Times went so far as to run a headline saying “Here’s Proof Barefoot Isn’t Better” – well, barefoot was in fact better for one-third of the subjects, but we don’t really know why. Given the tendency to jump to interpretations like this, it’s important to recognize that like every scientific study, there are some limitations that should be mentioned related to the interpretation of the results – below are some things to think about:
1. None of the study subjects were actually barefoot, which is why I have been using quotation marks whenever I refer to the “barefoot” condition. In the study Methods section it mentions that “For the duration of the experiment, subjects wore very thin, slip-resistant yoga socks for safety and hygienic purposes.”
Would this have any effect on the results? I don’t really have any idea (what do you barefoot runners think?). Certainly, wearing a sock does add a layer of material between the foot and the ground that could alter sensory perception and plantar abrasion/shear (reducing the latter could actually improve economy relative to barefoot when running on a treadmill – truly barefoot treadmill running can create friction with the belt and resulting discomfort for some people). Just as people get sensitive when the phrase “barefoot-shoes” gets thrown around, I think it’s important to be clear with terminology – barefoot means nothing on the foot.
2. For similar reasons to the above, it’s debatable whether adding weight to the bare foot tells us anything of practical relevance about barefoot running. Here is the description of how weight was added to the “bare” foot:
“To add mass to each foot during barefoot trials, we modified the uppers of a different model of running shoes to allow for easy attachment of small lead strips while still simulating barefoot running (Figure 3). We removed the outsole, midsole, and the entire front portion of the shoe upper, anterior to the mid-shaft of the fifth metatarsal, leaving only the heel counter, thin fabric arch section, tongue and laces.”
So, the runners were essentially wearing a chopped shoe upper with no sole or forefoot, with lead weights attached. I do understand the difficulty of doing an experiment like this, but running in a sock and a shoe upper with attached lead weights gets pretty far away from the barefoot condition, and should not be referred to as such (again, barefoot means nothing on the foot).
Rather, I think the more relevant description of what this comparison showed is that running in a “shoe” (and sock) of equivalent weight without a sole is less economical than running in a shoe with a cushioned sole – still an interesting finding. This demonstrates that presence of a shoe sole can improve economy (possibly due to cushioning effects reducing work needed to be performed by muscles, increased longitudinal stiffness, etc.). It would be interesting to compare a lightweight cushioned shoe like the Mayfly to an equal-weight, minimally cushioned shoe like a Merrell Road Glove or Inov-8 Bare-X 180 and see how they compare (the reality is that more people are running and racing in shoes like this than are running or racing truly barefoot anyway).
3. There appears to be some amount of variation among the study subjects in barefoot/minimalist running experience. One of the requirements for inclusion was running “8 km/week barefoot or in minimal running footwear (e.g. Vibram Five Fingers) for at least 3 months out of the last year.” So, the runners did not even have to have true barefoot experience. However, this study does a much better job than most previous studies in attempting to control for level of barefoot/minimalist experience when looking at unshod running (i.e., they weren’t asking a bunch of people who had only ever run in traditional trainers to run with their shoes off for the first time).
I don’t really have a problem with this level of variation as it can be very difficult to recruit subjects for this type of study who meet all of the required criteria, but I am intrigued to know if there is any relationship between amount of barefoot experience and whether or not the individual was more economical when “barefoot” or in the Mayfly’s (remember, one-third of the runners had higher economy when barefoot). I’m curious as to whether individuals who run more barefoot miles (or perhaps who are more fit) demonstrate soft tissue adaptations that might improve their economy in the barefoot condition.
4. In the press release, the authors state that “Extrapolating their data indicates that running in only slightly lighter shoes (~129 g) would offer a statistically significant 2.5% energetic advantage over running barefoot.”
Extrapolating requires following the dotted line in the above graph downward to the left, which I don’t personally feel is statistically valid. There are no data from this region of the graph, and one cannot simply assume that the relationship will remain linear – as cushioning is reduced with decreasing shoe weight, it is entirely possible that linearity will be lost if economy is reduced. In fact, if you look at the three dark circles on the bottom line, it looks like a non-linear relationship might be a better fit for the existing points (but it’s hard to say with only three data points). One of the authors indicated to me that this region of the graph will be the subject of future study, which is fine, but extrapolating based on data provided in the present study is speculative.
6. In his analysis of this study on Sweat Science, Alex Hutchinson makes an excellent point:
“One of the proposed advantages of barefoot-minimalist running is that it automatically helps to correct overstriding — an extremely common problem among inexperienced runners. The fact that all these runners were already forefoot strikers suggests that none of them were likely overstriding, which would make them less likely to benefit from barefoot running. It’s possible that a truly “random” group of runners might have been less efficient in the shod condition, because more of them would have been dramatically overstriding.”
Alex’s point raises an interesting question – what happens if we take a traditionally shod, overstriding runner and have them begin to incorporate some barefoot training. Does their economy improve over time if they are able to modify their stride in a positive way? This would be a very interesting study to see.
All of the above being said, this study does provide some interesting and useful results. To be quite honest, I would not be surprised in the least if most people are more economical when running in a lightweight racing flat than when barefoot. Personally, I would always opt for a lightweight shoe over barefoot in a race if for no other reason than shoes allow me to cut loose and doesn’t require that I pay attention to where I am stepping. I find the ability to be a bit more reckless in a race to be of benefit. In this sense, this study actually supports my personal approach and beliefs (and yes, though I would not call myself experienced, I have run barefoot and enjoyed it on multiple occasions). However, I also suspect that most barefoot runners aren’t doing so out of an expectation of improved economy or performance (How many barefoot runners do you see in a typical race? Answer: Very few.). Enjoyment and escaping injury seem far more often cited reasons, so if that’s why you sun sans shoes, by all means keep it up.
Even more importantly, and as is the case with any good scientific research, the limitations of this study raise some excellent questions. What happens if we continue to reduce shoe weight – does the relationship remain linear? How do equal weight shoes with cushioned vs. non-cushioned soles compare (e.g., compare the Merrell Road Glove to the Merrell Bare Access). How does true barefoot running differ when compared to running in socks on a treadmill? I’m also very intrigued by the individual variation observed. Why were four of the individuals more economical when barefoot? Why were the others more economical shod? That’s what I’d really like to know.
In the end, it’s always important to keep in mind that people are different, and not everybody is going to be best barefoot, and not everybody is going to be best wearing shoes (as was the case here). Factors like fitness, training history (e.g., number of weekly barefoot running miles), and peculiarities of individual anatomy and physiology could all have a bearing on what works best at an individual level. A study like this can reveal general patterns, but it cannot tell an individual runner what is best for them. It does not “prove” that barefoot running isn’t better for you. That comes instead from knowing your own body, experimenting with different footwear conditions, and finding out what works for you as an individual.
You might also like:
Foot Strike, Running Shoes, Barefooting, Injuries, and Biomechanics: The Importance of Both Science and Anecdote
Form Differences Among Barefoot Running, Minimalist Shoe Running, and Standard Shoe Running
The Future of Minimalist Running Shoes and the Value of Variety
Acclimation to Running in Minimalist or Barefoot-Style Shoes: Is Form Change Instantaneous, or Does it Adapt Over Time?
Foot Strike Patterns in Barefoot and Minimalist Runners
About Peter Larson
Excellent analysis. Barefoot is barefoot. But the study has its value.
As always, Pete, you have an excellent, experienced and intellectual take on information that many people are just expressing opinions about. (Lordy, the Runners World forums are atwitter.) Thank you for your careful take on yet another topic of discussion relating to the bare vs minimal vs traditional shoes.
To your point about over-striding:
“Alex’s point raises an interesting question – what happens if we take a traditionally shod, overstriding runner and have them begin to incorporate some barefoot training. Does their economy improve over time if they are able to modify their stride in a positive way? This would be a very interesting study to see.”
If you reference books like Hollowell’s Complete Idiot’s Guide to Barefoot Running, you’ll see that is *exactly* one of the reasons why they suggest beginning runners learn to run barefoot, regardless of whether they plan to continue to run fully bare or in a minimalist shoe.
I would think that it also would be interesting to replicate a study like this on treadmill, road and trail. In an environment where a shorter stride is imperative to successful running, I think you’d see significant variance in each unshod/shod state, which would secondarily indicate that runners’ efficiency is as related to their ability to adapt to the ground as to the weight and outsole thickness and flexibility of the shoes.
That said, I’m no scientist. Just someone who runs in a variety of minimalist shoes on a variety of surfaces, and who always varies stride for running stability and speed based on all of those factors.
Thanks Rachelle, I appreciate the comment!
One thing I have always wondered, is if barefoot runners can expect to enjoy a greater longevity to their running careers? I hear from a lot of people who say they used to run a lot but they can’t any more because of bad knees, bad hips, etc. Personally, I plan on running barefoot a lot, lot longer, and I’m now 58 years old (running barefoot 7 1/2 years and counting!)
Ryan
Good question, and I have no idea what the answer is!
I’ve wondered the same thing. I’m a fairly novice runner who switched to “barefoot”-style shoes because of discomfort in traditional ones. (I run on surfaces that are too frequently strewn with glass and other sharp objects to feel comfortable running fully barefoot.) Had I continued running with traditional shoes, I expect there was a sizable chance (I’m not going to proffer certainties or even “probablies”) that my discomforts and pains would have increased until I either couldn’t or didn’t want to run anymore. Personally — and I’m totally willing to chalk this up in part to individual preference and/or physiology — I think I’m likely to continue running longer period because it feels more enjoyable this way to me. :)
A very good analysis. But I think I don’t understand this explanation:
“However, the stars indicate that the only significant differences were when the lightweight 150g shoe (Nike Mayfly, photo at top of post) was compared to a “bare” foot with an equal amount of weight attached, and when the weight-matched “bare” foot with 300g attached was compared to the shoe with 150g attached.”I don’t know if my english is not good enough or what (I’m Spanish). Can you explain that?In the graph, the point of ‘shod’ with 150g, is ‘shod+150g’ or simply shod, which implies the 150g of the mayfly?
The shod 150 point is just the shoe. Shod 300 and 450 are shoe + weights.
Whether a study suggests barefoot is better than shod is highly dependent on the conditions under which the running is to be done and the overall goals.
While true barefoot may be better for *training*, where maximizing one’s healthiness and improving one’s running form efficiency to the detriment of speed is highly important, going barefoot during *competition*, where the exact opposite is true, may not be better. (You generally don’t run your heart out during a race for health reasons. You do it to win. That’s true of any competition in any sport.)
My suspicion is that when anyone says barefoot or shoes are better they are thinking of training or competition but are never clearly stating it. That import qualification is too often left off such statements.
All of the subjects ran at the same pace, which depending on their fitness would have a slightly different meaning for each.
Among the many problems with this study, which you’ve done a great job enumerating, probably the foremost is that it concentrates on “efficiency” for competitive speed, which is not the primary issue for non-professional runners.
What is the primary issue? Health. The ability to run free of pain, free of NSAIDs. That’s what shoes rob us of. That’s why so many who should be running are instead bikers, swimmers, or couch potatoes.
I have no problem that the study looked at economy – that is the topic that Rodger Kram’s lab has been studying for many years. Different research groups focus on different sub-specialties, and there are plenty of recreational runners looking to gain an edge in an effort to set a PR or qualify for Boston. I agree that health trumps all else, but we all have our own reasons for running, and some of us do have a competitive side even though we know full well that we may never win a race – I say this because I am one of those people :). That being said, I don’t think most people are considering running barefoot because of any competitive edge it might confer. But, if he showed that running barefoot was 10% more efficient, you can bet some people, probably even pros, would consider it!
Well, the next time someone asks me “why doesn’t Ryan Hall run barefoot?” I have an even better answer than usual. (He has PF. Which I had, when I wore shoes.)
Sad to hear Hall does all his runs on NSAIDs. Yeah, he’s a tough guy, but healthwise it’s a terrible choice and a terrible example.
really? All his runs? Too bad the miminalist aspect of barefoot runners also applies to honesty. Hall has been running( sucessfully) for over a dozen years in shoes but yeah, let’s blame a current issue on it. Get real.
I`m a competitive highschool track and XC runner who`s been dabbling in minimalism for a while now. In my experience, I`ve never been able to run for more than a lap at my 3km pace in VFF`s. It could be that my legs were never really that strong– I usually only did one run a week in VFF`s, about four or five miles (though I did the rest of my miles in MR10s) but I suspect that there was something more to it than that.
…In other words, my experience agrees with this experiment
If I had to guess, I could probably run up to about a 5K as fast in Vibrams as in flats (I ran 5K in Vibrams last summer only 40 seconds off my PR, and I was not in anywhere near PR shape at the time), but at a distance like the marathon I would definitely do better with some cushion.
Hey Pete, According to runningwarehouse.com, the Nike Mayfly has stack heights of 25mm/15mm for a 10mm offset. What impact (if any) do you think this relatively steep ramp angle had on the study?
I’m skeptical that those numbers are correct, but if they are it could reduce the work of the calves a bit. They did control for footstrike so they did not alter foot strike in the shoes.
Sent from my iPad
Pete:
Thank you for posting up an analysis of the recent paper by Jason Franz and colleagues. The results of the study somewhat surprised even me initially, but, intuitively, it makes complete sense. I have long suspected that there is a trade-off in the metabolic efficiency in running barefoot vs lightweight racing shoes.
With barefoot running, there is decreased mass on the foot which decreases the work of the forward recovery phase of running due to a decreased moment of inertia of the leg and helps increase the metabolic efficiency of running. However, having some minimal mass and protection on the foot (i.e. lightweight racing flat) probably allows the runner to extend their stride which will likely, if done optimally, allow the runner to not “chop their stride” as much as they would barefoot, therefore allowing a more metabolically efficient running stride to occur for a given pace.
Numerous studies have shown that with faster running velocities, the magnitude of ground reaction force also increases. Therefore, it certainly seems likely that running in a lightweight racing flat may allow most runners to more comfortably run faster on all surfaces at the higher ground reaction forces that would be expected at racing speeds.
A paper that I sent in about a month ago to Podiatry Today Magazine on “Barefoot vs Shod Running: Which is Best?” should be published online in a few months where I explore some of these concepts.
However, also, Pete, I am very much looking forward to your new book. Can’t wait to read it.
Great review of this very interesting research!
Cheers,
Kevin A. Kirby, DPM
Thanks for sharing your thoughts Kevin. I would always opt for shoes in a race situation for a variety of reasons, and I think even most competitive runners who do a lot of barefoot miles would agree (Mark Cucuzzella is a good example). One thing to consider though is that many people in shoes tend to overstride, and Hamill published a paper in the late 80s showing that decreasing stride length in shod runners can improve economy a bit, or at least not incur a metabolic penalty. Also have to consider that Nigg showed that running on a treadmill tends to shorten stride relative to running overground, so that needs to be considered when applying these results to overground running.
Pete
Pete:
Decreasing stride length can definitely improve metabolic efficiency when comparing one shod runner to themselves as Hamill showed.
However, the question that I am still pondering is why barefoot runners, who have the least mass on their feet and who should therefore be more metabolically efficient due to their decreased leg moment of inertia during the forward recovery phase of running, are not winning more races.
Here are my hypotheses:
1. Lightweight racing flat (LRFs) allows the runner to run faster with more comfort and less perceived risk of foot injury since faster running speeds have been shown to cause greater peak magnitudes of ground reaction force (GRF) than slower running speeds.
2. LRFs allows a longer stride length and a more posteriorly-positioned foot strike (i.e. away from the forefoot and toward the midfoot or heel) which, combined with the same stride frequency, will allow increased running velocity.
3. Elite runners, being the runners who are most likely to break the winner’s tape in a race, choose to run in LRFs since this will ensure continued income from their running shoe sponsors.
4. There not been enough barefoot runners that have won races in the last few decades to convince other elite runners, to try and imitate them and to try racing barefoot.
My bets are placed on #1 and #2, with maybe #3 in certain cases and #4 much lower down the list of likely possibilities.
Do you have any other hypotheses to add to my list?
By the way, the use of socks in the Franz study could have decreased metabolic efficiency since the subjects would have decreased the coefficient of friction between the plantar foot and the treadmill causing some slippage and some loss of propulsive force (i.e. like running on loose sand on cement). I would be much more excited about this study if the subjects had been truly barefoot and not in socks.
Cheers,
Kevin
One correction – there are lots of people winning races barefoot, they just happen to be kids in Kenya: link to guardian.co.uk…
I wouldn’t agree with #2 – sprinters land on the forefoot, and forefoot landings become more common, not less common among faster runners (e.g., Hasegawa’s study). I think speed is not so much the factor as fatigue – my own video analyses suggest that forefoot landings can be really hard on the muscles required for cushioning the landing (e.g., calf), and thus barefoot running in longer distance races may not be optimal for most people. But, might not be as big an issue in a shorter race.
Other reasons:
1. Psychology – a good looking pair of flats can make you feel fast, and I’d never discount the psychological affect that they might have.
2. Just not very many people running barefoot to begin with, and you’d have to be very well adapted to race barefoot when high speed creates greater risk to the feet and legs.
3. Danger of stepping on something – if your career and paycheck are dependent on not getting hurt, why risk stepping on something or getting spiked unless the benefit of going barefoot vastly outweighs the risk
(which it appears not to)? John Landy found this out the hard way before
his big race with Roger Bannister. During a race, more important to stay
focused on things other than where you are going to place your feet on each
step to avoid debris.
4. Unless you live in a conducive climate, very hard to stay acclimated to
running barefoot year round.
Probably many more reasons, wrote about this in a chapter in my book.
Hopefully out in May.
Pete:
I don’t think the fact that we have known that runners will land more toward the anterior aspect of their foot and less toward the posterior aspect of their foot as their running velocity is increased for the past 25+ years is pertinent to the point I was trying to make.
We already know that one of the most common research findings of barefoot runner kinematics is that their stride frequency increases and stride length decreases for a given running velocity vs running shod. We also know that barefoot runners will tend to preactivate their gastrocnemius and soleus muscles before foot contact, presumably to avoid heel strike. Therefore, the research to date tends to support the fact that barefoot runners, most likely to avoid heel injury, will shorten their stride. plantarflex their ankles all in an attempt to land more on their forefoot and less on their heels than when running in shoes.
Now, let’s say we have a runner who is asked to run with equivalent metabolic rate (i.e. oxygen consumption) both barefoot and in lightweight racing flats (LRFs) on a cement or asphalt road. This runner has a stride length during barefoot that is 1.0 cm shorter than the stride length they have during running with LRFs on the same cement/asphalt surface. This 10 mm shorter stride length is presumably used by the runner as a measure to avoid heel injury, but expends the same amount of metabolic energy as it takes the runner while in their LRFs to run with a slightly longer stride. Now multiply this 1.0 cm shortened stride length by a stride frequency of 180 strides/minute. This means now that the barefoot runner, due presumably to avoid any heel impact and to, in effect, “chop” their stride, will be running 108 meters less per hour than they did in their LRFs at equivalent metabolic cost.
Again, this is a hypothetical example but certainly seems like a biomechanically and physiologically coherent explanation as to why more elite runners nearly always choose to run races in LRFs vs running barefoot.
However, as I said earlier, my #1 reason why elite runners choose to run in LRFs is probably:
“1. Lightweight racing flat (LRFs) allows the runner to run faster with more comfort and less perceived risk of foot injury since faster running speeds have been shown to cause greater peak magnitudes of ground reaction force (GRF) than slower running speeds.”
This would include running on surfaces with irregularities that may increase peak pressure on the plantar skin, cause even greater localized GRF on the plantar foot and more chance of skin, subcutaneous tissue, fascial or bone injury.
And, as far as the Kenyan youth are concerned, if all the youth in the race are barefoot because none of them have the resources to buy shoes, then, of course, the barefoot runners will be the winners of the race…..and will also be the losers of the race.
Cheers,
Kevin A. Kirby, DPM
Adjunct Associate Professor
Department of Applied Biomechanics
California School of Podiatric Medicine
Kevin,
In your second paragraph you correctly state that in barefoot running stride length decreases and stride rate increases, yet in your example you omit the latter. Your example only works if stride rate remains constant.
If you read the article I linked, he points out that the kids that finish in the Kenyan race last are wearing shoes ;)
Pete
Sent from my iPad
Pete:
If you read my example, the velocity of the runner is not being controlled, running both barefoot and shod, but their metabolic cost or oxygen uptake is being controlled, running both barefoot and shod. There is a big difference between these two factors at submaximal steady state running velocities.
What I am saying is that the use of lightweight racing flats may allow the runner to use a slightly longer stride for the same metabolic cost as when they are barefoot, at the same stride frequency, therefore making them faster runners.
It would be a very difficult study to do, to control for constant metabolic cost, but this certainly makes sense to me.
Looking forward to reading your book.
Cheers,
Kevin
Theoretically yes, but that only works if stride frequency remains constant, which does not seem to happen in the real world when you compare barefoot and shod runners…
Narrow columns are quite inefficient for effective writing!!
It’s an issue with my comment system – they indent too much. I’d widen the center column, but all of my historical posts are formatted for 460px and would require an immense effort to change…
It’s not about efficiency! It’s about proper running form and whether or not your shoe has a logic-defying 6mm rise from heel to toe!
Pete and readers…great comments and good shared themes.
on the study…yes shoes are faster. I wear shoes in races….can go a bit reckless and less metabolic work. hard to run on gravel and rough surface too at a fast pace. As one of the few runners who have grown up shod and actually run pretty fast barefoot here is my take: Most make the fatal flaw of “lifting the legs” (prancing style gait) and not engaging glutes when barefoot. This is metabolically costly and actually may increase loading if foot placement is in front of COM. Thanks for posting our video on your last column on the use of the glutes.
We have made it clear at Natural Running Center that barefoot running makes no claim to be faster, better, less injury, or that there is one exact way one should do this in technique (i.e. does the foot hit the ground in one particular way and is anything other than that “wrong”). We give runners permission to ask themselves the more important question of “what can i learn from running barefoot?” and “what are the true principles of the natural human movement pattern and how can i best understand, feel, and apply these?”. i think with the perfect smooth surface a habitual barefoot runner could run faster barefoot. anything studying shod runners who remove shoes makes little sense. their default is shod and they do not have the “stiffness” in the system. not sure how “habitually shod” the subjects were.
all good stuff…now take off your shoes for a few strides :)
Mark Cucuzzella
Pete,
just saw the full article…they were not barefoot! Sock matter
link to trtreads.org…
the runners has stuff on top of their feet too. just though as folks interpret what all this means. Mark Cucuzzella
Mark:
Pete mentioned this problem of socks vs true barefoot in the research study in his article. I think the biggest problem with the study is not the “stuff on top of their feet”, since the weights would need to be placed dorsally on their feet by some method, but rather that the socks could have caused enough foot to ground slippage (i.e. decreased coefficient of friction) during propulsion that this may have negatively affected running economy of the barefoot runners.
I wonder why the authors didn’t use true barefoot running on a treadmill and then just tape the weights on top of their barefeet to determine the metabolic cost of adding mass to feet for running. I see the sock problem being the biggest issue with this study.
Maybe they couldn’t get IRB approval from the University of Colorado due to too much risk of plantar skin injury from running barefoot on a treadmill? I would think that experienced barefoot runners should have no problems of running on a treadmill without risk of injury. Can you run comfortably on a treadmill while barefoot?
Cheers,
Kevin
I asked them about this – it was an IRB issue. Seems kind of silly to me, but sometimes the IRB leaves no choice. I’d agree that if these are regular barefoot runners and the plantar skin was conditioned, then abrasion should not have been an issue for the length of time they were running without shoes.. There was also concern about hygiene, but I’d think a rub with alcohol could take care of that concern.
I agree it is silly and, unfortunately, affected the strength of the research, in my opinion. Human skin is the largest organ of the body and works very well at preventing organisms from penetrating internally, especially the thickest epidermis…located on the plantar foot. There are probably more harmful organisms transferred during handshakes or when pushing a shopping cart than during running on a treadmill barefoot!
Hi Pete,
Nice summary of the paper. The paper is interesting, but as you point out the headlines aren’t justified by the content, and some of the conclusions play a bit loose with the actual data. The straight line fitting of the shod tests results looks particularly dubious, the data sure looks like a curve would have been far more appropriate.
One thing that I have been pondering about recently is the role of mass of the shoe on the moment of inertia around the ankle. For moment of inertia the distance away from the ankle is as important as the mass itself. Consider a thick soled shoe and a thin soled shoe of the same mass – the thick soles shoe will have a higher moment of inertia as the mass on average will be placed further from the ankle.
The moment of inertia is important as it effects how much load and energy we have to put into movement of the foot through the cycle. I would also expect it’ll effect the angle of the foot on landing – the higher the moment of inertia the more likely a heel strike.
Thanks for the comment Robert – I though about the location of the weight too. In a shoe, most of the weight is in the sole, so adding weight only to the top of the foot on the laces might change things a bit.
Hi Pete,
Is there any chance you do an experiment on your tread-mill and slow motion camera to look at the effect of placement of mass on a shoe/barefoot. I’m thinking of placing 50g either side of the ankle, vs on/close to the sole. The greatest increase in moment of inertia would be achieved by placing a weight at the toe, this would probably change the COM of the foot/shoe system too much.
Another test on might be able to do just by oneself would be to place a weights at different places on each foot to see if one can feel a difference between them. Doing slow motion video would be a way of adding a quantitative way of assessing differences. Swapping the positions between the feet would enable one to double check whether asymmetries are caused by the weights rather than just natural asymmetries of the runner.
Robert:
I would expect the the main consideration of shoe mass on metabolic efficiency of a runner is not the moment of inertia relative to the ankle, but rather the main consideration will be the moment of inertia relative to the knee and to the hip, since moment of inertia varies as the square of the distance from the axis of rotataion to the added mass. I = mr^2
In addition, this additional moment of inertia from a shoe or mass added to a bare foot would only be important during the forward recovery phase, when the foot is being accelerated forward, off the ground, and wouldnt be as important during support phase, when the foot is relatively stationary on the ground.
In other words, it is likely the hip flexors and extensors and knee flexors and extensors are the main muscles that are working harder and causing the extra metaboic cost during the forward recovery phase of running with mass added onto a foot, rather than the ankle joint muscles.
Cheers,
Kevin
Good points about the knees and hips – makes me wonder how much of recovery is passive recoil vs. active contraction and how this impacts energy cost of added mass at the foot. The only time my hip flexors ever fatigue while running is late in a marathon.
The more obvious conclusion regarding all of this for the average runner is that supporting weight during stance is responsible for the majority of metabolic effort in running, so for a recreational runner with a few extra pounds around the midsection, controlling overall body weight is probably going to have more impact on performance than cutting a few ounces off your feet.
Pete:
Alternatively, if you are wanting to improve the metabolic efficiency of running, the best place to lose mass is at the ends of the lower extremities, on the feet. So, this is one of the best reasons, in my opinion, why running shoes should be a light as possible, in order to decrease the work of running, as long as the reduction of weight doesn’t cause some other problems, such as injury.
A very interesting related case to this discussion is the case of Oscar Pistorius, the “blade runner”, where it was found that he had extraordinarily fast forward recovery phases which was thought to be the main reason why he had an unfair advantage versus his competitors who had legs. This very short forward recovery phase was likely due to his “blade prostheses” having much less mass than other able-bodied runners and the moment of inertia at the hip being much less, therefore increasing the flexion acceleration at the hip during forward recovery phase. This directly ties in biomechanically and physiologically with our discussion on the effects of masses added to feet and the metabolic cost of barefoot vs shod running.
Ross Tucker and Jonathan Dugas have done an excellent job of detailing the very interesting biomechanical, physiological, ethical and legal case of Oscar Pistorius in their Science of Sport blog.
http://www.sportsscientists.co…
Cheers,
Kevin
I agree – I think light shoes are preferable whenever possible. But body weight can make a big difference if you have a decent amount to lose (as is the case with many recreation runners you see in races). If you are already whippet thin, then shoes will obviously have much more impact. I credit the fact that I was at my lowest weight in a decade during my BQ marathon as a big reason why I was able to make the time – 10 lbs less to carry has a big effect!
Interestingly on Pistorius, Kram, who was third author on the paper written up in my post, wrote the article saying that Pistorius does not have an advantage: link to jap.physiology.org…. I haven’t read enough on the debate to form an opinion, but I find the reduced moment of inertia argument that you make compelling.
Pete:
Ross Tucker has probably written the best stuff I have seen on the Oscar Pistorius biomechanics feud. As we approach the date for the 2012 London Olympics, believe me, this controversy will be front and center if Pistorius makes the cut into the finals. Should be interesting to see how it all unfolds. Track and field history is being made with this event!
link to telegraph.co.uk…
Cheers,
Kevin
Hi Kevin,
I don’t think you picked up on the point I was making, it wasn’t about the wider effects of mass of the shoe on efficiency, but the local effects on the motion of the foot itself. Whether you land on your forefoot, midfoot or heel depends upon motion of the ankle, motion of the ankle depends upon moment of inertia and forces applied by the ankle.
If you want the same motion of the ankle but have an increase moment of inertia around the ankle then you have to increase the moments applied by the muscles and tendons. If you don’t increase them then you don’t get the same motion and you don’t get the same final angle at landing.
If you dial back this observation back to some of the feedback that one of the participants of research you’ll know that he struggled to keep his normal form when adding the weights. When adding weights to the foot I would expect the increase in moment of inertia about the ankle to be far greater than the increase in moment of inertia about the hip, so I’d also expect the runner to find coordinating the motion of the ankle more difficult to tune correctly than tuning the gross motion when changing the mass on the foot. If the runner is struggling to keep good form then they won’t be running relaxed, and if they ain’t running relaxed they won’t be running efficiently.
A good way to factor out this issue would be to place the add mass nearer the ankle joint for one set of tests, then move the added mass further away from the ankle to increase the moment of inertia about the ankle without increasing relative to the knee or hip.
Robert:
How do you figure that “When adding weights to the foot I would expect the increase in moment of inertia about the ankle to be far greater than the increase in moment of inertia about the hip”??
The distance from the ankle joint axis to the added weights in this experiment is likely about 10-15 cm, whereas the distance from the added weights to the hip joint axis is closer to 80-90 cm. Since moment of inertia will increase as the square of the distance of the added mass to the axis of rotation, then I would estimate that the mass added to the foot would have at least 28 times more effect on the moment of inertia at the hip joint than at the ankle joint.
Please explain your rationale for your statement “When adding weights to the foot I would expect the increase in moment of inertia about the ankle to be far greater than the increase in moment of inertia about the hip.”
Cheers,
Kevin
I may have misunderstood, but I think he meant that varying the placement of the weights on the foot would have a relatively greater affect on the ankle than the hip – e.g., placing the weights on the sole vs. laces. vs. say the forefoot.
Pete:
Every single study that I know of that has measured the effects of added masses to feet/shoes on oxygen consumption during running have added the masses either medially/laterally on the forefoot or dorsally on the forefoot. Of course, ideally, to best simulate the mass that is added to the foot by a typical running shoe, the weights should actually be located on the plantar foot, but I don’t know how you would do this barefoot or even in a shoe without possibly affecting the cushioning properties in the shoe. Such are the technical difficulties of such experiments.
Cheers,
Kevin
Kevin, I’m not talking about an absolute increase in moment of inertia, but a relative increase in moment of inertia. When you are trying to work out the effect on gait it’s the relative increase that is important not the absolute values. I’m sorry that assumed that the readers might understand this as it really doesn’t make any sense to think in dimensional terms when comparing different parts of the body.
I don’t have figures for the moment of inertia of the leg or foot so can’t provide an accurate figures for the relative figures. Do you have these? Pete do you have figures for moment of inertia? If you do then we have a stab at estimating the relative effects of the inertia around the anke, knee and hip and there likely knock on effects for the dynamics.
Robert:
When you are talking about metabolic efficiency, one should consider the most significant mechanical effect of the experimental intervention. That would be the effect of added mass on the foot relative to the hip and knee joint axes, not to the very short distance to the ankle.
However, certainly we can agree to disagree on this one unless you have some data that proves me wrong.
Cheers,
Kevin
Hi Kevin,
My comments about the effect of moment of inertia about the ankle aren’t primarily about metabolic efficiency. Please go re-read and have a think about what I’ve written.
I also haven’t said once that the moment of inertia effects about the ankle are more important than the changes relative to the knee or hip. So it’s odd that you’re suggesting this.
One thing for sure is that shoes and the weights in this research trial have a direct effect on moment of inertia about the ankle. Changes of moment of inertia will have an effect on the kinematics of the foot. How much of an effect is something I’m really trying to ask. I don’t have the answers. You first have to ask the questions before you can answer them. It’s iterative process that science works by.
My guess is that it isn’t negligible, and will act to change the runners gait, or require a change in muscle activation to achieve the same gait as without shoes/weights.
Whether changes in kinematics of the foot will have an effect on overall efficiency is a another wider issue. If the moment of inertia changes don’t change the kinematics of the foot then yes we can ignore this from consideration with overall efficiency.
There are also other important aspect beyond efficiency – injury prevention. Here the balance of what is crucial to injury will be different to what this issues of efficiency. The angle of flexion of knee and ankle are critical to loads applied through the whole system.
So please don’t fixate on just what your current line of thought is. My original and subsequent comments have been about opening out the discussion to cover aspects to the dynamics that had been neglected.
Robert:
I do not need to reminded of how science works, am not “fixated” on a current line of thought as you suggest and don’t appreciate being talked down to.
End of discussion.
Cheers,
Kevin