For some reason I’ve spent some of the last few entries discussing flip-flops and the myths associated with them. My suspicion is that, because they look pretty close to bare feet, they relie on many of the same barefoot myths and attract the same animus directed towards bare feet.
I thought I’d take a deeper look at the science.
In Somethong Wrong I looked at how a pain management organization just passed along the myth that feet needed “arch support for optimum health” without looking into it. And in Huff-Po Bait-and-Switch, their advice for the benefits of walking had pictures showing people walking, barefoot, but included the specific advice to “Get the right shoes”, and flip-flops were definitely considered the wrong shoes.
The thing is, when you look at the science, there’s not a whole lot there. Claims are made that are impossible to track down. For instance, the whole premise in Flip-flopsr injure 200,000 a year’ costing the NHS an astonishing £40m, all the story does is make the claim.
Compared to high heels, they don’t look remotely hazardous. But flip-flop wearers would do well to think twice before slipping on a pair.
The NHS spends £40million a year treating injuries caused by wearing the casual footwear
No citation at all. How is one to even know that a study was done, or that the NHS is conflating all sorts of footwear? (I tried looking for a study and did not succeed.)
Or then there is this study, which in the introduction notes
In fact, according to the American College of Foot and Ankle Surgeons in 2007, an increase in the use of flip-flops by teens and young adults has led to an increase in heel pain.
And the source? A press release with unsupported assertions in it. All there is is a quote from a spokesperson.
“We’re seeing more heel pain than ever in patients 15 to 25 years old, a group that usually doesn’t have this problem,” said ACFAS spokesperson Marybeth Crane, DPM, FACFAS, a Dallas-area foot and ankle surgeon. “A major contributor is wearing flip-flop sandals with paper-thin soles everyday to school. Flip-flops have no arch support and can accentuate any abnormal biomechanics in foot motion, and this eventually brings pain and inflammation.”
OK, they’re seeing more heel pain than ever. But how does she know it’s not caused by something else, like the all-enclosing “athletic” footwear that all those young people wear? In fact, barefooters are well-aware of how those lead to plantar fasciitis and other pain.
They’ve got nothing.
Many of the studies find that the gait and stresses associated with flip-flops is pretty much the same as going barefoot. For instance, in Effects of common footwear on joint loading in osteoarthritis of the knee, four different shoe types (and bare feet) were compared for stresses on the knees. Those were clogs, stability shoes, flat walking shoes, and flip-flops.
The flat walking shoes, flip-flops, and bare feet all had significantly lower peak loads. (And we all recall that high-heels, not tested here, give incredibly higher peak loads on the knees.)
Peak plantar pressures for athletic shoes, flip-flops, and “barefoot” were compared in Computerized analysis of plantar pressure variation in flip-flops, athletic shoes, and bare feet. I put “barefoot” in quotes because here are the soles of one of their “barefoot” subjects.
Those are the pressure sensors. Oh, and the text of the study reveals that “a standardized thin cotton sock was worn to hold the sensor in place during ambulation.”
What they found was “flip-flops always demonstrated higher peak plantar pressures than athletic shoes but lower pressures than bare feet.” From that they extrapolated
Although these data demonstrate that flip-flops have a minor protective role as a shock absorber during the gait cycle compared with pressures measured while barefoot, compared with athletic shoes, they increase peak plantar pressures, placing the foot at greater risk for pathologic abnormalities.
But the data they present never says how much greater the peak pressures were. All they have is a graph showing the results that were statistically signficant, and by how much they were statistically significant. Here is their Figure 4. See if you can figure it out.
Or maybe the graph is mislabeled. It may be showing that the peak pressures only varied by, at most, 2%. (Also note the wide differences between the results in the right and left feet, which really rouses my suspicions.)
Of course there are all sorts of other questions: if people don't go barefoot regularly, how accurate can this be since well-know barefoot walking adaptations probably haven't occurred (and how much did the socks affect that?). Another thing to wonder about is a threshold effect. Sometimes more stress builds the body. Walking barefoot puts more stress on muscles, joints, and tendons, but the end result is that it strengthens them and help prevent the arch from collapsing. Also, for regular barefoot walkers, the skin builds up providing just the sort of cushion the body thinks it needs for itself.
But one thing it (purportedly) shows is that bare feet and flip-flops are pretty similar.
To move on to another issue, the other complaint about flip-flops is that the toe-scrunching required to hold them on is bad. OK, it certainly is different, but is that bad? Again, it gets to the question of whether using some muscles more really hurts or not?
There is one study, Effect of thong style flip-flops on children’s barefoot walking and jogging kinematics, that looked at this.
It turns out that, while an effect can be seen from toe gripping, it’s not much. As the “Conclusions” put it:
Ankle dorsiflexion during the contact phase of walking and jogging, combined with reduced hallux dorsiflexion during walking, suggests a mechanism to retain the thong during weight acceptance. Greater midfoot plantarflexion throughout midstance while walking and throughout midstance and propulsion while jogging may indicate a gripping action to sustain the thong during stance. While these compensations exist, the overall findings suggest that foot motion whilst wearing thongs may be more replicable of barefoot motion than originally thought.
The paper had a number of (rather neat) depictions of the measurements showing the similaries between bare feet and flip-flops. Here’s one of them.
What you can see there is that the standard deviations overlap the entire time.
The real differences between bare feet and flip-flops are ones that only barefooters would recognize, and care about. First, they prevent the direct feel of the ground, and proprioception that goes along with that. The other is that they can be unstable when it comes to the sole-sole contact between the bottom of the foot and the top of the flip-flop. That latter means that your foot can slide sideways (or forwards/back) if the toe-grip is not strong enough.
We’ve also seen from injury lawsuits that, particularly when wet, flip-flops can be particularly dangerous. Both the ground/flip-flop and the flip-flop/footsole areas are susceptible to leading to a slip-and-fall.
Again, as far as I’m concerned, bare feet are way better. I can only think of two times when they can be of use.
The first was when you are extremely footsore, from overdoing it on, let’s say, some long hike over really rough terrain. They’re not ideal, but they won’t put your feet into coffins and prevent your feet’s natural mechanisms from working properly. (I’ve done a 10-mile hike in flip-flops—worked fine, except for being isolated from the earth.)
The other use is as a ticket. If you need to get on an airplane and suddenly the airlines insists on footwear, it is easy to reach into a bag and pull out a pair and put them on for long enough to board the plane.
Finally, I think that it is recognized that flip-flops are pretty close to bare feet, and that leads to the myths and hatred by some folks. Even though they’ve become ubiquitous, a lot of people think they are just not right and they look for reasons to disapprove.
That is kind of illustrated by this “Stone Soup” cartoon from a few days ago.