Basically says the curves are helpful, but may replace muscle work, resulting in weaker muscles in foot. Even suggests potential connection to plantar fasciitis.
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Oh, interesting! Daniel Lieberman does fascinating research, and Nick Lehecka (who gave running mechanics classes here in Ithaca about a decade ago) did some graduate work with him. @JTuori, any thoughts about this study?
Speaking as someone who’s just coming out of my second 18-month bout of plantar fasciopathy (hopefully it’s only going to happen once per foot), I’d contribute that I think intrinsic foot muscle strength is a big deal. I’m a sample size of one, of course, but I’m giving some credit for my current recovery to doing a lot more barefoot walking (and running, before I embedded something in my right foot and had to go to a podiatrist to get it extracted). Part of the difference is that you walk differently barefoot—heel striking hurts, so you’re much more likely to walk on your forefoot; it’s almost a tiptoe motion. That reduces impact and stress on the heel, though I’m not sure how it loads the plantar fascia itself.
@Ian, are there shoes that have notably less toe spring? Altras, perhaps?
I chatted with Golden Harper (co-founder of Altra) years ago about that as we road on an airport shuttle together for a conference, and as we’ve been connected as one of their earliest accounts. At the time (i’ve visited the potential a couple of times over the years), I was working on a custom running shoe concept / company. One of my questions was just that…in regards to the toe spring. And, as Golden through Altra created a more natural design in drop and shape, why did he keep the toe spring? He said he’d had the same thoughts early on, and wanted his engineers / designers to create their shoes without them. Their engineers / designers said they could, but that he’d end up tripping over them. He was committed to the idea, had them manufacture the proto-types…only to do just that…catch or trip over them. So, that was that.
I’m not sure of specific measures…it’s felt more in some than others, but companies don’t have those values to pass on.
I’m wear-testing Skechers at the moment, a few different models…and, similar to Hoka’s, Pearl Izumi’s and Scott’s from prior, they have the dynamic platform or rocker bottom. Some people don’t mind if not love them, and have no issues, but I see that as a larger artificial impact than the toe spring. For me personally, my knees and connective tissue in my ankles don’t like the rocker bottoms. My subpatellar bursa gets inflamed, quad insertion a bit unappy as well, and the connective tissue around my medial malleolus in the ankle tears. I’m kinda fragile though in connective tissue and that’s just me.
Now I have to look at every shoe I own to see if they all turn up at the toes. 
Whoa – great backstory! I guess that makes sense if we are so used to this, that removing it would result in issues/trips. Who knew…
Let us know if you move forward with the Golden Racers so we can try out the prototypes! 
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Also, one of the individuals / researchers for that study, Nick Holowka, is an Ithaca H.S. Grad (2003).
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Yeah I saw this study blow up when it came out and I think it’s been taken a bit too far. The study itself had participants walk in sandals and in the discussion they were commenting on shoes, foot weakness, and plantar heel pain. We aren’t even actually sure that foot weakness is a risk factor for plantar heel pain in the first place. In fact, we’re just figuring out the actual role of the intrinsic foot muscles (which is mainly to stiffen the big toe during push-off to support the plantar fascia, a passive structure). It’s an unfortunate spin in research when the study you’re conducting isn’t anywhere close to being able to answer a complex question but you try to take it there anyway.
The more weight shifted onto the forefoot actually loads the plantar fascia more. I think the crux of the discussion is basically “are we strengthening the foot muscles or normalizing load tolerance in the plantar fascia?” We don’t really know but I would wager it’s closer to the latter and that strengthening the foot just helps to reduce some work that the already aggravated plantar fascia has to do.
Cool. So what does “normalizing load tolerance in the plantar fascia” really mean? Is it that by going barefoot (where the walking gait more closely approximates Rathleff’s heel raises) we’re moving the load from one portion of the plantar fascia to another? Or that we’re putting a more normal (ie, less supported by arch inserts) load on the plantar fascia?
On the side of strengthening the intrinsic foot muscles, Rathleff reports some delayed-onset muscle soreness when starting his heel raise exercises, which would suggest intrinsic muscle involvement. And anecdotally, I feel like I’m using my toes a lot more while being barefoot, and it feels good, to the point where, when I’m reading in bed, I’ll often put the soles of my feet together and wiggle my toes on each other, purely because I like the sensation.
In the short term it would be shifting load away from the sensitive structure (PF) via mechanical offloading (say foot orthoses or forcing the intrinsics to do more active work to reduce the amount of passive work that the PF has to do). In the long term it would be re-exposing the PF to higher loads so that it retains the capacity to take them on. A lot of these overuse injuries can be separated into a “pain-dominant” phase and a “load-dominant” phase where the goals of protecting vs exposing will be different. This might be a sneak peak at one or more of my future talks…
This is really fascinating! I had wonderings in the past about the upturned toe in running shoes. I also had PF many years ago in one foot, but it was the forefoot, not the heel. Being barefoot helped tremendously (I’m not a fan of shoes in general), and practicing load-bearing exercises barefoot plus chiropractic visits eventually fixed it.