@SC: sorry, totally missed your response till just today. One thing to point out: when I say "barefoot" running below, I'm also including "minimalist" shoes similar to VFFs. Of course, there is some gray area where the dividing line is between "minimalist" and "regular" shoes, but to generalize, I'd call shoes "minimal" if it's more or less impossible to run heel-to-toe in them (just like it is barefoot).
Whether a 250lbs person can run safely in general, shoes or no shoes, is a totally separate issue. The question to discuss here is if a 250lbs person is safer in "normal" shoes or "minimalist" shoes if they do decide to run.
Here's my problem with this type of thinking: if there are increased forces/pressure on certain parts of the foot (which is to be expected, to be honest), this does not automatically mean injury. Sure, if someone jumps in and runs 10 miles barefoot their first time, an injury is very likely. But if you build up to it gradually and allow the corresponding tissues and muscles to adapt, your threshold for injury is likely to be significantly higher. It's like saying that a 300lb deadlift is dangerous because of the pressure it puts on the spine/tissues. If some particularly strong newbie could somehow come in and deadlift 300lbs their first time, even with good technique, I'd bet the chance of injury would be high simply because their body doesn't have any of the adaptations for heavy lifting. But someone that worked up to it over months of lifting would do just fine.
In other words, a study that merely comes out and says "barefoot running puts increased pressure on parts of the foot that shod running doesn't" would be neither surprising nor particularly useful. On the other hand, I'd be much more interested in a study that comes out and says "barefoot running significantly increases injury rates over shod running", but somehow I doubt we'll be seeing that any time soon. The key is that there is no perfect solution here: whether you run shod or barefoot/minimalist, injuries will happen. The question is which one keeps the injury rates lower.
A few more questions come to mind when I read something like this:
1. Why do so many people have these foot abnormalities (varus, valgus, etc)? Are we all just genetically defective? Or is it because wearing shoes our whole lives has prevented proper foot development? Is it because we aren't active enough in our daily lives?
2. Is there any research that shows either (a) orthotics cure - not merely treat! - the abnormalities above or (b) barefoot running has more of negative impact on such abnormalities than shod running?
3. Disclaimer: the following is totally my personal opinion/rant. From personal experience - my entire family has flat feet & numerous other foot "abnormalities" - I am VERY dubious of the "solutions" proposed by many foot specialists. Orthotics, arch supports, motion control shoes, etc. can be useful in a few isolated cases, but they seem to be prescribed for every foot condition out there. These devices are a crutch and people become dependent on them, keeping many podiatrists happily employed. The real cure, of course, is a lot harder: exercise, PT and strengthening of the under-developed musculature. IMO, there is no way in hell the human species could have survived/evolved to have a totally messed up foot, especially if there is any truth to the "persistence hunting" theories. The fact that so many people believe they need correction for their over-pronating, under-pronating, motion control shoes, orthotics, etc is a sign that something in our environment is screwing up our feet. I'd bet an awful lot of money that shoes & inactivity are the cause. And I'd bet even more money that if people gradually switched to barefoot/minimalist shoes, many of these "foot abnormalities" would suddenly go away on their own.
Thanks, a nice read.
The analogy you make is sensible, but doesn't translate well to running itself. Running tends to be endurance related, requiring thousands of reps just to complete a few measly miles. Therein lies the difference. Sure, people's bodies will accommodate, but the likelihood of overtraining is much greater with a sport like running. People tend to run almost every day. Instead of a constant buildup of material to deal with the new stresses, they are actually weak in their compressive and tensile tissues due to the lack of time to build back up. This is why runners, barefoot and shod, get so many stress fractures, Achilles tendonitis injuries, shin splints, etc. It's very rare that someone deadlifts every single day, but extremely common for people to run every day.
The thing is that these forces are measured on one step. With thousands of steps, even a small increase in force becomes a big deal. This is where forefoot running comes in. It decreases ground reaction forces quite a bit and, in all likelihood, decreases the chance of injuries (especially stress fractures). On top of this, shoes have shown to reduce ground reaction forces as well - mostly with heelstrike conditions. In all honestly, I believe stresses at the forefoot will be decreased to a significant level as well, but there isn't research showing that yet. The difference, however, is that the raised heel of the shoe reduces dorsiflexion range of motion required, reducing extensive strain on both the medial arch and Achilles tendon. Since most people don't have proper dorsiflexion range of motion, they substitute by everting the weightbearing foot, resulting in lengthening of the arch, increasing the risk of plantar fasciitis.
To answer your questions:
1) Normal is the mean. As in everything related to population and bell curves, there is significant deviation from what is normal. These foot conditions can range from minor to severe, but all affect the way someone shock loads with running. The problem isn't that neutral for the subtalar is in a different place, the problem is that we have to set the bottom of our foot down. Because of this, many individuals will stay in their end range of motion, stretching out tissues that should be tighter. This leads to laxity, leading to instability and frequently injury or degeneration.
Also, these deformities are developmental in nature. They don't have anything to do with the footwear worn (unless your feet have been bound). You can get similar deformities at the tibia and femur - it's just a developmental issue.
2) Orthotics cannot modify an intrinsic factor that has developed in utero. The placement of the bone is permanent - not even surgery has good ways to correct them. This is like asking if crutches heal a paraplegic. Can they make the individual walk on his/her own? No. Can they keep the individual mobile while reducing chance of injury? Yes.
Also, since barefoot running research is pretty limited, I haven't see any articles addressing anatomical foot variation and barefoot running. However, there are hundreds of research studies on foot deformities and walking... and the incidence of injury, etc. As a whole, individuals with these foot deformities have a higher risk of pain or pathology just with walking. It's pretty safe to say that running will stress the pathological structures more than walking.
3) I used to very much believe what you're saying. However, I've learned quite a bit differently since I've begun physical therapy school. The musculature that maintains the ability to stabilize in the frontal plane (i.e. the everters and inverters) is extremely weak compared to the forces withstood at the subtalar joint. The inverters (which can resist excessive eversion in individuals with rearfoot or forefoot varus) can only generate about 8% of the force of the plantar flexors. Plantar flexors are strong enough to keep the ankle out of dangerous ROMs. The everters can only generate about 4% of that. These muscles cannot be strengthened so much to avoid extreme ROMs while walking, let alone running. I can find research supporting that, if you'd like. There have been some studies showing that physical therapy of all sorts (conservative and aggressive) is ineffective at treating these conditions. We can treat injuries related to these conditions and prevent injury by molding orthotics for individuals. With those two actions, related injuries are frequently cured for life.
To be perfectly honest (although you likely won't agree), I believe research has shown the surfaces that we run on and the frequency with which we train are the two most different factors nowadays. Harder surfaces lead to greater and quicker force transmission to the skeleton and elastic structures. Compromised shock absorption in people with foot deformities contributes to a great deal of injuries. On top of that, tribes didn't tend to run game down daily. They did it much less frequently and likely rotated through individuals within the tribe. And again, the surface was many times softer and more absorptive.