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I have treated a couple of runners recently who had a plantar plate dysfunction wearing Vibram Five fingers, but did not give a lot of thought to it until reading a blog post from Peter Larsen this morning. He and a few runners that he spoke too (and some more have shown up in the comments on the post) appear to have developed a plantar plate dysfunction from the Vibrams and got better when they started using a different minimalist shoe other the the Vibrams which has the pockets for each toe. Peter speculated that the problem was possibly due to the restricting of dorsiflexion of the toe in the Vibrams compared to other minimlaist shoes .... this would inhibit the reverse windlass and assume that this is related to the issues with the plantar plate.

Interesting observations. What say you?

(paradoxically, I get a plantar plate issue in my NB Minimus from time to time, that is quickly fixed with a couple of days in the Hoka One Ones)

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Related threads:
Other threads tagged with Vibram Five Fingers
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Here is another thought .... we have already has a thread on the epidemic of metatarsal stress fractures occurring in those using the Vibram Five fingers ....

Why do runners get metatarsal stress fractures?
They get a metatarsal stress fracture when the dorsiflexion bending moments in the metatarsal exceeds what the bone can tolerate. To prevent metatarsal stress fractures you need to increase the bone health (ie no osteoprorosis), increase the tissue adaptation (ie progressive overload) and decrease those dorsiflexion bending moments (ie increase the plantarflexion moments).

There are a number of ways to increase the plantarflexion moments in the forefoot and two mechanisms are the windlass mechanism and the retrograde pressure from the proximal phalanx on the metatarsal head. Do the individual pockets for the toes in the Vibram Five Finger restrict these mechanism of increasing the plantarflexion moment (ie decrease the dorsiflexion moment) and account for a possible increased risk for stress fractures in the metatarsals?

What say you?

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Craig Payne
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Hi Craig

Your idea sounds plausible even probable to me.

On another track on plantar plate issue; forgive my ignorance but can anyone answer this question.

In same subject/running velocity/environment/foot-wear would peak pressure and force time integral under metatarsal head (s) be greatest with heel/toe or forefoot gait pattern? I wonder if plantar plate injury may be more a factor generally of compressive stress @ initial contact rather than later tensile stress?

In which case material properties of foot-wear at metatarsal heads may be most important in those with little headroom before exceeding injury threshold.

Cheers

Martin

Foot and Ankle Clinic
1365 Grant Ave.
Winnipeg Manitoba R3M 1Z8
phone [204] 837 FOOT (3668)
fax [204] 774 9918
www.winnipegfootclinic.com

Force time integral is essentially the force times the time it is applied. The longer the forefoot is on the ground the higher the force time integral will be. (Well, if the forces are near zero then it won't be bigger by much.) Another question is whether the force time integral is what matters for a specific anatomical structure as opposed to peak force of some other measure.

Eric

Hi Eric

Yes I agree; but question remains on both accounts; is there an important difference in these metrics for heel/toe vs forefoot IC all other things being equal?

On first thoughts; force time integral would be much higher in forefoot because of longer contact period on other hand the knee / hip is extremely effective as a damper so those peak pressures may actually be lower in most runners therebye reducing force time integrals.

That is why I am asking question and not sure if this has ever been studied. Anyone know answer to this?

Cheers

Martin

One the key difference is the anterior- posterior shear component. Forefoot strike running has faster rate of loading, a biphasic pattern (double braking if you like) and if memory serves, higher peak magnitude. I'm away from home now but if you google forefoot strike kinetics there is a PDF where they looked knee joint moments, but also showed the differences in reaction forces.

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Thanks Simon

Almost a great memory and certainly a good call. As penance for my laziness in first instance here's some relevant info from the paper you remembered.

Bear in mind this comes from shod data (running shoes) primarily to consider knee abduction moments implicated in PFS.

Higher peak power absorption (eccentric work) could be observed concerning the MTP and ankle joint (sagittal plane) for FFS compared to RFS.

The active peak of FFS reveals sig. higher forces than RFS.

GRFs.jpg

The vertical loading rate was sig. higher during RFS.

The horizontal braking and acceleration forces as well as the loading rate (braking) indicated sig. higher values for FFS compared to RFS.

In this context a biphasic shape of the braking phase could be observed in FFS. This shape was due to the runner landing on his forefoot and the center of pressure moving posterior as the heel lowers.

I guess this is kind of obvious really but I wouldn't have realised it; I would think this this has more potential to mess up the plantar fibro-fatty pad in those sailing a bit close to the wind

There are no differences in the incidence of running related injuries between FFS and RFS. However, the location and the kind of injury and complaints are different

not definitive but some food for thought

entire paper attached below


DIFFERENCES BETWEEN FORE- AND REARFOOT STRIKE RUNNING.pdf

Cheers

Martin

Foot and Ankle Clinic
1365 Grant Ave.
Winnipeg Manitoba R3M 1Z8
phone [204] 837 FOOT (3668)
fax [204] 774 9918
www.winnipegfootclinic.com

My take on the cause of the forefoot problems (i.e. metatarsal stress fractures and plantar plate tears/inflammation) seen in barefoot running and in many of the thinner-soled minimalist shoes is that these injuries occur, not because of shearing forces or a "restriction of the reverse windlass", but because the runner is striking the ground with nearly all their weight on the the forefoot forefoot-striking running whereas, in rearfoot striking running, the runner first strikes the ground with the rearfoot then moves weight to the forefoot.

It is probably a combination of increased forefoot impact forces and duration of forefoot load in the forefoot striking runners that cause these injuries. There are certainly a couple of studies which show that barefoot running increases gastroc-soleus activity and Achilles tendon load which would need to be correlated with increased forefoot loads to make mechanical sense. I would need to go through my pile of barefoot running articles to see if any of them actually looked at this with in-shoe pressure or pressure mat technology which would be the best way to get at the reason for these injuries in forefoot-striking runners. I don't think the force plate would be able to discriminate metatarsal head loads very well and so the need for pressure insole or pressure mat technology. Off the top of my head, I don't know of any studies which have looked at this.

However, I do have Joe Hamill's recent lecture from the I-fab conference in Australia where he has pressure mat illustrations of barefoot vs shod running which clearly shows the increased plantar pressures on the metatarsal heads during barefoot running vs shod running. I'll see if Joe will allow me to display these images here.

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Kevin

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Hi Kevin

The more I think about it the more compelling I find the reverse windlass argument.

In both RFS and FFS, during the period of maximal potential MTP dorsiflexion moment (propulsive phase) if the foot-wear is essentially shifting force away from the toes then the "tie" effect of the windlass must be diminished during this period. If this is true, then it occurs when the GRF vector is most horizontal and whilst it is tempting to think of gravity resisting inner longitudinal arch excursion (foot is vertical) the horizontal vector may be quite deforming to the metatarsals because the shoe can't protect from that and neither can the tie.

Although we don't know the plantar pressures from this study I think that it would be reasonable to assume that the forefoot contact areas would remain pretty constant in which case the forefoot pressure would likely correlate closely with measured force. In which case we can infer that the maximum pressures, at this speed at least, are not very different between RFC and FFC. The force time integrals however would be much higher for FFC. I guess, since as Eric mentioned, we don't know how relevant peak pressure and force time integrals are to forefoot injury perhaps this is moot anyway.

The pressure sensor data ignores the shear; I don't understand why you might dismiss shear which is about 3X greater at contact with FFS compared to RFS. Also I assume that the contact period in FFS is fairly short compared to FFS which would make the shear load rate higher than the graph suggested (the data is normalised to % gait cycle).

No wonder I enjoy my elliptical machine; feet firmly planted, wearing "the works", beer in one hand, clutching iPhone in other whilst gracefully reading podarena.

Cheers

Martin


Foot and Ankle Clinic
1365 Grant Ave.
Winnipeg Manitoba R3M 1Z8
phone [204] 837 FOOT (3668)
fax [204] 774 9918
www.winnipegfootclinic.com

The shear data is interesting, and certainly could be the sole cause of the plantar plate injuries and metatarsal stress fractures. However, I don't see how AP shearing forces would cause metatarsal stress fractures since the AP shear forces are not perpendicular to the metatarsal shaft, they are more horizontal to the metatarsal shaft. In addition, I don't see how AP shearing forces would injure the plantar plate.

My gut level feeling is that the same forces that tend to cause metatarsal stress fractures are also the forces that tend to cause DMICS, plantar plate injuries and Achilles tendinitis in forefoot striking/barefoot runners: increased vertical ground reaction forces/pressures acting at the metatarsal head level.

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Sincerely,

Kevin

**************************************************
Kevin A. Kirby, DPM
Adjunct Associate Professor
Department of Applied Biomechanics
California School of Podiatric Medicine at Samuel Merritt College

e-mail: kevinakirby@comcast.net

Private Practice:
107 Scripps Drive, Suite 200
Sacramento, CA 95825 USA
My location

Voice: (916) 925-8111 Fax: (916) 925-8136
**************************************************

[quote=Kevin Kirby;264734 since the AP shear forces are not perpendicular to the metatarsal shaft, they are more horizontal to the metatarsal shaft. In addition, I don't see how AP shearing forces would injure the plantar plate.
.[/QUOTE]

Good point I had wrongly assumed with FFC the metatarsals would be quite perpendicular at contact. In Figure 6, what I assume is labelled "sole angle" refers to position of plantar surface to ground. So if I am interpreting this graph correctly that is consistent with what you say. I wonder if this true at higher speeds?

I guess I assume that evolutionary forces have favoured tethering of the plantar fibro-fatty pad to the fascia to counteract shear stress. When I said originally "those sailing close to the wind" I was inferring that "those" might have plantar fibro-fatty pad dysfunction in which case the plantar plate might be more vulnerable to shear; forgive the pun but I guess this is starting stretch the point a bit.

Cheers

Martin

What I was getting at was the difference noted by Pete Larsen in the Vibram vs other minimalist shoes - do the individual pockets for the toes in the Vibram increase the risk for plantar plate dysfunction by interfering with digital function?

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Hi Craig

Are you talking about those with both RFS and FFS or just FFS ?

According to this small study the saggital plane dorsiflexion late stance at metatarso-phalangeal joint is roughly same for FFS and RFS but the impact shear force and forefoot total stance force time integrals are much higher FFS.

sole angle.jpg


Perhaps you could test your idea a little by seeing if the metatarsalgia changed simply by changing, when symptomatic, from FFS to RFS with same foot-wear and see what happens.

Since the inferred effect on windlass attributed to metatarso-phalangeal joint dorsiflexion may, according to this study, be largely unchanged during propulsion in both FFS and RFS (with stiffness of foot-wear constant) if there were altered symptoms this would suggest another explanation other than windlass effect.

Cheers

Martin


Foot and Ankle Clinic
1365 Grant Ave.
Winnipeg Manitoba R3M 1Z8
phone [204] 837 FOOT (3668)
fax [204] 774 9918
www.winnipegfootclinic.com

I tend to doubt the "reverse windlass is inhibited" any more with the Vibram FiveFingers than other running shoes but possibly the pockets for the digits causes some compression irritation at the bases of the digits especially considering the shearing forces present at forefoot contact? Just guessing.

I still think that it is simply landing on the forefoot in a shoe with minimal forefoot cushioning that causes the plantar plate issues with the Vibram FiveFingers. Simply having excessive compression forces at two times body weight on an area of the plantar foot (i.e. 2nd MPJ) that may be particularly likely to experience such increases in compression forces due to its increased dorsiflexion stiffness relative to the other metatarsal rays seems to be the most likely cause to me.

__________________
Sincerely,

Kevin

**************************************************
Kevin A. Kirby, DPM
Adjunct Associate Professor
Department of Applied Biomechanics
California School of Podiatric Medicine at Samuel Merritt College

e-mail: kevinakirby@comcast.net

Private Practice:
107 Scripps Drive, Suite 200
Sacramento, CA 95825 USA
My location

Voice: (916) 925-8111 Fax: (916) 925-8136
**************************************************

I tend to agree, to an extent. I don't think you can ignore the shear forces though. Bojsen-Mollers work on forefoot anatomy and the tethering twixt skin and subcutaneous structures may be important here.

A couple of other points to consider: people who wear Vibram's probably don't wear socks, so there are less interfaces between the foot and the shoe; less interfaces that shear forces can be dissipated at. The design of Vibrams with their rubber toe pockets basically means that at strike with the high anterior-posterior shear, the foot could be driven forward onto the rubber that sits between the toes and effectively push the rubber into the toe-cleft because the shoe-ground interface has a higher co-efficent of friction than the foot-sockliner interface. Viz. the shoe stops before the foot does. Also, the thickness of the rubber between the toes may splay the toes excessively for some. Either way, I don't believe the toe-cleft area of the foot is designed to withstand direct distal to proximal loading. Hence some people find the toe posts of flip-flops uncomfortable- and that's just when they are walking in them (and usually just at the 1-2 interspace). If people want to talk about "natural", I'd say it's highly unnatural to have rubber in-between your toes when running. As I've said before, running in Vibram's nor running in any minimalist shoe is not the same as running barefoot.

Are the problems that are being observed actually just aggravations of pre-exisiting asymptomatic plantar plate tears, or are the Vibrams actively involved in the tearing of the plantar plate?

Tell you what would be interesting and pretty easy for someone- weightbearing dorsoplantar x-rays: barefoot, standard running shoe, Vibrams. You could also do it in a "false propulsion position", i.e single limb stance with tip-toe rise. Look forward to seeing that one. Hypothesis: the toes splay more in Vibrams than they do when barefoot.

__________________
Who? What? When? Why? Yeah? And? So? What?

"My mission drive is to open up my eyes, 'cause the wicked lies and all the sh!te you say..." http://www.youtube.com/watch?v=V4NW5S1UTPQ

"Science is the antidote to the poison of enthusiasm and superstition."

As promised, Joe Hamill, PhD gave me permission to show his slide here from his recent I-Fab presentation in Australia on "Rearfoot and Forefoot Footfall Patterns: Implications for Barefoot Running". It is interesting to see the concentraion of pressure in the metatarsal heads in the barefoot condition vs the shod condition. Of course, these appear to be pressure mat images, not pressure insole images...neither of which show shearing forces.

Attached Images

Barefoot vs Shod Pressure Mat.jpg (74.5 KB, 139 views)

__________________
Sincerely,

Kevin

**************************************************
Kevin A. Kirby, DPM
Adjunct Associate Professor
Department of Applied Biomechanics
California School of Podiatric Medicine at Samuel Merritt College

e-mail: kevinakirby@comcast.net

Private Practice:
107 Scripps Drive, Suite 200
Sacramento, CA 95825 USA
My location

Voice: (916) 925-8111 Fax: (916) 925-8136
**************************************************

Hi Kevin
Was there any accompanying interpretation for these maps? Looks like the footwear has descrete padded zones in forefoot which cause some unusual offloading. Do you know if these are averaged peak pressures or what?

Cheers. Martin

Another IMHO, would be to vault the foot in order to increase forefoot plantarflexion moments? Increase weightbearing MDA?
Yet another would be to improve P. longus ability to be a forefoot pronator providing addiotional forefoot pronatory moment?

Dennis

Another IMHO, would be to vault the foot in order to increase forefoot plantarflexion moments? Increase weightbearing MDA?
Yet another would be to improve P. longus ability to be a forefoot pronator providing additional forefoot pronatory moment?

Dennis

I think these were pressure mat recordings taken with runner first running barefoot then in shoes, so that the bare foot is contacting the pressure mat in the barefoot image and the shoe sole is contacting the pressure mat while running in shoes.

I just got a reply from Joe Hamill today saying that he thought the injuries seen in forefoot striking runners/barefoot runners/minimalist shoe runners that all tend to strike on their forefoot is due to:

1) The iniitial contact forces during forefoot strike has been shown both by his research group and Tim Derrick's research group at Iowa State University to be nearly of the same magnitude as rearfoot strikers.

2) The structures of the forefoot are more "delicate" than are the structures of the rearfoot so the forefoot structures are more likely to become injured than the rearfoot structures when subjected to the same loading forces during the initial contact phase of running.

Sounds logical to me.

__________________
Sincerely,

Kevin

**************************************************
Kevin A. Kirby, DPM
Adjunct Associate Professor
Department of Applied Biomechanics
California School of Podiatric Medicine at Samuel Merritt College

e-mail: kevinakirby@comcast.net

Private Practice:
107 Scripps Drive, Suite 200
Sacramento, CA 95825 USA
My location

Voice: (916) 925-8111 Fax: (916) 925-8136
**************************************************

Vertical component, shear components, all?

__________________
Who? What? When? Why? Yeah? And? So? What?

"My mission drive is to open up my eyes, 'cause the wicked lies and all the sh!te you say..." http://www.youtube.com/watch?v=V4NW5S1UTPQ

"Science is the antidote to the poison of enthusiasm and superstition."

Simon:

Not quite sure but I assume it was vertical component only?

__________________
Sincerely,

Kevin

**************************************************
Kevin A. Kirby, DPM
Adjunct Associate Professor
Department of Applied Biomechanics
California School of Podiatric Medicine at Samuel Merritt College

e-mail: kevinakirby@comcast.net

Private Practice:
107 Scripps Drive, Suite 200
Sacramento, CA 95825 USA
My location

Voice: (916) 925-8111 Fax: (916) 925-8136
**************************************************

As you said previously, even if all components of reaction forces are identical, the structural position of the lower limb is different in the two scenarios.

__________________
Who? What? When? Why? Yeah? And? So? What?

"My mission drive is to open up my eyes, 'cause the wicked lies and all the sh!te you say..." http://www.youtube.com/watch?v=V4NW5S1UTPQ

"Science is the antidote to the poison of enthusiasm and superstition."

Thanks Kevin - I agree that this sounds logical. I was curious though what the intent was for using the pressure mat illustration within the presentation. I tried to find the paper online but doesn't seem available.

This thread is helping me understand some of the features of FFS vs RFS running so if I am deviating from too much the initial post please ask me to take it elsewhere :).

One idea I have been thinking about is the position at which the foot hits the ground during FFC. I was surprised how horizontal this forefoot strike seems to be and I assume this is because the knee remained fairly extended at the speed measured in F. I. Kleindienst et al. Unfortunately there was no saggital knee kinematics presented.

I would guess that as velocity increases that knee flexion at FFC increases (increased cadence, less time for knee extension??) and that forefoot more vertical than at lower speeds. Someone please correct me if this is false. If that is the case then I would speculate that will have a couple of effects which may be pertinent (in healthy foot).

1. the involvement of the digits in spreading impact load would be increased and may protect metatarsal head area by reducing peak pressures and shear.

2. the earlier onset of aggressive "windlass tightening"

3. reduced impact to plantar plate

My understanding is that the actual velocity which people instinctively transition from RFS to FFS as velocity increases is unclear. Bit of a long shot but I wonder if it might be linked to this idea since we might speculate that sensory feedback may be involved in that "decision making" process.

Any comments anyone?

Cheers

Martin

Foot and Ankle Clinic
1365 Grant Ave.
Winnipeg Manitoba R3M 1Z8
phone [204] 837 FOOT (3668)
fax [204] 774 9918
www.winnipegfootclinic.com

Just found Hamil's abstract which is public domain at

http://www.jfootankleres.com/content...46-5-S1-K1.pdf

Doesn't contain any content such as the pressure mat which Kevin posted. I suspect that the presentation may address some of the issues in my previous post. Anyone able to legitimately post the presentation because it seems quite relevant?

Cheers

Martin

Foot and Ankle Clinic
1365 Grant Ave.
Winnipeg Manitoba R3M 1Z8
phone [204] 837 FOOT (3668)
fax [204] 774 9918
www.winnipegfootclinic.com

Martin:

Don't think I can post Joe's whole presentation on Podiatry Arena but, suffice it to say, it doesn't really have much else in it relevant to our discussion here.

__________________
Sincerely,

Kevin

**************************************************
Kevin A. Kirby, DPM
Adjunct Associate Professor
Department of Applied Biomechanics
California School of Podiatric Medicine at Samuel Merritt College

e-mail: kevinakirby@comcast.net

Private Practice:
107 Scripps Drive, Suite 200
Sacramento, CA 95825 USA
My location

Voice: (916) 925-8111 Fax: (916) 925-8136
**************************************************

Just ruminating and letting my imagination out of the bag a bit more since my last post;

I would speculate that with increased velocity coupled with increased vertical foot position ( I ran around at lunchtime and tested my thought - it seems correct) some more characteristics which might associated with FFC at higher velocities;

1 with earlier digital purchase the deforming forces around the metatarso-phalangeal joint would initially be more in sagittal than transverse plane (less influence from pre-existing vector associated with line of progression and more from vertical component)

2 the biphasic shearing under metatarsal heads might become simplified to anterior direction.

If these meanderings have some truth then it might beg the question regarding the potential negative effects of FFS below a certain velocity threshold.

Cheers

Martin


Foot and Ankle Clinic
1365 Grant Ave.
Winnipeg Manitoba R3M 1Z8
phone [204] 837 FOOT (3668)
fax [204] 774 9918
www.winnipegfootclinic.com

From a minimalist runner's perspective who wore a variety of minimalist shoes, including VFFs, and who ended up with 2nd metatarsal plantar plate issues:

For a variety of reasons, I don't believe restriction of plantar/dorsi flexion has anything to do with plantar plate injuries in runners who wear VFFs. First, the restriction seems to me to be outside the range of what the foot does while running. Yes, I can't curl my toes down completely in VFFs, but I would never want to do that while running. VFFs are flexible enough that the mechanics of the foot are not inhibited.

Second, my sense is that my plantar plate issue was a crushing type injury caused by landing on the ball of my foot far too often in thin-soled shoes on miles and miles of rocky, hilly trails.

Minimalist shoes, by design, promote a forefoot strike. However, there is a huge difference between the forefoot strike of me barefoot and me in VFFs (or others). When barefoot, I hit the ground lightly and with an acute awareness that one wrong move could cause pain. When shod in minimalist shoes, I hit the ground with force, still aware of the potential for pain, but with the sense that my feet are protected from the little stones (or whatever) that might sting if I step on them the wrong way. The difference is that I hit the ground with much more confidence in minimalist shoes, which translates into hitting the ground with much greater force.

The result of minimalist shoes, I believe, either is or will be plantar plate injuries in people who never in their lives would have developed this injury in traditional running shoes where the balls of their feet slapped the ground after a heel strike, then pushed off for propulsion.

Prior to minimalist shoes, and excluding turf toe-type injuries, I think you all saw plantar plate injuries that were caused by abnormal pressures during propulsion due to mechanical abnormalities of the foot, footwear that contorted the foot into abnormal positions, or some combination thereof. Now I suspect you are dealing with plantar plate injuries that are caused by forefoot striking in those wearing minimalist shoes, and my sense is that while the injuries may be similar, they may not always be identical.

For example, I read that most pp injuries are gradual, occurring over long periods of time. Mine happened in the space of 4 days and around 30 miles. Also, my joint was not unstable and my Lachman test was negative...but my injury was severe enough to keep me non-weightbearing for 8 weeks.

Anyway...my 2 cents. I'm not a doctor or in a field even remotely related to physiology. I'm just some random guy dealing with a crushing injury to a plantar plate four months ago and doctors that have been so unhelpful that I have lost my previously unshakable faith that they, meaning doctors in general, had at least a shadow of a clue what they were doing...present company excluded, of course.

This all depends on your natal foot type. That's part of the reason that some of us get injured and some of us don't.
The problem here is that most posters are championing forefoot, midfoot or heel contact for all when that is a red herring.
The fact is, there are exceptions to each camp clinically that deserve diagnosis and care.

You are not understanding the physics that is working here. Whether your foot moves into positions that are being forced when running or not, there are forces that are forcing (that's what forces do) you to morph into that position even if you can't or don't. This produces tissue stress that when compounded, results in overuse injuries.

As stated above

Only in those who train that way and wish to do so. We can all be habitually trained to rearfoot strike in minimalistic shoes or forefoot strike in thick heeled running shoes. In other words, because we are biological and not robotic machines, we can seemingly "counter the primary laws of physics". That is the challenge of biomechanics when compared to engineering machines or drawings.


Therein lies the fallacy of minimalistic shoe marketing.

Actually, if your running style is not altered with and without shoes, you hit the ground with exactly the same force

What you are describing here is the personal, BIOLOGICAL, intervention that you install to counter Newton's Primary Laws separating you from a robot or a drawing(even though your intervention doesn't obey the Laws of Physics as mentioned above). You play a vital part of the problem! That's what necessitates biomechanics, when practiced professionally to be custom.

Or not is my point!

Let's start a new thread with this in mind and end the Barefoot/FFT/Running shoe debate which is once again a red herring

In any biological system where the forces are pushing the subject into a scenario where tissue stress is being applied beyond the Compensatory Threshold, there are two mechanisms of injury.
1. An immediate injury caused by a short, strong force
2. A long term injury, occurring gradually where the tissue stress is small and repetitive eventually passing the clinical complaint threshold (Repetitive Microtrauma or RMT).
You are describing #1 as your pp injury.
As an example, when wearing Rocker Bottom Shoes whose purpose it is to create instability and sway so as to force additional muscle engine use, when this unstable shoe lives under a foot with an unstable functional foot type such as the flexible rearfoot FFT's, if you hit the ground on an incline or run over a stone, predictably, you could fracture your ankle more easily than those with a more stable or rigid RF FFT. On the other hand, if you train 40 miles a week at faster and faster pace, you predictably may get a plantar fascitis, Achilles tendonitis due to RMT easier than others.

I'm hoping that by using Foot Centering Language in responding, I am making this discussion clearer to you than by utilizing the language common to The Arena that may be more difficult to process for some.

Dennis