Kevin,
As a self taught mechanic prior to going to podiatry college, I can tell
you that springs do not dampen, shocks do.
I still think it is an interesting point about the spring effect of the
joints, which would make some sense for efficiency. My understanding is
that the connective tissue in the muscle is responsible for the spring
effect. This is what is developed in pliometric exercises.
Did the study you quote discuss muscles vs. ligaments? In John Jesse's
book Hidden Causes and Treatment of Athletic Injuries, he discusses an
unpublished study on foot exercises and its effect on vertical jump and
100 meter times on fifth graders.
For a spring effect to occur in the joints, the ligaments would have to
have elastic and possibly contractile properties.
Could you expand on your concept?
Regards,
Stanley
Kevin Kirby wrote:
> Kevin M:
>
> You wrote:
>
> <<In all of my cadaver work, I have seen the spring action to which
> you refer. However this action does not seem to dampen or dissipate
> force it seems to be a force transfer mechanism, which would follow
> the work of Gracovetsky very closely. Is this what you mean? In any
> case, perhaps, you might re-think what you are saying about midtarsal
> joint locking. Without midtarsal joint, locking the soft tissue
> structures of the midfoot could not store and return energy. So, the
> question is does the foot store and return energy or simply dissipate
> it.>>
>
> I don't think we are in disagreement . When I said dampen, I was
> using the analogy of the leaf springs of a truck which dampen the
> shock of an uneven road. However, dampening is also a force transfer
> mechanism in that the force is still transferred but at a slower rate
> and with decreased peak magnitudes.
>
> By the way, no need to rethink "midtarsal joint locking", I have been
> thinking about midtarsal joint locking for over 20 years. "Locking"
> implies that no further movement is allowed with increases in external
> loading forces, which is not what a foot or leaf spring in a truck
> does while functioning. Is it desirable in a truck to have a spring
> that "locks"?? Not really since we call that a "bottoming out" of the
> springs and causes a sudden vertical acceleration of the truck axle
> and an uncomfortable ride for the passenger. In the same way, we
> don't want a midtarsal joint that "locks" and suddenly stops forefoot
> dorsiflexion motion while walking or running or jumping down from a
> height....we rather want a longitudinal arch that functions like a
> leaf spring that will deform under increasing loads so that lower
> extremity accelerations are kept to a minimum during weightbearing
> activities.
>
> When it comes to the question of storage and release of energy in the
> longitudinal arch of the foot, the classic study was done 20 years ago
> (Ker RF, Bennett MB, Bibby SR, Kester RC, Alexander RMcN: The spring
> in the arch of the human foot. Nature, 325: 147-149, 1987). Ker et
> al showed that the human foot stores 17 joules of energy in the
> compliant elements (i.e. ligaments) of its longitudinal arch during
> running. However, the foot both stores and releases energy and also
> dissipates this energy as heat since the ligaments of the are arch are
> not perfectly elastic and have a hysteresis loop.
>
> Sincerely,
>
> Kevin
>
> ****************************************************************************
> Kevin A. Kirby, DPM
> Adjunct Associate Professor
> Department of Applied Biomechanics
> California School of Podiatric Medicine at Samuel Merritt College
>
> Private Practice:
> 107 Scripps Drive, Suite 200
> Sacramento, CA 95825 USA
>
> Voice: (916) 925-8111 Fax: (916) 925-8136
> ****************************************************************************
>
>
> Kevin Miller wrote:
>> Kevin K,
>>
>> I a long moment that I was about to agree with you. Perhaps I still
>> do agree with you however a little explanation would be in order. In
>> all of my cadaver work, I have seen the spring action to which you
>> refer. However this action does not seem to dampen or dissipate
>> force it seems to be a force transfer mechanism, which would follow
>> the work of Gracovetsky very closely. Is this what you mean? In any
>> case, perhaps, you might re-think what you are saying about midtarsal
>> joint locking. Without midtarsal joint, locking the soft tissue
>> structures of the midfoot could not store and return energy. So, the
>> question is does the foot store and return energy or simply dissipate it.
>>
>> Cheers,
>>
>> Kevin M.
>> ----- Original Message ----
>> From: Kevin Kirby <[log in to unmask]>
>> To: [log in to unmask]
>> Sent: Friday, April 27, 2007 9:15:37 AM
>> Subject: Re: Ankle Joint Dorsiflexion - Are We Really Measuring the
>> Ankle Joint?
>>
>> Neil and Colleagues:
>>
>> This idea that both the ankle joint and midtarsal-midfoot joints are
>> "spring-like" is very important mechanically. What does this concept
>> of "spring-like" mean? ......It means that there is not a hard
>> "end-point" or "locked" position for either the ankle joint or
>> midtarsal joint or midfoot joints. In other words, the greater the
>> magnitude of GRF loading the plantar forefoot, then the greater will
>> tend to be the dorsiflexion of the forefoot on the rearfoot and the
>> talus on the tibia, assuming no muscular contractile forces are
>> causing forefoot plantarflexion moments and/or ankle joint
>> plantarflexion moments. Therefore, to use the term, "midtarsal joint
>> locking" is not only erroneous but also is biomechanically misleading
>> since we don't want our midtarsal joint to "lock" we want the
>> midtarsal and midfoot joints to rather "dampen" forefoot dorsiflexion
>> moments. This is analagous to the leaf spring of a truck suspension
>> functioning to dampen the vertical oscillations of the truck axle
>> when the truck tires have suddenly increased magnitudes of GRF when
>> driving over a bump in the road.
>>
>> Sincerely,
>>
>> Kevin
>>
>> ****************************************************************************
>> Kevin A. Kirby, DPM
>> Adjunct Associate Professor
>> Department of Applied Biomechanics
>> California School of Podiatric Medicine at Samuel Merritt College
>>
>> Private Practice:
>> 107 Scripps Drive, Suite 200
>> Sacramento, CA 95825 USA
>>
>> Voice: (916) 925-8111 Fax: (916) 925-8136
>> ****************************************************************************
>>
>>
>> Neil Frame wrote:
>>>
>>> Dear Kevin
>>>
>>> I can relate to this 'spring-like' analogy that you use and I think
>>> it does convey more realistically what occurs within the foot during
>>> movement. I do feel, however, that we can complicate matters even
>>> further by taking into account the other factors that may just
>>> dictate the loading of your 'springs'. Biomechanics never was that
>>> straight forward ;-) One persons forefoot may dorsiflex to a far
>>> greater extent than that of anothers and then we will be noting that
>>> individuals ability to compensate for these 'interrelating, variably
>>> loaded springs'. To summarize; understand the 'spring-like' bit,
>>> but don't forget they are 'variably loaded and variably resistant'
>>> and compensation will occur in a multitude of ways throughout the
>>> body during locomotion.
>>>
>>> p.s. Who prefers examination/measurement of the ankle joint prone
>>> and who prefers supine and why and is there any difference?
>>> .................. neural tension?
>>>
>>> Best wishes
>>>
>>> Neil
>>>
>>> ------------------------------------------------------------------------
>>> From: /Kevin Kirby <[log in to unmask]>/
>>> Reply-To: /A group for the academic discussion of current issues
>>> in podiatry <[log in to unmask]>/
>>> To: [log in to unmask]
>>> Subject: /Re: Ankle Joint Dorsiflexion - Are We Really Measuring
>>> the Ankle Joint?/
>>> Date: /Thu, 26 Apr 2007 21:08:32 -0700/
>>>
>>> Jeff, Howie, Kevin, Stanley and Colleagues:
>>>
>>> My, my, my. I didn't expect such numerous and rapid responses
>>> to my first posting to JISC podiatry mailbase in many months.
>>> It is gratifying to see that the old gang is indeed back in
>>> action again. Maybe we can dig a few other fossils out of the
>>> woodwork to join in on these discussions. ;-)
>>>
>>> The purpose for my posting is to emphasize, not that our old
>>> measurement techniques are wrong or useless, but rather that
>>> when we say that a patient has, for example, 10 degrees of ankle
>>> joint dorsiflexion, that we are not truly measuring ankle joint
>>> dorsiflexion alone but rather also measuring dorsiflexion of the
>>> forefoot on the rearfoot. This may not seem like an important
>>> point until one realizes that the forces that we use on the
>>> forefoot to manually execute the ankle joint dorsiflexion
>>> measurement are probably at least 10 times less in magnitude
>>> than the ground reaction forces that will be present on the
>>> forefoot during late midstance and early propulsion. In
>>> addition, as the force is increased on the plantar forefoot not
>>> only will the talo-tibial joint continue to dorsiflex but also
>>> the midtarsal and midfoot joints will also continue to dorsiflex
>>> relative to the rearfoot. I like to describe these mechanical
>>> interactions as being rather than as being "end-ranges of
>>> motion" since if increased force if applied to the forefoot,
>>> such as would be present during a lunge-test, the apparent
>>> dorsiflexion of the plantar foot to the tibia is nearly always
>>> increased versus what would be apparent during manual ankle
>>> joint dorsiflexion testing. It is probably best that we think
>>> of both the talo-tibial joint and midtarsal-midfoot joints as
>>> spring-like joints with varying stiffnesses that mechanically
>>> interact to determine not only the foot posture during relaxed
>>> stance but also during dynamic function. It is the mechanical
>>> interaction of these spring-like joints with each other that may
>>> also be very important in determining the gait function and also
>>> the pathologies we see on a daily basis in our patients.
>>>
>>>
>>> Sincerely,
>>>
>>> Kevin
>>>
>>> ****************************************************************************
>>> Kevin A. Kirby, DPM
>>> Adjunct Associate Professor
>>> Department of Applied Biomechanics
>>> California School of Podiatric Medicine at Samuel Merritt College
>>>
>>> Private Practice:
>>> 107 Scripps Drive, Suite 200
>>> Sacramento, CA 95825 USA
>>>
>>> Voice: (916) 925-8111 Fax: (916) 925-8136
>>> ****************************************************************************
>>>
>>>
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