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You ask if symmetry has been established. Why would you want to establish symmetry as a measure of success? I'm not symmetrical, neither are you, nor most of the people reading this forum thread
So! Is symetry an important consideration in our therapeutic outcome?
Do we have any evidence either way regarding symetry and gait?
Regards
__________________
Graham Curryer
None of us know what we are doing, but some of us know more about what we are not doing than others!::
I do not think we know. We assume that symmetry might be a good thing, but if we have a patient with one bad foot and one good foot and we make an orthotic to make the good foot into a bad foot, then we have achieved symmetry - is that a good outcome?
This comes back to what clinical gait parameters do we need to change to get a clincal symptomatic outcome??
We have some good assumptions (that may well be correct), but we really do not know.
We have looked at asymmetry in relationship to the timing of heel off loading anf have certainly hypothesised that this asymmetry could cause an assymetry in proximal muscle activity to compensate - this may or may not be a facter in proximal problems (see this thread on Asymmetrical density heel raises)
__________________
Craig Payne
Department of Podiatry
La Trobe University
Melbourne, Australia http://www.latrobe.edu.au/podiatry
__________________________________________________ ___________________________________ God put me on this earth to accomplish a certain number of things - right now I am so far behind, I will never die.
The views expressed above are those of the author and not that of La Trobe University This is where I am, where are you?
Tissue stress model might be useful here. If there is an asymmetry which is pushing tissue stress past safe thresholds then correcting that asymmetry should be beneficial. By the same token if symmetry exists but tissue stress thresholds on one side are reduced it may be theraputically useful to create an asymmetry.
I would say that symmetry has inherent value only in that it equalises forces between the two sides distributing stress evenly. Not an ignoble goal but not the beall and endall in all cases.
Also symmetry in gait is only useful if it creates symmetry in the internal forces and movements in the pathological structures (wherever they may be.) If the body was symmetrical then symmetry of gait function would acheive this. If however the body is asymmetrical structurally (most / all are) we cannot rely on this.
For example, if there is a structural LLD and the longer leg pronates (shortening it) there will be an asymmetry in gait which creates a symmetry in pelvic level. Creating a symmetry in foot posture and gait here (measured for eg with force plate) will create a potentially harmful asymmetry in the pelvis, back, etc etc.
I suppose it depends on whether one approaches it from a root "style" (return the system to "normality" irrespective of the specific pathology) or the tissue stress style (assess the pathological stress and reduce it).
Tissue stress model might be useful here. If there is an asymmetry which is pushing tissue stress past safe thresholds then correcting that asymmetry should be beneficial. By the same token if symmetry exists but tissue stress thresholds on one side are reduced it may be theraputically useful to create an asymmetry.
I would say that symmetry has inherent value only in that it equalises forces between the two sides distributing stress evenly. Not an ignoble goal but not the beall and endall in all cases.
Also symmetry in gait is only useful if it creates symmetry in the internal forces and movements in the pathological structures (wherever they may be.) If the body was symmetrical then symmetry of gait function would acheive this. If however the body is asymmetrical structurally (most / all are) we cannot rely on this.
For example, if there is a structural LLD and the longer leg pronates (shortening it) there will be an asymmetry in gait which creates a symmetry in pelvic level. Creating a symmetry in foot posture and gait here (measured for eg with force plate) will create a potentially harmful asymmetry in the pelvis, back, etc etc.
I suppose it depends on whether one approaches it from a root "style" (return the system to "normality" irrespective of the specific pathology) or the tissue stress style (assess the pathological stress and reduce it).
Regards
Robert
Of course, symmetry is important since we are all bipedal organisms and the kinematics and kinetics of one foot and lower extremity will directly affect the kinematics and kinetics of the contralateral foot and lower extremity. However, focusing solely on making the feet and lower extremities function symmetrically, at the expense of increasing symptoms elsewhere for the patient, does not make good clinical sense.
The best practitioners of clinical biomechanics are artists that use science as the basis for their clinicial decision-making process.
__________________
Sincerely,
Kevin
**************************************************
Kevin A. Kirby, DPM
Adjunct Associate Professor
Department of Applied Biomechanics
California School of Podiatric Medicine at Samuel Merritt College
Of course, symmetry is important since we are all bipedal organisms and the kinematics and kinetics of one foot and lower extremity will directly affect the kinematics and kinetics of the contralateral foot and lower extremity. However, focusing solely on making the feet and lower extremities function symmetrically, at the expense of increasing symptoms elsewhere for the patient, does not make good clinical sense.
The best practitioners of clinical biomechanics are artists that use science as the basis for their clinicial decision-making process.
And assuming the left and right feet are ambulating upon identical surfaces, which they seldom are.
__________________ Science is the antidote to the poison of enthusiasm and superstition
And assuming the left and right feet are ambulating upon identical surfaces, which they seldom are.
Yes, the molecules under the left and right feet are different, Dr. Spooner. In many circumstances (i.e. the flat surfaces that David Holland likes to always emphasize), the surfaces are basically identical to each other.
__________________
Sincerely,
Kevin
**************************************************
Kevin A. Kirby, DPM
Adjunct Associate Professor
Department of Applied Biomechanics
California School of Podiatric Medicine at Samuel Merritt College
Yes, the molecules under the left and right feet are different, Dr. Spooner. In many circumstances (i.e. the flat surfaces that David Holland likes to always emphasize), the surfaces are basically identical to each other.
You need to get outside more Prof. Kirby, there you may find a whole host of surface geometry on which to place your feet.
__________________ Science is the antidote to the poison of enthusiasm and superstition
Symmetry is a nice place to visit but you wouldn't want to live there.
Like any position of reference, symmetry is a global position of reference and is a place to start from but not neccessarily a destination we need to arrive at to complete our journey. Like a star in the sky it is a guide to where we are relative to somewhere else but not somewhere we ever are likely to travel to.
That's the metaphors done,
Symmetry is or can be an artifice that satisfies our intuition in that it gives the illusion of balanced forces, which may or may not exist. Certainly symmetrical gait and posture with symmetrical internal forces can only exist in a symmetrical evironment.
Humans are only grossly symmetrical but then grossly asymmetrical in detail.
It would be unusual, wouldn't you agree, to find someone with identical feet, identical bilateral musculature, identical joint shapes, ambidextrousness, exactly equal limb length, equal muscle strength either side. No one even has a perfectly symmetrical face.
If not then kinematic symmetry what about kinetic symmetry? Are symmetrical forces a desired or optimal goal? If we have slightly different limb lengths and slightly different joint shapes and slightly different soft tissue structure, with slightly different mechanical properties, why would you expect symmetrical and identical forces.
How often do we observe a patient with unilateral symptoms yet very simmilar foot function or is even asymmetrical but the foot that appears far outside our reference of normal is not the one that is symptomatic? What then?
We can only address the symptomology in a logical fashion, diagnosing the pathology, deducing the aetiology and by intervention, reducing the forces for instance. Can we then concern ourselves with symmetry, I think not, symmetry was only our reference not our goal.
Having said that I often like to look for symmetry, it satisfies my intuition but that is just my own logical deceipt, which fortunately I can recognise before it becomes a rigid yet fanciful convention.
Cheers Dave
__________________
Descartes seems to consider here that beliefs formed by pure reasoning are less doubtful than those formed through perception.
In order to better understand the question of whether trying to achieve symmetry in gait should be a therapeutic goal of ours as clinicians of the human foot and lower extremity, we must first divide our discussion into two parts: kinetics and kinematics.
Symmetrical kinetics would indicate that the forces and moments acting on and within each and foot and lower extremity would be identical to each other during the specific weightbearing activities where each limb is performing the same biomechanical function as the other limb, such as walking and running. We may use in-shoe pressure insoles, pressure mats, force plates, strain gauges, or when combined with three-dimensional kinematic analysis, we may use inverse dynamics to gain useful information regarding the level of kinetic gait symmetry in the individual.
The question becomes, is having symmetrical kinetics something that is desirable as a bipedal organism during walking and running? I do believe that possessing symmetrical kinetics is desirable in the feet and lower extremities of our patients since, in mechanics, engineering and in nature, symmetry of forces between two halves of a machine or organism will tend to equalize the stresses acting on the structural components of each of the two halves. Equalization of stresses between two parts of a machine or organism will reduce the tendency for one of the halves to have reduced stresses at the expense of the other half having increased stresses. These increased asymmetrical stresses acting on a structural component of the human foot and lower extremity (i.e. bone, cartilage, ligament, muscle, fascia and tendon) will, over time, lead to increased likelihood that the structural component may develop internal damage to it, which leads to what we call "injury". Therefore, from a kinetics view, it is clear that if we can make the forces, moments and stresses between the two lower extremities symmetrical, or equalize them, then we can also minimize the risk of "higher stress" lower extremity musculoskeletal injury developing over time.
Symmetrical kinematics would indicate that the movement patterns of each foot and lower extremity would be identical to each other during the specific weightbearing activities where each limb is performing the same biomechanical function as the other limb. We may use visual gait examination, video analysis, or two-dimensional or three dimensional gait analysis techniques to determine the kinematics of each lower extremity. Being that visual gait analysis is the easiest, quickest and least expensive clinical gait evaluation technique, often this is what most of us rely on to detemine whether symmetrical function is occuring or not. Certainly, from a theoretical standpoint, having symmetrical kinematic function would be most desirable but if the structure of the two limbs is not symmetrical, this may not be a realistic or desirable goal.
For example, if one foot has a normal subtalar joint (STJ) axis location and functions normally during walking but the other has a significant medially deviated STJ axis and functions maximally pronated at the STJ throughout the stance phase of gait, then should we try to make each foot function the same? Since tissue stress theory is based on the fact that we need to 1) reduce the stress on the injured structural component, 2) optimize gait function, and 3) not cause any other pathology to occur, then the key phrase here is "optimize gait function".
In other words, we don't want to over-invert the medially deviated STJ axis foot so much in trying to make it function kinematically identical to the foot with the normal STJ axis because, in doing so, we may be subjecting the medially deviated STJ axis foot to abnormal and increased forces and stresses (i.e. abnormal kinetics) that are may cause injury elsewhere within that foot. For example, if we over-invert the foot orthosis for the medially deviated STJ axis foot, we may cause excessive painful plantar pressures on the medial heel and medial arch from the orthosis, excessive painful pressure on the lateral metatarsals due to over-supination, or may cause increased stress in the peroneal tendons by too much increase in STJ supination moment from the orthosis, in our desire to have the two feet function with symmetrical kinematics.
Therefore, when treating mechanical pathologies in patients with asymmetrical kinematic function, we should have the therapeutic goal of optimizing kinematic gait function, not necessarily focus on making the patient's kinematic function symmetrical at the expense of making the patient's gait kinetics less symmetrical that results in new injury. In this way, we can make our patients less painful, more productive, prevent new injuries and make them function as well as they possibly can during their weightbearing activities given their characteristic structural composition and their characteristic neuromuscular capabilities.
__________________
Sincerely,
Kevin
**************************************************
Kevin A. Kirby, DPM
Adjunct Associate Professor
Department of Applied Biomechanics
California School of Podiatric Medicine at Samuel Merritt College
All this talk of symmetry as got me thinking about a thought experiment I was playing with last week: If we had a foot that had equal pressure beneath every single point of it, where would the centre of pressure be? If this situation was constant with time, would it be capable of movement?
__________________ Science is the antidote to the poison of enthusiasm and superstition
Get your mother/wife to wear one stiletto on one foot; and a flat on the other foot whilst at home for the next few months. Alternatively, put a heel raise in one of their shoes full-time for the next few months.
If symmetry doesn't totally matter they wont notice any changes and neither will you.
Get your mother/wife to wear one stiletto on one foot; and a flat on the other foot whilst at home for the next few months. Alternatively, put a heel raise in one of their shoes full-time for the next few months.
If symmetry doesn't totally matter they wont notice any changes and neither will you.
Hi Ron,
Pretty extreme example, but I concede the point.
How does this relate to orthoses and F-scan
In his original post Graham was asking if evidence existed to show the importance of symmetry - I assumed he was talking about scientific evidence, but perhaps not...
One thing i think which has become clear through this thread is that to answer the OP one needs to define what is meant by symmetry.
The point i made and Kevin expanded on is that symmetry in one place / measured one way does not necessarily equate to symmetry throughout the system. We need to be clear on what symmetry we are talking about when we ask the question "is symmetry and important theraputic goal."
I contend that one cannot say that symmetry in, for example gait kinematics or vertical force measurement tracks, is an important theraputic goal as a standalone statement. It often is, but only if the circumstances around it indicate!
As so often with biomechanics it boils back down to tissue stress. Symmetry is good IF it has a benificial effect on internal tissue stresses.
I saw a patient last week who had a relevant presentation. structural LLD with a more pronated foot in WB on the longer limb. In that case seeking symmetry of foot posture could have had a deleterious effect on the proximal structures by increasing pelvic tilt. Seeking symmetry of the whole kinetic chain by seeking symmetry of the foot posture AND the pelvic level might have been more benificial.
Oh! Why can't I wear the stillettos? she always get to wear them it's just not fair
Making something asymmetrical when it was innately symmetrical in a symmetrical environment is the same as requiring something innately asymmetrical to be symmetrical in a symmetrical environment. What is the same is that you changed something that didn't need changing.
Take a box, say a kithchen cabinet, and twist it, take a tree and make it straight - both will be broken in the attempt. Are humans more like a tree than a box?
Does a body need to be perfectly symmetrical to avoid damaging stress? no. However a change to that symmetry, like a hip replacement for instance might result in some pathology. It wasn't the shape that caused the destructive stress it was the change in shape and the resulting local forces. This then might be viewed as a degree of asymmetry and a gross assymetry might indicate pathology in humans. It may well do this but I would say that, where the asymmetry is not due to recognizable change, this would also be a gross assumption. How can we recognise, just from observation of shape, where is the demarkation between pathological and non pathological asymmetry?
Symmetry is more relevant when the diagnosis indicates that the forces that lead to pathology also resulted in asymmetry or vice versa ie the change in symmetry or posture caused forces that led to pathology. This is the case where the symmetrical body in a symmetrical environment was changed into an asymmetrical body in a symmetrical environment. This is the case we as clinicans become familiar with and so form the opinion that asymmetry = pathology and all things asymmetrical would be better off if it were symmetrical, which is in my opinion a logical fallacy.
The logical fallacy of accident, also called destroying the exception or (This bit is specially fo Robert Isaacs and Graham) a dicto simpliciter ad dictum secundum quid, is a deductive fallacy occurring in statistical syllogisms (an argument based on a generalization) when an exception to the generalization is ignored. It is one of the thirteen fallacies originally identified by Aristotle. The fallacy occurs when one attempts to apply a general rule to an irrelevant situation. (http://en.wikipedia.org/wiki/Accident_%28fallacy%29)
Cheers Dave
__________________
Descartes seems to consider here that beliefs formed by pure reasoning are less doubtful than those formed through perception.
Does a body need to be perfectly symmetrical to avoid damaging stress? no. However a change to that symmetry, like a hip replacement for instance might result in some pathology. It wasn't the shape that caused the destructive stress it was the change in shape and the resulting local forces. This then might be viewed as a degree of asymmetry and a gross assymetry might indicate pathology in humans. It may well do this but I would say that, where the asymmetry is not due to recognizable change, this would also be a gross assumption. How can we recognise, just from observation of shape, where is the demarkation between pathological and non pathological asymmetry?
Dave and Colleagues:
Good thoughts, Dave. Rather, a better question in this regard is does a person that have perfect symmetry in their feet and lower extremities reduce that person's risk of musculoskeletal injury when compared to that person that has grossly abnormal asymmetry in their feet and lower extremities? I believe that most of us would argue that perfect symmetry is the ideal, that gross asymmetry is non-ideal and that gross asymmetry will lead to increased risk of abnormal tissue stresses and increased risk of musculoskeletal injury.
Therefore, as I said in my last posting, striving toward perfect kinematic symmetry is a reasonable therapeutic goal if we only knew, in striving to achieve that perfect kinematic symmetry, that abnormal asymmetrical kinetics did not result within the individual's body that could then lead to increased magnitudes of tissue stress and musculoskeletal injury. I really don't think we currently can determine whether our treatments result in kinetic symmetry of our patients at this stage of our abilities, other than observing for pathology or asking our patient if pain or discomfort is occurring.
Great discussion. In fact, I feel that this is one of the most clinically important theoretical discussions that have taken place here on Podiatry Arena in some time.
__________________
Sincerely,
Kevin
**************************************************
Kevin A. Kirby, DPM
Adjunct Associate Professor
Department of Applied Biomechanics
California School of Podiatric Medicine at Samuel Merritt College
All this talk of symmetry as got me thinking about a thought experiment I was playing with last week: If we had a foot that had equal pressure beneath every single point of it, where would the centre of pressure be? If this situation was constant with time, would it be capable of movement?
If memory serves - To estimate CoP (non calculus)
Define a matrix of discreet force areas, choose one longitudinal line in that matrix, find the discreet force for each unit area (uf), find the distance of each unit area from a common reference (dr) (usually where all the forces of interest cause a moment in the same direction) sum all the forces X distances [Sum(uf*df)], sum all the unit forces to find total force, find the distance that the total force times that distance is equal to the moments by [sum(uf*df)]. This = CoP for that line. Repeat across all longitudinal lines. THis will define a line of CoP. Repeat for all transverse lines, this gives a transverse line of CoP. Where the two lines cross = the characterisation of the total summation of CoP.
Therefore if all are equal then it is still possible to estimate a CoP where that is depends on the shape of the foot. If the foot was symmetrical about x and y axes, then the CoP would be in the centre of the total area. If asymmetrical, as it is then the CoP can't be guessed at. Although you could divide it up into symmetrical shapes, find the center of each shape then find the summed centre of the individual centres of CoP. This would give a good approximation more easily.
For the second part do you mean the whole surface area of the foot or the surface area in contact with the ground. Clearly the former could not move and the latter could in theory. (probably)
Dave
__________________
Descartes seems to consider here that beliefs formed by pure reasoning are less doubtful than those formed through perception.
Therefore if all are equal then it is still possible to estimate a CoP where that is depends on the shape of the foot. If the foot was symmetrical about x and y axes, then the CoP would be in the centre of the total area. If asymmetrical, as it is then the CoP can't be guessed at. Although you could divide it up into symmetrical shapes, find the center of each shape then find the summed centre of the individual centres of CoP. This would give a good approximation more easily.
I arrived at the same conclusion
Quote:
Originally Posted by David Smith
For the second part do you mean the whole surface area of the foot or the surface area in contact with the ground. Clearly the former could not move and the latter could in theory. (probably)
I was talking about plantar pressure. Considering the later, you suggest that foot movement is possible without centre of pressure displacement or velocity? Is this through vertical lift off?
__________________ Science is the antidote to the poison of enthusiasm and superstition
All this talk of symmetry as got me thinking about a thought experiment I was playing with last week: If we had a foot that had equal pressure beneath every single point of it, where would the centre of pressure be? If this situation was constant with time, would it be capable of movement?
Couldn't there be motion about its centre of mass? but not motion of same, mark c
I was talking about plantar pressure. Considering the later, you suggest that foot movement is possible without centre of pressure displacement or velocity? Is this through vertical lift off?
Re diagrams - Is this what you meant Simon?
I meant that as the foot progresses thru stance phase it may be possible under unusual circumstances for the pressure to remain uniform across the plantar surface on the ground and CoP at the centre of the plantar pressure matrix at any given point in time. Of course the pogression of CoP must move relative to a fixed reference, but this would be the same regardless of symmetry.
Dave
__________________
Descartes seems to consider here that beliefs formed by pure reasoning are less doubtful than those formed through perception.
All this talk of symmetry as got me thinking about a thought experiment I was playing with last week: If we had a foot that had equal pressure beneath every single point of it, ... If this situation was constant with time, would it be capable of movement?
My post was based on me thinking "movement" meant relative motion between parts of the foot, rather than displacement of the foot. I'll be quiet now.
All this talk of symmetry as got me thinking about a thought experiment I was playing with last week: If we had a foot that had equal pressure beneath every single point of it, where would the centre of pressure be? If this situation was constant with time, would it be capable of movement?
Well if we moved around on our legs like they were pogo sticks we could get close to even amount of pressure on the bottom of the foot for the entire stance phase. However, to have ankle push (power added to the leg in stance phase.) the heel has to lift off of the ground while the forefoot remains on the ground. It would be impossibe to have the same magnitude of pressure at all points throughout stance phase becasue of upward and downward acceleration of the body. The force changes with acceleration and the area of the foot does not change so the pressure would change.
Now, if you had 100 legs and you could pick one up and put it down without upward or downward acceleration of the center of mass you might be able to keep the pressure equal between all areas of the foot, but the magnitude would change as the foot and leg loaded.
If the sampling rate of pressure was low enough you could measure no change.
On symmetry: I recall a study, sorry don't have reference at hand, where there was a comparison of treatment of back pain with manipulation and physical therapy. There was more pain relief with physical therapy and the gait was closer to symmetrical with manipulation. Would rather be symmetrical, or would you rather have less pain?
All this talk of symmetry as got me thinking about a thought experiment I was playing with last week: If we had a foot that had equal pressure beneath every single point of it, where would the centre of pressure be? If this situation was constant with time, would it be capable of movement?
If the foot was an immovable, rigid platform that was attached at the ankle as a frictionless joint and the individual had no ability to exert either ankle joint plantarflexion moments or ankle joint dorsiflexion moments, then, yes, the center of pressure would show little to no movement on the plantar foot during "walking". The anterior to posterior movement of the center of mass over the planted foot during the stance phase of gait, in this case, could not be resisted by the foot and so the center of pressure would change very little since the foot would do nothing to either decelerate or accelerate locomotion than would a "peg leg". A person with this type of foot could perform a type of bipedal locomotion, but the muscle power for this activity would all need to come from proximal to the foot and ankle and any resistance to foot motion relative to the leg could not occur. I don't think that most of us would still call this type of bipedal locomotion "walking", even though it would still allow the individual to move from point A to point B.
__________________
Sincerely,
Kevin
**************************************************
Kevin A. Kirby, DPM
Adjunct Associate Professor
Department of Applied Biomechanics
California School of Podiatric Medicine at Samuel Merritt College
Thanks for taking the time to think about this, t'was just a bit of fun. I'd been thinking about a "magic" insole that could constantly change stiffness to equalise the pressures beneath the foot. Kevin, do you remember that sketch of the pistons beneath the met heads, you once sent me? That was the inspiration to this little head game . Anyway back to the real world, my nail drill just died and it's going to cost me the best part of a grand for a new one- ouch.
__________________ Science is the antidote to the poison of enthusiasm and superstition
Thanks for taking the time to think about this, t'was just a bit of fun. I'd been thinking about a "magic" insole that could constantly change stiffness to equalise the pressures beneath the foot. Kevin, do you remember that sketch of the pistons beneath the met heads, you once sent me? That was the inspiration to this little head game . Anyway back to the real world, my nail drill just died and it's going to cost me the best part of a grand for a new one- ouch.
Simon,
This drawing was based on an idea I had during my Biomechanics Fellowship (1984-1985) when I did the study on the Anterior Axial Radiographic Projection (The Kirby view: A radiographic view for flatfoot evaluation. The Journal of Foot and Ankle Surgery , Volume 43 , Issue 6 , Pages 436 - 439.J . Clark , J . Gerbert , W . Jenkin).
At the time, I was thinking how I could design an x-ray projection that could be done to allow the weightbearing metatarsal heads be evaluated radiographically with the same plantar force on each metatarsal head to see what "level" they would be at relative to each other in this "constant plantar force position". One thought was to use plungers under each metatarsal head that would apply equal force to each and then design the orthosis/surgery around this constant metatarsal head force position. In theory it makes a lot of sense.....however, there is only so much time in the day for me and someone with more time and a less busy life will need to take up this project for us in the future.
__________________
Sincerely,
Kevin
**************************************************
Kevin A. Kirby, DPM
Adjunct Associate Professor
Department of Applied Biomechanics
California School of Podiatric Medicine at Samuel Merritt College
Nature 438, 1148-1150 (22 December 2005) | doi:10.1038/nature04344; Received 23 September 2005; Accepted 20 October 2005
Zoran Popovihttp://www.ncbi.nlm.nih.gov/entrez/query.fcgi?cmd=search&term=Popovic+Z
more authors of this article
Dance reveals symmetry especially in young men
William M. Brown1, Lee Cronk1, Keith Grochow2, Amy Jacobson1, C. Karen Liu2, Zoran Popovi2 & Robert Trivers1
1. Center for Human Evolutionary Studies, Department of Anthropology, Rutgers University, 131 George Street, New Brunswick, New Jersey 08901-1414, USA
2. Department of Computer Science and Engineering, University of Washington, Box 352350 Seattle, Washington 98195-2350, USA
Correspondence to: William M. Brown1 Correspondence and requests for materials should be addressed to W.M.B. (Email: wmbrown@rci.rutgers.edu).
Top of page
Abstract
Dance is believed to be important in the courtship of a variety of species, including humans, but nothing is known about what dance reveals about the underlying phenotypic—or genotypic—quality of the dancer1, 2, 3, 4, 5, 6. One measure of quality in evolutionary studies is the degree of bodily symmetry (fluctuating asymmetry, FA), because it measures developmental stability7, 8. Does dance quality reveal FA to the observer and is the effect stronger for male dancers than female? To answer these questions, we chose a population that has been measured twice for FA since 1996 (ref. 9) in a society (Jamaican) in which dancing is important in the lives of both sexes. Motion-capture cameras created controlled stimuli (in the form of videos) that isolated dance movements from all other aspects of visual appearance (including FA), and the same population evaluated these videos for dancing ability. Here we report that there are strong positive associations between symmetry and dancing ability, and these associations were stronger in men than in women. In addition, women rate dances by symmetrical men relatively more positively than do men, and more-symmetrical men value symmetry in women dancers more than do less-symmetrical men. In summary, dance in Jamaica seems to show evidence of sexual selection and to reveal important information about the dancer.
__________________
Graham Curryer
None of us know what we are doing, but some of us know more about what we are not doing than others!::
Predominantly extra-retinotopic cortical response to pattern
symmetry
Christopher W. Tyler,a,* Heidi A. Baseler,a Leonid L. Kontsevich,a
Lora T. Likova,a Alex R. Wade,a and Brian A. Wandellb
aSmith-Kettlewell Eye Research Institute, San Francisco, CA, USA
bDepartment of Psychology, Stanford University, Stanford, CA, USA
Received 15 December 2003; revised 26 April 2004; accepted 17 September 2004
Available online 26 November 2004
Symmetry along one or more axes is a key property of objects and
biological organisms. We report on a bilateral visual region of occipital
cortex that responds strongly to the presence of multiple symmetries in
the viewed image. The stimuli consisted of random dots organized in
fourfold and onefold mirror-symmetric patterns, against random
control stimuli. The contrast between symmetric and random patterns
produced negligible or inconsistent activation of the primary visual
projection area V1 or of other medial occipital projection areas.
However, there was strong symmetry-specific activation in extraretinotopic
lateral occipital cortex. The high level of activation in this
region of cortex may represent part of a general class of computations
that require integration of information across a large span of the visual
field.
D 2004 Elsevier Inc. All rights reserved.
__________________
Graham Curryer
None of us know what we are doing, but some of us know more about what we are not doing than others!::
J Biomech. 2006 Jul 13; : 16843472 (P,S,G,E,B) Symmetry-based resistance as a novel means of lower limb rehabilitation.
[My paper] Ann M Simon, R Brent Gillespie, Daniel P Ferris
Department of Biomedical Engineering, The University of Michigan, Ann Arbor, MI 48109-2214, USA; Department of Mechanical Engineering, The University of Michigan, Ann Arbor, MI 48109-2214, USA.
Robotic devices hold much promise for use as rehabilitation aids but their success depends on identifying effective strategies for controlling human-robot interaction forces. We developed a robotic device to test a novel method of controlling interaction forces with the intent of improving force symmetry in the limbs. Users perform lower limb extensions against a computer-controlled resistive load. The control software increases resistance above baseline in proportion to lower limb force asymmetry (balance between left and right limb forces). As a preliminary trial to test the device and controller, we conducted two experiments on neurologically intact subjects. In experiment 1, one group of subjects received symmetry-based resistance while performing lower limb extensions (n=10). A control group performed the same movements with constant resistance (n=10). The symmetry-based resistance group improved lower limb symmetry during training (ANOVA, p<0.05), whereas the control subjects did not. In experiment 2, subjects (n=10) successfully used symmetry-based resistance to alter their lower limb force production towards a target asymmetry (ANOVA, p<0.05). These studies suggest that symmetry-based resistance may hold rehabilitation benefits after orthopedic or neurological injury. Specifically, performing strength training therapy with this controller may allow hemiparetic individuals to focus better on increasing strength and neuromuscular recruitment in their paretic limb while experiencing symmetric limb forces.
__________________
Graham Curryer
None of us know what we are doing, but some of us know more about what we are not doing than others!::
Is symmetry an important therapeutic goal?
:
In many circumstances (i.e. the flat surfaces that David Holland likes to always emphasize), the surfaces are basically identical to each other.
. Anyway back to the real world, my nail drill just died and it's going to cost me the best part of a grand for a new one- ouch.
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