View Full Version : Responses: Has Biomechanics come of age?

Peter Cavanagh
10-23-1996, 04:00 PM
In my last President's Message, I posed the question - "Has Biomechanics
come of age?
Here, for your reading pleasure, are the responses. (Beware - this is a
LONG posting)
Peter Cavanagh
ISB President

Responses are from:

John J. Buchanan
Dawn Cockell
Richard Hughes,
Dave Giurintano
Craig Nevin
Ian Stokes
Arved Vain
Jos Vander Sloten

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Response from:

John J. Buchanan, Ph.D.
RS Dow Neurological Sciences Institute
1120 NW 20th
Portland OR 97209
Phone: (503) 413-7390
Fax: (503) 413-7229

Although I am not a member of this mailing list, a colleague of
mine showed me your posting and asked if I would like to respond. It was
given to me a couple of days ago, I hope I am not to late. While I can not
respond directly to the "coming of age" of biomechanics as a scientific
discipline or sub-discipline, since this is not my field of expertise, I
can respond directly concerning the contributions of dynamical systems
theory to our understanding of human movement.

There are three significant contributions that arise directly from
the study of pattern formation and change in biological movement. First,
the numerous studies demonstrating transitions from one pattern to another
highlight the importance of how coordinative patterns are related to one
another. In other words, patterns are of a general class not because they
are modifications of a similar pattern, e.g., reaching or gait patterns,
but because of their stability. Thus, in-phase and anti-phase patterns are
very general patterns that can be performed in a variety of joint and limb
combinations, within a single limb, across limbs, between a person and an
environmental event, between people etc. Regardless of the components
being coordinated, very similar results emerge in terms of the direction of
the transition, changes in stability before the transitions and hysteresis.
Such results suggest that the same neural pattern (or as some people would
prefer motor program) or very similar neural pattern can be instantiated in
many situations, in turn, the CNS has many options arising from a very
small starting set of stable behavioral patterns.

Second, the dynamical systems approach has shown how important
fluctuations are in maintaining a pattern and selecting a pattern. Even
when a pattern is in a stable region of parameter space, fluctuations keep
the system from becoming overly stable. That is, so stable that it may
have eliminated other possibilities or viable options. Small fluctuations
allow the system to probe its phase space and search for other stable
patterns, (while maintaining a stable pattern) in case an environmental
change requires a switch from the current pattern to another pattern.
Without fluctuations, the ability to switch would be hampered, since
fluctuations can act as a starting point for the system to destabilize and
disassemble one pattern in order to assemble a new coordinative pattern.
Furthermore, the ability to switch between patterns has been shown to be a
function of the stability of the patterns, thus it is always easier to
switch from a less stable to more stable pattern than vice versa,
regardless of the joints, limbs or even people performing the patterns.
Again, such results demonstrate that the nervous system takes advantage of
very similar dynamical processes in many different situations.

Third, very similar dynamical processes have been observed across
a variety of levels of observation, single neuron, coupled neurons, chains
of neurons, brain EEG patterns and behavioral patterns (see above). For
example, single neurons have been shown to phase and frequency entrain and
undergo transitions when driven by an external source; coupled neurons and
chains of neurons frequency and phase entrain at only a few stable
patterns, e.g., in-phase anti-phase, 2:1, 1:1 3:1 etc.; EEG patterns or
local field oscillations in the visual cortex phase entrain to multiunit
firing, and EEG patterns in the human brain express the same dynamics
observed in bimanual switching (for review and references see Kelso 1995,
Dynamic Patterns: The self-organization of Brain and Behavior, especially
chapters 8 and 9 concerning neural processes.). Another feature of CPGs
is there multifunctionality. The same group of neurons can produce
different neural patterns and switch between patterns. Moreover, very
diverse neural systems produce the same patterns, even the
neurotransmitters, neuromodulators and connections are different. As in
behavioral studies, it seems that varied nervous systems take advantage of
very similar dynamical laws.

The above comments are directed at the contributions of the
dynamical approach. At this point I would like to say a few words about
the shortcomings of the approach and how they may directly relate to the
field of biomechanics. As a general statement, I think that the dynamic
people have ignored the role (to the most part) of the body's biomechanical
properties. My own view, is that biomechanics are important in that they
set constraints on the functioning of the nervous system, it can only move
so fast, move a specific mass so fast, generate so much force etc., while
theoretically the nervous system can produce an infinite number of joint
and limb combinations, only a few are usually observed. Why? I believe
the reason is that biomechanical factors set boundaries conditions that
constrains the nervous system to operate in a more limited parameter space
than is theoretically possible. Thus, the nervous system, while it is a
dynamic self-organizing system, must function within these constraints.
Biomechanical properties do not dictate the nature (stability, loss of
stability, hysteresis) or direction of a pattern change, but instead set
the boundaries over which certain patterns can be performed and maintained.

To arrive at a complete understanding of the neural and behavioral
functioning, I think it is necessary for biomechanists, dynamical systems
people and neuroscientists to view themselves all as sub-disciplines of the
field of animal and human biology. Each approach independently will never
provide all the answers. Only through the merger of the information
provided by each area on biological functioning will complete answers
actually be found.

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Response from:

Dawn Cockell, M.Sc. student,
McMaster University
Hamilton, Ontario

The following are some thoughts in response to "Biomechanics:
Has it come of age?". Several issues are presented in the article which
have successfully sparked much discussion around our biomechanics lab group.
As a result, I would like to share some of my opinions about biomechanics
and its development as a science.
"Biomechanics as a Discipline: Have we progressed beyond the
point where Biomechanics could be said to be an array of techniqes in
search of a problem?" YES!! Evidence of the reversal of this thought
comes from the number of people who are now seeking out the aid of
biomechanists to help to solve their problems. Analysis of new exercise
equipment, orthotic materials and rehabilitation devices are just a few
sectors where our expertise is being sought. At the same time, I do
believe that there is much methodological research that is being
undertaken that will be of use in achieving a greater understanding of
human movements and environmental interactions. Both forms of research,
at least in my opinion, are evidence of the maturation of the science

"Motor Control: Do we yet have a clear understanding of the manner
in which voluntary movements are controlled and has Biomechanics made a
difference?" I am not sure that the choice of the word "clear" is
appropriate. One area which has indeed changed as a result of kinetic
analysis revealed from EMG has been rehabilitation. The insight gained
from EMG studies of movement has been applied to aid in rehabilitation.
For an example see:

Glousman, R., Electromyographic analysis and its role in the athletic
shoulder. Clinical Orthopaedics and Related Research, 288,27-?, 1993.

In this article, Glousman demonstrated that timing and relative
intensity of muscle activities could be used to identify the strengthening
program for specific musculature around the shoulder. As biofeedback,
EMG has been used in rehabilitation to provide an indication to patients
as to which muscles need to be activated or deactivated. In a sense to
help them to see which muscles need to be turned on or off.

"Sport Biomechanics: Is sports equipment better and safer than it
was 20 years ago? Is the performance of sport better and safer today
because of the involvement of sport biomechanists?" Again, evidence can
be found in numerous avenues. I will use hockey and cervical spine
injuries as one example. In hockey, biomechanical analysis of the
mechanism for injury revealed that when a hockey player went head first
into the boards, or other object for that matter, if their spine was
aligned in a column (ie. their neck in a slightly flexed position), a
burst fracture was likely to result. In response to this, and
admittedly other factors too, the no hitting from behind rule was put into
effect. Changing materials in helmets have also aided to decrease the
impulse that must be absorbed by the individual. Other sports have also
been impacted by the application of biomechanics to injury prevention.
Performance has also been affected by the application of biomechanics by
coaches to improve skill, and to analyze skill. One just has to turn on
the television during these Olympic games and listen to the coaches and
athletes discuss reasons for improved or decreased performance to see
evidence of biomechanical application.

I would like to express thanks to Dr. Cavanagh for causing me to
stop and reflect on my own discipline.

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Response from:
Richard Hughes, Ph.D.

From: ErgoHughes@aol.com
Date: Fri, 26 Jul 1996 16:47:49 -0400
To: prc@psu.edu
cc: SILB235@lni.wa.gov
Subject: Maturity of biomechanics

Dr. Cavanagh,

I would like to address the impact of biomechanics on occupational health in
the US, specifically in the area of policy.

The recent experience with the Occupational Health and Safety
Administration's (OSHA's) efforts to develop an ergonomics standard
illustrates the relative importance of biomechanics in the ergonomics policy
arena. When one lines up all of the biomechanics research that has been
conducted over the last several decades against the United Parcel Service's
lobbyist, biomechanics gets creamed (as was demonstrated by the Congressional
rider directed at prohibiting OSHA to work on an ergonomics standard). This
merely illustrates how larger economic forces in the US are much more
powerful than biomechanics research when it comes to occupational health

However, the recent policy debate about industrial ergonomics has pointed out
a critically important limitation of biomechanics research in the prevention
of work-related musculoskeletal disorders (CTDs, RSIs, etc). Specifically,
the most elegant three-dimensional dynamic biomechanical model is not nearly
as important - in terms of policy - as a large scale prospective study using
well defined clinical endpoints and realiable exposure assessment
methodologies to identify the relative contribution and interactions of
putative physical and psychosocial risk factors. Without causality, the
whole concept of "work-relatedness" comes under attack.

The importance of the relative absence of well designed prospective
epidemiologic studies was illustrated by the Berverly Enterprises victory
over the US Department of Labor's citation against them under the general
duty clause of the OSHA act. In that case, the administrative law judge who
was considering the legality of OSHA citation for low back pain in Beverly's
nursing home aides found that (1) low back pain doesn't constitute "harm" to
employees, and (2) even it it did harm employees, there are no sufficiently
large and well designed studies of LBP in nursing aides that show
biomechanics factors cause LBP. More importantly, the judge made some
scathing comments about the relative unimportance of biomechanical models in
his decision. Some think this decision, if upheld at higher levels, will
severely curtail OSHA's ability to cite employers for excessive rates of
musculoskeletal disorders under the general duty clause. That had a direct
public policy impact. Of course it is wrong to decry biomechanical modeling
simply becase a lawyer couldn't understand a biomechanical model; however,
this example merely illustrates how the policy world values clinical and
epidemiological studies versus biomechanical modeling and laboratory

I would argue that the most important contributions of biomechanics to
policy-relevant studies has been the development of exposure assessment
methodologies. One of the most important policy-related piece of science in
this area is Silverstein et al. (1986, 1987), which associated cumulative
trauma disorders with repetitiveness and hand grip forces. This study could
not have been conducted without the methodology for estimating grip forces
from surface EMG developed and published as a technical note in the Journal
of Biomechanics (Armstrong et al., 1979).

Similarly, the seminal epidemiological study of Chaffin and Park (1973) that
showed biomechanical parameters to be associated with reports of LBP used a a
biomechanically based measure of mechanical loading.

More recently, Marras and colleagues have extended exposure assessment in
occupational epidemiology studies to include electrogoniometry (Marras et
al., 1993). Some other groups have also used principles of biomechanics and
instrumentation to develop novel exposure assessment methods using EMG (for
example, Moore et al., 1991).

In short, I feel that the major contributions of biomechanics to occupational
health policy has been by developing methods for characterizing employee
exposure to physical stresses ("exposure assessment") in epidemiological
studies, because epidemiological studies have the most policy impact. It
should also be noted that the key to successfully finding risk factors for
disease is often improved exposure assessment methods: biomechanics can make
a tremendous contribution to developing better methods of exposure assessment
than traditional ones (traditional methods, for example, use job
classification as a gross measure of physical stresses).

If the preceeding hasn't been provocative enough, I would like to suggest
that exposure assessment is sometimes treated as the ugly stepdaughter of
biomechanics. I have heard laboratory-based biomechanists complain at
meetings that papers reporting the use of surface electrodes on the forearm
flexors and extensors are "junk," because surface electrodes are not as
specific as wire electrodes. What these critics may not recognize is that in
field epidemiological studies, wire electrodes are just not feasible. If the
purpose of a study is to develop and test new protocols for exposure
assessment, it is entirely reasonable to use technology that is more suitable
for the field than for the lab. It may be useful for such critics to
remember that ergonomists attempting to develop exposure assessmen tools for
epidemiological studies are not trying to achieve the level of sophistication
of laboratory wire EMG studies; rather, they are trying to provide
epidemiologists with tools that are superior to using job classification as a
surrogate for physical stresses.

If one accepts the thesis that developing tools for epidemiological exposure
assessment is critical for answering the ergonomics questions of the day
("what causes CTDs?," "what is the dose-response relationship of physical
factors to CTDs?", "what is a more important factor in CTDs, physical or
psychosocial factors?"), then it may seem logical that organizations such as
the National Institute for Occupational Safety and Health (NIOSH) should fund
more of this type of research.

Finally, I will directly address the question of the "maturity" of
biomechanics as applied to work-related musculoskeletal disorders. I have
been most actively involved in developing computerized biomechanical models,
and I think that area has reached a reasonable level of maturity. There is a
substantial body of literature available arguing about the general
distribution problem. However, the critically important area of
epidemiological exposure assessment is in its infancy. Comparatively little
attention has been given to this area, and relatively small progress has been
made since surface EMGs and electrogoniometric techniques were introduced.
This is an area of research that is under-funded, under-studied, and
extremely policy-relevant.


1. Armstrong, T.J., Chaffin, D.B., and Foulke, J. (1979) A method for
documenting hand positions and forces during manual work. J. Biom. 12:

2. Silverstein, B.A., Fine, L.J., and Armstrong, T.J. (1987) Occupational
factors and carpal tunnel syndrome. Am. J. Ind. Med. 11: 343-358.

3. Silverstein, B.A., Fine, L.J, and Armstrong, T.J. (1986) Hand wrist
cumulative trauma disorders in industry. Br. J. Ind. Med. 43: 779-784.

4. Chaffin, D.B. and Park, K.S. (1973) A longitudinal study of low-back pain
as associated with occupational weight lifting factors. Am. Ind. Hygiene
Assoc. J. 34: 513-529.

5. Marras, W.S., Lavender, S.A., Leurgans, S.E., Rajulu, S.L., Allread,
W.G., Fathallah, F.A., and Ferguson, S.A. (1993) The role of dynamic
three-dimensional trunk motion in occupationally-related low back disorders.
Spine 18: 617-628

6. Moore, A., Wells, R.P., Ranney, D.A. (1991) Quantifying exposure in
occupational manual tasks with cumulative trauma disorder potential.
Ergonomics 34: 1433-1453.

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Response from:
Dave Giurintano

Paul Brand Biomechancis Lab giurin@resdjg.dnet.lsu.edu
GWL Hansen's Disease Center (504) 642-4731 W
Carville LA 70721 (504) 642-4738 F

As I get older I believe Dave Thompson's advice about going into biomechanics
make the most sense. He suggested that I get a traditional engineering degree
and then pursue my interest. His feeling was that a BME degree did not give one
all the tools to tackle the problems encountered. After doing this for 10+
years, I think my ME degrees have served me well. If I had not had all the
exposures (from EE and IE courses) and outside ME stuff (comparative anatomy,
microbiology, computer graphics) I might feel undertrained. As a research
discipline, I feel that the person with a traditional degree and
non-traditional experiences is best prepared to contribute to our field. As a
commerical filed, biomechanics is not much at all. Implant companies perform
more "black magic" than design. Having little thorough research performed on
implants is frighting to me. If the FDA did not require testing I wonder if the
companies would do anything other than get high profile MDs to certify their

> Orthopaedic Biomechanics: ...

Paul Brand and Dave Thompson's work on the rat footpad studies that lead the
determination that Hansen's Disease patients did not have "bad" tissues but it
was the rsult of repeative stress to the tissue that did have time to
remodel(callous) to accomadate to the theses stresses. Then Paul Brand's
transfer of this fact to diabetes because of the mechanical similarities to HD
(peripheral neuorpathy).

> Functional Anatomy: ...

Paul Brand et al's work on the 1981 JHS paper quantified the force
potential and
excursion capabilites of the muscles of the forearm to give real parameters to
determine effective candidates for tendon transfer surgery.

> Rehabilitation Biomechanics: ...

PWB's work in creating the voluminter to measure the amount of reduction in
edema of the hand. The use of cylinder casing to gradually lengthen tissues to
prepare them for tendon reconstruction surgery.


For myself, I have spent 12 years perfecting an idea of PWB and DET's to
visulaize the mechanics related to tendon transfer surgery in the hand. Has
this work been practical? The goal 12 years ago was to have this software
running on a workstation at surgery. Today with the advances in computing
the availablity of PCs and visualization software like AVS, this goal is fast
approaching a reality. Patient billing and surgeical planning all on one
machine. Pretty cool and soon to be possible. But I still would initially see
tools like this used in specialty residency programs. With time maybe private
practice surgeons would acquire workstations to practice proposed surgeries to
simulate the outcome. I do see managed care providers using the research
of biomechanics to validate outcomes and judge the cost effectiveness of

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Response from:

From: "Craig Nevin"
To: prc@psu.edu
Date: Thu, 8 Aug 1996 12:01:39 SAST-2
Subject: Re: President's message
Priority: normal


The ISB President recently enquired if the scientific sub-
discipline of Biomechanics has come of age. Here is my reply.

When Braune and Fischer first analysed the human gait in 1896,
Biomechanics was undisputably scientific. The scientific method used
Newton's scientific theories of motion (and even Newtonian style
differential calculus). However, in 1904 Einstein published a paper
that changed the face of science itself; Newton's Laws of motion were
revealed to be incomplete.

Although Newton's Laws of motion were the scientific heros of the
Mechanical Age, in the twentieth century, Newton's Laws are merely a
scientific sub-discipline. Since Biomechanics is undeniably a sub-
discipline of Newtonian science, modern Biomechanics can, at best,
claim to be a sub-scientific sub-discipline. Perhaps we, as a sub-
scientific sub-discipline, have come of age, but in the global
picture who really cares? And rightly so. Biomechanics remains a
small scientific fish in a small scientific pond. This is due almost
entirely to our Newtonian heritage of which we are so proud.

If we wish to mature as a science, we need to moult from within our
juvenile (sub-scientific) Newtonian skin (the inertial frame of
reference). Have not Newtons Laws (orginally derieved for particles)
met their match when applied to the complex linkages of the human
body? If so, where do we turn for inspiration?

Einstein is the obvious answer. "Yes, but Einstein only applies near
the speed of light" is the likely response. However, this needs to
be examined more closely. Newton's laws were first derieved for
particles, yet we apply them, rather unsuccessfully, to the human
body. We have no scrupples about this mis-application. Newtonian
mechanics has been applied to particles (atomic, earthly, and cosmic)
fairly successfully.

Einstein's theories have been used to describe atomic and cosmic
particles much more successfully than Newton. Yet there is a missing
link in Einstein's chain of logic. Mysteriously Einstein's theories
"do not apply" on a day-today level! Why not? The answer is simple,
because no one has bothered to explained it to us.

A characteristic of basic science (rather than applied science) is
that there is no one to explain the next step the staircase of
scientific logic as opposed to applied logic. As Biomechanists we
seek the safe route, application of others knowledge. Although at
first this is easier, it becomes a problem when we discover that the
rules of Newton don't quite work as well as we might have hoped (why
should they?) It was not up to Einstein to explain all the
ramifications of his theories to us -- afterall WE are supposed to be
the Bio-scientists.

Unfortunately, we proudly claim Newton (ironically the leading
scientist of the Mechanical Age) to be our guru in the Biological Age
(of DNA and genetic engineering). Science itself is bypassing us.

To reach maturity we need to put our thinking caps on rather than to
look to others for science to apply. I am convinced that
Biomechanics is the correct name for Einstein's earthly mechanics.

But, we will never "discover" new Biomechanical principles by
application of old Newton's Mechanical Laws, no matter how much we
persist. To make the required headway, we may well need, like
Einstein, to completely discard the hallowed Mechanical Age concepts
(1) inertial frames of reference
(2) static equilibrium
(3) constant translation of the center of mass
(4) forces

No one said it would be easy!

The future is there to be discovered, not applied.
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Ian Stokes