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perry75
05-16-2007, 07:47 AM
Dear fellow biomechanists,

I am responding to the previous message posted by Ton van den Bogert
regarding the New York Times article on the amputee sprinter. As a
mechanical engineer and previously a collegiate athlete, I find this to
be a fascinating topic. I spent 10 years competing in track & field as a
high jumper, and also worked on a powered prosthesis project during my
master's degree. Although not an expert on energy storing feet, I'm am
quite familiar with them.

From a biomechanics standpoint, I see two basic issues that should be
highlighted. One is the rate of turnover achievable by the athlete,
which is affected primarily by muscular power across the hip and knee
joints and by limb mass properties. The second involves the energy
storing (ES) and return phase of the prosthesis while in contact with
the ground.

The first point is that if the effective mass and inertial properties of
the prosthesis with respect to the hip and knee joints are less than
would be expected in an intact individual, then the athlete has an
advantage during the swing phase. Shorter swing phases means more With
the athlete being a quite distally below-knee (BK) amputee, the
musculature for the hip and knee should be normal and could take
advantage of a "light" prosthesis.

The second point applies to the stance phase. In sprinting, once up to
speed, there is a significant amount of co-contraction about the ankle
joint where the sprinter relies primarily on tendon properties for
energy storage and return. Although this is not unlike the effect of an
ES prosthesis, it should be acknowledged that no co-contraction is
required in order to benefit from the properties of the prosthetic
"tendon". There will be no fatigue associated with this portion of
musculature during the event. At full speed and over longer distances,
this would be more of an advantage since getting past "2nd gear" plays
less of a role in the overall race time (Pistorius was described by a
coach as "a 5-speed engine with no 2nd gear"). Also, the argument that
ES foot returns only 80% in comparison to physiological returns of up to
240%, this is true for walking but I doubt it's validity in full-speed
sprinting. From what I have experienced and observed, the faster you
run, the more the ankle relies on tendon stiffness for it's behavior,
and less so from timed contraction. However, there is obviously a
disadvantage during early acceleration due to the constant stiffness of
the prosthesis which is, no doubt, tuned for full-speed sprinting.

I have not mentioned the aspects that would make running with a
prosthesis a disadvantage, as there are many. However, I think in terms
of an I.A.A.F. decision, the important part is showing strickly that
there are no advantages, or in coming up with criteria such as mass,
inertial, and stiffness properties that maintain strict adherance to
human biomechanics. A difficult issue still remains with respect to
purity of the sport, regarding whether the properties of the prosthesis,
although within biomechanical ranges, may not be within the "God-given"
range of the athlete.

Clearly, this is a complex issue where some simultaneous motion capture,
ground reaction forces, and emg acquisition in athletes would be useful.
This was something I had thought about doing for my degrees, but was
unsure that funding would be available.

I would be very interested in reading the summary of replies, when compiled.

Best regards,

Joel

_____________
Joel C. Perry, Ph.D.
Biorobotics Laboratory
University of Washington
brl.ee.washington.edu



Ton van den Bogert wrote:

>Yesterday's New York Times had an article about a double amputee from South
>Africa who runs 100 m in 10.9 seconds and appears to be still improving.
>There is debate whether he should be allowed to run in the 2008 Olympics, if
>he qualifies.
>
>The IAAF says that his energy-storing feet are an unfair advantage. Others
>say they are not, since they only return 80% of the energy. There are calls
>for further research.
>
>The athlete, Oscar Pistorius, said "I think they’re afraid to do the research.
>They’re afraid of what they’re going to find, that I don’t have an advantage
>and they’ll have to let me compete."
>
>What do the Biomch-L subscribers think? I know we have some subscribers who
>are experts on this topic.
>
>The full article is here:
>http://www.nytimes.com/2007/05/15/sports/othersports/15runner.html
>
>--
>
>Ton van den Bogert, Biomch-L co-moderator
>http://www.Biomch-L.org
>
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