1 New Message
Digest #4601
Message
Sat Aug 4, 2012 10:12 am (PDT) . Posted by:
"Giovanni Ciriani" gciriani
Ken, thank you for the follow up (I had missed it, and found it only
now). I understand the problem better now.
I find the following explanation in principle intuitive, but more complex
than it would appear: " Optimal contact time is therefore one-half the
natural period of the system." I will try to read the study to get a better
grasp of the problem.
In found the following presentation by Ross Tucker extremely interesting.
http://prezi.com/y0zzjdnmgson/science-of-olympics-oscar-pistorius/
Giovanni Ciriani - West Hartford, CT - USA
On Mon, Jul 23, 2012 at 2:16 PM, <CoachJ1@aol.com > wrote:
> **
>
>
> >I'm not sure who is reporting what in this debate, but if the statement
> attributed to John Buckley is correct, it seems that he doesn't understand
> how storage of elastic energy works:
>
> John Buckley is a clinical biomechanist at the University of Bradford
> Division of Medical Bradford.
>
> Buckley wrote the following as part of his comment on the JAP
> Point/Counterpoint relative to the Pistorius research:
>
> "A runner and prosthesis comprise a mass-spring system with nearly
> constant
> natural frequency. If the prosthesis has high stiffness, the system has a
> high frequency and a short period. If it has low stiffness, the system has
> a low frequency and a long period. In the first quarter period, kinetic
> energy is stored as
> elastic energy in the carbon fiber keel. In the second quarter period,
> this elastic energy is returned as kinetic energy. Optimal contact time is
> therefore one-half the natural period of the system. Ground contact time
> is
> determined by a runner's speed and leg compliance, with the actual contact
> time matching the optimal time at only one speed."
>
> Cavagna also wrote a response, which supported the Weyand/Bundle position:
>
> "At high running speeds, a large fraction of the power developed each step
> during the push appears to be
> sustained by elastic energy stored within muscle-tendon units during the
> brake . Elastic storage and recovery is improved at high speeds by
> privileging the role of tendon relative to muscle at the expense of a high
> muscle
> activation Replacing muscle-tendon units with a passive, inexpensive,
> elastic structure may result in more efficient elastic rebound by
> increasing the
> power developed at low cost during the push.
>
> At low running speeds, the step frequency f is advantageously tuned to the
> resonant frequency of the bouncing system fs With increasing running
> speed, f increases less than fs to contain the power spent to reset the
> limbs at
> each step If the half period of the bouncing system is measured in Fig. 1
> of
> Weyand and Bundle , as the time where the vertical force exceeds body
> weight, the resonant frequency fs of the bouncing system results 60%
> greater
> than the step frequency f in the intact-limb subject and 30% greater in
> the
> amputee.If this is confirmed by measuring f and fs at different running
> speeds, the advantage of a reduced mass of the lower limb may be
> considered.
>
> These two observations favor the hypothesis that artificial limbs may make
> artificially fast running speeds possible, even if, as stated by Kram et
> al, this hypothesis cannot be statistically proven.
>
> Ken Jakalski
> Lisle HS
> Lisle, Illinois USA
>
>
> [Non-text portions of this message have been removed]
>
>
>
[Non-text portions of this message have been removed]
now). I understand the problem better now.
I find the following explanation in principle intuitive, but more complex
than it would appear: " Optimal contact time is therefore one-half the
natural period of the system." I will try to read the study to get a better
grasp of the problem.
In found the following presentation by Ross Tucker extremely interesting.
http://prezi.
Giovanni Ciriani - West Hartford, CT - USA
On Mon, Jul 23, 2012 at 2:16 PM, <CoachJ1@aol.
> **
>
>
> >I'm not sure who is reporting what in this debate, but if the statement
> attributed to John Buckley is correct, it seems that he doesn't understand
> how storage of elastic energy works:
>
> John Buckley is a clinical biomechanist at the University of Bradford
> Division of Medical Bradford.
>
> Buckley wrote the following as part of his comment on the JAP
> Point/Counterpoint relative to the Pistorius research:
>
> "A runner and prosthesis comprise a mass-spring system with nearly
> constant
> natural frequency. If the prosthesis has high stiffness, the system has a
> high frequency and a short period. If it has low stiffness, the system has
> a low frequency and a long period. In the first quarter period, kinetic
> energy is stored as
> elastic energy in the carbon fiber keel. In the second quarter period,
> this elastic energy is returned as kinetic energy. Optimal contact time is
> therefore one-half the natural period of the system. Ground contact time
> is
> determined by a runner's speed and leg compliance, with the actual contact
> time matching the optimal time at only one speed."
>
> Cavagna also wrote a response, which supported the Weyand/Bundle position:
>
> "At high running speeds, a large fraction of the power developed each step
> during the push appears to be
> sustained by elastic energy stored within muscle-tendon units during the
> brake . Elastic storage and recovery is improved at high speeds by
> privileging the role of tendon relative to muscle at the expense of a high
> muscle
> activation Replacing muscle-tendon units with a passive, inexpensive,
> elastic structure may result in more efficient elastic rebound by
> increasing the
> power developed at low cost during the push.
>
> At low running speeds, the step frequency f is advantageously tuned to the
> resonant frequency of the bouncing system fs With increasing running
> speed, f increases less than fs to contain the power spent to reset the
> limbs at
> each step If the half period of the bouncing system is measured in Fig. 1
> of
> Weyand and Bundle , as the time where the vertical force exceeds body
> weight, the resonant frequency fs of the bouncing system results 60%
> greater
> than the step frequency f in the intact-limb subject and 30% greater in
> the
> amputee.If this is confirmed by measuring f and fs at different running
> speeds, the advantage of a reduced mass of the lower limb may be
> considered.
>
> These two observations favor the hypothesis that artificial limbs may make
> artificially fast running speeds possible, even if, as stated by Kram et
> al, this hypothesis cannot be statistically proven.
>
> Ken Jakalski
> Lisle HS
> Lisle, Illinois USA
>
>
> [Non-text portions of this message have been removed]
>
>
>
[Non-text portions of this message have been removed]
GROUP FOOTER MESSAGE
Modify/cancel your subscription at:
http://groups.yahoo.com/mygroups
Sign all letters with full name & city of residence if you
wish them to be published!
http://groups.yahoo.com/mygroups
Sign all letters with full name & city of residence if you
wish them to be published!
No comments:
Post a Comment
Finish Reading ? Make Your Comment Now..!