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Chris Kirtley
04-29-1996, 04:21 PM
.. sharp intake of breath...

I've spent quite a bit of time lately developing a nice multimedia tool for
analysing gait. It does the full inverse dynamics analysis to derive joint
moments and powers. I've been stuck lately on a discrepancy between the
results using my system and the published results of David Winter. I've
now, as we say in Australia, spat the dummy!

I simply cannot see how Winter's group could get their curves for the
normal knee and hip kinetics. Specifically, the joint (resultant) moments
and powers during push-off (around 55% of cycle) peak at the following
values:

Moment Power
Knee 0.85 Nm/kg extensor 4.8 W/kg eccentric
Hip 1.35 Nm/kg flexor 1.45 W/kg concentric

=46or comparison, Winter reports:

Moment Power
Knee 0.16 Nm/kg extensor 0.76 W/kg eccentric
Hip 0.4 Nm/kg flexor 0.67 W/kg concentric

I have found only one other set of normal curves, from Kabada's (1989)
study, which I took from Dwight Meglans's chapter in "Human Walking". There
are no powers quoted (Dwight seems to use Winter's data for these), and
unfortunately his units are rather obscure, since he normalises for leg
length (LL) as well as body weight:

Moment
Knee 8 Nm/kg.LL extensor
Hip 14 Nm/kg.LL flexor

I don't know how to convert these values to Nm/kg, but scaling for the
ankle moments (which all our results seem to agree on!) indicate dividing
by a factor of about 10:

Moment
Knee 0.8 Nm/kg extensor
Hip 1.4 Nm/kg flexor

i.e. the same as our results (and different from Winter's).


Our results are quite repeatable - we so far have not examined anyone who
gives curves like Winter's. At this point in time I still feel reluctant to
criticise Winter, since his normal data is the gold standard. But since we
seem to agree with Kabada, I now have the confidence to ask you all:

???????????????

What values are you getting?

???????????????

By the way, this experience has highlighted to me the need for more
published data on normal joint kinetics. I even traced back through all the
ISB proceedings and found very little except for Winter's reports. Does
this mean that there's noone else doing joint kinetics? I'm sure there must
be...

I'll send a summary of responses.

Many thanks,

Chris




__________________________________________________ __________________
Dr. Chris Kirtley MB ChB, PhD c.kirtley@info.curtin.edu.au
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Lecturer, Bio-engineering --_ / \
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School of Physiotherapy, Perth #_.---._/
Curtin University of Technology, V
GPO Box U1987,
Perth 6001, Tel +61 9 351 3649
Western Australia. Fax +61 9 351 3636

WWW: http://www.curtin.edu.au/curtin/dept/physio/pt/staff/kirtley/
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