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Dear biomch-l readers:
In the following letter (some parts deleted) from Chris Kirtley):
>=20
> 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:
>=20
> Moment Power
> Knee 0.85 Nm/kg extensor 4.8 W/kg eccentric
> Hip 1.35 Nm/kg flexor 1.45 W/kg concentric
>=20
> For comparison, Winter reports:
>=20
> Moment Power
> Knee 0.16 Nm/kg extensor 0.76 W/kg eccentric
> Hip 0.4 Nm/kg flexor 0.67 W/kg concentric
>=20
In Dave Winter's text book "Biomechanics and motor control of human =
movement (2nd edition)" the 'peak' knee moment just prior to toe-off is =
around -13.3 n-m.(page 259). The peak hip moment just prior to toe-off =
is around 37 n-m. (page 259). The subjects body weight is 56.7 kg.(page =
213). The numbers should then be .23 and .65. Also remember this is the =
data for an INDIVIDUAL, and does not necessarily represent the AVERAGE. =
Dave has a spiral bound textbook called "The Biomechanics and Motor =
Control of Human Gait: Normal, Elderly and Pathological" in which we =
have a better measure of average results.=20
From the curves of inter-subject averages, it is quite difficult to =
generalize about 'peak' values. They have been three-point normalized to =
heelstrike=3D0%, toe-off=3D60%, 2nd heelstrike=3D100%. There are =
distinct peaks at a little less than 50% for ankle and hip, and a broad =
indistinct peak at about 55% for the knee. There is a lot of variation, =
if you plot one standard deviation above and below the averaged data, =
you find an enormous range of values. At 50% of the cycle (60%=3Dtoeoff) =
the hip moment's average is about 0.4 n-m/kg, and one standard deviation =
covers approximately 0.4 n-m/kg. So who can say? For the knee at 50%, =
it's about 0.2 n-m/kg, one standard deviation covers about 0.3 n-m/kg. =
The ankle is much tighter, it's about 1.5 n-m/kg, with 1 std.dev=3D0.3.
If you did read Dave's book, you would understand that a lot of the =
variability can be accomodated by his theory of support moment, where =
the variability in one direction at one of the joints, is partly =
neutralized by variability in the opposite direction by one of the other =
two joints. There appears to be a 'synergy' that exists between the hip, =
knee, ankle joints such that if you add up the moments (with the correct =
polarity), then the variability of the sum is less than you'd expect, =
and much less than variability of the hip or knee moments.
Before you get up on a soapbox, check it out! It might put your fears =
to rest. It would be worthwhile for you to read the spiral bound book =
referred to above, then you can go for the jugular!
Check out our web page (barely finished): =
http://gaitlab6.uwaterloo.ca/default.htm for information on his text =
books, and how to get them. There's some other 'stuff' you might find =
useful, please send me comments if you can think of good changes to make =
to the web page contents.
...stuff deleted
> 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:
>=20
It's definitely not a gold standard! It represents data from ONE of =
our subjects. Not every person walks the same way. It is still within =
plus-minus one standard deviation of our 'average'.
> 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...
=20
Again, check out Dave's other books! Don't be ready to accept one =
measured result as an average! For sure, don't put a lot of faith in =
simple numbers without knowing the story that goes behind them.
-Paul
(paul@gaitlab1.uwaterloo.ca)
In the following letter (some parts deleted) from Chris Kirtley):
>=20
> 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:
>=20
> Moment Power
> Knee 0.85 Nm/kg extensor 4.8 W/kg eccentric
> Hip 1.35 Nm/kg flexor 1.45 W/kg concentric
>=20
> For comparison, Winter reports:
>=20
> Moment Power
> Knee 0.16 Nm/kg extensor 0.76 W/kg eccentric
> Hip 0.4 Nm/kg flexor 0.67 W/kg concentric
>=20
In Dave Winter's text book "Biomechanics and motor control of human =
movement (2nd edition)" the 'peak' knee moment just prior to toe-off is =
around -13.3 n-m.(page 259). The peak hip moment just prior to toe-off =
is around 37 n-m. (page 259). The subjects body weight is 56.7 kg.(page =
213). The numbers should then be .23 and .65. Also remember this is the =
data for an INDIVIDUAL, and does not necessarily represent the AVERAGE. =
Dave has a spiral bound textbook called "The Biomechanics and Motor =
Control of Human Gait: Normal, Elderly and Pathological" in which we =
have a better measure of average results.=20
From the curves of inter-subject averages, it is quite difficult to =
generalize about 'peak' values. They have been three-point normalized to =
heelstrike=3D0%, toe-off=3D60%, 2nd heelstrike=3D100%. There are =
distinct peaks at a little less than 50% for ankle and hip, and a broad =
indistinct peak at about 55% for the knee. There is a lot of variation, =
if you plot one standard deviation above and below the averaged data, =
you find an enormous range of values. At 50% of the cycle (60%=3Dtoeoff) =
the hip moment's average is about 0.4 n-m/kg, and one standard deviation =
covers approximately 0.4 n-m/kg. So who can say? For the knee at 50%, =
it's about 0.2 n-m/kg, one standard deviation covers about 0.3 n-m/kg. =
The ankle is much tighter, it's about 1.5 n-m/kg, with 1 std.dev=3D0.3.
If you did read Dave's book, you would understand that a lot of the =
variability can be accomodated by his theory of support moment, where =
the variability in one direction at one of the joints, is partly =
neutralized by variability in the opposite direction by one of the other =
two joints. There appears to be a 'synergy' that exists between the hip, =
knee, ankle joints such that if you add up the moments (with the correct =
polarity), then the variability of the sum is less than you'd expect, =
and much less than variability of the hip or knee moments.
Before you get up on a soapbox, check it out! It might put your fears =
to rest. It would be worthwhile for you to read the spiral bound book =
referred to above, then you can go for the jugular!
Check out our web page (barely finished): =
http://gaitlab6.uwaterloo.ca/default.htm for information on his text =
books, and how to get them. There's some other 'stuff' you might find =
useful, please send me comments if you can think of good changes to make =
to the web page contents.
...stuff deleted
> 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:
>=20
It's definitely not a gold standard! It represents data from ONE of =
our subjects. Not every person walks the same way. It is still within =
plus-minus one standard deviation of our 'average'.
> 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...
=20
Again, check out Dave's other books! Don't be ready to accept one =
measured result as an average! For sure, don't put a lot of faith in =
simple numbers without knowing the story that goes behind them.
-Paul
(paul@gaitlab1.uwaterloo.ca)