To All,

First Question - Recent papers reporting the net joint moments have
taken two approaches to
decreasing variability across subjects. Some studies (Eng and Winter, J
Biomech, 1995) divide the net joint moment by body mass. Other papers
(Berchuck, JBJS 1990, Holden and Stanhope, Gait & Posture, 7:1-6, 1998)
the net joint moment by % body weight * height. The reasoning behind
second approach is that both the ground reaction force (which is
correlated with body weight)
and segment length (which is correlated with height) are used to
estimate net joint

However, a recent abstract by Sum et al(Sum et al, Gait & Posture, 7,
1998) suggests that using % body weight * height generally doesn't
variability, except for the ankle dorsiflexion peak during walking. In
height explained little of the variability in the frontal plane moments
(< 11%) and
explained no additional variability once the moments had been normalized
to body mass.

This appears to suggest that normalizing to % body weight * height
does not
significantly reduce variability, and therefore, dividing net joint
moments by
body mass such as in the Eng and Winter(Eng and Winter, J Biomech, 1995)
is adequate. Yet current studies appear to be dividing the net joint
moments by % Body weight * height (Holden and Stanhope, Gait & Posture,
7:1-6, 1998).
Are there other compelling arguments to make % body weight * height the
over body mass?

Second question -- When moving to reporting three dimensional joint
moments there are three options when mapping the moments into the local
coordinate system. The moments can be reported in the proximal segments
system, distal segments coordinate system or mapped into the non -
orthogonal axes of
the joint coordinates used to estimate kinematics (JCS).

Siegler and Liu (In Allard et al, Three Dimensional Analysis of Human
Locomotion, Wiley and Sons, Ltd, 1997 page 203) suggest that the moments
be mapped into the JCS. However, Andrews (Andrews, JG, J Biomech,
17(2):155-158, 1984) raised the issue that the joint center is not
common to all 3 axes when using the JCS. And therefore, "...the vector
sum [of the three joint torques] does not represent the combined turning
effect of all joint structures about a single point because the the
three axes do intersect at a common point."

Comparisons of mapping the net moments into the femoral coordinate
system and
tibial coordinate system during walking suggest very close
approximations in
the sagittal and frontal planes, however, the differences are > 100 % in
transverse plane(Pilot data). In terms of the transverse plane it
appears to make sense for interpreting muscle function to map the
moments into the local coordinate system of the distal segment. For
example the hamstrings are considered internal/external rotators because
of their relationship to the tibial long axis not the femoral long

What should the standard be for reporting local joint moments?

I will post all replies.


Jeff Houck, PhD, PT
Ithaca College - Rochester Campus
300 East River Road Suite 1-102
Rochester, NY 14623

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