Ankle torque inconsistency during inverse dynamics calculations

[Krisanne E. Bothner]

THE QUESTION:
What could account for a *dramatic* difference between the ankle
muscle moment when it is calculated using the equation of motion for the
shank compared to the moment when it is calculated from the equation
of motion of the foot?

THE BIOMECHANICAL MODEL
Consider a four segment planar model of a human (two feet, two
legs, two thighs and HAT) for the purpose of an inverse dynamics analysis
of standing balance. The equations of motion for this system can be generated
for each segment, and we are able to solve for the residual torque, as the
generalized muscle moment, acting at each of the three joints. By the
nature of
this approach, one can use either the shank segment or the foot segment
to solve for the generalized muscle moment acting at the ankle. My question
to the list is AGAIN: Given this biomechanical model, what might account for
a *dramatic* difference between the ankle muscle moment calculated using
the equation of motion for the shank compared to the calculated from the
equation of motion of the foot?

As usual, a summary of replies will be posted.

Krisanne Bothner


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Krisanne E. Bothner Motor Control Laboratory
Dept. of Exercise & Movement Science 330 Gerlinger Hall
1240 University of Oregon voice: 541.346.0275
Eugene, Oregon USA 97403-1240 FAX: 541.346.2841