ARUP; ISBN: 978-0-9562121-5-3 - CMBBE 2012 - Cardiff University

compartments as well as a single muscle force are presented (Figure 4) as a first
approximation, similar to that described within the work of [8]. The process was
simplified by astutely choosing the arbitrary virtual displacement when all the wrenches
are to equilibrate. For instance, we took as the small displacement the IAK which is
reciprocal to the five workless constraints in Figure 1.
The instrumented knee data for the trunk-sway gait trials for the data sets were
compared to the model prediction. The predicted maximum medial contact force—
642N, which was scaled to subject’s body weight (BW) as 1.01, as referred to in Figure
4. The maximum in vivo medial contact force that was reported ranged from 1.2 to 2.0
BW, typically remaining between 1.2 and 1.7 BW [1]. These results could be an
indicator of our framework performance. During the initial contact of the foot with the
ground (the first 25% of the stance phase in Figure 4), where the muscle contraction is
thought to be passive, the two curves were closely matched.
5. DISCUSSION
Figure 3: Model predictions of the
individual force contributions from
the GRF in terms of the medial
compartment, lateral compartment,
and total muscle force during the
stance phase using the IAK. The
second peak is a result of the
quadriceps identified during actual
measurements and confirmed in this
approach. As a limitation, the
model here was constructed with
only one muscle group.
Figure 4:
A comparison between the results of this
theoretical approach and those data
gathered from an instrumented knee
acquired during trunk-sway gait trials [1].
The force in the medial compartment is
compared between Predicted and
Measured values. As a limitation, the
model applied a single muscle force. Also
note that the magnitude is consistently
lower than the measured entry due to the
lack of inertial effects included for the
lower limb. A similar trend is evident in
both approaches.
The purpose of this study was to obtain the desired reciprocal configuration diagrams
connecting the instantaneous screw to the external reaction in the estimation of
constraint forces. By the careful generation of the knee ISA, the workless constraints are
connected to the IAK with their virtual works being automatically zero, then only the
muscle forces are to equilibrate to the GRF. The connection diagram is very easy to