Biomedical Engineering Reference
In-Depth Information
100% B.W.
F
y
M
z
1 sec
F
x
200 N
Figure 5.11
Force plate record obtained during gait, using a central support type as
shown in Figure 5.10.
themselves. We must first know where the foot is, relative to the midline of
the plate. The type of force plate used to collect these data is the centrally
instrumented pillar type depicted in Figure 5.10. The student should note that
M
z
is positive at heel contact and then becomes negative as the body weight
moves forward. The centers of pressure
X
cp
and
Y
cp
are calculated in absolute
coordinates to match those given in the kinematics listing.
Y
cp
was set at 0
to indicate ground level.
It is very important to realize that these reaction forces are merely the
algebraic summation of all mass-acceleration products of all body segments.
In
other
words,
for
an
N
-segment
system
the
reaction
force
in
the
x
direction is:
N
F
x
=
m
i
a
xi
(5.7)
i
=
1
where:
m
i
=
mass of
i
th segment
a
xi
=
acceleration of
i
th-segment COM in the
x
direction
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