Biomedical Engineering Reference
In-Depth Information
The negative sign is associated with hip adduction of the left thigh or hip abduction of
the right thigh.
Further substitution of values of
f
g
and
f
g
into Eqs. (4.33) and (4.34) yields
e
pa
e
ta
20
hip internal-external rotation y
z
¼
hip flexion-extension y
y
¼
8
For hip internal-external rotation, the negative sign is associated with hip internal rotation
of the left thigh or hip external rotation of the right thigh. A negative hip flexion-extension
angle corresponds to hip extension, independent of side. This process may be repeated for
other body segments such as the shank (lower leg), foot, trunk, arms, and head with the avail-
ability of properly defined anatomical coordinate systems.
4.6.3 Kinetic Data Analysis
The marker displacement or motion data provide an opportunity to appreciate segment
and joint kinematics. Kinematic data can be combined with ground reaction data—that is,
forces and torques and their points of application, which are referred to as the centers of
pressure. Combined with estimates of segment mass and mass moments of inertia, the
net joint reaction forces and moments may then be computed.
To illustrate the details of this computational process, consider the following determina-
tion of the reactions at the ankle (Figure 4.30) for an individual with mass of 25.2 kg. Data
for one instant in the gait cycle are shown in the following table.
Symbol
Units
x
lab
y
lab
z
lab
Ankle center location
A
[m]
0.357
0.823
0.056
Toe marker location
T
[m]
0.421
0.819
0.051
Center of pressure location
CP
[m]
0.422
0.816
0.000
Ground reaction force vector
F
g
[N]
3.94
15.21
242.36
Ground reaction torque vector
T
g
[N-m]
0.000
0.000
0.995
Foot anatomical coordinate system
e
fax
0.977
-0.0624
0.202
e
fay
0.0815
0.993
0.0877
e
faz
0.195
0.102
0.975
[m/s
2
]
Foot linear acceleration vector
a
foot
2.09
0.357
0.266
Foot angular velocity vector
v
foot
[rad/s]
0.0420
2.22
0.585
[rad/sec
2
]
Foot angular acceleration vector
a
foot
0.937
8.85
5.16
Ankle angular velocity vector
v
ankle
[rad/s]
0.000759
1.47
0.0106
Anthropomorphic relationships presented in Table 4.1 are used to estimate the mass and
mass moments of inertia of the foot, as well as the location of its center of gravity. The mass
of the foot,
m
foot
, may be estimated to be 1.45 percent of the body mass, or 0.365 kg, and the
location of the center of gravity is approximated as 50 percent of the foot length. The length
