Biomedical Engineering Reference
In-Depth Information
1
Thigh Angle-
q
21
q
21
q
KNEE
-
q
21
-
q
43
2
+
ve
FOR FLEXION
−
ve
FOR EXTENSION
3
Shank Angle-
q
43
q
43
4
90
°
q
ANKLE
-
q
43
-
q
65
+
ve
FOR PLANTARFLEXION
5
+
ve
FOR DORSIFLEXION
q
65
−
q
76
q
MT-PH
-
q
65
-
q
76
6
7
Figure 3.23
Marker location and limb and joint angles using an established conven-
tion. Limb angles in the spatial reference system are determined using counterclockwise
from the horizontal as positive. Thus, angular velocities and accelerations are also pos-
itive in the counterclockwise direction in the plane of movement; this is essential for
consistent convention use in subsequent kinetic analyses. Conventions for joint angles
(which are relative) are subject to wide variation among researchers; thus, the conven-
tion used must be clarified.
shows the outline of a leg with seven anatomical markers in a four-segment
three-joint system. Markers 1 and 2 define the thigh in the sagittal plane. Note
that, by convention, all angles are measured in a counterclockwise direction,
starting with the horizontal equal to 0
◦
. Thus,
θ
43
is the angle of the leg in
space and can be calculated from:
arctan
y
3
−
y
4
x
3
−
θ
43
=
(3.13)
x
4
or, in more general notation,
=
arctan
y
j
−
y
i
θ
ij
(3.14)
x
j
−
x
i
As has already been noted, these segment angles are absolute in the defined
spatial reference system. It is, therefore, quite easy to calculate the joint angles
from the angles of the two adjacent segments.
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