Biomedical Engineering Reference
In-Depth Information
samples over the 100% stride period; we will call this normalized curve
y
.
Therefore, each interval of the normalized curve would be
n/N
samples in
duration. Assume that
n
=
107 samples and
N
=
100. At
N
=
1, we need
the value of the variable at the 1.07
th
sample; thus, by linear interpolation,
2 we need the value at the 2.14
th
y
1
=
0
.
93
x
1
+
0
.
07
x
2
;for
N
=
sample,
3 we need the value at the 3.21
th
or
y
2
=
0
.
86
x
2
+
0
.
14
x
;
for
N
=
sample,
or
y
3
=
0
.
79
x
3
+
0
.
21
x
4
, and so on; for
N
=
99 we need the value at the
105.93
th
sample, or
y
99
=
0
.
07
x
105
+
0
.
93
x
106;
and finally
y
100
=
x
107
.
2.3.3 Measure of Average Variability about the Mean Waveform
The most common descriptive statistical measure of data where a single
measure is taken is the coefficient of variation,
CV
σ
/X
, where
σ
is the
standard deviation and
X
is the sample mean. The CV is a variability to
mean ratio, and with the ensemble average, we wish to calculate a similar
variability score; this score is the average
σ
over the stride period of N points
divided by the average signal (absolute value). Some researchers suggest that
the rms value of the signal replace the absolute value in the denominator, but
this changes the CV scores very little.
=
N
1
N
σ
i
i
=
1
CV
=
(2.20)
N
1
N
1
|
X
i
|
i
=
2.4
REFERENCES
Bobet, J. and R. W. Norman. “Least Squares Identification of the Dynamic Relation
between the Electromyogram and Joint Moment.''
J. Biomech.
23
: 1275 - 1276,
1990.
Brigham, E.O.
The Fast Fourier Transform
. (Prentice-Hall, Englewood Cliffs, N.J.,
1974).
Carpenter, M. G., J. S. Frank, D. A. Winter, and G. W. Paysar. “Sampling Duration
Effects on Centre of Pressure Summary Measures,''
Gait and Posture
13
:35 - 40,
2001.
Gage, W. G., D. A. Winter, and J. S. Frank. “Kinematic and Kinetic Validation of
Inverted Pendulum Model in Quiet Standing,''
Gait and Posture
19
: 124 - 132,
2004.
Nelson-Wong, E., D. E. Gregory, D. A. Winter, and J. P. Callaghan. “Gluteus Medius
Muscle Activation Patterns as a Predictor of Low Back Pain during Standing,''
Clinical Biomechanics
23
:545 -553, 2008.
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