Biomedical Engineering Reference
In-Depth Information
C7
T2
T4
T6
T8
T10
T12
T2
Original Data
Exponential Approx.
L4
−
80
−
60
−
40
Shift (ms)
−
20
0
Figure 2.8
Phase shift (ms) of the activation profiles of the paraspinal muscles relative
to the profile at the L
4
level. The negative shift indicates the activation was in advance of
L
4
. The curve fit was exponential. (Reproduced by permission from
Gait and Posture
)
et al. (2008) reported a study of left and right gluteus medius patterns during
a long duration standing manual task. Because these patterns are an excellent
example of motor synergies and are also related to another medial/lateral
postural strategy their details are presented in Chapter 11.
2.2
FREQUENCY ANALYSIS
2.2.1 Introduction — Time Domain vs. Frequency Domain
All the signals that we measure and analyze have a characteristic frequency
content, which we refer to as the signal spectrum; this is a plot of all the
harmonics in the signal from the lowest to the highest. The purpose of this
section is to provide a conceptual background with sufficient mathematical
derivations to help the student collect and process data and be an intelligent
collector and consumer of commercial software. Frequency domain analysis
uses a powerful transform called the Fourier transform, named after Baron
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