A Full-Body Wireless Wearable UWB-Based Human Motion Capture and Gait Analysis System - E-Healthcare Systems and Wireless Communications - page 439

into the initial-swing phase, the mid-swing and the
terminal swing sub-phases (Medved 2000; Kiss,
Kocsis et al. 2004; Cappozzo, Della Croce et al.
2005; Ferrari, Benedetti et al. 2008; Joseph 2008).
Essentially, this phase represents the recovery of
the limb in preparation for the next contact with
the ground.
Sophisticated measurement systems employ
optical tracking systems to track the displace-
ment of markers 2 placed at particular anatomical
sites on the limb segments (Kiss, Kocsis et al.
2004; Cappozzo, Della Croce et al. 2005; Ferrari,
Benedetti et al. 2008). Standard gait analysis is
based on either optical, magnetic, or ultrasound
motion tracking systems. These systems allow for
the assessment of a complete three-dimensional
kinematic analysis of the human movement (Kiss,
Kocsis et al. 2004; Corrales, Candelas et al. 2008).
Measurements with quite large random errors
can result in meaningful conclusions in clinical
research, but are not valid for clinical testing.
For instance, for the base-of-support (BOS) 3 , the
reported measurement accuracy is not sufficiently
high to be clinically accepted. It is equal to 8.5
cm for normal adults, and the reported error is
1.17 cm, thus the relative error is ≈ 14.6% (Menz,
Latt et al. 2004; Barker, Freedman et al. 2006).
Abnormalities in the BOS are observed in older
people, children with Down's syndrome, and
people with Parkinson's disease 4 . In particular,
people that suffer from the Parkinson's disease
have narrower BOS than normal people (Menz,
Latt et al. 2004; Barker, Freedman et al. 2006;
Carpinella, Crenna et al. 2007). Thus, the accuracy
and reliability of the BOS measurement needs to
be addressed, as it is one of important parameters
to clinicians. Moreover, its measurement requires
a certain level of accuracy that is not provided by
current measuring systems.
The choice of a suitable measurement system
is controlled by multiple factors, such as the ac-
curacy and reliability, cost, and power consump-
tion. Optical tracking systems are based on the

use of charge-coupled device CCD-cameras and
a set of markers attached to the subject's body,
where the markers positions are estimated via the
triangulation of the position and orientation of
two or more cameras (Cappozzo, Della Croce et
al. 2005; Corrales, Candelas et al. 2008). Optical
systems are accurate and use high sampling rates,
which enables acquiring real-time data. The main
disadvantage of these systems is that they require
dedicated laboratories, complex settings, and
highly skilled operators. In addition, they have
the line-of-sight (LOS) restriction, where if the
marker is not detected by at least two-cameras its
position is not recorded (Cappozzo, Della Croce
et al. 2005). Other systems include motion sen-
sors attached to the human body that enable direct
detection of motion. There are several types of
sensory motion tracking systems, such as the me-
chanical, magnetic, and inertial tracking systems.
Mechanical systems employ electromechanical
transducers attached to the subject's body, where
the motion is detected through the voltage varia-
tions. On the other hand, magnetic motion tracking
systems use active transducers (Kiss, Kocsis et al.
2004; Cappozzo, Della Croce et al. 2005; Corrales,
Candelas et al. 2008). These systems are accurate
and do not have the LOS restriction. However,
the performance of these systems suffers from
the interference from magnetic materials in the
surroundings. For the inertial tracking systems,
they are based on gyroscopes and accelerometers
(Cappozzo, Della Croce et al. 2005; Corrales,
Candelas et al. 2008). Inertial sensors have the
advantage of being self-contained, can be sampled
at high rates, and do not have the LOS restriction.
Nevertheless, these systems have the disadvan-
tage of error accumulation over time. A possible
solution for a more accurate and reliable tracking
is to use hybrid systems (Corrales, Candelas et
al. 2008; Rodriguez-Silva, Gil-Castineira et al.
2008). However, current motion tracking systems
are expensive, and hybrid systems are expected
to be more expensive.