See discussions, stats, and author profiles for this publication at: https://www.researchgate.net/publication/6441258
`
`Clinical Applications of Sensors for Human Posture and Movement Analysis: A
`Review
`
`Article(cid:160)(cid:160)in(cid:160)(cid:160)Prosthetics and Orthotics International · April 2007
`
`DOI: 10.1080/03093640600983949(cid:160)·(cid:160)Source: PubMed
`
`CITATIONS
`181
`
`3 authors, including:
`
`Wai Yin Wong
`
`Institute of Vocational Education
`
`7 PUBLICATIONS(cid:160)(cid:160)(cid:160)485 CITATIONS(cid:160)(cid:160)(cid:160)
`
`READS
`5,529
`
`M. S. Wong
`
`The Hong Kong Polytechnic University
`
`64 PUBLICATIONS(cid:160)(cid:160)(cid:160)1,408 CITATIONS(cid:160)(cid:160)(cid:160)
`
`SEE PROFILE
`
`SEE PROFILE
`
`All content following this page was uploaded by M. S. Wong on 25 November 2015.
`
`The user has requested enhancement of the downloaded file.
`
`1
`
`APPLE 1037
`
`

`

`Prosthetics and Orthotics International
`March 2007; 31(1): 62 – 75
`
`Clinical applications of sensors for human posture
`and movement analysis: A review
`
`WAI YIN WONG, MAN SANG WONG, & KAM HO LO
`
`Department of Health Technology and Informatics, The Hong Kong Polytechnic University, Hong Kong,
`China
`
`Abstract
`Measurement of human posture and movement is an important area of research in the bioengineering
`and rehabilitation fields. Various attempts have been initiated for different clinical application goals,
`such as diagnosis of pathological posture and movements, assessment of pre- and post-treatment efficacy
`and comparison of different treatment protocols. Image-based methods for measurements of human
`posture and movements have been developed, such as the photogrammetry, optoelectric technique and
`video analysis. However, it is found that these methods are complicated to set up, time-consuming to
`operate and could only be applied in laboratory environments. Electronic sensors and systems with
`advanced technology, namely accelerometer, gyroscope, flexible angular sensor, electromagnetic
`tracking system and sensing fabrics, have been developed and applied to solve the relevant application
`problems of the image-based methods. Nonetheless, other problems for using these electronic sensors
`emerged, including the environment influence and signal extraction difficulties. Further development of
`these electronic sensors and measurement methods could enhance their clinical applications in
`institutional as well as community levels. This article reviews the possible applications of these electronic
`sensors and systems, and precautions of their applications in analysis of human posture and movement.
`Such information would help researchers and clinicians in selecting and developing the most appropriate
`measurement techniques of using the electronic sensors for clinical applications of human posture and
`movement analysis.
`
`Keywords: Sensors, human posture and movement, review
`
`Introduction
`
`Measurement of human posture and movement is an essential area of research in the
`bioengineering and rehabilitation fields. It
`is motivated by different goals in clinical
`application, such as in comparing normal movements with pathological movements, planning
`and evaluating treatment protocols, and evaluating design of orthosis and prosthesis. Human
`postures and movements have been measured by using different image-based methods
`including photogrammetry (Weissman 1968; Bullock and Harley 1972; Thometz et al. 2000;
`Liu et al. 2001), optoelectric analysis (Pearcy et al. 1987; Dawson et al. 1993; Gracovetsky
`et al. 1995), and video analysis (Robinson et al. 1993; Masso and Gorton 2000; Nault et al.
`2002; Engsberg et al. 2003). The characteristics of different image-based methods were
`
`Correspondence: Allison W. Y. Wong, Department of Health Technology and Informatics, The Hong Kong Polytechnic University,
`Hung Hom, Kowloon, Hong Kong, China. Tel: þ852 2766 7667. Fax: þ852 2362 4365. E-mail: allison.wong@polyu.edu.hk
`
`ISSN 0309-3646 print/ISSN 1746-1553 online Ó 2007 ISPO
`DOI: 10.1080/03093640600983949
`
`2
`
`

`

`Clinical applications of sensors for posture and movement analysis
`
`63
`
`summarized by Hsiao and Keyserling (1990). Photogrammetric systems have been used to
`record two- or three-dimensional image of posture. This type of system uses either light-
`reflective markers or light-emitting diodes affixed to the human body, and captures data with
`cameras and films for measuring the orientation of body segments through data reduction
`processing. Optoelectric analysis applies the same principles as photogrammetric system to
`measure the position of joints and body segments. The optoelectric sensing unit is used for
`collecting the data instead of films. Video systems also use the similar basic principles as both
`photogrammetric and optoelectric systems but capture data with optoelectric units or cameras
`of higher sampling rate. These systems can be used to capture and record three-dimensional
`body movements. The availability of these image-based methods has helped to achieve the
`goals of monitoring and analysing human posture and movement. However,
`inherent
`limitations of these methods, which are complicated to set up, time-consuming to operate,
`and limited to the laboratory environment (Hsiao and Keyserling 1990), so the chance of
`using these methods in the clinical applications are restricted. In recent years, low-powered
`and miniaturized electronic sensors, which are for use in robotic, industrial, aerospace and
`biomedical applications, have been developed by using advanced electronic circuit
`technology. The use of these electronic sensors has been considered as alternative methods
`for human posture and movement analysis in clinical applications. The purpose of this article
`is to review the possible clinical applications of different types of electronic sensors and
`systems, and their problems and limitations which are faced in the human posture and
`movement measurements. Such information would help researchers and clinicians in
`developing and selecting the most appropriate measurement
`techniques of using the
`electronic sensors for clinical applications of human posture and movement analysis.
`
`Electronic positional sensors and systems
`
`Five types of electronic positional sensors and systems for tracking human posture and
`movement are reviewed in this article, namely accelerometer, gyroscope, flexible angular
`sensor, electromagnetic tracking system and sensing fabric.
`
`Accelerometer
`
`Accelerometer is a type of positional sensor operated by measuring acceleration along the
`sensitive axis of the sensor based on Newton’s second law (Force ¼ Mass 6 Acceleration).
`Most accelerometers use a sensing method as a proof mass excited in a mass-spring-damper
`system as shown in Figure 1 (Gardner 1994; Westbrook 1994).
`There are three common types of accelerometers, namely piezoelectric, piezoresistive and
`capacitive types. The characteristics of these types of accelerometers are shown in Table I
`(Westbrook 1994). In general, the capacitive accelerometers have higher stability, sensitivity
`and resolution than piezoresistive ones (Gardner 1994). The measured acceleration of
`piezoresistive and capacitive accelerometers consists of
`two components,
`including a
`gravitational component and a component from other acceleration force (Bouten et al.
`1997; Mathie et al. 2001; Westbrook 1994). During static acceleration, accelerometers can
`function as inclinometers for measuring inclination or tilting angle with respect to axis of the
`gravitational field. The piezoresistive and capacitive accelerometers are suitable for measuring
`human posture and movement because they can provide dual acceleration components.
`Commercial accelerometers are now available in the market. One of
`the surface-
`micromachined capacitive accelerometers (Analog Devices, Model: ADXL203) is shown in
`Figure 2.
`
`3
`
`

`

`64
`
`W. Y. Wong et al.
`
`Figure 1. Basic layout of accelerometer. In the mass-spring-damper system, the loading force drives a second order
`damped harmonic oscillator, where the displacement of the proof mass relative to the rigid frame is considered
`(Gardner 1994). Under a constant acceleration condition, the displacement is directly proportional to the given
`acceleration.
`
`Table I. Comparison of different accelerometer types (Westbook 1994).
`
`Piezoresistive
`
`Parameters
`
`Piezoelectric
`
`Silicon
`
`Thick film
`
`Capacitive
`
`Gravitational component
`Bandwidth
`Self-generating
`Impedance
`Signal level
`Temperature range (8C)
`Linearity
`Static calibration (turnover)
`Cost
`Ruggedness
`Suitable for shock
`
`No
`Wide
`Yes
`High
`High
`755 to 100
`Good
`No
`High
`Good
`Yes
`
`Yes
`Moderate
`No
`Low
`Low
`755 to 150
`Moderate
`Yes
`Low
`Moderate
`No
`
`Yes
`Low
`No
`Low
`Low
`750 to 120
`Moderate
`Yes
`Low
`Moderate
`No
`
`Yes
`Wide
`No
`Very high
`Moderate
`7200 to 200
`Excellent
`Yes
`High
`Good
`No
`
`The reliability and accuracy of accelerometers should be evaluated before applying them to
`measure human posture and movement. Hansson et al. (2001) found that the angular error of
`a tri-axial accelerometer system is 1.38, the reproducibility is 0.28, and the inherent angular
`noise is 0.048 and its operation is independent of the orientation of the device. This finding
`could demonstrate technological advancements and their potential for clinical applications. It
`is likely that sensors with the capacity to quantify dynamic accelerations and some features like
`low-power consumption and small size could be suitable for the objective assessment of body
`posture and movement in daily activities.
`
`Gyroscope
`
`Gyroscope is an angular velocity sensor which is commonly used for measurement of human
`posture and movement. It is generally based on the concept of measuring the Coriolis force of
`
`4
`
`

`

`Clinical applications of sensors for posture and movement analysis
`
`65
`
`vibrating devices (Senturia 2001). Coriolis force is an apparent force that arises in a rotating
`reference frame. It is proportional to the angular rate of rotation. A simple model for analysing
`gyroscope behaviour is shown in Figure 3. The angular orientation can then be obtained from
`integration of the gyroscopic signal (Senturia 2001). One type of commercial gyroscope that
`has been considered for measuring human posture and motion analysis is shown in Figure 4
`(Aminian et al. 2002; Sabatini et al. 2005).
`
`Flexible angular sensor
`
`Flexible angular sensor is not a type of inertial sensor as the aforementioned sensors. It is
`operated by measuring change of electrical output or displacement with respect to angular
`change. However, it may be applicable for measurement of movements between human body
`segments.
`Strain gauges have been used in flexible electro-goniometer for angle measurement
`in clinical use (Nicol 1987). The device produces a linear relationship between electrical
`output and the subtended angle between one encapsulated end and the other. Flexible
`
`Figure 2. Photo of a capacitive accelerometer (Analog Devices, Model: ADXL203, Size: 56562 mm).
`
`Figure 3. A simple model for analysing gyro behaviour. A single mass is suspended by four springs in x and y
`directions. The frame is presumed to rotate about the z-axis. Assuming small-amplitude motions which will be true in
`resonant gyroscopes, the x-motion and y-motion can be coupled only through the Coriolis-force term and the term
`involving angular acceleration. The Coriolis force then induces motion in the third direction which is perpendicular
`both to the direction of rotation and to the driven motion.
`
`5
`
`

`

`66
`
`W. Y. Wong et al.
`
`Figure 4. Photo of a piezoelectric vibrating gyroscope (Murata, Model: ENC-03J, Size: 15.56864.3 mm).
`
`electro-goniometer is available commercially (Penny and Giles, Blackwood, UK) for
`measurement of posture and spinal motion in two planes (sagittal and coronal planes). It
`consists of two lightweight plastic end-blocks which are separated by a flexible spring.
`A mechanical flexible device was developed with different mechanism by Roduit et al.
`(1998), using a pair of wires to measure bending angles. The wires were anchored at one end.
`The angular change could be collected and calculated by measuring the displacement
`between the ends of two wires during bending along different paths.
`
`Electromagnetic tracking system
`
`Electromagnetic tracking system is a three-dimensional measurement device that has been
`used in human posture and movement analysis. In general, the system consists of a
`transmitter and receivers. A low-frequency magnetic field is generated by the transmitter
`and detected by the receivers. The positions and orientations of the receiver relative to the
`transmitter can be calculated by the system. Systems with similar design are commercially
`available for kinematics studies in movements in different body segments, including upper
`limbs (Finley and Lee 2003; Ramanathan et al. 2000) and spine (Bull and McGregor
`2000; Lee 2001; Mannion and Troke 1999; Pearcy and Hindle 1989; Willems et al.
`1996).
`
`Sensing fabric
`
`Knitted stretch fabrics sensors have been introduced for detecting the posture and movement
`of the users. The operational concept of this type of sensor is to measure the changes of
`resistance in knitted strips. It gives a linearly increasing asymptotic resistance when it is
`stretched, up to almost maximum stretch (Farringdon et al. 1999). De Rossi et al. (2000)
`developed a minimally intrusive wearable system consisting of a Lycra leotard with conductive
`polymer strain sensors chemically deposited in selected areas. A wet process included in the
`direct deposition of polypyrrole layers onto fibres with a mask based procedure for appropriate
`patterning of the sensorized areas. Other combinations of materials and polymers were used
`to optimize the response time of the sensors. Scilingo et al. (2003) postulated that polymeric
`conductors and semiconductors offer several advantages with respect to metal and inorganic
`conductors: lightness, large elasticity and resilience, resistance to corrosion, high flexibility,
`impact strength, etc. Because of its elasticity, ergonomic comfort, and high piezoresistive and
`thermoresistive coefficients, the combination of polypyrrole as conducting polymer and
`Lycra/cotton as fabric is particularly effective.
`
`6
`
`

`

`Clinical applications of sensors for posture and movement analysis
`
`67
`
`Clinical applications
`
`The previously introduced electronic positional sensors have been found in various clinical
`applications including the analyses of general physical activity, gait, posture, trunk and upper
`limb movement.
`
`General physical activity analysis
`
`Several studies used both ‘‘acceleration vector’’ and ‘‘gravitational vector’’ components of the
`signals of accelerometers to analyse the static and dynamic activities of the subjects. The static
`and dynamic activities could be discriminated, and the postures and the orientations of body
`segments could also be detected (Bouten et al. 1997; Fahrenberg et al. 1997; Foerster et al.
`1999; Lyons et al. 2005; Mathie et al. 2001; Veltink et al. 1993; 1996). Therefore, the
`accelerometer was found to be useful for physical activity monitoring in everyday life.
`
`Gait analysis
`
`In 1973, Morris suggested an accelerometry technique to study the movement of shank, using
`accelerometers. The angular velocity, angle, translational acceleration, velocity and position
`of the shank in walking were assessed. The findings showed that accelerometers could be used
`to provide sufficient information to define the movement of the body segment in gait analysis.
`In recent years, accelerometers have been miniaturized in size and advanced in circuit
`technology to improve reliability. Several locomotion studies have tried to use accelerometers
`to determine the stages of lower limb movement in gait analysis (Veltink and Franken 1996;
`Veltink et al. 1998; Willemsen et al. 1991). The accelerometers were usually mounted on the
`thigh and shank. In addition, the use of accelerometer on the trunk for gait analysis was
`pursued. Villanueva et al. (2002) studied an electronic instrument with accelerometers for
`monitoring the trunk trajectory of human body walking on a treadmill. A pair of uniaxial
`accelerometers was affixed to the waist of the subject at the level of the second sacral vertebra
`with an elastic belt. The instrument was able to assess gait cycle time and the number of
`walking steps from measured trunk acceleration. This study demonstrated that the feasibility
`of using accelerometers for studying the kinematics of human lower limbs and trunk during
`locomotion. The accelerometer could be considered as a component of a portable instrument
`used for studying standing balance and temporal gait parameters in both experimental and
`clinical environment. Its operation is simple and the disturbance in gait could be minimized.
`It could be applied to different potential patient groups including post-stroke and cerebral
`palsy.
`Miniaturized gyroscopes have been employed for measuring lower limb movement in
`walking. Tong and Granat (1999) investigated the possibility of using uniaxial gyroscopes to
`develop a practical gait analysis system by evaluating the angular parameters derived from the
`gyroscope with motion analysis system, and described solutions for solving the problem of
`gyroscope’s signal drifting. The results showed that the knee joint angles derived from
`the gyroscopes was highly correlated (correlation coefficient ¼ 0.93) with those from motion
`analysis system, and the correlation has been further upgraded (correlation coefficient ¼ 0.98)
`by using a high-pass filter to correct the drift of the knee angle. This confirmed the feasibility
`of using the gyroscopes to measure angular parameters in gait analysis. Aminian et al. (2002)
`described an ambulatory system with miniaturized gyroscopes to estimate spatio-temporal
`parameters during long periods of walking. The gyroscopes were attached on the thigh and
`shank. The system errors for velocity and stride length estimations were 0.06 m/s and 0.07 m
`
`7
`
`

`

`68
`
`W. Y. Wong et al.
`
`respectively and these accuracies were not high enough in measuring spatio-temporal
`parameters in clinical gait analysis and should be improved further before routine
`applications. Tsuruoka et al. (1999) suggested a method to evaluate human movement
`stability by analyzing the relative power contribution in head, trunk and pelvic movement
`derived from the measured signals of gyroscopes during walking. By analysing the relationship
`of the three body parts, it could provide useful information for planning treatment protocols
`for hemi-paresis patients.
`In order to collect more information at the same time, some research studies made use of a
`combination of accelerometer and gyroscope to form a measuring system. Wu and Ladin
`(1999) used this combination to study the kinematics variables of
`lower limb during
`locomotion. The system directly measured the linear displacement, angular velocity, and
`linear acceleration of the lower limb segments, and identified the heel strike transients.
`Sabatini et al. (2005) used the combined sensing unit affixed to the foot instep to estimate
`spatio-temporal gait parameters. The signals of the accelerometer were modeled and double-
`integrated to obtain the position of the foot. The gyroscope was used to measure angular
`velocity for assessing the sagittal orientation of
`the foot
`to remove the gravitational
`contribution of the accelerometer signals before applying the integration. The measured
`walking speed and inclination, which derived from signals of the system, were comparable to
`the preset treadmill speed and inclination.
`Apart from inertial sensors, mechanical flexible angular sensing device was applied to
`measure knee angles during walking (Roduit et al. 1998). Roduit’s research team used the
`captioned device to compare against a conventional goniometer in testing real conditions by
`binding it on the leg of the subject. The measured accuracy of the system was +28 on a stroke
`of 1008. It also achieved a resolution of less than 0.18 and the temperature dependence of less
`than 0.28/C. It was possible to recognize clearly the different phases of gait cycle. The possible
`source of error in the results may be due to the misalignment of the flexible sensor and
`conventional goniometer, and the instruments shift during the walking. However, it is a
`potential portable system for ambulatory monitoring due to its small size and sturdiness, and
`it can be easily fastened on a leg.
`
`Posture and trunk movement analysis
`
`Several commercial systems have been applied to measure posture and trunk motions. One of
`these systems, commercial electromagnetic tracking systems, has been employed in some
`research studies of posture and trunk motion analysis (Bull and McGregor 2000; Lee 2001;
`Mannion and Troke 1999; Pearcy and Hindle 1989; Willems et al. 1996). In 1989, Pearcy
`and Hindle demonstrated that electromagnetic tracking system could provide high resolution
`accuracy (error less than 18) and repeatability (less than 0.28) in spinal motion analysis. In the
`experimental setup, the receivers were attached on the body segment and the transmitter was
`placed in a fixed position within specific operational zone. The accuracy of the measurement
`was affected by the distance between the transmitter and receivers. The separation of receivers
`from the electromagnetic transmitter was recommended to be between 271 and 723 mm in
`order to have an optimal operational zone for minimizing error by Bull and McGregor.
`(2000). However, this would depend on the specification of the system. Therefore, the
`experimental setup and design are limited and cannot be used to take measurements in
`activities such as walking and lifting.
`Besides commercial electromagnetic tracking system, non-commercial portable electro-
`magnetic system has been developed to measure human physical trunk features, e.g.,
`shoulders tilting (Lou 1998). The system was combined with a feedback unit to provide a
`
`8
`
`

`

`Clinical applications of sensors for posture and movement analysis
`
`69
`
`signal to the scoliotic children for informing them to adjust their posture. The accuracy of the
`system was evaluated by comparing the measurement from the images of the back. The results
`demonstrated that the accuracy of the system could be 5 mm for the distance measurement in
`the distance 300 – 480 mm and 58 for angle measurements from 0 – 908 (Lou et al. 1999,
`2000). The authors concluded that the portable electromagnetic tracking system could be
`used for measuring the shoulders asymmetry and detecting the postural changes. This
`portable design could be used in more clinical applications if the accuracy of this device is
`comparable to the commercial products.
`The use of commercial flexible electro-goniometer to provide continuous quantitative
`information on lumbar spinal motion has been reported by Boocock et al. (1994) and
`Thoumie et al. (1998). The electro-goniometer was directly attached onto the surface of the
`lower back. The findings of Boocock’s team showed that the measurements on the lumbar
`sagittal motion were comparable with those measured by a fluid-filled inclinometer or a
`flexicurve. Thoumie et al. (1998) compared the results of radiography with the electro-
`goniometer in measuring lumbar curvature and motion change during flexion-extension of
`the spine. Although the measurements of electro-goniometer were not comparable with the
`value of radiographic data in lumbar curvature and range of motion, the device could provide
`quantitative information of lumbar sagittal motion in continuous measurement and was
`recommended for use in a variety of occupational and recreational environments (Boocock
`et al. 1994). The inherent limitations of the flexible strain-gauged electro-goniometer should
`be considered in its application. The flexible strain gauge of the commercial electro-
`goniometer may be susceptible to bending or buckling during studies of seated tasks with
`lumbar support (Boocock et al. 1994). The measurement range of the spinal motion could be
`limited by exceeding the maximum preset distance between the two attachments with linear
`displacements occurring during flexion and extension of the lumbar spine.
`Non-commercial accelerometer system with one accelerometer was developed by Lou et al.
`(2001) for posture monitoring and training. The sensor was attached to the upper trunk of a
`kyphotic subject. It was claimed to be capable of detecting the postural change of thoracic
`spine. In fact, using one accelerometer on the trunk could only provide measurement of the
`trunk tilting but could not give enough information for posture training to patients with
`hyperkyphosis. Therefore, more accelerometers should be used on different body segments as
`reference points such as lower thoracic, lumbar or pelvic region to collect more postural
`information. Nevins et al. (2002) made use of six accelerometers for continuous monitoring
`of spinal posture on the sagittal plane. Spinal posture was measured during daily activities by
`positioning accelerometers along the vertical axis of the spine on the mid-sagittal plane.
`Although more sensors could provide more information about the orientation of spine, their
`disturbance of trunk movement should not be neglected. A comprehensive consideration
`could give a more practical design in posture sensing system for daily activities.
`Moreover, a combination of accelerometer and gyroscope has been considered to be
`applied in tracking the pattern of trunk movement. Seo and Uda (1997) monitored the low
`back risk imposed by asymmetric posture at workplaces using detectors which consisted of
`gyroscopes and accelerometers, and compared with the data measured by motion analysis
`system. Trunk rotation could be calculated from the angular velocities and inclination
`measured at both the waist and shoulder. There was a high correlation in angular velocity
`between the two methods for the model tasks of box transfer (correlation coefficient ¼ 0.949)
`and box lifting (correlation coefficient ¼ 0.815) respectively. This design demonstrated a
`practical use for monitoring trunk rotation in terms of angular velocity and repeated pattern of
`trunk motion. Ochi et al. (1997) evaluated the trunk motions of stroke patients, cerebral palsy
`patients and normal subjects in walking. Three sensing units were put on top of the head,
`
`9
`
`

`

`70
`
`W. Y. Wong et al.
`
`spinous processes of T1 and S1 for measuring the motion of the head, trunk and pelvis
`respectively. The results suggested the feasibility of using gyroscopes and accelerometers in
`detecting walking characteristics before and after treatment.
`The use of gyroscopes was not only combined with accelerometer. Lee et al. (2003)
`described a method of using an inertial tracking device to measure three-dimensional
`movement patterns of the lumbar spine in real time, which consisted of gyroscopes, and also
`with gravitometers and magnetometers. The additional sensors rather than gyroscopes were
`used to sense the gravitational and magnetic fields of the earth respectively, which could
`provide additional information for eliminating drift of gyroscopes. One sensing unit of the
`system was placed over the spinous process of L1 and the second sensor over the sacrum. The
`results of
`this study showed that
`the reliability of gyroscope measurement was high
`(correlation coefficient ranged from 0.972 – 0.991) in motions of the anatomical planes. The
`findings showed that the inertial tracking device could be a reliable tool
`for clinical
`measurement as well as biomechanical investigations.
`Sensors with more flexibility,
`‘‘sensing fabrics’’, were also shown to be possible for
`tracking the posture and movement of the body segments. De Rossi et al. (2000) used up
`to 20 sensors which were deposited onto fabrics by using a wet process. Each appropriate
`set of sensors was mapped in different parts of body such as vertebral column, scapular
`segment, gleno-humeral and elbow joints to detect posture and movement of the trunk.
`The movements of the body segments were determined by measuring changes of relative
`resistance. It could minimize disturbance in movement measurement and be utilized for
`long-term application due to its flexibility. Sensing fabrics could be employed in
`rehabilitation by embedding them into garments or gloves for physical exercise monitoring
`and evaluation for the patients with stroke, cerebral palsy, postural disorders or instability.
`However,
`the accuracy of
`the sensing fabrics in the measurement of human body
`movement depends on the calibration methods because the electrical resistance of the
`fabrics varies with orientation, stress and temperature. Therefore, a well developed
`calibration process is essential
`for the development of sensing fabrics in posture and
`movement measurements.
`
`Upper limb movement analysis
`
`Commercial electromagnetic tracking systems have been used for measuring upper limb
`movements (Finley and Lee 2003; Ramanathan et al. 2000). A sensorized glove was
`developed by De Rossi et al. (2001), who used elastic textile fibres and strain sensors to
`monitor movement of hand segments. Van Someren (1996) suggested using an accelerometer
`to measure the duration and intensity of wrist movement in patients with Parkinson’s disease.
`This study demonstrated that accelerometers are appropriately sensitive to the age-related
`decrease in activity and a continuous assessment of wrist movements and rest activity rhythm
`of aging patients with either Alzheimer or Parkinson’s disease. Veltink et al. (1997) used tri-
`axial accelerometers to measure the cyclic movement of the forearm in terms of angle rather
`than frequency for providing objective continuous assessment of the momentary severity of
`bradykinesia (defined as the slow execution of movement) over a long period of time. The
`feasibility of using accelerometers for kinematic analysis was established in the assessment of
`bradykinesia for near static circumstances. The devices in the above two studies were
`designed as wrist-watch format which could facilitate long-term assessment during daily
`activity. Therefore, accelerometers have demonstrated its clinical value for continuous
`assessment and evaluation of tremor in different parameters to provide more information for
`clinicians to plan for treatment protocol.
`
`10
`
`

`

`Clinical applications of sensors for posture and movement analysis
`
`71
`
`Summary of the sensor applications
`
`Tables II and III are the summaries of the sensors’ applications and measured parameters in
`different studies respectively. Accelerometer tends to be the most commonly used and has the
`widest range of applications on different body parts among the five types of sensors.
`
`Limitations of different sensors
`
`From the literature, it was found that the electronic positional sensors have many attractive
`advantages such as miniature in size, lower power consumption and portable. However, there
`are typical limitations and problems of different sensors in the application of human posture
`and movement analysis.
`
`Environment effects
`
`Signals of sensors would be affected by the surrounding environments. In the case of sensing
`fabric, its signals could be affected by humidity and temperature (Scilingo et al. 2003). The
`major limitation of accelerometers is the detection of rotational angle around the axis of
`gravity that is the basic operation theory of the accelerometer (Hansson et al. 2001).
`In the electromagnetic system, the accuracy can be adversely affected by the presence of
`metallic objects. Lou et al. (2000) found that metallic interference occurred when a metal
`object was placed within 100 mm of the transmitter or the receiver of the system. The
`resolution of the system was affected by the distance between the transmitter and the receiver,
`the smaller distance between them, the better the resolution (Lou 1998; Lou et al. 1999,
`2000). The transmitter and receivers of the electromagnetic tracking system should be set
`within the optimum operation zone based on the specification of each system. As such, the
`electromagnetic system would be used only in the prepared environment (such as clinic or
`laboratory) without any metallic interference. Therefore, it is not suitable for the patient with
`metallic implants and prostheses, and the experimental environment should be free from
`metallic objects.
`the flexible strain-gauged electro-goniometer should be
`limitations of
`The inherent
`considered in its application. The flexible strain gauge may be susceptible to bending or
`buckling during studies of seated tasks with lumbar support (Boocock et al. 1994). The
`measurement range of the spinal motion could be limited by exceeding the maximum preset
`distance between the two attachments with linear displacements occurring during flexion and
`extension of the lumbar spine.
`
`Table II. Summary of applications of different sensors.