Hoehne-Hückstädt, Ulrike
Ergonomics - Physical Environmental Factors / BG-Institute for Occupational Safety and Health (of HVBG) / Alte Heerstrasse 111/ 53757 Sankt Augustin, Germany 49 (0)2241 231-2633 / ulrike.hueckstaedt@hvbg.de
Ellegast, Rolf
Ergonomics - Physical Environmental Factors / BG-Institute for Occupational Safety and Health (of HVBG) / Alte Heerstrasse 111/ 53757 Sankt Augustin, Germany49 (0)2241 231-2605 / rolf.ellegast@hvbg.deLesser, WernerDepartment 06 Precision- and Micro-EngineeringFachschule / Munich University of Applied Sciences / Lothstr. 34/80335 München, Germany 49 /(0)89 / 1265-1353 / werner.lesser@fhm.edu
ABSTRACT
The purpose of this work is to examine the capability of a newly developed measurement method with regard to measuring and assessing risk factors of work- related musculo-skeletal disorders of the upper limb. The data of body posture and movements is gathered using a person-centred measurement system accompanied by video recordings. The specially designed software allows fast access to the data and their statistical evaluation. In addition to this heart rate and electrical activity of individual muscles of the upper limb are measured. The suitability of the method is tested by applying various evaluation schemes.
Keywords
Measurement method, risk assessment, work-related musculo-skeletal disorders of the upper limb
INTRODUCTION
According to national labour statistics, health-related absenteeism caused by musculo- skeletal disorders have accounted for a nearly constant 30-percent rate in Germany over the last several years. Aside from the physical work load caused by manual materials handling such as lifting and carrying loads, the impacts of lighter repetitive activities are now acknowledged as risk factors for musculo-skeletal disorders,
especially to the upper limb. Measuring the risk factors involved in repetitive activities (frequency, exertion, posture, and lack of recovery) is complicated by the number of parameters which need consideration. Various evaluation schemes described in the literature are available for evaluating the individual parameters and for integrating these parameters into an overall assessment that also reflects the interaction of the different factors.
The present work examines a newly developed measurement method of risk factors by trying to apply the various evaluation schemes to the data.
METHODS
In the framework of an ergonomic intervention study at sewing machine workplaces in different fields of industry, the newly developed, person-centered measurement system named CUELA (computer-supported registration and long-term analysis of musculo-skeletal load) was used to collect data on body posture and movement (spinal column, head, hand-arm system, lower limb) [5]. The CUELA device is composed of electronic angle and angular velocity sensors mounted on several parts of the body.
Table 1 shows the detected body angles in relation to the bodily region and type of sensor.
head inclination, flexion/extension inclinometer cervical vertebrae flexion/extension calculated dorsal vertebrae and lumbar vertebrae (separately) inclination, side inclination, flexion/extension inclinometer, gyroscope pelvis inclination (sagittal) inclinometer, gyroscope hip joint flexion/extension potentiometer knee joint flexion/extension potentiometer scapula depression/elevation, anterior/posterior potentiometer shoulder joint ad-/abduction, inner/outer rotation, flexion/extension potentiometer elbow joint flexion/extension potentiometer forearm pronation/supination potentiometer hand joint radial deviation /ulnar deviation, flexion/extension potentiometer Table 1: Measured body angles and type of sensors in the CUELA device joint/bodily region degree of freedom Sensor
In order to preprocess and to store the data obtained, the measurement system includes a logger with a flash card and its own battery supply worn on the body of the test subject. In this way the CUELA system is able to register movement data with a sampling rate of 50 Hz over several hours, e. g. a whole work shift, at the workplace under real working conditions. The measurements are accompanied by video recordings that were later synchronized with the measurement data. This procedure permits the documentation of workplace conditions at every moment of measurement.
After concluding a measuring period, the data can be easily transferred to a personal computer using the flash card. The specially designed software provides the possibility to display the data as time-angle graphs and as kinematic reconstruction in form of a three-dimensional computerised figure in combination with the corresponding video images at any random time of the measurement; see figure 1.
Figure 1: Visualization of the data
Moreover, the software allows for an export to statistical evaluation.
In addition to this method heart rate and electrical activity of individual muscles of the upper limb were measured and evaluated as benchmarks of bodily strain.
Various evaluation schemes were then selected. In a first step we identified work cycles, which fulfil the conditions of high repetitiveness mentioned by Silverstein et al. [11]. Besides, we tried to verify the repetition by comparing the cycle time and the pattern of the time-angle graphs of successive cycles.
Then the different parameters, such as repetition, awkward and static posture and force were assessed separately. Repetitive movements of the upper limb were counted considering each joint region. Benchmarks gathered from the literature by Kilbom indicated high repetitiveness [8]. The postures were categorised as almost neutral (I = green), middle (II = yellow) or extreme (III = red) range of excursion. Therefore we used values which were derived from International Standard or from often cited literature [4, 7, 9]. Table 2 specifies the defined categories of excursion.
Table 2: Categories of excursion
|
joint |
benchmarks |
|
shoulderflexion: positive values extension: negative values |
green: 0° - 20° yellow: 20° - 60° red: |
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