Improving technical methods for assessment of workplace ergonomic exposure

AbstractBackground: Repetitive work, work performed in awkward and constrained postures and work with excessive or sustained muscular load is common in many occupational settings. Such work is known to be risk factors for developing musculoskeletal disorders in the neck/shoulder region and in arms and hands. One method that can be used to assess the exposure to these risk factors is technical recordings that rely on sensors attached directly to a subject. However, there is a commonly held belief that the methods are time consuming, require expensive equipment and also demand technical knowledge to perform and are therefore not suitable for all. Aims: To simplify the inclinometry method in order to make it easier to use for different actors in the work environment field, and to refine the surface electromyography (sEMG) method of the forearm extensor muscles for more accurate estimates of recorded muscular load. Methods: For the inclinometry method in the laboratory, one model of the new generation of triaxial accelerometers with integrated data loggers (GC inclinometer) were validated against traditional ones (LT inclinometer). Also the deviation angles of two simplified reference postures for upper arms from a standard reference posture were evaluated. For the field study, self-recordings of upper arm elevations were evaluated by analysing each recording twice; once with a simplified reference posture and once with a standard reference posture. For the sEMG method in the laboratory, the electrical activity of right forearm extensor muscles was recorded from four electrode pair positions during two maximal voluntary contractions (MVC; hand grip and resisted wrist extension). In the field study, the electrical activity was recorded using two electrode pair positions and the two MVCs during one working day of hotel room cleaning. Each recording was analysed twice; once with hand grip as reference contraction and once with resisted wrist extension as reference. Results: For the inclinometry method in the laboratory, all group mean absolute differences of simulated work tasks and body parts between the two inclinometers were less than 2.5°. In the field study, the upper arm elevations during work (50th percentile) were almost identical (group mean difference of 0.2°) for the two analyses using different reference postures. For sEMG in the laboratory, resisted wrist extension showed 1.2 – 1.7 times higher EMG amplitudes and lower coefficient of variation than hand grip. In the field study, the workload during cleaning was lower when using resisted wrist extension as the reference than when using hand grip. The workload (99th percentile) was overestimated in two subjects when hand grip was used as reference contraction. Conclusions: For the inclinometry method, the obtained data from the GC inclinometers were fully comparable to the data from the LT inclinometers. The simplified reference posture deviated somewhat from the standard reference, but the effect of this deviation on group recordings of work was negligible. The hotel room cleaners managed to perform self-recordings of upper arm elevations and velocities. For the sEMG, the use of resisted wrist extension may be a more accurate maximal effort of forearm extensor contraction than using hand grip. Problems associated with poorly activated forearm extensors can be overcome by using resisted wrist extension as reference. (Less)