PHYSICAL WORKLOAD AS A RISK FACTOR FOR SYMPTOMS IN THE NECK AND UPPER LIMBS: EXPOSURE ASSESSMENT AND ERGONOMIC INTERVENTION^*

^*Doctoral dissertation presented on Friday 12^th September 2003 at the the Faculty of Medicine of the University of Kuopio, Finland, by permission of the Faculty of Medicine of the University of Kuopio, Finnish Institute of Occupational Health, Helsinki, Finland.

The aims of this study were to investigate work related and individual factors as predictors of insident neck pain among video display unit (VDU) workers, to assess the effects of an ergonomic intervention and education on musculoskeletal symptoms, and to study the repeatability and validity of an expert assessment method of VDU workstation ergonomics. A method to assess the risk factors for upper limb disorders was developed, and its validity and repeatability were studied.

The annual incidence of neck pain was 34.4%. A poor physical work environment and placement of the keyboard were work-related factors increasing the risk of neck pain. Among the individual factors, female sex was a strong predictor.

The randomized intervention study included questionnaire survey, a diary of discomfort, and ergonomic rating of the workstations. The subjects (n=124) were allocated into three groups. The intensive and the education groups had less musculoskeletal discomfort than the control group at the 2-month follow-up. After the intervention, the level of ergonomics was distinctly higher in the intensive ergonomic group than in the education or control group.

Two experts in ergonomics analyzed and rated the ergonomics of workstations before and after intervention. The validity of the assessment method was rated against the technical measurements, assessment of tidiness and space, and work chair ergonomics. The intraclass correlation coefficient between ratings of the two experts was 0.74. Changes in the location of the input devises and the screen, as well as the values of tidiness and space and work chair ergonomics showed a significant association with the ratings of both experts.

The method to assess the loads imposed on the upper limbs was validated against the expert observations from the video, continuous recordings of myoelectric activity of forearm muscles, and wrist posture, measured with goniometers. Inter-observer repeatability and validity were good or moderate.

Both intensive ergonomics approach and education in ergonomics have effects in reducing discomfort in VDU work. In attemps to improve the ergonomics of VDU workstation, the best result will be achieved with cooperative palaning in which both workers and pratitioners are actively invoved. The assessment methods for VDU work ergonomics and upper limb load studied here can be utilized in a repeatable manner.

KEY WORDS: Human engineering, computer terminals, neck pain, upper extremity, workload, risk factors, risk assessment, randomized controlled trials, observation, video recording.