Comparing two methods to record maximal voluntary contractions and different electrode positions in recordings of forearm extensor muscle activity: Refining risk assessments for work-related wrist disorders.

BACKGROUND: Wrist disorders are common in force demanding industrial repetitive work. Visual assessment of force demands have a low reliability, instead surface electromyography (EMG) may be used as part of a risk assessment for work-related wrist disorders. For normalization of EMG recordings, a power grip (hand grip) is often used as maximal voluntary contraction (MVC) of the forearm extensor muscles. However, the test-retest reproducibility is poor and EMG amplitudes exceeding 100% have occasionally been recorded during work. An alternative MVC is resisted wrist extension, which may be more reliable. OBJECTIVE: To compare hand grip and resisted wrist extension MVCs, in terms of amplitude and reproducibility, and to examine the effect of electrode positioning. METHODS: Twelve subjects participated. EMG from right forearm extensors, from four electrode pairs, was recorded during MVCs, on three separate occasions. RESULTS: The group mean EMG amplitudes for resisted wrist extension were 1.2-1.7 times greater than those for hand grip. Resisted wrist extension showed better reproducibility than hand grip. CONCLUSIONS: The results indicate that the use of resisted wrist extension is a more accurate measurement of maximal effort of wrist extensor contractions than using hand grip and should increase the precision in EMG recordings from forearm extensor muscles, which in turn will increase the quality of risk assessments that are based on these.

Discrepancies in pain presentation caused by adverse psychosocial conditions as compared to pain due to high physical workload?

Disorders in the musculoskeletal system have been associated with a high physical workload as well as psychosocial and individual factors. It is however not obvious which of these factors that is most important to prevent. Musculoskeletal disorders in neck and upper extremity was assessed by interview and clinical examination in 79 teachers and 93 assisting nurses, all females. Psychosocial work environment was assessed by questionnaire. The physical workload was recorded by technical measurements of postures, movements and muscular load, in 9 teachers and 12 nurses. The physical workload was lower among the teachers, but they had a more demanding psychosocial work environment. Among the nurses, but not in the teachers, the neck-shoulder disorders were associated with a high body mass index (BMI). The teachers reported neck-shoulder complaints to a higher extent than the nurses, but had much lower prevalence of diagnoses in the clinical examination (12% vs. 25%; POR 0.3 CI 0.1 - 1.2; adjusted for age and BMI). The results suggest that adverse psychosocial conditions among the teachers give rise to a different kind of pain in the neck-shoulder region than from physical overload, troublesome but not as severe as the one afflicting the nurses.

Postures and movements in the most common tasks of power line workers.

The repair and maintenance of electrical power lines involves awkward postures, which are known risk factors for developing musculoskeletal disorders. The aim of the present study was to quantify postures and movements of upper arm, head, upper back and neck in the main tasks performed by line workers. Posture of twelve right-handed line workers was recorded by inclinometry and presented as percentiles of angular and angular velocity distributions. All tasks involved considerable upper-arm elevation, ranging from 73° to 115° for the 90th percentile. Upper-arm elevation showed significant differences between tasks, but no consistent differences between right and left sides. Regarding velocity, the right arm presented higher levels than the left arm. All tasks required significant extension of head, upper back and neck, ranging from 7° to 67° for head (10th percentile). All tasks, except the one performed with a continuous extension, also involved pronounced flexion, ranging from 33° to 60° for the head (90th percentile). Work which required highly elevated arms also required significant head extension (r(2)=0.56). Awkward postures of upper arms, head, upper back and neck were identified by inclinometry, demonstrating the need for preventative interventions to reduce musculoskeletal disorders among line workers.