title: EMG median frequency changes in the neck-shoulder stabilizers of symptomatic office workers when challenged by different physical stressors.
abstract: The problem of work-related neck and upper limb disorders among computer users has been reported extensively in the literature, and commonly cited risk factors include static posture, speed and force of keyboard operation. The present study examined changes in median frequency (MF) of the neck-shoulder muscles in symptomatic and asymptomatic office workers when they were exposed to these three physical stressors. A quasi-experimental Case-Control design was used to examine MF changes in two groups of female office workers when they were subjected to controlled doses of computer work involving prolonged static posture, increased typing speed and increased typing force. The MF of four major neck-shoulder muscles were examined bilaterally and compared between groups. The MF changes over time-at-task did not clearly illustrate any muscle fatigue mechanism. However, Case Group consistently showed trends for higher MF than the Control Group, and this pattern was observed in response to all three physical stressors. The consistent group differences in MF suggest different muscle recruitment strategies between symptomatic and asymptomatic office workers. These results implied that symptomatic individuals had altered motor control, which may have important implications in understanding the etiology of work-related musculoskeletal disorders.
authors.affiliation: Department of Rehabilitation Sciences, Hong Kong Polytechnic University, Hong Kong SAR, China. rsgszeto@poly.edu.hk
authors.forename: Grace Pui Yuk
authors.initials: GP
authors.lastname: Szeto
authors.forename: Leon Melville
authors.initials: LM
authors.lastname: Straker
authors.forename: Peter Bruce
authors.initials: PB
authors.lastname: O'Sullivan
mesh_terms: D000222:Adaptation, Physiological; D000328:Adult; D001315:Australia / Q000453:epidemiology; D003201:Computers / Q000706:statistics & numerical data; D004576:Electromyography / Q000379:methods* / Q000706:statistics & numerical data; D005260:Female; D006801:Humans; D008875:Middle Aged; D009043:Motor Activity; D009119:Muscle Contraction; D018482:Muscle, Skeletal / Q000503:physiopathology*; D019547:Neck Pain / Q000175:diagnosis / Q000453:epidemiology / Q000503:physiopathology*; D009784:Occupational Diseases / Q000453:epidemiology / Q000503:physiopathology*; D005082:Physical Exertion; D018570:Risk Assessment / Q000379:methods; D012307:Risk Factors; D020069:Shoulder Pain / Q000175:diagnosis / Q000453:epidemiology / Q000503:physiopathology*; D013647:Task Performance and Analysis; D017132:Workplace / Q000706:statistics & numerical data