Physical workload in various types of work: Part II. Neck, shoulder and upper arm

To explore the correlation between, and the variation in, various measures of exposure to potential risk factors for work-related upper extremity musculoskeletal disorders (UE-WMSDs), physical workload was measured in 43 types of work (713 individuals), using inclinometry for the head and upper arms, and electromyography (EMG) for the trapezius muscles. Many exposure measures were highly correlated. Head flexion (90th percentile), extension (1st percentile), and movements (50th percentile); arm elevation (99th percentile) and movements (50th percentile); trapezius muscular rest (fraction of time) and peak load (90th percentile), constitute main exposure dimensions. The variations were large: head: flexion 9 degrees-63 degrees, extension -39 degrees-4 degrees, movements 2.3-33 degrees/s; arm: elevation 49 degrees-124 degrees, movements 3.0-103 degrees/s; trapezius: muscular rest 0.8%-52% of time, peak load 3.1%-24% of maximal EMC. Even within work categories, e.g. "repetitive industrial", there were large variations. Somewhat higher loads were recorded on the right as compared to the left side (differences: arm elevation 2, arm movements 19%; trapezius peak load 18%), but these were small compared to the differences due to work. There were high correlations between movements of arm and head (r(s) = 0.96), as well as arm and wrist (r(s) = 0.92), and between, on the one hand, trapezius muscular rest and peak load, and on the other, arm and head movements (vertical bar r(s)vertical bar = 0.47-0.62), as well as arm elevation (vertical bar r(s)vertical bar = 0.54-0.85), which has to be considered when assessing exposure-response relations. Relevance to industry: Direct measurements provide objective and quantitative data of the main physical risk factors for UE-WMSDs, appropriate for estimating the risk, as well as giving priority to and evaluating interventions. (C) 2009 Elsevier B.V. All rights reserved.