Physical workload in various types of work: Part I. Wrist and forearm

The quantitative relationship between exposure to physical risk factors and upper extremity work-related musculoskeletal disorders (UE-WMSDs) is virtually unknown. To explore the variation, objective measurements were derived in 43 types of work (686 individuals), using goniometry for the wrists and electromyography (EMG) for the forearm extensor muscles. The variations due to work were great for wrist movements, wrist positions, muscular rest, as well as peak load, ranging 1.4-54 degrees/s (flexion velocity; 50th percentile), -30 degrees-3 degrees (flexion angle; 50th percentile), 0.2-23% of time, and 3.4-41% of maximal EMG (90th percentile), respectively. Even within work categories, e.g. "repetitive industrial", there were large variations for all measures. Hence, classification without measurements has limited value. All movement measures were highly correlated (vertical bar r(s)vertical bar=0.82-0.99), but only weakly so to positions (vertical bar r(s)vertical bar = 0.01-0.43). Muscular rest and "static load" (10th percentile), were highly correlated (r(s) = -0.92), but not associated to peak load (90th percentile; vertical bar r(s)vertical bar= 0.05 and 0.08, respectively). Most low-velocity work was accompanied by much muscular rest; however, the low velocity for mouse-intensive computer-work meant very little rest. Technical measurements are suitable as exposure measures in epidemiological studies, as well as a base for decisions about interventions. The multidimensional character of exposure - wrist movements, wrist postures, muscular recovery, and peak load - has to be considered. Relevance to industry: Direct measurements provide objective and quantitative measures of the main physical risk factors for UE-WMSDs, appropriate for estimating the risk, as well as giving priority to, and evaluating, interventions. (c) 2008 Elsevier B.V. All rights reserved.