Sources of variance in exposure to postural load on the back in occupational groups.

Bootstrap exploration of the duration of surface electromyography sampling in relation to the precision of exposure estimation

“…Several investigators have sought to quantify the contributions of the different sources of variability affecting estimates of exposure to physical risk factors obtained with both observational and direct quantitative measures, including surface EMG (29,(42)(43)(44)(45)(46)(47). Understanding the nature of exposure variance is essential when exposure assessment strategies are being developed, especially in field studies with large numbers of participants performing multiple and varied tasks.…”

Systematic evaluation of observational methods assessing biomechanical exposures at work

“…Most jobs and tasks show daily or seasonal variability in biomechanical exposures, and, therefore, the sampling strategy -in terms of the number of subjects and measurements per subject -is decisive for the precision and credibility of the obtained result (148)(149)(150)(151)(152)(153)(154)(155)(156). Some of the methods included in the present selection are based on sampling at fixed-time intervals (eg, OWAS, PATH), while others apply continuous observation for longer periods (eg, PEO, TRAC).…”

Bias in risk estimates from variability of exposure to postural load on the back in occupational groups.

“…Misclassification below 10% was found only in compari sons of occupational groups with at least a 14-fold level of exposure, compared with the lowexposure group. The high rates of miscla ssification reflect the considerable variance in exposure between workers in the same group and between parts of a shift within workers (12). Under the assumption that the exposure variability and the concomitant concept of a log-normal distribution can be generalized to other occupational group s and work situations, misclassification of postural load due to nonneutral postures is easily obtained .…”

“…Essential for estimating this probability is inference about the underlying distributions. The distribution of measurements of aspects of postural load on the back is described best by the log-normal distribution, characterized by the geometric mean (GM) and the geometric standard deviation (GSD) (12). Thus the probability can be obtained by the following equation:…”

“…The principle measure of exposure was th e percentage of worktime with trunk flexion or trunk rotation (12). Straddlecarrier dr ivers were found to be the occ upationa l group with the lo west ex pos ure to trunk flexion , and crane oper ators formed the occupational group with the lowest exposure to trunk rotation.…”