| The objective of the three studies in this dissertation was to improve methods to prevent musculoskeletal disorders among workers in high-risk occupations.;The first two studies, Strain Index (SI) Studies I & II, addressed this problem by better characterizing the performance of a commonly used observational method of estimating potentially hazardous biomechanical exposures, the SI. The SI combines measures of several biomechanical risk factors into a single value (SI score). Strain Index scores are usually categorized into four ordinal SI "risk categories." In Strain Index Study I, multivariate survival analysis models were compared to evaluate the predictive validity of the original SI risk category cut-points to a new set of empirically derived cut-point values among 276 manufacturing workers. The results from this prospective study indicated that the empirically derived cut-points were a better predictor of incident hand-arm symptoms than the original cut-points, especially among women.;In Strain Index Study II, Aim 1, exposures to forceful exertions, repetition and non-neutral wrist posture estimated with SI methods were compared to analogous exposures estimated with alternate methods. Statistically significant associations between separate methods designed to assess specific risk factors were observed only for those measuring non-neutral wrist posture. In Aim 2, a multivariate survival analysis model examining associations between incident hand-arm symptoms and biomechanical exposures estimated with the SI was compared to a model examining associations between incident hand-arm symptoms and biomechanical exposures estimated with separate estimates of biomechanical risk factors. Results favored the SI risk category metric to characterize biomechanical exposures compared to separate measures of exposure.;The third study, light-weight block (LWB) Intervention Study, was a repeated measures laboratory study of 25 bricklayers performed to estimate the effect of block weight (LWB vs. standard-weight block (SWB)) and course height on low back disorder (LBD) risk factor exposure. Mixed-effect models showed that LWB was associated with reduced exposure for percent time spent in sagittal flexion >30°, lifting rate, LBD risk probability score, and non-dominant upper trapezius muscle activity. Bricklaying at ankle or chest heights was generally associated with higher exposure to risk factors than bricklaying at knuckle height. |
