Prevalence of back discomfort and estimates of back load in two manufacturing facilities

This study evaluated the association between the prevalence of back discomfort and estimates of back load posed by nine jobs in two manufacturing facilities. Prevalence of back discomfort experienced was estimated through self-administered questionnaires. A total of 266 questionnaires were distributed to workers randomly selected from nine jobs in two factories. Workers were asked to rate on a 0-5 scale the discomfort level they experienced in the back for a one-month period before and at the time of the survey. The return rate for each job ranges from 57% to 100%. Overall, 14.5% of the survey respondents experienced some discomfort in the back. With the assistance of a checklist, nine supervisors rated each task of the job they supervised by the magnitude of the force (low, moderate, or high) and by the duration, (less than 30% time, 30% to 50% time, and greater than 50% time) that workers typically spent in awkward back postures, such as back flexion, extension, twisting, and lateral bending. An additional total back load estimate was provided independently by an ergonomist. Logistic regression analysis found a positive association between the back discomfort prevalence observed in the present study and the load estimates both by the ergonomist and by task information based on back twisting. Significant concordance was found between the ergonomist's load estimates and the supervisors' estimate of the duration of twisted back. This study demonstrated not only that a checklist approach could provide useful task information for deriving exposure estimates, but also that exposure estimate for a job could be derived from its constituent tasks. Though in this study it was the supervisor who utilized the checklist to estimate the back loads, there is no reason why experienced workers could not use the checklist to provide similar estimates. A large-scale study should be conducted to improve the design of this checklist approach.