Developing Models to Study Relationships between Tibial Acceleration Measures and Lower Extremity Musculoskeletal Disorder Symptoms Experienced by Distribution Center Workers

The relationship between cumulative biomechanical exposures and occupational injuries to the back and the upper extremities has been a primary focus of ergonomists. However, very little is known about the occupational biomechanical exposures associated with development of lower extremity musculoskeletal disorders (MSD). In occupations such as material handling, workers spend a majority of their workday on their feet and are often exposed to walking on hard surfaces for long durations and stepping up or down between work surfaces. The goal of this research was to develop risk models that use biomechanical exposure measures in material handling jobs and relevant individual factors to determine where there is an increased risk of lower extremity MSD symptoms.;Study 1 was a laboratory study to develop and validate an accelerometer-based instrumentation system that can be used in the field to quantify lower extremity biomechanical exposures. Instrumented with accelerometers that quantified their bilateral tibial acceleration, participants were asked to carry out tasks representative of those performed by material handlers in distribution centers. The findings from this study showed that the instrumentation and associated peak tibial acceleration metrics could differentiate between the tasks at three exposure levels.;Study 2 was a cross-sectional field study performed at three distribution centers. At each facility, workers were recruited to complete a lower extremity questionnaire to collect symptom data. Using the questionnaire response data, the self-reported prevalence of MSD symptoms in the lower extremities amongst material handlers in distribution center environments was studied. Two-thirds of the 341 material handlers who completed the questionnaire self-reported lower extremity work-related musculoskeletal symptoms. These were most common in the ankles & feet, followed by symptoms in the knees and the hip & thighs. Significant associations between symptoms and variables such as age, gender, work experience and smoking status were also found.;In Study 3, conducted at the same three distribution centers, bilateral tibial accelerations were obtained from 132 workers as they performed their normal work activities for a two-hour period. The survey data from Study 2 and the accelerometer data were used to develop logistic regression models for the hip & thighs, knees, lower legs and ankles & feet. The resulting models indicate which biomechanical and individual exposure variables were most predictive of self-reported lower extremity symptoms. Cut points were identified for the different exposure measures, thereby suggesting threshold exposure levels for the lower extremities that may determine when exposure levels are safe or unsafe for workers.;In sum, this research has shown that lower extremity musculoskeletal symptoms are prevalent among material handlers. The etiology is multifactorial and biomechanical exposures as well as individual risk factors are contributory to their development. Specifically, the models developed were able to quantify associations between the likelihood of presence of symptom as a function of peak and cumulative tibial accelerations. The models quantified threshold levels at which the workers are at an increased the risk to develop MSD symptoms.