Biomechanical differences between obese and healthy-weight workers in manual materials handling

Abstract

The objective of this study was to evaluate the work strategies of obese and healthy-weight workers in manual materials handling. Seventeen obese and 20 healthy-weight manual materials handlers participated in this laboratory study. The tasks consisted of transferring four boxes between a hand trolley and a conveyor. The weight of the box (15 vs. 23 kg), the handling height and the working configuration were modified to see what impact these changes had on the participants’ manual materials handling. Biomechanical measures included net moments, expressed in the pelvic system (flexion–extension, lateral bending and torsion moments), kinematics of body segments and box displacements. The results indicated that trunk and knee postures and horizontal hand distances from L5/S1 were not significantly different between the two groups. Peak moments of force around the transverse, sagittal and longitudinal axes at L5/S1 were 13.3% to 59.0% higher during box lifting and lowering for the obese than for the non-obese workers. The individuals’ body weight explained 57% of the variability in the maximal transverse moments of force at L5/S1 during the lifting of the boxes from the ground. These results suggest that the extra mass of an obese worker causes additional stress for the musculoskeletal structures of the back. These biomechanical differences potentially place obese workers at a greater risk of developing musculoskeletal problems during manual materials handling.