Load Distribution and Lifting Duration Effects on Upper Limb Strain for Manual Handling

The effects of load distribution and lifting duration on muscular strain of upper limbs were examined in the study. Fifteen task conditions that consisted of 5 load distributions (1 balanced and 4 unbalanced patterns) and 3 lifting durations (1, 2 and 3 s/lift) were performed in the experiment. A total of 15 subjects were recruited. Electromyographic data were measured from 5 muscles of right upper limb. Hand forces were obtained at both handles, which were equipped with load cells. The results showed that the upper limb muscular strains increased when the load distribution of objects lifted was not balanced. The lifting durations had the significant effect on the biomechanical behavior of upper limbs. The risk of musculoskeletal disorders of upper limbs became higher when fast lifting was performed. The study results suggested that the center of mass should be located at the center of the load and the lifting duration should not be shorter to reduce the risk of musculoskeletal injury to the operator.