The effects of cognitive load and task precision restrictions on trunk and shoulder kinematics in a manual material handling task

Abstract

This study examined how a concurrent mental task and precision restrictions affected the kinematics of the trunk and shoulder during a simulated lifting task. Musculoskeletal disorders in material handling operations are highly prevalent. In addition to completing physically demanding work, workers must also manage concurrent mental demands. Few studies have examined the effect of concurrent mental demands in occupationally relevant tasks. This study quantified the effects of varying degrees of cognitive loads and task precision demands on a material handling task by examining these effects on the kinematics of the trunk and shoulders. Eleven subjects lifted and placed a 5 kg box at one of three destination heights (low, middle, high) while performing a simultaneous cognitive task (no task, a simple task, a complex task) and under two precision conditions (low precision, high precision). The cognitive task consisted of time-based arithmetic questions at two levels of difficulty. The primary dependent measures were the angular velocities of the trunk and shoulders. Significant decreases in angular velocities for both higher cognitive load complexities and higher precision conditions were observed, which differed depending on the destination height. Overall, this study found that increased complexity of a simultaneous cognitive task and higher task precision requirements led to longer lift times and decreased joint velocities.