The effects of concurrent physical and psychosocial demands on muscle activation, subjective workload, and performance

Abstract

Work-related musculoskeletal disorders (MSD) continue to be a serious health problem in the workplace. Past research has showed that not only physical factors (e.g. excessive repetition, awkward postures, and heavy lifting) impact the risk of developing an MSD but also psychosocial factors, such as the mental demands associated with a job. This research explored the impact of two additional psychosocial factors on the risk of developing an MSD, which are time pressure and workplace distractions. The specific objective of this research was to examine the concurrent effects of physical factors and psychosocial factors on muscle activation, mental performance, and the perceived workload level. Fifteen participants were recruited for this research. Two levels of the physical factor were investigated, including a static lift in: a neutral posture and an awkward posture. Five levels of psychosocial factors were considered, including: 1) the absence of psychosocial factors (serving as the control); 2) a mental task; 3) a mental task with time pressure; 4) a mental task with distractions; and 5) a mental task with both time pressure and distractions. The mental task involved solving a series of subtraction arithmetic equations. The time pressure was simulated by urging participants to answer as many math problems as possible in 30 seconds and by displaying a countdown. Distractions were in the form of incorrect answers presented visually and verbally by the computer. The experiment consisted of 10 trials (2 physical factors × 5 psychosocial factors). During each trial, the level of muscle activation from shoulder and low back muscles was recorded using an electromyography (EMG) device. The math performance in each trial was assessed based on the percentage of errors made and the number of correct responses. Also, participants were asked to rate their perceived workload level on the National Aeronautics and Space Administration - Task Load Index (NASA-TLX) questionnaire. The results showed that the addition of a me