Exertion-Dependent Effects of Physical and Mental Workload on Physiological Outcomes and Task Performance

Abstract

OCCUPATIONAL APPLICATIONS The findings from the current study illustrate the adverse effects of concurrent physical and mental demands on shoulder muscle activation. Furthermore, the results also suggest that the effects of concurrent physical and mental demands are more pronounced during static, as opposed to dynamic, exertions. As such, it is important to consider the interaction of said work parameters (i.e., force levels, mental demands, and type of exertion) when evaluating/designing tasks. Occupational tasks requiring concurrent physical and mental work should be redesigned to reduce static loading (by changing postures or providing frequent breaks). With tasks requiring static exertions, other physical parameters (such as force) should be reduced to minimize interference due to additional cognitive processing. To conclude, concurrent physical and mental demands affect muscle activation and impede worker performance; ergonomists should consider this interaction during task design/redesign, evaluations of injury risk, and potential causal models of injury development. TECHNICAL ABSTRACT Background: Static work is considered an occupational risk factor in the development of injuries, thus there is an emphasis on employing dynamic exertions to work tasks. With workers experiencing concurrent physical and mental demands in their daily jobs, it is unclear whether these exertion types affect overall task demands differentially. Objective: The aim of this study was to compare exertion-dependent physiological responses due to concurrent physical and mental workload during intermittent shoulder exertion. Methods: Twelve young participants, balanced by gender, performed intermittent static and dynamic shoulder abduction for 3 minutes at three levels of physical workload (low, moderate, and high) in the absence and presence of a mental arithmetic task. Study measures included muscle activity, muscle oxygenation, motor and mental arithmetic task performance, and subjective responses (NASA-Task Load Index and Borg CR10 Scale). Results: Static exertions and higher physical demands adversely affected physiological responses (i.e., muscle activity and oxygenation) and performance measures, and they were associated with higher levels of perceived exertion and workload. Additional mental demands negatively affected muscle activity, mental task performance, and subjective workload measures. However, these results were more pronounced during static exertions at high physical demand levels. Conclusions: Results indicated that certain job parameters (static exertions and high physical demands) are more susceptible to interference with mental demands than others (dynamic exertions and low demands). When assessing overall demands placed on workers during concurrent physical and mental work, it is important to consider the interaction of work parameters, specifically physical demand levels and exertion type, with mental demands.