Evaluation of Fatigue and Workload among Workers Conducting Complex Manual Assembly in Manufacturing

Abstract

OCCUPATIONAL APPLICATIONS We conducted a study to evaluate fatigue and workload among workers performing complex assembly tasks. We investigate several predictors of fatigue, including subjective workload estimates, sleep duration, the shift being worked, and production levels. High levels of fatigue were reported in one-third of the shifts evaluated. The main predictors of high fatigue were workload estimates, working evening shifts, and baseline fatigue. Among the six dimensions of workload, only mental demand and frustration were predictors of high fatigue. Mental demand was also rated highest. Participants reported less than seven hours of sleep in 60% of the nights evaluated. These results suggest that managers and supervisors should consider cognitive workload as a key contributing factor to fatigue in complex manual assembly. Similarly, work schedule planning should consider shift duration, start times, and end times, because of the negative influence on fatigue and the potential disruptions on sleep among workers. TECHNICAL ABSTRACT Background: General fatigue and mental workload have been studied extensively in safety-critical contexts; wherein human performance degradation can lead to catastrophic outcomes. In the manufacturing sector, the physical demands of a job have received most of the attention because of the presence of biomechanical loads and the incidence of musculoskeletal disorders. However, in complex manual assembly, cognitive and chronobiology aspects of work can contribute to fatigue and degrade worker performance. Purpose: We aimed to evaluate self-reported levels of fatigue and workload among a group of workers performing complex assembly tasks. We also sought to investigate several predictors of fatigue, including workload estimates, sleep duration, the shift being worked, and production levels. Methods: Fourteen assembly line workers participated in a two-week study. They evaluated their levels of fatigue at the beginning and end of each shift using the Samn-Perelli Fatigue Scale. They also evaluated their workload according to the NASA-TLX scale at the end of each shift. Results: High levels of fatigue (fatigue score ≥ 5) were reported in approximately one-third of 114 work shifts evaluated. Binary logistic regression indicated that fatigue scores at the beginning of the shift, NASA-TLX scores, and working evening shifts were significant predictors of high levels of fatigue. Among the six dimensions measured by NASA-TLX, only mental demand and frustration were predictors of high fatigue. Mental demand was also rated highest by the workers. Participants reported less than seven hours of sleep in 60% of the nights evaluated. Conclusions: These results suggest that cognitive load can contribute to fatigue in complex manual assembly work. Circadian and homeostatic processes related to shift duration, start times, and end times are also potential contributing factors. Similarly, existing work schedules may be contributing to sleep disruptions among workers.