Can a single-item measure assess physical load at work? Evidence from the GAZEL cohort

Background: While detailed occupational exposure assessment is critical to establish work-related health risk factors and set policy, such methods are highly labor-intensive. We aimed to test whether the question “Do you find your work physically fatiguing” was a reliable and valid measure of physical load that could be used when a complete assessment was not feasible. Methods: The study was conducted among members of GAZEL, a cohort of 20,625 French utility workers. Reliability of the measure was tested among workers reporting the same physical load factors in two successive years. Validity was studied using association between the measure and an index of physical workplace constraints (also taking into account gender, occupational grade, and depression). Results: The measure showed differential distribution by occupational grade and gender, with higher fatigue among men and those in low employment grades. It showed good test-retest reliability (0.606-0.627). The measure had an adjusted correlation (r) of 0.6 with physical load. There was a strong linear relationship between physical fatigue and physical load (analyzed categorically), which was robust to stratification by gender, occupational grade, and depression. Conclusion: A single-item measure of work-related physical fatigue is a reliable and valid indicator of physical load at work for future non-occupational epidemiologic studies.