[Long-term trends of occupational physical activity intensity in Japan]

Objectives　Although physical inactivity is a global concern, quantitative data on its long-term trends in physical activity (PA) are limited. This study aimed to estimate long-term trends in the intensity of occupational PA, constituting the largest portion of PA in Japan.Methods　Data on the number of workers in Japan by occupational category were obtained from the Labour Force Survey. PA intensity (metabolic equivalents [METs]) was assigned to 329 occupations in the Japanese Standard Occupational Classification based on the methods and data of Tudor-Locke et al. (2011), and representative intensity values for 11 occupational categories were calculated. Based on intensity, occupational categories were reclassified into sedentary (≤1.5 METs), light (1.6-2.9 METs), and moderate (≥3 METs). Trends in the prevalence of workers in each category were analyzed, along with the annual mean occupation-related METs from 1953 to 2022. The mean occupation-related METs represented the weighted average of PA intensity, calculated based on the annual worker population for each occupational category. Results　From 1953-2022, the prevalence of moderate-intensity occupations significantly declined, whereas sedentary and light-intensity occupations increased. The mean occupation-related METs decreased continuously for 70 years. During the 48-year period from 1962 to 2010, when there were no major changes in occupational classification methods, there was a decline of 0.25 METs, representing a 9.6% decrease, from 2.60 to 2.35 METs.Conclusion　Over the past 70 years, occupations in Japan have transitioned to ones with lower PA intensity. Consequently, the average PA intensity across all occupations decreased by at least one-tenth. Since this study assumes a constant intensity for each occupation, the actual decline in occupational PA intensity may be even more significant because of societal automation.