Sedentary accumulation patterns and mental health among university teachers: longitudinal evidence from a single-university two-wave cohort

Objective To examine whether 12-month changes in sedentary accumulation were associated with mental-health outcomes among university teachers while accounting for concurrent changes in total sitting time. Methods Full-time teachers ( n  = 769) completed 7-day activPAL4 monitoring and the World Health Organization–Five Well-Being Index (WHO-5), 10-item Perceived Stress Scale (PSS-10), and Maslach Burnout Inventory–Emotional Exhaustion (MBI-EE) at baseline and 12 months. Changes in mean sitting-bout length (MBL), the proportion of sitting time accumulated in bouts ≥30 min (Prolonged30%), and total sitting time were entered simultaneously in ANCOVA models adjusted for the corresponding baseline outcome, changes in moderate-to-vigorous physical activity and sleep quality, age, sex, and baseline BMI. Model 2 additionally adjusted for T1 levels of the three sedentary exposures. Results In Model 2, greater reductions in MBL were associated with higher WHO-5 scores ( β  = −0.236, 95% CI − 0.441 to −0.032; p  = 0.023) and lower MBI-EE scores ( β  = 0.125, 95% CI 0.034 to 0.217; p  = 0.007), while greater reductions in Prolonged30% were associated with lower PSS-10 scores ( β  = 0.043, 95% CI 0.006 to 0.079; p  = 0.022). Reductions in total sitting time were favorably associated with all three outcomes. An interquartile-range reduction in MBL corresponded to a 0.97-point higher WHO-5 score, about one-tenth of the ~10-point contextual reference value; the corresponding 0.44-point lower PSS-10 estimate for an interquartile-range reduction in Prolonged30% was about 16–20% of the 2.2–2.7-point contextual reference range. All semi-partial f 2 values for focal predictors in the primary Model 2 analyses were Conclusion More favorable changes in sedentary accumulation were associated with better mental-health outcomes, but the estimated incremental effects were small. Because MBL is structurally linked to sitting volume and bout frequency, its associations are better interpreted as reflecting a more frequently interrupted pattern of sitting rather than an isolated effect of bout duration.