| Summary: | Abstract Physical activity (PA) influences bone tissue throughout the lifespan and is believed to have a positive effect on vertebral size also during adulthood, thus potentially improving vertebral strength and reducing fracture risk. Modic changes (MC), divided in three subgroups (MC1, MC2, MC3), are vertebral bone marrow changes visible in magnetic resonance imaging (MRI) that are associated with non-specific low back pain (LBP). This thesis includes three population-based cohort studies (I, II, III) which aim was to investigate the association between device-measured moderate to vigorous intensity PA (MVPA, ≥ 3.5 METs), vertebral cross-sectional area (CSA) (I), and lumbar MC (II), and to determine the relationship between vertebral dimensions and lumbar MC (III), using a subsample (n = 1202–1374) of the Northern Finland Birth Cohort 1966. Participants aged 46 to 48 underwent lumbar MRI from which vertebral dimensions and lumbar MC were assessed, and their daily MVPA was determined by a wrist-worn activity monitor. The results showed that MVPA was positively associated with vertebral CSA among both sexes. Among men, a higher amount of MVPA was associated with increased odds of any lumbar MC, particularly MC2, whereas among women no such association was found. Exploration of the relationship between vertebral dimensions and lumbar MC revealed that vertebral height was positively associated with the presence of lumbar MC2, whereas vertebral CSA and volume were not associated with MC. The results of this thesis propose that MVPA has a positive impact on vertebral size among both sexes at midlife, thus lifelong MVPA might be a preventive action for reducing future vertebral fractures. Lumbar MC seem to be associated with higher vertebrae. MVPA seems to be associated with an increased likelihood of lumbar MC, but only among men and especially with MC2, strengthening the hypothesis that changed mechanical conditions due to hyperloading are connected to MC2. Further studies are needed to verify these findings and to ...
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