Longitudinal trajectories of physical activity in women using latent class growth analysis: The WIN Study

PURPOSE: This study aimed (1) to examine the longitudinal trajectories in objectively measured physical activity (PA); (2) to identify unknown (i.e., latent) subgroups with distinct trajectories; and (3) to examine the correlates of latent subgroups among community dwelling women. METHODS: The study sample included a total of 669 women from the Women's Injury Study, a 5-year prospective cohort study conducted from 2007 in the Southwest Central region of the US. Pedometer-based step-count data across 18 consecutive months were fitted to a latent growth model (LGM) and a latent class growth model (LCGM). Baseline characteristics were regressed on latent class membership. RESULTS: The longitudinal change in PA was best fit to a piecewise LGM with seasonal transitions. Significantly increased and decreased levels of PA were observed during the spring, fall, and winter, respectively (p < 0.001). Three latent subgroups with distinct PA trajectories were identified (low-active (46.8%), somewhat-active (41.3%), and active (11.9%)). Age and body fat percentage at the baseline significantly explained the likelihoods of being in low-active subgroup. CONCLUSION: Seasonal variations in PA among women were observed but may not be practically significant. A relatively large portion of the sample showed low levels of PA for long periods. Intervention strategies should be considered for women who are overweight or obese, and aged >40 years old to promote PA during the life course.