Background: Understanding physical activity (PA) after discharge from the military can inform theory on the role of habit and reinforcement in behavior maintenance and has implications for this population's future health.
Methods: Using data from 28,866 Millennium Cohort Study participants (n = 3782 of whom were discharged during the years between assessments), we 1) investigated changes in meeting federal PA guidelines for moderate-to-vigorous activity (MVPA) following military discharge and 2) determined predictors of meeting these guidelines after discharge.
Results: MVPA declined more in those who were discharged than in those who were not (-17.8 percentage points vs. -2.7 percentage points), with greater declines in former active-duty personnel, those who had deployed with combat exposures, had 14 to 25 years of service, and had been discharged more recently (>2 years prior). In those who were discharged, being normal or overweight (vs. obese), and a nonsmoker or former smoker (vs. current smoker) were positively associated with meeting MVPA Guidelines at follow-up, while meeting MVPA Guidelines at baseline and depression were inversely associated.
Conclusions: Reductions in MVPA were substantial and unexpected. Increased understanding of transitional periods that may benefit from interventions to mitigate declines in PA will help prevent excess weight gain and physical inactivity-associated health consequences.