Belief-level markers of physical activity among young adult couples: comparisons across couples without children and new parents.

The health benefits of regular moderate-vigorous intensity physical activity (MVPA) are well established, yet young adults, particularly parents, often show declines in MVPA and may represent a critical population for intervention. Theory-based correlates used to guide future interventions are scant in this population. The purpose of this study was to examine theory of planned behaviour (TPB) belief-level constructs as correlates of directly assessed MVPA across cohorts of couples without children and with their first child over the initial 12 months. Participants were 238 adults (102 not expecting a child, 136 expecting first child) who completed baseline demographics, belief measures of the TPB and seven-day accelerometry, followed by assessments at 6 and 12 months. Results showed select medium-sized belief-PA correlations with sex and cohort interactions. Overall, women had larger affect-based behavioural belief associations with MVPA than men (e.g. PA relieves stress), and among new parents, mothers showed larger associations with control over MVPA than fathers. Mothers also had larger associations between control beliefs and MVPA compared to women without children (e.g. domestic duties, bad weather). Extremely high means and low variability on the behavioural beliefs show limited room for possible changes in intervention while control beliefs had low means suggesting room for change. Interventions targeting control among new mothers may be paramount for increasing MVPA, yet the TPB yielded less insight into the targets for promoting MVPA among young men.