Background: To examine if major life changes over a 4-year period among 34- to 49-year-old adults (mean = 41.8, SD = 5.0) were associated with a change in physical activity in men (37.7%) and women (62.3%).

Methods: Daily steps and aerobic steps (steps that lasted for at least 10 min without interruption at a pace of >60 steps/min) were collected from 1051 participants in 2007 and 2011. Changes in marital status, work status, and residence and the birth of a child were determined from both time points. A latent change score model was used to examine mean changes in daily total steps, aerobic steps, and nonaerobic steps (total steps minus aerobic steps).

Results: Women who had a first child in the 4-year period had a decrease in their nonaerobic steps (P = .001). Men who divorced in the 4-year period had a decrease in their nonaerobic steps (P = .020), whereas women who recoupled decreased their total steps (P = .030).

Conclusions: Counseling for parents having a first child on how to increase physical activity in their everyday life could potentially have an influence on an individual's physical activity.