Purpose: This study aimed to investigate the tracking and changes of steps per day in adults and their determinants over 13 yr.

Methods: A total of 2195 subjects (1236 women) 30–45 yr of age were randomly recruited from the ongoing Cardiovascular Risk in Young Finns Study in 2007 and were followed up in 2020. Steps per day, including both total and aerobic steps per day, were monitored for seven consecutive days with a pedometer in 2007–2008 and 2011–2012 and with an accelerometer in 2018–2020. Tracking was analyzed using Spearman’s correlation. Stability and changes of steps per day over time in both low-active and high-active groups (based on median values) were described by percentage agreements, kappa statistics, and logistic regression. Associations of sex, age, and body mass index with the initial number and changes in steps per day were analyzed using linear growth curve modeling.

Results: Tracking correlations of total steps per day at 4-, 9-, and 13-yr intervals were 0.45–0.66, 0.33–0.70, and 0.29–0.60, while corresponding correlations for aerobic steps per day were 0.28–0.55, 0.23–0.52, and 0.08–0.55, respectively. Percentage agreements were higher than 54%, and kappa statistics ranged from slight to fair over time. Compared with the low-active group, the high-active group at baseline had a higher probability of being active later in adulthood. Female sex and higher age were associated directly with the initial number of steps per day and inversely with changes in the number of steps per day. Body mass index was inversely associated with the initial number of steps per day and changes in the number of total steps per day.

Conclusion: The 13-yr tracking of steps per day in adulthood was found to be low to moderately high. Daily ambulatory activity is essential to maintaining an active lifestyle throughout adulthood. Changes in the amount of adult steps per day vary by sex, age, and BMI.