Objectives: The 2014 Australian Physical Activity and Sedentary Behaviour Guidelines (Adults) recommend muscle-strengthening activities ≥2 days/week. This study aimed to identify factors associated with 5-year change and stability in adherence to these guidelines.

Design: Two adult follow-ups of the Childhood Determinants of Adult Health (CDAH) Study. Participants (n = 1510) were 26-36 years (CDAH-1, 2004-06) and 31-41 years (CDAH-2, 2009-11).

Methods: Information on muscle-strengthening activities, sociodemographics, health, physical activity and sedentary behaviour was collected. Participants reporting muscle-strengthening activities ≥2 days/week 'met guidelines', with change and stability categorised as 'persistent adherence', 'increasing adherence', 'decreasing adherence' and 'persistent non-adherence'. Differences in sociodemographic, health and behavioural factors were analysed using log multinomial regression.

Results: Between 15-21% of women (CDAH-1: 14.5%, 95% confidence interval = 12.5-16.9; CDAH-2: 20.7%, 95% confidence interval = 18.3-23.4) and ~21% of men (CDAH-1: 22.2%, 95% confidence interval = 19.0-26.0; CDAH-2: 21.0%, 95% confidence interval = 17.8-24.7) met muscle-strengthening guidelines, but only 8.5% (95% confidence interval = 7.2-10.1) of participants were persistently adherent. Remaining in or moving from a major city, CDAH-1 weight status, cumulative self-rated health and vigorous physical activity were positively associated with persistent adherence (relative risk range = 1.51-3.92), while female gender, becoming partnered and having children at any timepoint were negatively associated with persistent adherence (relative risk range = 0.38-0.58).

Conclusions: Adherence - particularly persistent adherence - to muscle-strengthening guidelines in this sample was low. Gender, marital status, weight status, BMI, self-rated health, urban-rural status, parental status, physical activity and sedentary behaviour were associated with adherence, and should be considered in intervention development to maximise effectiveness.