Purpose: To promote greater muscular strength across the life course and in turn, help improve long-term health outcomes, strategies aimed at increasing muscular strength are required. To inform these strategies, this study identified childhood factors associated with muscular strength trajectories.

Methods: Prospective longitudinal study of 1,280 Childhood Determinants of Adult Health participants who had a range of potentially modifiable factors (e.g., anthropometric measures, physical activity) and health and risk motivation items (e.g., attitudes, beliefs, and intentions on health-related actions) measured in childhood and had their muscular strength assessed up to three times between childhood and midlife. Associations between childhood factors and three predetermined life course muscular strength trajectories (identified previously using group-base trajectory modelling as: above average and increasing; average; below average and decreasing) were examined using log multinomial regression.

Results: Greater physical fitness, physical activity, fat-free mass, enjoyment of physical activity, physical education, and school sports, and positive attitudes regarding the importance of exercising, staying fit, and body image were associated with a lower likelihood of being in the below average and decreasing muscular strength trajectory (relative risk range: 0.45-0.98). Greater physical fitness, physical activity, and fat-free mass, and attending an independent school were associated with a higher likelihood of being in the above average and increasing muscular strength trajectory (relative risk range: 1.03- 1.93).

Conclusions: As well as providing health benefits in the short term, physical activity, physical fitness, positive health attitudes and healthy weight in childhood may lead to better muscular strength in the long term.