- OBJECTIVES: To examine if the associations between motor competence and physical activity and musculoskeletal fitness change over time, whether motor competence is associated with longitudinal trajectories of physical activity and fitness, and mediating pathways among these constructs across early childhood. METHODS: Four hundred and eighteen children 3 to 5 yr of age (210 boys; age, 4.5 ± 1.0 yr) were recruited and completed three annual assessments as part of the Health Outcomes and Physical activity in Preschoolers study. Motor competence was assessed using the Bruininks-Oseretsky Test of Motor Proficiency Second Edition-Short Form. Musculoskeletal fitness (short-term muscle power) was evaluated using a modified 10-s Wingate protocol on a cycle ergometer. Physical activity was measured over 7 d using accelerometers. RESULTS: At baseline, the cross-sectional relationship between motor competence and vigorous physical activity was not significant; however, a significant, weak positive association emerged across time. Results from longitudinal mixed-effect models found motor competence to be a significant positive predictor of musculoskeletal fitness and vigorous physical activity and to be associated with steeper increases in physical activity across time. Motor competence was independently associated with musculoskeletal fitness and physical activity during this early childhood period. CONCLUSIONS: Motor competence is an important independent predictor of physical activity and musculoskeletal fitness levels across early childhood. Motor competence may be an important target for early interventions to improve both physical activity and fitness in the early years.