Postural Stability and Physical Fitness in Preschool Children: Associations with Lower-Limb Muscular Strength, Speed/Agility, and Cardiorespiratory Fitness

Background/Objectives: Postural stability is considered a key component of motor development during early childhood; however, its specific association with different components of physical fitness in preschool children remains insufficiently explored. This study aimed to evaluate the association between postural stability and physical fitness components in preschool children. Methods: A cross-sectional study was conducted in 134 preschool children. Physical fitness was assessed through lower-limb muscular strength (standing long jump), speed/agility (4 × 10 m shuttle run), cardiorespiratory fitness (20 m shuttle run), and flexibility (sit-and-reach test). Object-control skills and postural stability were evaluated using selected tasks from the Movement Assessment Battery for Children-2. Composite indices were created for object-control skills and postural stability. Multiple linear regression analyses were performed adjusting for age, sex, body mass index (BMI), and object-control skills. Additional analyses included ANCOVA by postural stability tertiles and sensitivity analyses using HC3 robust standard errors, exclusion of influential observations, and bootstrap resampling. Results: Greater postural stability was independently associated with better lower-limb muscular strength (B = 9.49; 95% CI: 4.39–14.60; p ≤ 0.001) and cardiorespiratory fitness (B = 0.27; 95% CI: 0.06–0.49; p = 0.014). An association with speed/agility was observed in the primary model but lost statistical significance in sensitivity analyses. No significant association was found with flexibility. ANCOVA analyses confirmed significant differences across postural stability tertiles for lower-limb muscular strength (p = 0.033) and cardiorespiratory fitness (p = 0.011). Sensitivity analyses supported the robustness of the associations for lower-limb muscular strength and cardiorespiratory fitness. Conclusions: Greater postural stability was consistently associated with better lower-limb muscular strength and cardiorespiratory fitness in preschool children. These findings suggest that postural stability is associated with selected components of physical fitness during early childhood. Longitudinal and intervention studies are needed to clarify the direction and potential implications of these associations.