The influence of upper-body dimensions and physical fitness on performance in young swimmers: a PLS-PM mediation-effect analysis

This study applied partial least squares path modeling (PLS-PM) to examine the relationships among upper-body dimensions, dry-land physical fitness, trunk muscular endurance, and sprint freestyle performance in adolescent swimmers. Forty-seven competitive swimmers aged 14–18 years were assessed for body morphology and physical fitness using standardized strength and endurance tests. Their recent official race times for 50 and 100 m freestyle were recorded. PLS-PM was used to evaluate model fit and the significance of path coefficients. The model showed a good fit (R² = 0.77 for 50 m; R² = 0.56 for 100 m). Upper-body dimensions had significant positive effects on dry-land physical fitness and endurance ( p < 0.01), but no direct effect on performance. Dry-land physical fitness strongly predicted 50 m (β = −1.04) and 100 m (β = −0.85) race times, with negative β coefficients indicating that higher dry-land physical fitness levels were associated with shorter race times, thereby reflecting improved swimming performance. In adolescent swimmers, upper-body dimensions underpin physical fitness development, and physical fitness is the key determinant of short-distance freestyle performance. Body morphology exerted a significant indirect positive effect on performance primarily through enhanced physical fitness.