Shoulder strength, scapular displacement, and supraspinatus morphology in male and female competitive water polo players: a cross-sectional study

Background Water polo is an Olympic team sport played by both men and women that combines repetitive throwing and aquatic propulsion, placing unique biomechanical demands on the shoulder. However, sex-related differences in shoulder function and structure remain poorly understood. This study compared the functional and structural shoulder profiles of male and female competitive water polo players. Methods A cross-sectional study included 52 competitive water polo players (26 men and 26 women; 18–30 years). Internal and external rotator strength was assessed using a handheld dynamometer, and the internal-to-external rotation strength ratio (IR/ER ratio) was calculated. Scapular position and displacement were evaluated using a PALM® device, and supraspinatus tendon thickness was measured by ultrasound. Univariate analyses were followed by multiple linear regression adjusted for height and body mass. Results Men showed greater internal rotation strength ( p = 0.011) and a higher IR/ER ratio ( p = 0.004), whereas women exhibited greater scapular displacement ( p = 0.004). No significant sex differences were observed in external rotation strength ( p = 0.052), supraspinatus tendon thickness ( p = 0.384), or arm dominance ( p > 0.05). After adjustment, sex was no longer associated with internal rotation strength or the IR/ER ratio. However, greater scapular displacement in women remained independently associated with sex ( p = 0.005; adjusted p = 0.020). Conclusions Sex differences in shoulder strength were largely explained by anthropometric characteristics. In contrast, greater scapular displacement in female players remained independent of body size, suggesting a sex-specific biomechanical adaptation that may be relevant for shoulder injury prevention. These findings contribute to a better understanding of sex-specific shoulder adaptations in water polo and may support the development of more individualized assessment and injury prevention strategies.