Introduction:
Upper-extremity stability plays an important role in the application of technical skills that require repetitive and precise upper-extremity movements, such as serving in volleyball. Functional asymmetries in the upper extremities can negatively affect motor control and performance by disrupting balance and strength transfer.

Aim of the study:
The research aimed to investigate whether upper-extremity balance asymmetry predicts serve-accuracy performance in young female volleyball players.

Material and methods:
A total of 31 female athletes, aged 14 to 18 years with at least two years of licensed sports experience, participated in the study. Upper-extremity balance asymmetries were assessed using the Upper Quarter Y Balance Test (UQYBT) in the medial, inferolateral, superolateral, and composite directions. Serve-accuracy performance was measured based on scores obtained from 10 serves targeting predefined target zones. Data were analyzed using descriptive statistics and multiple linear regression analysis.

Results:
The findings showed that among the four asymmetry variables, only composite asymmetry significantly predicted serve-accuracy performance (p = 0.002) and explained 35.7% of the variance in the model (R² = 0.357). Direction asymmetry measurements (medial, superolateral, inferolateral) did not show a significant relationship with serve performance.

Conclusions:
The findings suggest that upper-extremity composite balance asymmetry is a functional factor influencing serve accuracy in young volleyball players. Moreover, higher composite asymmetry values, particularly those within the upper range of the sample distribution, may be associated with reduced motor control and movement accuracy.