Background: The Upper Quarter Y Balance test (YBT-UQ) is a field test for measuring shoulder mobility/stability. However, there is a lack of information regarding age- and sex-specific reference values for classifying the YBT-UQ performance of children and adolescents.

Objective: The aim was to investigate YBT-UQ performance in youth and to provide age- and sex-specific normative values.

Method: Six hundred and sixty-five persons (325 girls, 340 boys) aged between 10 and 17 years carried out the YBT-UQ test. Following this, maximum reach values, normalised in terms of arm length, were calculated for each arm (i.e., left and right) and reach direction (i.e., medial [MD], inferolateral [IL], superolateral [SL]), and the composite score (CS) per arm. Additionally, percentiles were displayed graphically and in tabular form, distinguished according to age and gender.

Results: In boys, those aged 14-15 years showed a higher achievement (e.g., MD direction) compared with both younger (12-13-year-olds) and older (16-17-year-olds) persons. In girls, differences related to age could only be observed for the IL direction and the CS, where the youngest age group (10-11-year-olds) achieved better results than the older groups. Sex-specific differences to the girls' advantage could be observed in 12-13-year-olds (i.e., SL and CS), and to the boys' advantage in 14-15-year-olds (i.e., for all reach directions) and 16-17-year-olds (i.e., IL and SL direction and CS). Further, curvilinear developments were observed with regard to the 10th, 50th, and 90th percentiles, and were more strongly marked in boys than in girls.

Conclusions: The obtained age- and sex-specific normative values for the YBT-UQ can be used by teachers, coaches, and therapists to classify the level of shoulder mobility/stability among 10-17 year-old children and adolescents.