Physical performance tests are commonly applied in sports injury prevention and rehabilitation to measure abilities linked to athletic demands, including muscle strength, explosive power, and agility. These assessments offer insight into an athlete's functional capacity. The Upper Quarter Y Test (UQYBT) has been widely used for assessment of athletes. However, there is limited information on its reliability in swimmers.

To assess the reliability, standard error of measurement (SEM), and minimal detectable change (MDC) of the UQYBT in swimmers.

This is a cross-sectional study. This study was approved by Ethics Research Committee. Swimmers of both sexes, aged 12 to 60 years, with at least one year of competitive experience and a minimum of two training sessions per week were eligible. Two assessments were conducted with an average interval of 10.37 ± 3.15 days between them. Three ground lines were marked: medial, superolateral, and inferolateral. With one hand on the center mark, the individual reached with the free limb three times per direction. The mean, normalized by limb length, and the composite score were analyzed. The reliability of the UQYBT was assessed using the Intraclass Correlation Coefficient (ICC 3.3), Standard Error of Measurement, and 95% Minimal Detectable Change. The ICC was classified as excellent (ICC > 0,90), good (0,75-0,90), moderate (0,50-0,75) and poor (ICC < 0,50). Data analysis was performed using the Statistical Package for the Social Sciences, version 23.0 (SPSS Inc, Chicago, IL).

A total of 51 athletes participated in the study. The non-normalized UQYBT for the dominant side demonstrated good reliability across all three directions, with ICC values ranging from 0.80 to 0.84. The SEM ranged from 4.11 to 6.28, while the MDC ranged from 11.41 to 17.42. For the normalized scores, reliability ranged from moderate to good, with ICC values of 0.68 for medial (SEM = 6.12, MDC = 16.97), 0.82 for superolateral (SEM = 4.80, MDC = 13.31), and 0.72 for inferolateral (SEM = 7.43, MDC = 20.61). The composite score for the dominant side also showed good reliability (ICC = 0.82, SEM = 3.73, MDC = 10.34). On the non-dominant side, the non-normalized score of all three directions demonstrated good reliability, with ICC values ranging from 0.86 to 0.89, SEM from 3.66 to 5.65, and MDC from 10.17 to 12.76. For the normalized scores, reliability ranged from moderate to good, with ICC values of 0.70 for medial (SEM = 5.65, MDC = 15.66), 0.87 for superolateral (SEM = 4.43, MDC = 12.30), and 0.80 for inferolateral (SEM = 6.06, MDC = 16.80). The composite score for the non-dominant side demonstrated good reliability (ICC = 0.86, SEM = 3.61, MDC = 10.02).

The UQYBT demonstrated moderate to good reliability for assessing swimmers. The SEM and MDC values were provided to help clinicians interpret the test results.

Clinicians can use the UQYBT for assessing swimmers, considering the moderate to good reliability. In addition, clinicians should consider the SEM and MDC for interpreting the results of UQYBT.