Discriminative validity of the lower and upper quarter Y balance test performance: a comparison between healthy trained and untrained youth

Background The Lower (YBT-LQ) and Upper (YBT-UQ) Quarter Y Balance Test have been widely used for the assessment of dynamic balance and shoulder mobility/stability, respectively. However, investigations on the validity of the two tests in youth are lacking. Therefore, we performed two studies to determine discriminative validity of the YBT-LQ (study 1) and the YBT-UQ (study 2) in healthy youth. Methods Sixty-nine male soccer players (age: 14.4 +/- 1.9 yrs) and 69 age-matched untrained male subjects (14.3 +/- 1.6 yrs) participated in study 1 and 37 young swimmers (age: 12.3 +/- 2.1 yrs) as well as 37 age-/sex-matched individuals (age: 12.5 +/- 2.0 yrs) took part in study 2. Absolute (cm) and relative (% leg/arm length) maximal reach distances per reach direction and the composite score of the YBT-LQ/UQ were used as outcome measures. One-way analysis of variance and the receiver operator characteristic curve analysis (i.e., calculating the area under the curve [AUC]) were conducted to assess discriminative validity. Results Concerning the relative values, youth athletes showed significantly better YBT-LQ (study 1: p < 0.001, d = 0.86-1.21) and YBT-UQ (study 2: p < 0.001, d = 0.88-1.48) test performances compared to age- and sex-matched untrained subjects. Further, AUC-values indicated a chance of >= 74% (YBT-LQ) and >= 71% (YBT-UQ) to discriminate between youth athletes and controls. These findings were confirmed when using the absolute data for analysis. Conclusions According to our results, the YBT-LQ and the YBT-UQ seem to be useful test instruments to discriminate trained and untrained healthy youth performance for dynamic balance and shoulder mobility/stability, respectively.