Motion tracking in young male football players: a preliminary study of within-session movement reliability

Purpose We assessed the reliability of fundamental movement skills in young male footballers within one session. Methods: 197 players from 5 English category 3 football academies across U9 - U18 age groups volunteered (mean: age = 12.6 +/- 2.8 years; stature = 156 +/- 17 cm; weight = 47 +/- 15 kg; years from peak height velocity (PHV) = - 1.1 +/- 2.3). Motion tracking of squat depth and anterior Y-balance test maximum reach was recorded. Reliability was assessed (trial 1 vs. 2; trial 2 vs. 3) via mean change, intraclass correlation coefficient (ICC), and typical error. Results: The overall mean change was trivial (-1.8-2.9%), while Y-balance left showed a small negative change (trial 2 vs. 3; -3.2%). All ICCs across the tests ranged from moderate to high (0.71-0.79). Typical errors for Y-balance tests ranged from 8.3-10.8% and squats from 19.3-21.8%. Pre-PHV vs. post-PHV players had similar typical errors for Y-balance left and right (9.0 vs. 11.5%; 9.0 vs. 7.1%, respectively), and the squat (21.1 vs. 20%). Conclusions: The high within-player typical error scores obtained over three trials suggest that, contrary to some movement screening guidelines, prior habituation is needed to increase both the stability and reliability of these tests.