Accurate interpretation of physical test results is essential to objectively measure parameters both at a single point in time and throughout longitudinal assessments. This is particularly relevant for tests of speed and change of direction, which are among the most commonly used assessments for soccer players at different levels. This study aimed to quantify the impact of start-line distance (30 cm vs. 100 cm) on linear sprint splits (5-30 m), change-of-direction (COD), and T-test performance in elite youth soccer players, while also examining potential order effects. The study involved 82 youth soccer players (14-19 y; 180.68 ± 6.97 cm; 71.65 ± 7.91 kg; BMI 21.90 ± 1.57) from an elite academy, divided into two groups. The first group started trials at 30 cm from the starting line, then at 100 cm, while the second group performed in the reverse order. All participants underwent a standard sequence of tests: anthropometric measurements, 5, 10, 20, and 30 m sprints, change-of-direction running, and the T-test. The longer start (100 cm) improved sprint times with large effects tapering with distance: 5 m (Hedges` g = 1.00, 95% CI 0.80-1.25; Delta = 0.076 s, 0.060-0.093; 6.99%), 10 m (g = 1.37, 1.14-1.68; Delta = 0.102 s, 0.086-0.119; 5.63%), 20 m (g = 1.58, 1.36-1.88; Delta = 0.112 s, 0.096-0.127; 3.66%), 30 m (g = 1.48, 1.26-1.80; Delta = 0.114 s, 0.097-0.131; 2.71%). COD also improved (rank-biserial r = 0.516, 0.294-0.717; Delta = 0.075 s, 0.034-0.116; 1.00%) and the T-test improved (g = 0.61, 0.37-0.86; Delta = 0.107 s, 0.068-0.145; 1.26%). Order effects on Delta were evident for 30 m (Welch t = -3.05, p_Holm = 0.0157, d = -0.67) and COD (MWU p_Holm = 0.0048, r = -0.43). Protocols must specify and report the start geometry; the order should be randomised or counter-balanced, particularly for 30 m and COD.
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