Pacing Strategies and Variability During Time- vs Distance- Based Trials for Estimating Maximal Aerobic Speed in Academy Soccer Players

Time-and distance-based trials are widely used to estimate Maximal Aerobic Speed (MAS) in soccer, yet pacing strategies during these tests are under-explored.This study examined pacing profiles during a 6-minute distance trial (6minDT) and 1800-m time trial (1800mTT) in twenty-seven highly trained male academy players (17.1 ± 0.6 years; 178.9 ± 5.5 cm; 71.9 ± 7.6 kg; MAS: 15.71 ± 0.89 km•h⁻¹).Both tests were performed in counterbalanced order, with instantaneous velocity sampled at 10 Hz using Global Positioning System (GPS) units.Rolling mean velocity was rescaled to 10% intervals of test completion, and a spline model separated pacing into three phases (0-30%, 30-80%, 80-100%).Parabolic pacing strategies were identified; U-shaped in the 1800mTT and reverse J-shaped in the 6minDT.Linear mixed-effects modelling revealed a higher starting velocity during the 6minDT (β0 = 18.4 km•h⁻¹) versus the 1800mTT (β0 = 17.9 km•h⁻¹).A greater velocity increase occurred in the final phase of the 1800mTT (β1 = 1.05 km•h⁻¹) versus 6minDT (β1 = 0.26 km•h⁻¹).Between-athlete variability reduced meaningfully in the middle phase (1800mTT: 0.19; 6minDT: 0.21 km•h⁻¹), with total variance attributed to within-athlete variability (2.68 km•h⁻¹; 95.4%).Both trials elicited parabolic pacing, though distinct within-athlete differences emerged across phases.