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Standardized differences of the performance tests comparing pre- and post- the 6-week preseason period in young soccer players. LJ, loaded jump group; UJ, unloaded jump group; SJ, squat jump; CMJ, countermovement jump; VEL, velocity; MPP, maximum mean propulsive power relative to the players' body mass; error bars represent 90% confidence limits; gray area represents the smallest worthwhile change based on Cohen's units (effect size > 0.2).
