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Coratella, G, Beato, M, Milanese, C, Longo, S, Limonta, E, Rampichini, S, Cè, E, Bisconti, AV, Schena, F, and Esposito, F. Specific adaptations in performance and muscle architecture after weighted jump-squat vs. body mass squat jump training in recreational soccer players. J Strength Cond Res 32(4): 921–929, 2018—The aim of the present study was to compare the effects of weighted jump-squat training (WJST) vs. body mass squat jump training (BMSJT) on quadriceps' muscle architecture, lower-limb lean-mass (LM) and muscle strength, performance in change of direction (COD), and sprint and jump in recreational soccer players. Forty-eight healthy soccer players participated in an offseason randomized controlled trial. Before and after an 8-week training intervention, vastus lateralis pennation angle, fascicle length, muscle thickness, LM, squat 1RM, quadriceps and hamstrings isokinetic peak torque, agility T-test, 10-and 30-m sprints, and squat-jump (SJ) were measured. Although similar increases were observed in muscle thickness, fascicle length increased more in WJST (Effect size [ES] = 1.18, 0.82–1.54) than in BMSJT (ES = 0.54, 0.40–0.68), and pennation angle increased only in BMSJT (ES = 1.03, 0.78–1.29). Greater increases in LM were observed in WJST (ES = 0.44, 0.29–0.59) than in BMSJT (ES = 0.21, 0.07–0.37). The agility T-test (ES = 2.95, 2.72–3.18), 10-m (ES = 0.52, 0.22–0.82), and 30-m sprints (ES = 0.52, 0.23–0.81) improved only in WJST, whereas SJ improved in BMSJT (ES = 0.89, 0.43–1.35) more than in WJST (ES = 0.30, 0.03–0.58). Similar increases in squat 1RM and peak torque occurred in both groups. The greater inertia accumulated within the landing phase in WJST vs. BMSJT has increased the eccentric workload, leading to specific eccentric-like adaptations in muscle architecture. The selective improvements in COD in WJST may be related to the increased braking ability generated by the enhanced eccentric workload.