Acute and Delayed Effects of Strength and Plyometric Activation Exercises on Jumping, Sprinting, Ball Shot Velocity and Muscle Stiffness in Youth Soccer Players

Purpose This study investigated the acute (10 min) and delayed (5 h) effects of strength, plyometric, and control priming protocols on neuromuscular performance in youth soccer players. Methods Fifteen male soccer players (15.6 ± 0.6 years; BMI = 19.7 ± 1.9 kg/m 2 ) completed three randomized sessions: strength training (ST, 1 × 5 × 40% + 2 × 5 × 70% 1RM squat and hip thrust), plyometric training (PT, 3 × 5 hurdle jumps, 3 × 6 bounds), and control training (CT, 12 min jogging/walking). Assessments included countermovement jump (CMJ), repeated sprint ability (RSA, 6 × 20 m), ball shot velocity (BSV), and vastus medialis stiffness via myotonometry at baseline, acute (AE), and delayed (DE) time points. Results In the ST, CMJ height declined at AE (34.45 ± 4.62 vs. 32.84 ± 4.69 cm) but significantly improved to DE (35.74 ± 5.02 cm; d = 0.59) compared to baseline (34.45 ± 4.62 cm). No significant CMJ height changes occurred in the PT or CT. CMJ maximal force significantly increased in the PT from AE (1130.4 ± 155.0 N) to DE (1221.7 ± 203.4 N) and also exceeded baseline (1184.8 ± 180 N; d = 0.17). RSA increased across all protocols acutely, but only the CT showed significant improvement from AE (3.46 ± 0.15 s) to DE (3.32 ± 0.15 s; d = 0.89) and from baseline (3.39 ± 0.13 s; d = 0.44) to DE. Neither BSV nor stiffness changed significantly. Conclusion Strength priming may enhance jump performance after sufficient recovery, while inconsistent effects on sprinting and shooting highlight the need for individualized strategies in youth soccer.