Auswirkungen eines spezifischen Schnellkrafttraining im Fussball

Introduction: Speed and power abilities are considered important prerequisites for match performance in soccer. Previously, several studies predominantly focused on the training of endurance capacity. Scientific studies addressing specific strength and power training methods, particularly when conducted during the competitive season, are scarce so far. Heavy-load training is rarely possible during the soccer competitive season.  As most lower-body movements in soccer are performed unilaterally, one-legged strength exercises using lighter additional loads have recently been proposed as promising alternative to bilateral exercises to increase lower leg strength and power. The aim of this study was to investigate the effects of a 7 weeks combined strength and power training program during the competitive season on various fitness parameters in high-level amateur soccer players. Methods: Sixteen male soccer players (age: 22.7 (SD 2.5) y, height: 1.79 (5.8) m, weight: 76.9 (6.5) kg) from one team of the third Swiss league were randomly stratified (strata: one-repetition maximum (1-RM), 10 m sprint time) to either a combined strength-power training (ST, N= 8) or a control (CON, N= 8) group. The intervention was conducted twice per week during 7 weeks of competitive season. ST comprised strength exercises (uni- and bilateral half squats and calf raises with additional weights) combined with plyometrics and/or sprints. CON performed technical and tactical training during the same time period. Before and after the training period, several physical fitness parameters were measured: 1-RM (half squat), isometric peak strength and rate of force development (RFD), vertical jump height (countermovement jump, CMJ (one- and two-legged); drop jump, DJ), 10 and 30 m sprint times, agility testing with the ball, and intermittent endurance performance (yo-yo intermittent recovery test 1). Results: Players attended on average 10.9 (1.1) training sessions during the 7 weeks period. Large significant test x group interactions were found for 1-RM (p < 0.001, partial eta squared (η2) = 0.76), CMJ (p = 0.001, η2 = 0.56) and CMJ with the left leg (p = 0.015, η2 = 0.35) with increases after ST (+3 to 18%) and similar or decreased values (+0.6 to -6.9%) in CON. Although not significant (0.16 ≤ p < 0.35) comparable results were observed in several other parameters (isokinetic peak strength, CMJ with right leg, DJ, 30 m sprint time, and intermittent endurance) with effect sizes indicating at least medium effects (0.07 ≤ η2 < 0.15). No relevant between-group differences were observed for agility testing and 10 m sprint. Conclusion: It is concluded that a 7 weeks in-season strength and power training can improve relevant physical performance compared to routine technical and tactical training in high-level amateur soccer players. The medium effects in sprint time, jumping and intermittent endurance need further verification in randomized-controlled trials with more participants.