Effect of Six Weeks’ Isometric Strength Training Compared to Traditional Strength Training on Gains in Strength, Power, and Speed in Male Academy Soccer Players

<b>Purpose:</b> Elevated sport-specific physical demands and congested fixture schedules leave little recovery time and augment fatigue levels in soccer players. Compared to traditional strength training (TST), isometric strength training (IST) may elicit comparative improvements in strength and performance-related parameters in soccer players, while reducing fatigue during periods of elevated competitive loading. <b>Methods:</b> This study compared the effects of 6-weeks' IST and TST on gains in strength, power, and speed in male academy soccer players. Eighteen athletes from a Football Association League 2 club's academy (age: 17.2 ± 0.6 years, height: 1.79 ± 0.06 m, body mass: 71.6 ± 3.4 kg) were randomly assigned to either the IST (<i>n</i> = 9) or TST (<i>n</i> = 9) group. Baseline and post-training testing included trap bar squat one-repetition maximum (1-RM), isometric mid-thigh pull (IMTP), bilateral vertical countermovement jump (CMJ), and 10 m and 40 m linear sprints. Each group completed 12 training intervention sessions over six weeks, which comprised either an isometric or dynamic variation of a mid-thigh (clean) pull, split squat, and hip thrust. <b>Results:</b> Results indicated no group × time interaction effect on trap bar squat 1-RM (<i>p</i> = .171, η_p² = 0.107), IMTP peak force (<i>p</i> = .478, η_p² = 0.039), CMJ jump height (JH; <i>p</i> = .463, η_p² = 0.028), CMJ peak power (PP; <i>p</i> = .868, η_p² = 0.001), 10 m acceleration (<i>p</i> = .074, η_p² = 0.186), or sprint velocity (<i>p</i> = .348, η_p² = 0.058). However, there were main effects of time on trap bar squat 1-RM (<i>p</i> < .001, η_p² = 0.634), CMJ JH (<i>p</i> = .031, η_p² = 0.255) and sprint velocity (<i>p</i> = .012, η_p² = 0.324). <b>Conclusion:</b> In conclusion, IST is just as effective as TST in improving (or maintaining) strength, power, and speed during fixture-congested schedules in men's academy soccer.