Plyometric Jump Training Effects on Maximal Strength in Soccer Players: A Systematic Review with Meta-analysis of Randomized-Controlled Studies

Background: Maximal strength may contribute to soccer players’ performance. Several resistance training modalities offer the potential to improve maximal strength. During recent years, a large number of plyometric jump training (PJT) studies showed evidence for maximal strength improvements in soccer players. However, a comprehensive summary of the available data is lacking. Objective: To examine the effects of PJT compared with active, passive or intervention controls on the maximal strength of soccer players, irrespective of age, sex or competitive level. Methods: To perform a systematic review with meta-analysis following PRISMA 2020. Three electronic databases (PubMed, Web of Science, and SCOPUS) were systematically searched. Studies published from inception until March 2023 were included. A PICOS approach was used to rate studies for eligibility. The PEDro scale was used to assess risk of bias. Meta-analyses were performed using the DerSimonian and Laird random-effects model if ≥ 3 studies were available. Moderator and sensitivity analyses were performed, and meta-regression was conducted when ≥ 10 studies were available for a given comparison. We rated the certainty of evidence using GRADE. Results: The search identified 13,029 documents, and from these 30 studies were eligible for the systematic review, and 27 for the meta-analyses. Overall, 1,274 soccer players aged 10.7–25.0 years participated in the included studies. Only one study recruited females. The PJT interventions lasted between 5 and 40 weeks (median = 8 weeks), with 1–3 weekly sessions. Compared to controls, PJT improved maximal dynamic strength (18 studies, 632 participants [7 females], aged 12.7–24.5 y; effect size [ES] = 0.43, 95% confidence interval [CI] = 0.08–0.78, p = 0.017, impact of statistical heterogeneity [I²] = 77.9%), isometric strength (7 studies; 245 participants, males, aged 11.1–22.5 y; ES = 0.58, 95% CI = 0.28–0.87, p < 0.001, I² = 17.7%), and isokinetic peak torque (5 studies; 183 participants, males, aged 12.6–25.0 y; ES = 0.51, 95% CI = 0.22–0.80, p = 0.001, I² = 0.0%). The PJT-induced maximal dynamic strength changes were independent of participants’ age (median = 18.0 y), weeks of intervention (median = 8 weeks), and total number of training sessions (median = 16 sessions). The certainty of evidence was considered low to very low for the main analyses. Conclusions: Interventions involving PJT are more effective to improve maximal strength in soccer players compared to control conditions involving traditional sport-specific training. Trial Registration The trial registration protocol was published on the Open Science Framework (OSF) platform in December 2022, with the following links to the project (https://osf.io/rpxjk) and to the registration (https://osf.io/3ruyj).