Plyometric training is an effective method for enhancing lower-body muscle power, and modulating external loads may further optimize its training effects. Currently, there is a lack of systematic comparisons between externally loaded and unloaded plyometric training with respect to performance outcomes, such as vertical jump, horizontal jump, and sprint performance. Moreover, the differential effects of various load intensities remain unclear. Therefore, this study employs a meta-analysis to systematically evaluate the effects of plyometric training under different loads on jump and sprint performance. Following PRISMA guidelines, randomized controlled trials published between January 2010 and April 2025 were systematically searched in PubMed, Web of Science, Scopus, EBSCO, and CNKI databases. Inclusion criteria were: healthy participants, an experimental group performing externally loaded plyometric training, a control group performing unloaded plyometric training, and outcome measures including jump and/or sprint performance. Fourteen studies were ultimately included. Externally loaded training was categorized into four groups based on load intensity: assisted load (APT, 15% body weight). A meta-analysis was conducted using RevMan 5.4 software to pool effect sizes, test heterogeneity, perform subgroup analyses, and generate forest plots. Data were synthesized using random-effects or fixed-effects models, with effect sizes expressed as standardized mean differences. The significance level was set at p < 0.05. Vertical Jump: Only MPT significantly improved performance vs. UPT (ES = 0.43, p < 0.0001). APT, LPT, and HPT showed no significant difference. Horizontal Jump: No significant differences found among any load intensities vs. UPT (ES = 0.09, p = 0.40). Sprint: LPT (ES=-0.92, p = 0.0005) and MPT (ES=-0.23, p = 0.04) significantly improved performance vs. UPT. HPT showed no significant effect. Medium-load (5–15% body weight) plyometric training is most effective for improving vertical jump performance. Both low-load and medium-load training are more effective than unloaded training in enhancing sprint performance. Assisted-load training yields effects similar to those of unloaded training on jump performance. No significant differences were observed among various load intensities in improving horizontal jump performance. It is recommended to select appropriate load intensities based on specific performance goals in practice and to avoid excessive loading (i.e., 15% of body weight) to maintain movement quality and training adaptability.
Zhang et al. (Mon,) studied this question.