Acute and Chronic Effects of Accentuated Eccentric Loading vs. Constant-Load Resistance Training: A Systematic Review and Meta-analysis

BACKGROUND: Accentuated eccentric loading (AEL) is a resistance training (RT) method applying greater eccentric- than concentric-phase load to intensify the training stimulus; however, despite its common use, a comprehensive and quantitative review remains lacking. OBJECTIVE: The aim was to compare acute responses and chronic adaptations between AEL and constant-load RT, and examine whether effects vary by AEL protocol (submaximal, maximal, supramaximal). METHODS: PubMed, Web of Science, Embase, and EBSCO were searched from inception through July 3, 2024; eligible English-language studies were included. Pooled and subgroup meta-analyses were performed using random-effects models. RESULTS: Forty-nine studies involving 773 participants were included. Although considerable variance exists in certain outcomes, our estimated effects suggest that, compared to constant-load RT, AEL results in (1) similar acute responses in loads lifted during the concentric phase (standardized mean difference [SMD] = - 0.16; p = 0.48), mechanical performance at submaximal loads during the concentric phase (SMD = - 0.07; p = 0.37), countermovement jump height both immediately (SMD = - 0.06; p = 0.86) and delayed (SMD = - 0.23; p = 0.44) post-intervention, maximal voluntary isometric force immediately post-intervention (SMD = 0.03; p = 0.89), blood lactate concentration during the intervention (SMD = - 0.06; p = 0.78), testosterone concentration immediately post-intervention (SMD = 0.68; p = 0.15), creatine kinase concentration both immediately (SMD = 0.09; p = 0.72) and delayed (SMD = 0.14; p = 0.48) post-intervention, cortisol concentration immediately post-intervention (SMD = 0.39; p = 0.05), heart rate during the intervention (SMD = 1.18; p = 0.07), acute muscle swelling immediately post-intervention (SMD = 0.26; p = 0.42), muscle electrical activity during the concentric phase (SMD = - 0.01; p = 0.90), and muscle soreness both immediately (SMD = 0.28; p = 0.30) and delayed (SMD = 0.18; p = 0.28) post-intervention; (2) greater acute responses in blood lactate concentration immediately post-intervention (SMD = 0.44; p = 0.03), growth hormone concentration immediately post-intervention (SMD = 0.50; p = 0.01), muscle electrical activity during the eccentric phase (SMD = 0.37; p = 0.01), and rating of perceived exertion immediately post-intervention (SMD = 1.72; p = 0.01); (3) similar chronic adaptations in maximal concentric strength (SMD = 0.12; p = 0.41), maximal eccentric strength (SMD = 0.19; p = 0.58), maximal isometric strength (SMD = 0.03; p = 0.93), countermovement jump height (SMD = 0.04; p = 0.87), muscle fascicle angle (SMD = - 0.10; p = 0.77), muscle fascicle length (SMD = 0.90; p = 0.17), and muscle cross-sectional area (SMD = - 0.06; p = 0.84). CONCLUSION: While AEL augments the eccentric-phase stimulus (higher eccentric load and muscle electrical activity), it also increases metabolic stress and perceived effort, implying a need for longer, more frequent inter-set rests and longer between-session recovery. Given the lack of evidence for superior chronic benefits in strength or muscle architecture over constant-load RT, practitioners should consider these factors carefully. PROTOCOL REGISTRATION: The original protocol for this review was prospectively registered with the International Prospective Register of Systematic Reviews (PROSPERO) in July 2024 (CRD42024561673).