Amdi, Christian HoumannKing, Andrew2025-12-102025-12-102025-07-21Journal of Sports Sciences, ISSN: 0264-0414 (Print); 1466-447X (Online), Taylor and Francis Group, 43(20), 2447-2464. doi: 10.1080/02640414.2025.25351980264-04141466-447Xhttp://hdl.handle.net/10292/20375The duration of the eccentric phase may affect resistance training (RT) adaptations, with narrative reviews yielding equivocal conclusions. Thus, five databases were searched following Cochrane and PRISMA-guidelines, to compare RT outcomes following shorter (SEG) and longer (LEG) eccentric phase durations. A prospectively registered (https://osf.io/s6uqn/) random-effects multi-level meta-analysis with robust variance estimation was performed for strength, hypertrophy and countermovement jump height (CMJ), with results interpreted relative to a region of practical equivalence. Evidence quality was assessed using the Cochrane RoB 2 and GRADE criteria. Nine studies involving 166 participants (46% trained, 77% male) were included. SEG enhanced CMJ by a practically worthwhile degree with moderate certainty (Hedge's g = -0.73 [90% CI = -1.34, -0.12; 90% PI = -1.34, -0.12]), while uncertain estimates were observed for maximal strength (g = 0.25 [90% CI = -0.17, 0.67; 90% PI = -0.86, 1.36]) and muscle hypertrophy (g = 0.05 [90% CI = -0.22, 0.33; 90% PI = -0.54, 0.64]). LEG led to practically equivalent or enhanced strength gains, compared to SEG, in trained participants (g = 0.33 [90% CI = 0.07, 0.60; 90% PI = 0.07, 0.60]) and volume-load matched trials (g = 0.25 [90% CI = 0.04, 0.45; 90% PI = 0.04, 0.45]) with moderate certainty in subgroup analyses. Therefore, SEG enhance CMJ, while LEG may cause similar or higher strength increases in trained participants and volume-load matched conditions. However, more research is needed.© 2025 The Author(s). Published by Informa UK Limited, trading as Taylor & Francis Group. This is an Open Access article distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/4.0/), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. The terms on which this article has been published allow the posting of the Accepted Manuscript in a repository by the author(s) or with their consent.Tempocadencepowerrepetition durationresistance training32 Biomedical and Clinical Sciences3202 Clinical Sciences42 Health Sciences1106 Human Movement and Sports Sciences1302 Curriculum and PedagogySport Sciences3202 Clinical sciences4207 Sports science and exercise5201 Applied and developmental psychologyHumansMaleAdaptation, PhysiologicalHypertrophyMuscle StrengthMuscle, SkeletalPlyometric ExerciseResistance TrainingTime FactorsFemaleMuscle, SkeletalHumansHypertrophyAdaptation, PhysiologicalTime FactorsFemaleMaleMuscle StrengthResistance TrainingPlyometric ExerciseHumansMaleAdaptation, PhysiologicalHypertrophyMuscle StrengthMuscle, SkeletalPlyometric ExerciseResistance TrainingTime FactorsFemaleJournal ArticleOpenAccess10.1080/02640414.2025.2535198