Systematic review and meta-analysis of eccentric-only versus concentric-only strength training effects on maximal voluntary eccentric, concentric and isometric contraction strength

Abstract

Background Conflicting results have been reported regarding the effects of resistance exercise training with eccentric (lengthening muscle) versus concentric (shortening muscle) contractions on changes in muscle mechanical function assessed by different contraction modes. Objective The main objective of this systematic review with meta-analyses was to compare effectiveness of maximal isokinetic eccentric-only and concentric-only strength training for changes in maximal voluntary eccentric (MVC_ECC), concentric (MVC_CON), and isometric contraction (MVC_ISO) strength in healthy adults. Methods We conducted a systematic search in PubMed, SPORTDiscus, and Google Scholar from February to March 2024 for studies that met the following criteria: (1) randomized controlled trials; (2) inclusion of eccentric-only and concentric-only strength training groups; (3) use of an isokinetic dynamometer for training and testing; (4) reporting changes over time in MVC_CON and MVC_ECC; and (5) using healthy adult participants. The certainty of evidence was assessed using the Grading of Recommendations Assessment, Development and Evaluation approach. A multilevel random-effects model meta‑analyses with robust variance estimation were performed in Rstudio software using metaphor and clubSandwich packages. Moreover, sensitivity analysis was performed, excluding the highly influential studies. The potential moderating role of sex, training status and age of the participants, muscles, velocity in training and testing, initial MVC_ECC, MVC_CON, and MVC_ECC/MVC_CON ratio, and training-related variables such as number of repetitions per set, number of sets, number of sessions per week, and duration of the training protocol were also assessed. Results Twenty-seven studies matched with the criteria, and overall 162 study results were identified and included in the meta-analyses. Greater effects on MVC_ECC was found after eccentric-only versus concentric-only training (Hedge’s g: 1.51; 27% vs. 10%; p < .05). However, no differences were evident between the training modalities for changes in MVC_CON (Hedge’s g: − 0.10; 13% vs. 14%, p = .726) and MVC_ISO (Hedge’s g: − 0.04; 18% vs. 17%; p = .923). The subgroup analyses showed smaller effect of eccentric-only than concentric-only training on MVC_CON when eccentric-only training was performed at higher velocities than the velocities of MVC_CON testing (Hedge’s g: − 0.99; p < .05). Meta-regressions showed that the longer the training period, the greater the superior effect of eccentric over concentric training on MVC_ECC. Conclusions Eccentric-only strength training is more effective for improving MVC_ECC, but both concentric-only and eccentric-only training provide similar effects on improving MVC_CON and MVC_ISO. Further studies are necessary to investigate the mechanisms underpinning the superior effect of eccentric-only training.