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Every dynamic repetition has two main phases. During the concentric phase, the muscle shortens as it lifts the resistance. During the eccentric phase, the active muscle lengthens while controlling the load. It is not scientifically accurate to claim that the concentric phase is useless for hypertrophy. Both phases can build muscle, but eccentric work has considerable practical value because it can create high mechanical tension while the muscle lengthens.
What the eccentric phase is
The main difference is mechanical. Eccentric contractions can produce more force than concentric contractions while using less energy. Franchi et al. describe differences in maximum force production, metabolic cost and neural control. Put simply, a muscle can often control a heavier resistance on the way down than it can lift. That is why controlled lowering matters. If you simply let the load fall, you lose much of the eccentric stimulus. If you control it, the muscle remains under tension through a valuable part of the movement.
An older meta-analysis by Roig et al. compared eccentric and concentric training in healthy adults. Eccentric training was particularly effective for strength, while muscle-mass results tended to favour eccentric work, especially when it used a higher relative intensity. That distinction matters. An eccentric phase is not automatically better merely because it is slow or uncomfortable. Its value appears when it is genuinely loaded, controlled and technically sound.
Newer evidence is more cautious and therefore more useful. A meta-analysis by Schoenfeld et al. found an average difference favouring eccentric actions, but it was not statistically significant, so the authors recommended including both actions in hypertrophy training. A 2025 meta-analysis by da Silva et al. likewise concluded that overall hypertrophy is similar between eccentric and concentric work, although some subgroups favoured eccentric training. Muscle growth does not come from one magic phase, but the eccentric is the part of a repetition that people most often waste.
What the research shows
Muscle architecture provides another reason to value eccentric work. A systematic review by Douglas et al. reported that eccentric training is at least as effective as other forms of training for increasing muscle cross-sectional area and may produce different architectural adaptations, including changes related to growth in length. A muscle does not merely become larger; its internal arrangement can also change, and eccentric loading provides a specific stimulus for that remodelling.
The practical conclusion is simple. The concentric phase matters because it lifts the resistance, while the eccentric phase often determines the quality of the whole repetition by keeping the muscle under tension as the load returns. For hypertrophy, sets, repetitions and kilograms are not enough; you also need to control the resistance through the movement. The eccentric need not be endlessly slow or painful. It should be deliberate, stable and appropriately loaded.
How to use it in training
References
- Roig, M., O’Brien, K., Kirk, G., et al. The effects of eccentric versus concentric resistance training on muscle strength and mass in healthy adults: a systematic review with meta-analysis. British Journal of Sports Medicine, 2009. https://pubmed.ncbi.nlm.nih.gov/18981046/
- Schoenfeld, B. J., Ogborn, D. I., Vigotsky, A. D., Franchi, M. V., Krieger, J. W. Hypertrophic Effects of Concentric vs. Eccentric Muscle Actions: A Systematic Review and Meta-analysis. Journal of Strength and Conditioning Research, 2017. https://pubmed.ncbi.nlm.nih.gov/28486337/
- da Silva, L. S. L., Gonçalves, L. S., Alves Campos, P. H., et al. Comparison Between Eccentric vs. Concentric Muscle Actions on Hypertrophy: A Systematic Review and Meta-analysis. Journal of Strength and Conditioning Research, 2025. https://pubmed.ncbi.nlm.nih.gov/39652733/
- Douglas, J., Pearson, S., Ross, A., McGuigan, M. Chronic Adaptations to Eccentric Training: A Systematic Review. Sports Medicine, 2017. https://pubmed.ncbi.nlm.nih.gov/27647157/
- Franchi, M. V., Reeves, N. D., Narici, M. V. Skeletal Muscle Remodeling in Response to Eccentric vs. Concentric Loading: Morphological, Molecular, and Metabolic Adaptations. Frontiers in Physiology, 2017. https://www.frontiersin.org/journals/physiology/articles/10.3389/fphys.2017.00447/full