Eccentric or Concentric: Neither Builds More Muscle

Opener

Every rep has two halves: the concentric, where the muscle shortens and lifts the weight, and the eccentric, where it lengthens under control and lowers it. For years, the lowering half has had a reputation as the part that really builds muscle, which is why slow negatives, eccentric-only machines and "accentuated" lowering get sold as growth tricks.

A 2025 meta-analysis from da Silva, Benjamim, Alves and colleagues in the Journal of Strength and Conditioning Research put that idea to the test. Across 26 trials, training with only eccentric actions did not build more muscle overall than training with only concentric actions. The edges that did show up were in narrow places: arm muscles, short studies, one way of measuring muscle, and lab machines most people never train on.

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1. What this review is asking

Eccentric and concentric actions are produced differently inside the muscle. Eccentric work lets a muscle produce more force for less energy, and it takes more eccentric reps than concentric reps to reach the same level of fatigue. That difference is why people expected eccentric training to grow muscle faster.