Why Your First Strength Gains Come From Your Nerves

Opener

Almost everyone who starts lifting gets stronger fast. The weights go up week after week, yet the mirror barely changes. That isn't a trick of the eye. In the first weeks of training, most of the new strength comes from the nervous system learning to drive the muscle harder, not from the muscle getting bigger.

A 2025 topical review in The Journal of Physiology by Edoardo Lecce, Paolo Amoruso, Francesco Felici and Ilenia Bazzucchi, from the University of Rome Foro Italico, pulled together what is known about how the brain, spinal cord, motor units and muscle each change with resistance training, and how those changes add up to strength, power and size.

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1. What this review is asking

Resistance training makes you stronger, more powerful and more muscular. The question here is where those gains come from: how much is the nervous system getting better at using the muscle you already have, how much is new muscle, and how the timing of the two fits together.

The authors also asked how the way you train (load, speed, volume and rest) steers which of those changes you get.