This is a bit outdated.

Muscle damage and metabolic fatigue are no longer believed to be major factors for driving hypertrophy. 

Mechanical *tension* is the main thing driving muscle growth.

Tension is created when muscle fibers pull on bones under resistance.  

That tension is sensed by mechanosensors within the muscle, which send signals for the muscle cell to start making more muscle proteins (then they grow bigger).

Based on the last decade of research, muscle damage and metabolic stress simply don’t correlate well with muscle growth, which is why soreness is not the key to growth, but progressive overload is.