Three proposed drivers of growth
Muscle growth has often been framed around three contributing mechanisms: mechanical tension, metabolic stress, and muscle damage. Mechanical tension, the force a muscle generates against resistance through a range of motion, is widely regarded as the primary driver and the one most directly tied to hypertrophy.
Metabolic stress refers to the buildup of byproducts such as lactate and hydrogen ions during higher-rep, shorter-rest work, often felt as the pump. Muscle damage is the microscopic disruption of fibers that triggers repair and remodeling.
How the current picture has shifted
More recent interpretation leans heavily toward mechanical tension as the dominant factor, while the independent contributions of metabolic stress and muscle damage are now seen as smaller or as side effects that often accompany high-tension training rather than necessary causes of growth. Excessive muscle damage in particular may impair recovery rather than help.
All three still describe real phenomena and the model remains a useful way to organize training thinking, but it is best read as overlapping influences rather than three equal, separate switches. This is general educational information only.