Metabolic Stress & Hypertrophy: do metabolites create muscle growth ?

In the current model of hypertrophy, and the mechanisms behind it, 3 are the "main" ways through which hypertrophy occurs: ⁣

1) Mechanical Tension⁣
2) Metabolic Stress⁣
3) Muscle Damage (which we've already seen it actually doesn't cause muscle growth by itself) [1]⁣

But if point 3 is "out" of the triade, let's see whether or not metabolic stress is actually a separate (or different ?) way through which muscle growth occurs. ⁣

When we're performing a long training set and our muscle fibers fatigue, metabolites accumulate within our muscles. Generally motor unit recruitment increases, but NOT because the lower-threshold motor units stop working or because metabolite accumulation causes it by itself [2] but rather because our CNS *responds* to this fatigue mechanism by increasing the level of effort perceived, and thus increasing motor unit recruitment [3]: ⁣

This causes higher threshold motor units to be recruited and muscle fibers to be activated: as fibers keep working, they experience greater level of mechanical tension, which is what ultimately leads to muscle growth, over time. ⁣

Therefore, in reality, Mechanical Tension is the main driver of muscle growth and we never see hypertrophy when the other mechanisms happen *alone* (without Mechanical Tension, which is what actually matters!)⁣


1) Regenerated rat skeletal muscle after periodic contusions - PubMed
2) Elevated plasma lactate levels via exogenous lactate infusion do not alter resistance exercise-induced signaling or protein synthesis in human skeletal muscle - PubMed
3) Changes of the force-velocity relation, isometric tension and relaxation rate during fatigue in intact, single fibres of Xenopus skeletal muscle - PubMed