drtbear1967
Musclechemistry Board Certified Member
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!)
References:
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
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!)
References:
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
