so a few things i've come across that are reshaping the way I train:
muscle protein synthesis (MPS) and muscle protein breakdown (MPB) are separate processes that determine the size of a muscle. (MPS>MPB = hypertrophy). traditionally, MPS has been shown to be greatest at moderate to low loads, moderate to high volume/repetitions. This advocates for the "bodybuilding" style of lifting. HOWEVER, i have now seen several studies that decided to investigate this more in depth and found:
- type I fibers show the greatest amount of markers for MPS but also far more markers of MPB.
- there is genetic interaction with the load placed on a muscle, more activation --> less energy within the muscle --> activation of certain factors such as AMPK that have direct interaction with DNA to essentially create a more efficient muscle (which would mean smaller and more oxidative)
- increased activation of muscle increases the amount of intracellular calcium --> which activates certain factors that degrade tissue (proteases)
- mTOR (which a protein that basically interprets many different signals and activates MPS) is most directly stimulated by stress applied to the surface of the muscle cell; also, the more intense the force, the more muscle fibers are activated (almost) always beginning with the "smaller" low threshold type I oxidative and generally gradually recruiting the "larger" type II. so basically, if mTOR/MPS is stimulated by dynamic tension on the muscle, a heavy force will generally stimulate more fibers than lighter, more reps. another piece of this is that another major stimulator is IGF, but IGF is produced in many cells in the body. The kind that most readily stimulates muscle mass is the kind that the muscle cell produces within itself (as opposed to the liver) which can be stimulated by...you guessed it, tension. I know that there was another forum on bb.com about the role of hormones in hypertrophy referenced here, so I'd definitely check out some of that and not take my word for anything here.
so the question i'm struggling with is of course, why train with lighter weights and/or high volume if these things apparently demonstrate a means to inhibit muscle growth? INJURY not withstanding. I must say that I cannot find a threshold to call "high" or "light", so this is kinda in the grey, I know.
