All EAA precursors used for muscle protein synthesis in the post-absorption state are derived from muscle protein breakdown. It has been reported that in humans after normal absorption, the rate of muscle protein decomposition exceeds the rate of muscle protein synthesis by about 30%.
Using BCAA alone (that is, without using other EAAs) can only increase the protein synthesis of the muscle after absorption by improving the recycling efficiency of EAA from protein breakdown to protein synthesis, rather than being released to plasma or oxidized.
This is because all 9 EAA (and 11 NEAA) need to produce muscle protein, and EAA cannot be produced in the body.
If only 3 EAA are consumed, just like BCAA, then protein breakdown is the only source of remaining EAA, and the remaining EAA is the precursor of muscle protein synthesis.
Therefore, it is theoretically impossible to produce an anabolic state by only consuming BCAA-in this state, the synthesis of muscle protein exceeds the breakdown of muscle protein.
If a generous assumption is made that the consumption of BCAAs can increase the recycling efficiency of EAA from muscle protein breakdown to muscle protein synthesis by 50%, then this will translate into a 15% increase in muscle protein synthesis rate. In addition, from muscle to plasma A 50% reduction in EAA released will also reduce the pool of free EAA in plasma and cells.
Since a 50% increase in circulation efficiency is approximately a reasonable maximum, this means that the maximum stimulation of muscle protein synthesis cannot exceed 15%; this is equivalent to an increase in the partial synthesis rate of muscle from approximately 0.050%/h in the basal state to 0.057%/ h, and the difference in the partial synthesis rate (FSR) of this protein is difficult to accurately measure.