What is Muscle Protein Synthesis?
MPS (muscle protein synthesis or myofibrillar protein synthesis) is a measure of how your muscles take up protein from the blood at add to their mass.
After a workout when protein is consumed, many studies use MPS to draw conclusions about where something is good or bad for increasing muscle mass.
The problem is many studies measure this effect in the short term and assume that this increase in MPS will persist or at least lead to more muscle mass in the long term.
A study investigating how well MPS predicts long term muscle gains followed 23 untrained men doing a 16 week upper/lower body split 4 times a week with linear progression from 12RM och 6RM. Subjects were given protein, carb and fat supplements after their workouts and on the morning of rest-days and their muscle mass was followed using MRI (gold standard).
The study found no significant or relevant correlation between MPS 6h post-workout and the amount of muscle gained (1). Thus short-term MPS should not be used to draw long-term conclusions.
This doesn’t exclude the fact that the effect of whey protein/BCAAs may still have an effect, as the population was untrained and, although unlikely from this result of this study, well trained people may still build more muscle than they otherwise would’ve if they didn’t take whey/BCAA (2).
1: Mitchell CJ. Acute post-exercise myofibrillar protein synthesis is not correlated with resistance training-induced muscle hypertrophy in young men. PLoS One. 2014 Feb 24;9(2):e89431.
2: Pasiakos SM. The effects of protein supplements on muscle mass, strength, and aerobic and anaerobic power in healthy adults: a systematic review. Sports Med. 2015 Jan;45(1):111-31.