Study Confirms: Acute Post-Exercise Myofibrillar Protein Synthesis Is Not Correlated with Resistance Training-Induced Muscle Hypertrophy in Young Men

FSR ≠ more muscle = no news for ya!

For the average SuppVersity reader the sentence "Acute Post-Exercise Myofibrillar Protein Synthesis Is Not Correlated with Resistance Training-Induced Muscle Hypertrophy in Young Men" is not just the title of a recent paper in the open access journal PLOS|ONE, it's also the experimental verification of a claim I've made in almost all my articles about the acute effects of certain training modalities and/or supplements on myofibrillar protein synthesis and the corresponding increases in muscle size some people appear to expect from a 2h-long 10% increase in fractional protein synthesis (learn more).

UPDATE: There is new data that extends the results of the study at hand and indicates that there is a link between MPS and muscle gains, after the initial adapation response to exercise.

And yes, practically speaking these findings imply that we have to question the real world significance of all the neat studies on the "superior muscle building effects" of whey protein, BCAAs and even more so leucine, in which the authors base their recommendations on acute increases in post-exercise protein synthesis.

Don't worry, you have not been "wheysting" your money: While there is a paucity of data to confirm the long(er) term muscle building effects of isolated amino acids (EAA, BCAA and leucine), there is plenty of data from 6-12 week human trials to support the pro-anabolic effects of whey protein. What we don't have, though is evidence to support the notion that the long-term muscle building effects are as superior to those of other protein sources (e.g. casein) as the increases in acute protein synthesis would suggest.

In the corresponding experiment that was funded by the National Science and Engineering Research Council (NSERC) of Canada Cameron J. Mitchell et al. determined whether the acute myofibrillar protein synthesis measured acutely in training-naive subjects after their first bout of resistance exercise with protein consumption would correlate with the actual increase in muscle size after 16 weeks of resistance training.

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Before the actual experiment began, the subjects, healthy young recreationally active normal-weight men (177 cm; body mass index = 26.4 kg/m²; men age 22 years) without previous strength training experience, underwent a magnetic resonance imagining (MRI) scans of their right thigh to determine muscle volume, a dual, energy x-ray absorptiometry (DXA) scan to assess whole body fat and bone-free mass (lean mass) and standardized strength tests to determine their maximal isotonic strength (often labeled the 1RM) for all training exercises.

After all baseline measurements (including baseline muscle protein synthesis) were recorded, the subjects completed 16 weeks of RT while ingesting a protein rich beverage (30g of the same whey protein of which Burd et al. showed in 2012 that it elicits a higher increase in MPS than casein) immediately after their exercise session and with breakfast on non-training days.

"Briefly, participants trained four times weekly with two upper and two lower body workouts. Lower body exercises are described above in the acute exercise session. Upper body exercises consisted of chest press, shoulder press, seated row, lat pulldown, bicep curl and tricep extension. The program was progressive in linear manner moving from 3 sets of 12 repetitions to 4 sets of 6  repetitions. At the end of the training period, MRI, DXA scans and strength testing were repeated." (Mitchell. 2014)

If you look at the above description of the workout (and supplementation regimen) you will probably agree that this is pretty much what the majority of resistance physique oriented gym-goers do.

Figure 1: Myofibrillar fractional protein synthesis rate (left) measured acutely after a single workout and changes in muscle volume (%) over the whole 16-week study period as a function of the 1-6h post-workout FSR (Mitchell. 2014).

People who hope that the often reported increases in fractional protein synthesis would pay off and yield increased net muscle gains and thus exactly what Mitchell et al. did not observe in their study, which could not establish the corresponding correlation between the actute increase in post-workout fractional protein synthesis (Figure 1, left) and the chronic change in muscle volume (Figure 1, right).

Figure 2: Changes in muscle volume (%) expressed relative to acute increases in 4E-BP (Mitchell. 2014).

If anything, it was the expression of the Eukaryotic translation initiation factor 4E-binding protein 1 aka 4E-BP1 one of the motors of protein synthesis, but not the increase in myofibrillar fractional protein synthesis that looked as if it could have any predictive value with respect to the increase in muscle volume, the young men experienced in the course of the 16-week training period.

After thinking about the implications of these findings for a minute, I do yet have to admit that the assumption that this would refute the previously invoked recommendations completely, is probably premature.

SuppVersity Suggested Read: "Protein Wheysting?! No Significant Increase in PWO Protein Synthesis W/ 40g vs. 20g Whey, But 100% Higher Insulin, 340% More Urea & 52x Higher Oxidative Amino Acid "Loss" | more

"Though shalt not make quantitative predictions about long(er) term muscle gains based on acute FSR measurements!" - This statement is unquestionably correct. It's something I have written about before and it's a statement that is supported (if not confirmed) by the data of the study at hand.

The statement "though shalt not make qualitative predictions about long(er) term muscle gains based on acute FSR measurements", on the other hand, would yet be unwarranted and is probably incorrect. We do after all have more than enough evidence that increases in post-workout protein synthesis will (sooner or later) result increases in muscle size. The fact that we cannot predict the extent of long(er) term hypertophy effects based on measuring acute changes in FSR does not imply that these changes would not matter at all. It does only mean that we have to be careful about overestimating the real-world effects of differences in protein synthesis between training modalities and supplements, even if they are statistically significant in the hours after a workout.

Reference:

• Burd, Nicholas A., et al. "Greater stimulation of myofibrillar protein synthesis with ingestion of whey protein isolate v. micellar casein at rest and after resistance exercise in elderly men." British Journal of Nutrition 108.06 (2012): 958-962.
• Mitchell, Cameron J., et al. "Acute post-exercise myofibrillar protein synthesis is not correlated with resistance training-induced muscle hypertrophy in young men." PLoS One 9.2 (2014): e89431.