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When the satellite cells merge with the existing muscle cells to form new myonuclei this is more than muscle repair, its also the foundation for future muscle growth - beyond previous limits | more

If youve read the Intermittent Thoughts On Building Muscle (read it) you are beyond the simplistic view of muscle growth as a one-way process in the course of which muscle cells balloon up endlessly. Without the incorporation of "new" myonuclei (cell kernels) from the periphery your muscle would become dysfunctional sooner or later (learn more); and while myostatin will prevent that from happening the recruitment of new muscle cells from the satellite cell pool will provide the basis for future muscle growth.

I dont want to go into more detail, here. If you want to develop a better understanding of this process(es), I suggest you head back to the initially mentioned series about the physiological underpinnings of skeletal muscle hypertrophy.
Next to the inclusion of new myonuclei and facilitation of future muscle growth, the satellite cell pool will also provide the raw material for the repair or I should say replacement of damaged muscle cells. For strength trainees like you and me, its thus of paramount importance to ensure that our satellite cells are happy and healthy. And you know what? Thats not even difficult!

According to a recent study from the Aarhus University all it takes to  help your muscle precursor cells happily proliferating (grow, divide and mature to "real" muscle cells) is the mix of carbohydrates and whey protein youre probably consuming after each workout, anyway: A shake containing 28 g whey protein hydrolysate high in leucine (4 %) an 28 g of carbohydrate (4 %) - a 56h carbohydrate supplement served as control.

Figure 1: Overview of the experimental procedure (Farup. 2014)

As you can see in Figure 1 this supplement was not ingested once, but rather thrice a day - with the first serving being ingested immediately after the fasted subjects, 24 healthy young recreational active men,  initiated the exercise protocol, which lasted for approximately 30 min.

Its the whey that does the trick, but we dont know if we dont need CHOs as an adjunct

The provision of extra whey protein (but nor carbohydrates; white bars in Figure 2) lead to significant increases in satellite cell activity in both mixed muscle and type II fibers, but not type I fibers (not shown in Figure 2).

Figure 2: Number of satellite cells per muscle fiber (higher number = higher chance of incorporation; Farup. 2014)

Still, in view of the fact that regeneration is an energetically costly process, its not 100% certain that a certain amount of carbohydrates may be necessary to see the beneficial effects on satellite cell activity and the changes in maximal voluntary contraction force (not shown).
Reference:

• Farup, et al. "Whey protein supplementation accelerates satellite cell proliferation during recovery from eccentric exercise." Amino Acids (2014). Ahead of print.

Scientific evidence suggests: There is not one optimal protein to build muscle - its the mix of fast to slow proteins thats key.

For someone like yourself, whos making sure to get his daily dose of SuppVersity Science News, the results Reidy et al. present in their latest paper in the Journal of Applied Physiology can hardly be surprising. I have, after all, written about the superiority of whey + casein blends as potential muscle builders only recently ("When Whey & Casein Unite in the Spirit of True Physique Improvements, BCAAs & Glutamine Better Shut the F*** Up"  | (re-)read the article). It was thus only to be expected that a study in which the scientists from the University of Texas Medical Branch compared the effects of the prolonged hyperaminoacidemia thats associated with the ingestion of a blend of plant (25% soy) and dairy (50% casein, 25% whey) proteins (with varying digestion rates) to that of a pure rapidly digested whey would yield a definite points win for the "time-released" formula.
The reasons why its still well worth taking a closer look at the study results are (a) the fact that the f**** up supplement industry is still trying to tell you that protein blends would be inferior to overpriced isolates and (b) the educative value of the post-workout + post-supplementation serum amino acid profiles Reidy et al. observed the 16 healthy, young subjects (age range: 19 –30 yr) who participated in their double-blind, randomized clinical trial (with body fat levels of >24% those were certainly no physical culturists, though ;-)

Figure 1: Graphical overview of the study design (Reidy. 2014)

As you can see in Figure 1 the study protocol involved a standardized resistance training session in the course of which the subjects who had been kept on a diet containing 20% protein, 60% carbohydrate, and 20% fat at 12 kcal/kg for 72h, performed leg extensions on a Cybex-VR2 (Medway, MA), i.e. 8 sets of 10 repetitions at 55% (set 1), 60% (set 2), 65% (set 3), and 70% (sets 4 – 8) of the participants previously determined 1 RM with 3-min rest between sets, before they consumed the protein beverages (Whey or Blend) exactly 1 h postexercise.

Figure 2: Net phenylalanine enrichment (left) and inward and outward transport (right)

The ingestion of the beverages of which the blend and the whey protein contained of 20.1 g total protein (providing 1.9 g leucine, 1.0 g phenylalanine, 1.3 g valine, and 9.0 g EAA; 50% protein from sodium caseinate, 25% protein from whey protein isolate, and 25% protein from soy protein isolate) and 17.3 g of protein (providing 1.9 g leucine, 0.6 g phenylalanine, 1.1 g valine, and 8.7 g EAA; 100% whey protein isolate), respectively, lead to significant increases in amino acid transporter activity (2/SLC38A2, proton-assisted amino acid transporter 1/SLC36A1, cationic amino acid transporter 1/SLC7A1).

"However, the ingestion of the protein blend resulted in a prolonged and positive net phenylalanine balance during postexercise recovery compared with whey protein (P 0.05)." (Reidy)

In view of identical postexercise myofibrillar protein synthesis in both groups this difference may appear negligible. If youve been following my articles about the often oversimplified protein synthesis and increases in skeletal muscle mass, you should be aware that net retention and not fractional synthesis is the term you have to look for, when youre analyzing corresponding studies.
Reference: 

• Reidy, Paul T., et al. "Soy-dairy protein blend and whey protein ingestion after resistance exercise increases amino acid transport and transporter expression in human skeletal muscle." Journal of Applied Physiology 116.11 (2014): 1353-1364.