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07.09.2017

BCAAs stimulate post-workout muscle gain - but need help

Right now in Blogland it's de rigueur to slag BCAAs off as ineffective strength sport supplements, but that's not quite fair. According to a human study that English sports scientists led by Kevin Tipton published in Frontiers in Physiology, taking a couple of grams of BCAAs after a workout does stimulate the synthesis of muscle protein. But strength athletes who only use BCAAs around training sessions and don't supplement these with complete proteins or essential amino acids are missing out on a lot.

Study
The researchers got 11 male students, all experienced weight trainers, to train their legs on two different occasions three hours after breakfast. The workout consisted of four sets on the leg press and four sets on the leg extension machine.

On one occasion the participants were given 5.6 g BCAAs after the workout – the amount found in 20 g whey. On the other occasion the participants were given a placebo supplement containing 5.6 g carbohydrates.

Results
As expected, the concentrations of leucine, isoleucine and valine in the participant' blood increased after they had been given BCAAs. And the concentration of phenylalanine decreased more after taking BCAAs than after taking the placebo. That suggests that the muscle cells were stimulated by the BCAAs to absorb amino acids from the blood.

At the same time the BCAAs in the samples of leg muscle cells that the researchers had taken from the students caused an extra increase in the activity of anabolic signal molecules like AKT and S6K.

There was a bigger increase in synthesis of contractile muscle protein in the muscle cells after the participants had been given BCAAs than after they'd been given a placebo.

Conclusion
"The present study demonstrated that ingesting of all three BCAAs alone, without concurrent ingestion of other essential amino acids, protein, or macronutrients, stimulated a 22% greater response of muscle myofibrillar protein synthesis following resistance exercise compared with a placebo," the researchers wrote. "The magnitude of this increased response of muscle myofibrillar protein synthesis was approximately 50% less than the previously reported muscle myofibrillar protein synthesis response to a dose of whey protein containing similar amounts of BCAAs."

"Taken together, these results demonstrate that BCAAs exhibit the capacity to stimulate muscle myofibrillar protein synthesis, however a full complement of essential amino acids could be necessary to stimulate a maximal response of muscle myofibrillar protein synthesis following resistance exercise."

"This information potentially has important nutritional implications for selecting amino acid supplements to facilitate skeletal muscle hypertrophy in response to resistance exercise training and the maintenance of muscle mass during aging, unloading, or disease."

"It is well-established that BCAA ingestion stimulates the activation of mTORC1 signaling pathways that regulate the translational activity of muscle protein synthesis. [Am J Physiol Endocrinol Metab. 2004 Jul;287(1):E1-7.] [Acta Physiol (Oxf). 2010 Nov;200(3):237-48.] [Am J Physiol Cell Physiol. 2016 Jun 1;310(11):C874-84.] Moreover, recent results demonstrate that the presence of the valine and isoleucine enhances the response of mTORC1 to leucine."

"However, results from the present study suggest that ingesting BCAAs alone, without the other EAA, provides limited substrate for protein synthesis in exercised muscles. Thus, the overall response of muscle protein synthesis is not maximized."

"Thus, whereas our data clearly show that BCAA ingestion activates cell-signaling pathways that result in increased myofibrillar muscle protein synthesis, ingestion of BCAAs alone may not be the optimal nutritional regimen to stimulate a maximal muscle protein synthesis response to resistance exercise training."

Source:
Front Physiol. 2017 Jun 7;8:390.

More:
BCAAs prevent muscle loss at high altitude 12.02.2017
BCAAs help dieting strength athletes retain muscle mass 08.06.2016
Effect of BCAAs on muscles is dose dependent 21.01.2016

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