The research team, a collaboration between Stirling, Birmingham and Exeter Universities reconfirmed that ingesting a drink containing BCAAs stimulates muscle protein synthesis (MPS) after resistance training.
However, the post-exercise muscle building effect from consuming BCAAs in isolation was sub-optimal. The study, published in Frontiers in Physiology, revealed that the body needs additional essential amino acids (EAAs), contained in intact whey protein, to maximise muscle growth response.
"Our results show that the common practice of taking BCAA supplements in isolation will stimulate muscle protein synthesis - the metabolic mechanism that leads to muscle growth - but the total response will not be maximal because BCAA supplements do not provide other amino acids essential for the best response,” commented study leader Professor Kevin Tipton from the University of Stirling.
Consequently, athletes should consider using whole protein powders such as whey, which contain BCAAs and other EAAs, rather than BCAAs in isolation.
"A sufficient amount of the full complement of amino acids is necessary for maximum muscle building, following exercise. Athletes interested in enhancing muscle growth with training should not rely on these BCAA supplements alone," the researchers concluded.
Muscle protein synthesis
Resistance-training induced muscle growth is achieved through the increase in thickness and number of muscle fibres known as myofibrils. The scientific term for this process is called myofibrillar-MPS.
Early studies had suggested that leucine was the single amino acid responsible for myofibrillar-MPS. Newer data has revealed that other BCAAs - valine and isoleucine - might enhance the response to leucine of the signalling pathway responsible for MPS after exercise.
Researchers in this trial confirmed that BCAAs, taken without other EAAs. stimulated MPS in resistance-trained males. However, the degree of MPS was less than in previous studies using whole whey protein.
The scientists observed a decline in arterial phenylalanine content three hours after consuming the BCAA drink, which was consistent with previous findings of decreased EAA concentrations following leucine ingestion.
They proposed that BCAAs alone did not provide enough total amino acids to satisfy the body’s demand, limiting the muscle building effect. Consequently, they concluded that an additional source of EAAs is necessary to enable maximum MPS.
“Taken together, past and present data suggest that the availability of EAA may be a critical factor for the optimal response of MPS following resistance exercise. Since the ingestion of BCAAs alone stimulates myofibrillar-MPS, but does not increase the supply of all EAA, the overall response of myofibrillar-MPS following resistance exercise is limited,” wrote the researchers.
The findings also explain why earlier studies observed greater MPS response from ingesting BCAAs as part of intact whey protein versus identical amounts of BCAAs alone.
Source: Frontiers in Physiology
Published online. DOI : 10.3389/fphys.2017.00390
“Branched-Chain Amino Acid Ingestion Stimulates Muscle Myofibrillar Protein Synthesis following Resistance Exercise in Humans”
Authors: Sarah R. Jackman, Kevin D Tipton et al