Why Branched-Chain Amino Acid Supplements Don’t Help Marathoners

You can cross branched-chain amino acid supplements off the list that might make your next marathon easier, according to new research published in the journal Amino Acids.

Although branched-chain amino acid supplements are most often associated with weightlifters and bodybuilders, they’ve been theorised to be potentially useful for endurance athletes. Briefly stated, the central fatigue theory says that changes in the central nervous system and how it communicates with muscles and the brain can cause endurance performance to deteriorate. When other indicators of central fatigue are present, there’s a decline in plasma levels of branched-chain amino acids. Therefore, the thinking goes, supplementing with branched-chain amino acids could lead to postponing central fatigue.

In the study, 46 marathoners consumed a branched-chain amino acid supplement from powder or a placebo with similar kilojoule content every day in the week before a marathon. Before and after the race, the runners provided a urine sample and did a jump test to measure muscular power.

There was no difference in the two groups’ finish times, jump tests or markers of muscle damage in urine. Psychologically, the groups reported similar feelings of muscle pain. Simply put, there was no evidence that the branched-chain amino acid supplements helped the marathoners in any way.

This study’s findings are consistent with other research finding no benefit of branched-chain amino acid supplements for distance runners.

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