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Leucine: The Super Amino Acid

Among the amino acids important to CrossFit performance, leucine stands out for its involvement in muscle protein production.


In grade school, we were taught simple algebra skills, skills that we use every day as adults and that clearly demonstrate time and time again that the “net��� of any situation is based on the balance (or imbalance) between positive and negative factors. Simple algebra also helps us understand how muscle can change over time. On a daily basis, muscle is broken down (negative muscle mass) while it is simultaneously being built up (positive muscle mass). But how does that happen and what are the key signals involved? And, more specifically, what nutrients promote optimal gains in training-induced muscle development, improvements in WOD performance and general fitness? In this article, we pick one critical factor, leucine, to develop a better understanding of how this amino acid is critically important in supporting optimal muscle gains from CrossFit training.

Tipping the Scale: Protein Intake, Timing and Type

If muscle is constantly and simultaneously being built and broken down, how can we tip the balance toward anabolism so that muscle gets bigger, stronger and more powerful? Clearly, resistance-based and high-intensity training increases signaling systems for muscle protein synthesis. What’s more, this amplification is strongest in the first couple of hours after training and wanes over the next 12 to 24 hours. However, there’s a catch. Muscle protein synthesis can only be maximized when protein is consumed at levels exceeding 20 grams, either immediately before or after training.

While that addresses the muscle-protein-synthesis side of the equation, strenuous training actually promotes muscle protein breakdown, which can endure for hours after training. The way to counteract that also involves eating. Postworkout carbohydrate consumption, in combination with the insulin response that drives carbohydrates into muscles to refuel and aid recovery, is the key to minimizing muscle protein breakdown.

The Power of Leucine

Maximizing muscle protein gains by consuming protein and flooding muscle tissue with amino-acid building blocks before and after training and throughout the remainder of the day is a no-brainer. However, this is only the first step in understanding the signals that turn on muscle growth. University researchers determined that when a special subset of amino acids, called essential amino acids, were provided alone, they had the same impact on protein synthesis as when twice the amount of whole protein (but delivering the same levels of essential amino acids) was given. Further still, leucine appears to be the key signaling essential amino acid, and there is a base need of 2.5 grams of leucine to really turn up protein synthesis.

Locating Leucine

Now that we understand that leucine is the amino-acid barometer for determining whether a meal or supplement is going to help ensure maximal muscle gains, the next question is what foods and supplements best provide this amino acid. Leucine is found in all protein sources, but the amount an athlete will get depends on the food (or supplement) and how much he or she consumes. It’s more concentrated in animal protein like milk and meat versus plant foods, and among the protein supplements you just can’t beat milk-derived proteins like whey protein isolate and concentrate and milk protein isolates because it only takes 23 grams of whey protein to deliver 2.5 grams of leucine.

So there you have it. Protein may be king in ruling muscle protein synthesis, but leucine just might be the king’s secret weapon that stokes and helps optimize the process. And animal proteins, especially milk-based foods and whey supplements, really deliver the leucine payload, thereby improving muscle development and the kinds of performance gains that can result from CrossFit training.