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Muscle & Strength Builders

Enhance Muscle Recovery with Leucine

Learn how leucine and its metabolites boost muscle growth and enhance recovery.

Amino acids are the major constituents of proteins and are generally described as the building blocks necessary for muscular growth. 

Essential amino acids are those that cannot be synthesized by the body and must therefore be supplied in the foods and supplements we consume. Of all EAAs, the branched-chain amino acids — leucine, isoleucine and valine — have received the most attention as bodybuilding supplements because they make up approximately one-third of muscle protein. They’re released from skeletal muscle and catabolized (broken down) during exercise and in cases of injury to be used for energy and tissue repair. Early studies showed that supplementing with BCAAs slows catabolism during exercise and boosts anabolism during recovery.

Of the three branched-chain aminos, leucine is metabolized at the greatest rate during exercise. Not only that, but research has shown that enriching BCAAs with at least twice the amount of leucine is more anabolic than taking BCAAs in equal amounts. This finding has led to a number of studies aimed at unraveling the anabolic-activating potential of leucine and its metabolites — alpha-hydroxy-isocaproic acid (HICA), alpha-ketoisocaproic acid (KIC) and β-hydroxy-β-methylbutyric acid (HMB) — and how they can contribute to your muscular gains.


Research has proven leucine to be an unequivocal anabolic activator and muscle builder because it’s primarily involved in protein synthesis. In fact, a study published in The American Journal of Clinical Nutrition in 2011 showed that taking leucine-enriched amino-acid supplements during exercise enhances protein synthesis by more than 30 percent.

Leucine makes up only 5 to 10 percent of proteins, and blood leucine levels are known to decline by about 30 percent during strength training and 11 to 33 percent during fat-burning cardio sessions. As such, leucine requirements are much higher in athletes. It has also been reported that supplementing with leucine at 50 milligrams per kilogram of bodyweight per day prevents the decrease in blood leucine levels during intense strength training. For bodybuilders, leucine supplements make sense as a means to boost or enrich the leucine you currently get in your protein intake. 

Most research has investigated the use of leucine in conjunction with amino-acid blends or protein powders more so than leucine as a stand-alone. In fact, data show that it works best when taken along with other amino acids (like whey protein) and/or carbohydrates. 

Leucine Dosing: Take 4 to 6 grams twice daily. Take the first dose with your preworkout protein shake and the second dose 90 minutes after your postworkout meal. On non-workout days, take one dose of leucine with your first whey protein shake and another 90 minutes after your last meal.


Alpha-Ketoisocaproic Acid

The amino acid leucine and its metabolic intermediate KIC have been recognized as potent anticatabolic compounds for about 40 years. The transamination of leucine (a metabolic reaction that involves a transfer of an amino group from one molecule to another) forms KIC; many studies suggest KIC is responsible for decreased proteolysis (catabolism) observed with leucine supplementation. KIC also helps reduce toxic ammonia levels in working muscle, which may increase muscle performance. However, studies that support KIC as a stand-alone supplement are rare. Pure KIC is therefore not commonly sold in supplement stores, but you may be familiar with commercially available patented compounded formulas of KIC. 

β-Hydroxy-β-Methylbutyric Acid

HMB, an active anabolic compound found in skeletal muscle, is also formed through transamination of leucine. HMB has been around for a long time but lost its glamour after a handful of studies questioned its efficacy in fit and trained individuals. Hence, it has generally been prescribed for those beginning a workout program. Notably, past HMB studies using highly trained/fit subjects were generally fraught with problems in research design, wherein workout programs weren’t intense enough and/or HMB doses were not high enough to promote gains.

Recent evidence from a pair of relatively new studies provides support for HMB as a potent supplement that helps build aerobic fitness, strength and muscularity. In a recent clinical trial published in the Journal of the International Society of Sports Nutrition, researchers from the University of Central Florida tested the efficacy of HMB supplementation or placebo (3 grams per day) on boosting the training effect of high-intensity interval training in fit and active male and female subjects. They reported that after only four weeks of training, subjects who took HMB raised their VO2 peak (a measure of aerobic fitness) by approximately 5 percent, a remarkable figure considering the subjects commenced the study with relatively high levels of aerobic fitness.

In another recent study, published in the European Journal of Applied Physiology, scientists from the University of Tampa in Florida tested the effects of HMB supplementation or placebo (3 grams per day) in combination with a 12-week periodized resistance-training program in well-trained men. They reported that those who took HMB saw greater gains in overall body mass, lean body mass, strength and power, as well as decreased bodyfat, compared to those who took the placebo. Furthermore, subjects who took HMB had significantly lower cortisol (a catabolic hormone) levels and greater perceptions of recovery between training bouts. 

Finally, a recent study published in the Journal of the American College of Nutrition shows for the first time that an HMB-containing amino-acid supplement favorably alters the immune response to heavy resistance training in young men. Researchers concluded that 12 weeks of heavy resistance training with an HMB supplement augments the muscle cytokine environment in favor of growth and repair better than a placebo. These findings provide another viable mechanism by which HMB increases strength and lean mass with weight training. 

HMB Dosing: To get full advantage of its benefits, take 3 to 6 grams of HMB with a protein shake two to three times per day. Make sure one dose is taken 30 minutes preworkout. 

Alpha-Hydroxy-Isocaproic Acid

Alpha-hydroxy-isocaproic acid — aka leucic acid — is a product of leucine metabolism and occurs naturally in many fermented protein products such as cheese, wine and soy sauce. Recent clinical evidence shows that HICA is a potent anticatabolic (protein-sparing) supplement. It’s believed that its anticatabolic effects are a result of HICA’s ability to reduce the effect of enzymes (called metalloproteinases) that break down muscle tissue. 

In a placebo-controlled study published in the Journal of the International Society of Sports Nutrition, researchers reported that four weeks of HICA supplementation combined with strength training resulted in a 0.66-pound gain in lean body mass, with no change reported in the placebo group. Subjects who took HICA also reported significant decreases in muscle soreness during recovery. However, despite improvements in lean mass, test subjects’ muscular strength and performance did not differ among groups. 

HICA Dosing: Take 1.5 grams per day split into three doses of 500 milligrams with a protein shake immediately upon waking, preworkout and postworkout.