Amino acids, the molecules that make up protein, help build everything from our hair to our skin to our eyes (and more!). They’re also crucial for a type of tissue we hold particularly dear—our muscle.
Five aminos have earned some extra spotlight for their muscle-boosting benefits, and may be particularly important for anyone who hits the gym and goes hard on the reg. Whether you’re considering adding an amino acid supplement to your fitness routine, don’t know much about the one you’re already taking, or just want to understand the magic that happens inside your muscles—we’ve got all the amino info you need.
The best-known—and perhaps most important—amino acids are the three branched-chain amino acids: leucine, isoleucine, and valine. These aminos, called BCAAs, are found in food protein sources like meat and dairy, explains Brian Tanzer, M.S., nutritionist and manager of scientific affairs for The Vitamin Shoppe. “These amino acids work to protect lean body mass—a.k.a. your muscle,” he says.
The importance of branched-chain aminos for our muscles has been well-researched, with one review (published in the Journal of Animal Science and Biotechnology) concluding that the BCAAs—especially leucine—“enhance protein synthesis.” They’re often found in a 2:1:1 ratio of leucine-isoleucine-valine—both in natural food sources and supplements. All three work together, but each has a slightly different function.
Leucine
The first BCAA is an all-star when it comes to muscle-building. Leucine plays a crucial role in muscle protein synthesis (the process in which muscle is repaired and built) and in the production of growth hormones, which also support muscle mass, according to the National Center for Biotechnology Information (NCBI). “Leucine also protects muscle tissue from breaking down when under stress, like vigorous strength-training,” adds Tanzer.
Since leucine is also an essential amino acid, meaning our body can’t produce it, we have to get it from food or supplements.
Isoleucine
The second BCAA, ‘isoleucine,’ might sound a lot like ‘leucine,’ but the magic it works in your muscles is a bit different. This BCAA can be converted to glucose and used as an energy source by your muscles when you’re working out, Tanzer says. In addition to regulating energy levels, isoleucine also regulates blood sugar and stimulates hormone production and immune function, according to the NCBI.
Valine
Like isoleucine, our third BCAA can also be used as an energy source by the muscle when you’re on your grind. But it also supports your workouts in another, unexpected way. “When you exercise, your body’s serotonin (its feel-good hormone) goes up, which can make you feel a little drowsy after a while,” says Tanzer. “Valine actually blocks the uptake of serotonin in your brain, which can help prevent that drowsy, fatigued feeling.” (This is known as the ‘central fatigue theory,’ in case you want to drop some science knowledge on your gym buddies.)
How To Benefit From BCAAs
To get the max benefits from these BCAAs, you’ll want to get between five and 10 grams into your system both before and after a workout, recommends Tanzer. This can be tough to pull off with food alone, since your body needs to digest the food, absorb the amino acids, and process them in the liver before it can transport them to the muscles through the blood.
That’s where a supplement comes in: “With an amino acid supplement, you skip the breakdown process and can send those BCAAs straight into the bloodstream and to the muscles,” Tanzer says.
You can start sipping on a BCAA supp—most are in powder form—a half-hour or so before your workout and keep on sipping as you sweat. (And since isoleucine and valine can both be used for energy, getting your BCAAs in before the gym can be especially beneficial if you haven’t eaten in a while.) Shake another scoop or two into your water bottle for post-sweat recovery, too.
Related: 4 Possible Reasons Why You’re Still Feeling Wrecked Days After A Workout
In addition to the three ever-important BCAAs, there are two other aminos you may want to keep in mind—and possibly in your shaker cup.
Glutamine
This amino acid plays a role in your post-workout recovery—and just so happens to be the most abundant amino in the body, according to the University of Maryland Medical Center. Glutamine supports your immune function, which takes a hit whenever your body is under stress—including when you work out, says Tanzer. “Your immune system might pull glutamine from your muscle tissue, leading to gradual muscle breakdown, so replacing that glutamine post-workout can help preserve your muscle mass,” he explains.
One study published in the Journal of Exercise Science and Fitness found that glutamine helped active men preserve muscle strength—and avoid soreness—following strength-training tests.
Tanzer recommends mixing five to 10 grams of glutamine into your post-workout BCAA drink. More bang for every sip!
Citrulline
The last noteworthy amino might be in another supplement you already take: your pre-workout. “Citrulline is a precursor to nitric oxide synthesis, which helps relax the blood vessels and boost circulation to your working muscle tissue,” explains Tanzer. Better circulation to your muscles benefits both your workout performance—and later recovery.
Because of its effect on blood vessels, you’ll also find citrulline in some ‘pump’ supps. (You’ll probably also see a similar amino acid, arginine, in these products—but citrulline appears to be the more effective of the two because it is better absorbed, according to Tanzer.)
Along with boosting blood-flow, the nitric oxide produced by citrulline can also boost the muscle’s ability to use energy, according to a study published in the Journal of the International Society of Sports Nutrition. The researchers found that cyclists performed better on a time trial and reported feeling less fatigued after taking citrulline regularly.
Citrulline may also help remove ammonia and lactic acid (which build up throughout exercise) from the muscles, and may help you grind on without that muscle ‘burn’ feeling, says Tanzer.
Somewhere around six grams of citrulline pre-workout is ideal, says Tanzer, though you’ll still benefit from the lower doses found in many preworkout formulas. You can add extra to your usual preworkout before you hit the gym, and add some to your recovery drink, as well, he says.
Just check with your doc before taking citrulline if you have any kidney issues, Tanzer recommends. The ammonia citrulline helps pull from the muscles has to go through the kidneys before leaving the body.