Branched-chain amino acids (BCAAs), which include the amino acids leucine, isoleucine and valine, are one of the most popular sports nutrition supplements on the market today. But many people don’t know how to consume them properly. For instance, when exactly should you take them? Here, we break it all down for you.

First, The BCAA Backstory

The workout-related benefits of BCAAs are two-fold. First, they help muscle repair and grow after exercise. Second, they may also help delay fatigue during exercise itself.

When it comes to muscle repair, leucine is the star player. This BCAA has been credited for kick-starting muscle protein synthesis, the process through which muscle tissues repair and build. It also supports our production of growth hormones that help us build muscle.

Isoleucine’s claim to fame: Muscles can use it for fuel during higher-volume exercise (endurance training or higher-intensity resistance training) when glycogen—our muscles’ primary fuel source—gets used up, explains Michael Roberts, Ph.D., director of the Molecular and Applied Sciences and Applied Physiology Laboratories at Auburn University. That said, consuming extra BCAAs could spare the breakdown of the BCAAs already in muscle cells during training.

Our muscles can also use valine to make fuel, but the final BCAA plays another role, too. Research suggests that it “may work in the central nervous system to reduce what’s termed ‘central fatigue,’” says Roberts. When you exercise, your body ups its production of the feel-good hormone serotonin, which makes you feel a little drowsy. Valine blocks serotonin’s receptors, helping you stay focused and driven as you sweat.

Related: 6 Reasons Why You’re Not Building Muscle

Together, the BCAAs can have legitimate impact on fitness over time. One study published in the journal Amino Acids, for example, found that well-trained cyclists who supplemented with 12 grams of BCAAs per day for 10 weeks increased cycling power and improved time trial performances.

BCAA Timing

Though we know BCAAs can benefit weight lifters and cardio junkies alike, research on the ideal time to take them is still a bit mixed.

For a long time, research on amino acid ingestion focused heavily on timing. But it’s now beginning to focus more on the total amount consumed per day, says Roberts. (While there is a clear window of time post-workout when your body better uses carbs to replace muscle glycogen and recover, the muscle protein synthesis process lasts longer. This means we may not need amino acids as urgently.)

“However, given that muscles can use BCAAs as fuel—especially during exercise—I think there’s good reason to supplement peri-exercise,” he says. ‘Peri-exercise’ refers to the general window of time around your workout, which includes before, during, and after you train.

Though traditional advice recommended taking BCAAs post-exercise, “studies that have compared pre-exercise and post-exercise have found no real difference,” adds Darryn Willoughby, Ph.D., director of the Exercise and Biochemical Nutrition Laboratory at Baylor University.

One study published in Frontiers in Physiology found that supplementing with 5.6 grams of BCAAs right after resistance training produced a 22 percent higher rate of muscle protein synthesis. However, a recent Journal of the International Society of Sports Nutrition suggests consuming BCAAs has similar effects on performance and muscle mass when taken either pre- or post-workout.

Rules For The Road

Generally, as long as you get your BCAAs in sometime around your workout (whether before, during, or after), you’ll still reap their muscle and performance benefits.

Related: 11 Sports Nutrition Supplements That Taste Like Candy

However, since BCAAs take about 30 minutes to really hit your bloodstream, take a dose (at least six grams) half an hour before getting sweaty to really get the most out of their potential fatigue-busting benefits. Take this approach if you’re:

• working out first thing in the morning
• working out hours after your last meal
• are on a low-carb diet (and don’t have as much glycogen stashed for fuel)

To really do your BCAA due-diligence, take five to 10 grams both before and after your workout.

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