If you’ve spent any time at the gym lately, you’ve likely heard at least one person say something like, “Man, I can’t believe I forgot to take my pre-workout!” And given the growth of the pre-workout supplement market, you’ll likely hear a lot more comments like that in the near future.

But all this talk—and marketing—has left many fitness enthusiasts wondering exactly what constitutes a quality pre-workout supplement, or if the formulas work at all. The bad news is that a lot of the pre-workout supplements out there are filled with nonsense ingredients. The good news is that some ingredients really are proven to up your workout game.

Here’s our quick rundown of the common pre-workout supplement ingredients that have actually been shown to boost fitness performance in major research studies.

Beetroot juice

Beetroot juice has become the fitness world’s darling following a series of very promising studies. Research in the journal Physiology found that men who drank beetroot juice for two weeks could work out longer and experienced more muscle growth. Another study showed that heart failure patients who drank beetroot juice daily experienced nearly 25% better aerobic endurance within just one week. Another major article published last year confirmed the juice’s ability to boost cardio performance.

Why all the buzz about beetroot juice? It’s rich in nitrates, which the body converts into nitric oxide once consumed. Nitric oxide, in turn, relaxes the blood vessels and helps ensure oxygen makes it to your muscles during a tough workout. (Want to know more about nitric oxide supplements? Check out our essential list.)

Creatine

Although some studies show that creatine works best when taken after a workout, it’s still one of the most well-researched supplements on the market today—and a common supplement in post-workout blends. High doses of creatine help build muscle mass and increase your strength, and the Mayo Clinic calls it effective especially for athletes seeking short bursts of strength or speed. HIIT, anyone?

L-Arginine

This amino acid is a key ingredient in most nitric oxide supplements. Like beetroot juice, L-Arginine plays an indirect role in ensuring enough oxygen makes it to your muscles while you’re working them out, all by triggering the release of nitric oxide. In one study, cyclists who took a powdered arginine supplement had a 16.7% better anaerobic threshold after three weeks when compared with men given only a placebo. In case you’re wondering, the anaerobic threshold is the point in your workout where lactic acid starts accumulating in your muscles.

Branched-Chain Amino Acids (BCAAs)

BCAAs are the building blocks of life, stimulating the synthesis of protein. BCAAs contain valine, isoleucine and leucine, which are called “essential” amino acids because your body can’t make them on its own. BCAAs are scientifically proven to aid recovery and help you work out longer. In one study, BCAAs were found to be effective for recovery as well as building the muscle’s anaerobic power. Beta-alanine is one of the more common BCAAs found in pre-workout supplements.

Caffeine

Caffeine has been scientifically proven to boost your energy while working out, all while making you feel like you’re not working as hard. Pretty great, right? It’s not surprising that caffeine’s ability to increase alertness and energy translates into better athletic performance. One study found that pre-workout supplements boosted performance only marginally, but formulas containing caffeine had the biggest impact.

Carbohydrates

Carbs provide crucial workout fuel. Consuming them in the right quantity before a workout can boost your energy and performance. Just ask LeBron James or the countless other athletes who make sure to get in some carbs before every big game.

When choosing a pre-workout supplement, it’s important to follow recommended doses; it is possible to overdo it, even on good ingredients. General guidelines say that you should aim for 250 milliliters of beetroot juice pre-workout, 30 grams to 40 grams of carbs, 3 milligrams of caffeine per kilogram of body weight, and between 5 grams and 10 grams of amino acids. But every person is different. If you’re not sure if your pre-workout supplement is working the way it should, listen to your body and consult your doctor. You can also find the essential ingredients in most pre-workout supplements through whole foods.

Now that you know a  bit about the pre-workout ingredient landscape, check out our reviews of the top pre workout products. And if you’re after a different kind of supplement, check out our lists on the best nitric oxide supplements and the most effective protein powders.