Using a pre-workout supplement can help you reap the benefits of every rep you put in at the gym—but sometimes it feels like you need a degree in chemistry to figure out which one is best for your goals.

Here’s the full breakdown of the most popular pre-workout ingredients in the game, so you can sprint faster, lift heavier, or cycle further without having to wonder what the heck you’re sipping on.

1. Caffeine

Many fitness enthusiasts have one major demand of their pre-workout: energy. So more often than not, caffeine will be one of a pre-workout’s MVPs. Stimulants like caffeine don’t actually give you extra energy (only food can do that), but they can make you feel more energized and alert by stimulating your central nervous system, boosting your heart rate, opening up your blood vessels, and increasing the flow of oxygen and nutrients throughout your body.

You’ll find anywhere from 100 to 300 milligrams of caffeine in pre-workout supplements. (400 milligrams total of caffeine per day seems to be the safe upper limit.) If you don’t do caffeine or work out at night, look for a pre-workout labeled ‘caffeine-free’ or ‘stim-free.’

2. Creatine

This natural compound, which is made from three amino acids, affects how energy is used, recycled, and stored in your muscles, and helps you use your finite supply efficiently during weight-lifting or high-intensity interval training, according to Tod Cooperman, M.D., President and CEO of ConsumerLab.com, which independently tests health and nutritional products. Creatine also helps jump-start the muscle-building process by drawing in water and stimulating a compound called insulin-like growth factor, or IGF. Research shows creatine can support muscle growth and strength, as well as improve sprint performance.

Related: How Many Times A Week Should You Strength Train?

Since creatine takes a few weeks to build up in your system, you have to use it consistently, according to Cooperman. In addition to your pre-workout supp, you can also find it in foods like eggs, beef, and fish. Experts typically recommend about five grams a day.

3. L-Arginine And L-Citrulline

The amino acids arginine and citrulline are used to produce nitric oxide, a chemical that relaxes our blood vessels to increase blood flow.  “And since your blood carries oxygen and nutrients to your tissues, this increased flow ups the supply of the good stuff to your muscles.” Research show citrulline to be the more effective of the two, with one study, for example, finding that citrulline helped cyclists feel less fatigued and perform better on time trial tests. Fitness enthusiasts also often find this nitric oxide-induced blood flow boost contributes to a satisfying muscle ‘pump’ and extra ‘vascular’ look.

The amount of arginine and/or citrulline in pre-workouts varies greatly from brand to brand—but experts often recommend up to six grams total before getting sweaty. (If you have any cardiovascular issues, check with your doc before supplementing with these, advises Cooperman.)

4. B Vitamins

B vitamins are often credited for giving us energy, but what they really do is help our body better convert the energy from food into energy it can use. The four you’ll most often see in pre-workout formulas: vitamin B6 (involved in hundreds of functions, including central nervous system activity), folic acid (key for brain function and production of DNA), vitamin B12 (important for nerve health and energy production), and niacin (supports the metabolism of fats, carbs, and protein into energy.)

Different formulas pack different amounts of these B vitamins, but they’re often higher in B12 than the other Bs.

5. BCAAs

Of the 20 amino acids (the building blocks of protein) our body needs, three in particular—leucine, isoleucine, and valine—are especially crucial for our muscles. These three aminos are known as the BCAAs, or ‘branched-chain amino acids.’ Of the three, leucine gets the most glory for its pivotal role in triggering muscle protein synthesis, the process through which our muscles recover and grow. Meanwhile, isoleucine can be converted to energy in our cells, regulate our blood sugar, and enhance our hormonal and immune responses. Valine can also be converted into energy, but also helps keep the ‘feel-good’ hormone serotonin—which can make us a little drowsy—from getting in the way of our performance.

Supplementing with about five grams of BCAAs before a workout can promote muscle-building and ward off soreness afterwards, says Cooperman. A study published in the Journal of Sports Medicine and Physical Fitness confirms this, finding that athletes who supplemented with BCAAs during intense training reported less fatigue and soreness and had lower measures of muscle damage than those who did not.

6. Beta-Alanine

Beta-alanine, which is produced in the liver, contributes to our levels of muscle carnosine, another amino acid-like compound that supports performance and endurance by buffering the compounds that cause that burning, fatigued feeling in your muscles. Carnosine is found in type-two muscle fibers, which help you power through high-intensity activities like sprinting or heavy lifting, so beta-alanine offers a boost for circuit- or interval-style workouts that involve bouts of effort lasting one to four minutes, according to the International Society of Sports Nutrition (ISSN).

You can find beta-alanine in protein-rich foods like eggs and meat, but a supplement can best ramp up your muscles’ concentrations of carnosine. According to the ISSN, it takes about four weeks of four to six grams of beta-alanine a day to make the magic happen.

7. Betaine

Though this amino acid-like compound has been understood for a while, betaine has recently gained popularity with fitness enthusiasts for its ability to help the body utilize protein efficiently. One recent study tested betaine’s potential and found that fit men who supplemented with 2.5 grams daily throughout a six-week training period increased muscle size and power, and improved their body composition (amount of body fat compared to lean mass, like muscle), better than those who took a placebo.

Since other studies on less-active individuals did not return such favorable results, researchers believe that betaine is most effective in already-fit people performing high-intensity exercise.

Read pre-workout labels like a pro with this infographic: