A pre-workout is any supplement—usually a powder drink mix, but also available in the forms listed above—that claims to boost workout performance if you consume it beforehand.


While some pre-workout supplements have carbs, many are carb- and calorie-free. Others contain caffeine, beet juice, or amino acids such as arginine, citrulline, and ornithine, which companies market as revving up your “fight or flight” response, dilating your blood vessels, and increasing blood flow to your muscles, she says. Some supplements even contain esoteric ingredients like deer antler velvet to increase levels of insulin growth factor-1, a hormone that your body naturally produces in response to resistance training to increase muscle and tissue growth