Popeye the Sailor Man was on to something when he guzzled cans of spinach. Turns out the green stuff, along with other vegetables like beets, radishes and lettuce, really does help grow meaner muscles — just not as dramatically as Popeye’s burgeoning biceps.

According to a new study published in Cell Metabolism, a substance called nitrate, found in spinach and other leafy greens, helps muscles work more efficiently.

Healthy participants in the study who took nitrate supplements for three days consumed less oxygen, and therefore expended less energy, when riding exercise bikes. Thanks to the nitrates, the participants were able to work out longer and harder.

Here’s how: When nitrate — found in spinach, for example — combines with certain bacteria in saliva, it converts to nitric oxide, a molecule that helps transport oxygen to cells. The harder muscles work, the more oxygen they need to function efficiently.

Ironically, the researchers also found that it’s the lower levels of protein in natural sources of nitrate, like spinach, that help cells deliver nutrients and oxygen better. Typically, protein makes these cells leak nutrients, rendering them less efficient.

Even if you’re not a super athlete, you can enjoy the benefits of dietary nitrates, too. In addition to improving muscle efficiency, nitrates have been shown to open up blood vessels, which could help people with diabetes and those with cardiovascular disease.

Nitrate’s “chemical cousin,” nitrite, which is also found in leafy greens, could even save your life during a heart attack. Nitrites help heal tissue damage by returning oxygen to blood quicker.

So take a hint from the spinach-swallowing cartoon sailor — eat your leafy greens and veggies for smarter, meaner muscles and a stronger heart.