It's time you start taking Popeye's advice on eating spinach seriously as new research says that nitrates from vegetables like spinach really make muscles stronger.

In the study from Karolinska Institute in Stockholm, mice were fed nitrates from spinach for a week. They were then dissected and the muscles of these mice were compared to the muscles of mice that weren't given nitrates in food.

"The mice that had been on consistent nitrate had much stronger muscles," researchers said in a statement.

The amount of nitrate given to these mice was roughly equal to the amount of nitrate present in about 250 grams or (9 ounces) of spinach, the researchers told AFP.

We get about 80 percent of our dietary nitrates from vegetables. Nitrates are considered beneficial at low quantities however high concentration of nitrates in our food can be harmful to one's health.

In addition to nitrates, spinach has phytochemicals and research has shown that these phytochemicals can prevent or at least delay cognitive decline in people.

The benefit for your muscles is obvious, "well, it is if you eat spinach. For people who don't eat their vegetables it will be more tricky," said Andres Hernandez, one of the researchers at the Department of Physiology and Pharmacology, to AFP.

The researchers discovered the mechanism by which nitrates help tone muscles. According to study, nitrates act on two proteins that are known to be associated with calcium regulation in humans. When the level of these proteins increases, more calcium is released in the body. This in turn increases muscle contraction.

"If you have more calcium released, you have a stronger contraction," said Hernandez. The change was more prominent in muscles that are used for high-intensity exercises.

The study doesn't just help those who are keen on muscle toning but helps those who need to increase the strength of muscles like senior citizens.

"The really exciting part is to go ahead and look at people with muscle weakness, with muscle diseases, and even aging, and see if this can actually improve their muscle function," Hernandez said.

The study will be published in the Journal of Physiology.