The comic hero Popeye said that spinach makes you strong [1]. At that time, many people believed that it was merely a myth that was supposed to make children like spinach. But Popeye is actually right with his statement. For a long time, people believed that it was the high content of iron that made you strong. But according to the magazine European Food Research and Technology spinach contains 0.66% iron and is not even among the foods richest in iron [2,3].

Researchers from the Swedish Karolinska Institute proved that it is not iron, but the spinach's nitrate that is responsible for improving muscle strength [2]. Other Swedish researchers found out that increased nitrate intake, as found in spinach, helps to perform at the same level even when less oxygen is available. The nitrates seal mitochondria and thus improve their function.

Thereby, more energy is available per unit of oxygen [4].

In a nutshell: it's truethat spinach helps strengthen muscles and perform better.