The cartoon character Popeye was right to scoff a can of spinach when he wanted his biceps to bulge, according to a study showing why the leafy vegetable makes us stronger.

Researchers at the Karolinska Institute in Stockholm, Sweden, discovered that nitrate, found naturally in spinach and several other vegetables, tones up muscles used for high-intensity activities like sprinting up a steep hill.

(a warning: was briefly mentioned study using mice but I don't think they were killed.)

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