Not just for bodybuilders, muscle matters for runners of the fairer sex, too. "The benefits of having a healthy amount of lean body mass are enormous for women," says Monica Vazquez, a marathoner and master trainer with New York Sports Clubs. "It reduces injury risk and boosts metabolic rate, which increases fat burning all day long." Achieving a toned physique requires more than just pumping iron. Proper nutrition plays a key role in a woman's muscle-building efforts. Incorporate these muscle-building foods into your diet to meet your protein quota.