Scientists have evidence that Popeye was right: spinach makes you stronger. But it's the high nitrate content in the leafy greens -- not the iron -- that creates the effect. Building on a growing body of work that suggests dietary nitrate improves muscle performance in many elite athletes, researchers at Washington University School of Medicine in St. Louis found that drinking concentrated beet juice -- also high in nitrates -- increases muscle power in patients with heart failure. Cardiology fellow Nishtha Sodhi, M.D., (center) demonstrates equipment used to measure muscle power. According to the study authors, including Andrew Coggan, Ph.D., (left) and Linda Peterson, M.D., the magnitude of the improvement is comparable to that seen in heart failure patients who have done two to three months of resistance training.