A new Swedish study suggests that Popeye may have been onto something: In tests with mice, nitrates like those found naturally in spinach, beetroot, chard and lettuce had a powerful effect on boosting muscle strength. Researchers fed one group of mice water enriched with nitrate for a week, then compared the animals muscles to those of a control group. The mice given nitrate had much stronger muscles, particularly in the legs and feet. They also had higher concentrations of two proteins involved in the bodys calcium balance, an important factor in muscle contraction. The mighty mice were given an amount of nitrate equivalent to what a human would obtain from 7 to 10 ounces of fresh spinach. It was noteworthy, researchers wrote in the Journal of Physiology, that the development of stronger muscles was linked to doses obtainable from a normal diet-and foods already known to be healthy.