Watermelon is rich in the amino acid citrulline, which helps relax blood vessels and improve circulation.  This explains why the fruit (or even just the juice) can soothe muscle soreness and fight many of the circulatory issues that we become more and more prone to with age.  As an added bonus, the vessel-relaxing properties yield some “Viagra-like” effects, making the superfruit a natural libido booster.  To work watermelon into any meal (other than a family picnic), try serving it hors d’oeuvre-style with small cubes of feta cheese, mint leaves, and balsamic drizzle.