Big, sloppy slices of watermelon served at a picnic table are the quintessential summer snack—sweet enough to be dessert but, as several recent studies remind us, good for our health as well. (And only 84 calories per wedge!)

1. It soothes sore muscles.

According to a new study in the Journal of Agricultural Food and Chemistry, drinking watermelon juice before a hard workout helped reduce athletes' heart rate and next-day muscle soreness. That's because watermelon is rich in an amino acid called L-citrulline, which the body converts to L-arginine, an essential amino acid that helps relax blood vessels and improve circulation.

The study's seven participants, all men, were given 17 ounces (500 mL) of either natural watermelon juice, watermelon juice enriched with additional citrulline, or a placebo drink an hour before their workouts. Interestingly, the natural juice was just as effective as the enriched juice. The researchers also determined that intestinal cells can absorb more citrulline from watermelon juice than from citrulline supplements, especially when the juice is unpasteurized.

2. It helps heart health.

Postmenopausal women experienced improved cardiovascular health after six weeks of taking commercially available watermelon extract supplements containing citrulline and arginine, according to a study published earlier this year by Florida State University physiologist Arturo Figueroa.

And in a 2012 study—also led by Figueroa—such supplements helped alleviate high blood pressure in obese, middle-aged adults. (Not surprisingly, he's received two grants from the Watermelon Promotion Board.)

3. It could be a natural Viagra.

Improved circulation can benefit more than just the heart, as at least one watermelon researcher has pointed out. But you'd probably have to eat an awful lot to achieve the desired effect--and eating too much could cause unfortunate side effects, since watermelon has long had a reputation as a natural diuretic.

4. It's rich in vitamins and minerals, but low in calories.

Given its name, you might assume the fruit has little nutritional value—and it is more than 90 percent water. But a 10-ounce (300-mL) wedge of watermelon packs in about one-third of the recommended daily value of vitamins A and C, as well as a modest amount of potassium (9 percent of the daily value).