Watermelon Juice Can Prevent Muscle Fatigue from Exercise

Drinking watermelon juice can prevent muscle fatigue after intense exercise because of a naturally occurring but under-studied amino acid naturally present in the juice, according to a paper published in the Journal of Agricultural and Food Chemistry.

Researchers attribute the amino acid L-citrulline to reducing muscle soreness after 24 hours, as well as contributing to reducing heart rate recovery time in athletes.

In clinical tests, people who drank watermelon juice before exercising felt less sore the next day than those who drank a pink placebo beverage. The researchers also found that the L-citrulline compound was more readily absorbed into the body when delivered in the form of unpasteurized watermelon juice than from plain water fortified with L-citrulline, which suggests that the natural source is the optimum mode of delivery.

When muscle fatigue sets in, the accompanying unpleasant burning sensation is associated with the build-up of lactic acid. Encarna Aguayo, a researcher from Spain's Technical University of Cartagena, was aware from prior studies that L-citrulline was shown to contribute to the quick removal of lactic acid in the muscles. Because watermelon is one of just a few foods that have naturally high levels of L-citrulline, Aguayo became interested in developing a sports drink enhanced with the naturally beneficial properties of watermelon, according to report by Chemical and Engineering News.

Aguayo and her colleagues' experiment tested a standardized measure of pasteurized and unpasteurized watermelon juice and water spiked with L-citrulline. The compounds were then added to human cell cultures and and measured how much of the L-citrulline was absorbed by the cells after eight minutes.

The researchers found that cells exposed to unpasteurized watermelon juice absorbed 19 percent of the L-citrulline.

While pasteurization kills harmful pathogens, it also can "reduce the bioavailability of many bioactive compounds, reducing the food's functional properties," Aguayo said, which explains why the absorption rate was lower -- 13 percent -- for cells exposed to pasteurized juice. Cells exposed to the L-citrulline-spiked water absorbed 12 percent of the compound.

For the next stage of the experiment, the researchers developed three beverages: a watermelon drink with a low concentration of L-citrulline, a watermelon drink with a higher concentration of L-citrulline and a third drink which was pink like watermelon but contained none of the fruit or any L-citrulline.

Then the researchers recruited seven men who regularly played sports but who were not competitive athletes. The men were each asked to drink one of the seven test beverages before an 11-minute session on an exercise bike that included periods of intense pedaling and some rest. The next day the men were asked to evaluate the soreness in their legs. All of the man who drank either of the watermelon drinks reported essentially no soreness, while the men who drank the placebo did report sore legs after the intense exercise.

For future studies Aguayo wants to determine the optimal ratio of L-citrulline that will promote maximum cell absorption, according to Chemical and Engineering News.