Competitive athletes often swallow amino acid supplements to boost their performance and aid recovery from muscle fatigue. For the amino acid L-citrulline, a better way to reap its benefits may be to partake of a natural source—watermelons. A small study shows that drinking watermelon juice before a bout of hard exercise helps prevent muscle soreness the next day more effectively than a placebo beverage (J. Agric. Food Chem. 2013, DOI: 10.1021/jf400964r). Encarna Aguayo of the Technical University of Cartagena, in Spain, and her colleagues recruited seven men to participate in an intense stationary cycling test on three separate days. Before each test, the participants drank a half-liter of one of three beverages: natural watermelon juice containing about 1 g of L-citrulline, watermelon juice enriched to have 6 g of L-citrulline, or a fruity placebo drink without watermelon or L-citrulline. When the team monitored the athletes’ lactate levels in blood during exercise, they found no differences due to the beverages they imbibed. The day after drinking either watermelon juice, however, the men reported essentially no leg soreness. But the day after drinking the placebo, they reported feeling sore. Aguayo is now determining the optimal concentration of L-citrulline in watermelon juice that might help prevent muscle fatigue.