Aging is associated with increased risk of high blood pressure, an important risk factor for cardiovascular diseases and loss of muscle fitness (i.e., mass, strength and exercise capacity). Endothelial cells lining the wall of blood vessels maintain normal blood pressure and blood flow control through production of nitric oxide, a substance that causes the widening of blood vessels known as vasodilation. Lower nitric oxide production with aging causes less blood flow and nutrient delivery to the muscles, contributing to the loss of muscle fitness. Evidence suggests that supplementation with L-citrulline (L-CIT), a substance found in watermelon, improves vascular function by providing L-arginine, the substance that is converted to nitric oxide in endothelial cells. In addition to the blood pressure-lowering effects, L-CIT may contribute to increased muscle fitness by stimulating the production of muscle protein. In recent studies researchers found that L-CIT combined with exercise training had additive benefits on both muscle fitness and blood pressure in older adults. Further research focus on the potential benefits of various L-CIT dosages and types of exercise, especially strength training, on vascular and muscular functions in older adults are needed.