Can Watermelon Relieve Muscle Soreness?

Gayle Nicholas Scott, PharmD

Disclosures

October 22, 2013

Question

Can watermelon relieve soreness after exercise?

Response from Gayle Nicholas Scott, PharmD
Assistant Professor, Eastern Virginia Medical School, Norfolk, Virginia; Clinical Pharmacist, Chesapeake Regional Medical Center, Chesapeake, Virginia

True to its name, watermelon (Citrullus lanatus) is made up of greater than 90% water.[1] Watermelon is low in calories (a 2-cup serving contains about 90 calories) and is regarded as a healthy food. Watermelon contains a high concentration of lycopene,[1,2] a carotenoid that may have beneficial effects on cancer and cardiovascular disease risk.[2] Watermelon is also high in vitamins A and C.[1]

In addition, watermelon is a rare food source of citrulline, an amino acid that was first isolated in 1930 from watermelon.[3,4,5] Citrulline is an antioxidant and is thought to allow watermelon to survive drought-related oxidative stress.[6]

Citrulline is a precursor for arginine, which is involved in the formation of nitric oxide and creatine, and is a key constituent of the urea cycle, which detoxifies ammonia.[7] Nitric oxide is involved in many physiologic processes, such as mediating noradrenergic and noncholinergic neurotransmission, learning, memory, and neuroprotection.[7,8] Nitric oxide also appears to modulate blood flow and mitochondrial respiration during physical exercise.[7]

Interest in watermelon to enhance exercise centers around its ability to increase plasma citrulline and arginine levels.[3,4] In theory, citrulline via arginine and nitric oxide could augment detoxification of ammonia generated during exercise and improve recovery.[7] Citrulline has been shown to increase renal reabsorption of bicarbonate, which could lessen the effects of exercise-induced acidosis.[9] Research in rats suggests that citrulline may reduce muscle fatigue.[10]

Studies of citrulline supplements in humans have shown mixed results. One group of researchers found that a single 8-g dose of citrulline malate enhanced aerobic exercise performance and ameliorated muscle soreness; however, the researchers did not measure any serum metabolites that would indicate enhanced buffering of lactic acid or hyperammonemia.[11]

Another group of researchers found that citrulline supplementation decreased time to exhaustion on a treadmill test.[12] Interest in citrulline supplementation to enhance physical performance was sufficient to induce the Air Force to conduct a randomized, double-blind, cross-over study of citrulline malate (6 g/day).[13] The researchers found no differences between citrulline and placebo in measures of respiration, lactate production, or time to exhaustion during incremental cycle ergometry.

Watermelon juice was tested in 7 athletes using cycle ergometry. Researchers compared the effect of watermelon juice (containing 1.17 g of citrulline), enriched watermelon juice (4.83 g of citrulline plus 1.17 g from watermelon), and placebo. Watermelon juice and watermelon juice enriched with citrulline similarly reduced perceived muscle soreness better than placebo, but no significant differences among any of the 3 treatments were observed in terms of lactate levels.[6]

More research is required to clarify the effect of watermelon or citrulline on exercise in general and muscle soreness in particular. Until such research is available, watermelon can be recommended as a healthy, low-calorie food for everyone except patients with rare inborn disorders involving citrulline or arginine metabolism.[3] For patients interested in trying watermelon to lessen muscle soreness after exercise, suggest exercising with and without eating watermelon and comparing the results. Tell patients that research on citrulline supplements has shown conflicting results, and watermelon enhanced with additional citrulline does not appear to offer any benefit.

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