Watermelon juice may assist with muscle fatigue

Summary

• Intense exercise can cause acute muscle damage and subsequent muscle fatigue, as well as muscle soreness that can last up to several days 
• Recent studies indicate that natural juices without added sugar and containing bioactive compounds, such as watermelon juice, may be used as ergogenic aids 

Exercise can cause acute muscle damage and subsequent muscle fatigue, as well as muscle soreness that can last several days. High-intensity exercise increases the rate of glycolysis, increases blood levels of lactate and ammonia, the latter being a by-product of muscle (protein) catabolism that contribute to feelings of fatigue. Athletes often use various ergogenic aids to address fatigue and enhance exercise performance. Natural juices without added sugar and containing bioactive compounds are of interest to the juice industry as possible ergogenic aids.

A recent study from Spain has shown that supplementation with watermelon juice enriched with l-citrulline (3.3 g/200 mL) and pomegranate ellagitannins (22 mg/200 mL) had a beneficial effect on exercise performance in 19 young men. Watermelon juice naturally contains l-citrulline (0.5 g/200 mL). L-citrulline is a non-essential amino acid that can reduce the accumulation of lactic acid in the blood and has been shown to allow for a higher levels of exercise resistance performance to exhaustion. L-citrulline is also an important component of the liver urea cycle that is responsible for detoxification of ammonia into urea. In addition, l-citrulline is a precursor to arginine, an amino acid that can be converted to nitric oxide, a potent vasodilator that could aid in increasing blood flow and performance during exercise. The study was a double-blind, randomized, placebo-controlled, crossover study design so that all subjects received all four treatments: placebo, watermelon juice alone, watermelon with 3.3 g/200 mL added l-citrulline, and watermelon juice with both 3.3 g/200mL l-citrulline and 22 mg / 200 mL pomegranate ellagitannins. A high-intensity exercise test and isometric exercises were performed every 7 days to allow sufficient time for washout between exercise tests. A 200 mL dose of the various beverage treatments were consumed one hour before exercise testing.  

The investigators tested the knee extension peak torque in an isokinetic exercise test after the subjects performed the intensive exercise test and observed an increase in peak average force after the consumption of watermelon juice with added l-citrulline. They measured lower peak torque (5-fold) after participants consumed the watermelon juice plus citrulline and ellagitannins compared to the placebo beverage ( -52 vs -10.4 N•m). Besides these objective measures of exercise performance, the subjects also rated their perceived exertion and level of muscle soreness up to 48h post-exercise. The perceived exertion and muscle soreness following exercise was lower after the beverage treatment containing added citrulline alone and citrulline plus ellagitannins than after consuming the placebo. The findings from this small study are encouraging, but additional study in women and older subjects are warranted.