Purple grape juice, a natural alternative to pre-workout formulas
Practitioners of sports disciplines who demand a lot of calories can improve their performance if they drink a few glasses of purple grape juice 2 hours before a training or competition. According to a human study, Brazilian researchers from the Universidade Federal da Paraiba published in the European Journal of Nutrition.
The researchers got 14 reasonably fit recreational runners to run on 2 different occasions on a treadmill with an intensity of 80 percent of their maximum oxygen intake until they were literally no longer able to.
On one occasion, the test subjects drank 10 milliliters of grape juice per kilo of body weight 2 hours before they had to run. That is for a test person who weighs 80 kilos, down to 800 milliliters.
There were 128 grams of carbohydrates in 800 milliliters of grape juice. That amounts to 512 kilocalories.
On the other occasion, the subjects were given a placebo juice with the same amount of carbohydrates, but without the bioactive substances that are naturally present in purple grape juice.
Compared to the placebo drink, grape juice increased the time that the test subjects could keep running by almost 16 percent.
The researchers cannot determine from their data how grape juice increases endurance. They found no effect on traditional biomarkers such as MDA, A1GPA, hs-CRP, CK and LDH. They did find an increase in antioxidant activity in blood samples from the subjects they had taken shortly after the test.
"The mechanism of muscle fatigue for long-term exercise is not fully understood in the literature, but it is known that metabolic acidosis and glycogen depletion are well established causes", the researchers think aloud. "Once the placebo drink in this study was isoglycidic, we cannot attribute the ergogenic effect of grape juice to carbohydrates."
"On the other hand, Jing-Jing et al. [Exp Mol Med. 49:e384-e394.] indicate that oxidative stress hinders the mechanism of muscle contraction, so we can assume that antioxidant compounds may retard this mechanism of fatigue. However, further studies are needed to confirm this mechanism or even to determine other components involved in delaying polyphenol fatigue."
"Additionally, the polyphenols present in grapes also have anti-inflammatory and vasodilator properties, which may contribute to increase the supply of muscle oxygen."
"A practical implication of this study is the recommendation of whole grape juice as a potentially ergogenic food for recreational athletes", the researchers summarize their findings. "Grape juice may be considered an interesting option for athletes to consume daily or even ingest in the hours before a competition."
"Grape juice may be considered a complete preworkout food for athletes because it presents high caloric value from its composition of carbohydrates and still contains several antioxidants capable of delaying fatigue and optimizing recovery."
Eur J Nutr. 2019 Nov 15;10.1007/s00394-019-02139-6. [Epub ahead of print].
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