Dietary nitrates have hemodynamic and metabolic effects on the body. This study aimed to investigate nitrate intake's effect on quadricep muscle oxygen saturation (StO2) of semi-professional soccer players during a repeated speed test (RSA). In a randomized, crossover design, 10 semi-professional soccer men players (21.3 ± 0.9yrs) performed two conditions: In one they consumed a nitrate-rich concentrated beetroot juice (250 mL/150 mg of NO3-) and in the other a placebo, 2h before a repeated sprint test. StO2 of the right vastus lateralis muscle was measured by near-infrared spectroscopy. A paired samples t-test was used to compute any differences in the subjects` performance on the StO2 and on RSA test. The level of significance was set at p < 0.05. The supplementation of nitrates limited the decrease in muscle oxygenation during the six sprints of RSA test (p < 0.001) and also, there seemed to be a tendency for limited the decrement of performance on RSA test (t = -1.586, p = 0.157, ?2 = 0.218). In conclusion, acute nitrate supplementation reduces the decrement of muscle oxygenation during exercise with repeated sprints and leads to a tendency of fatigue resistance during repeated sprints under controlled situations. Nitrate supplementation may have an ergogenic effect during exercise with repeated sprints via the higher muscle oxygenation.
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