Research code: -
Ethics code: IR.SUMS.REHAB.REC.1399.007
Clinical trials code: -

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Assistant Professor of Exercise Physiology, Department of Sport Sciences, Shiraz University, Shiraz, Iran. , m.hemmatinafar@shirazu.ac.ir
Abstract:   (136 Views)
Aims: The popularity of exercise nutrition is growing exponentially among athletes to boost their athletic performance. Nitrate and nitrite supplements act as an ergogenic aid for high-intensity exercise and can reduce the cost of oxygen for ATP synthesis, as well as the cost of ATP for muscle contraction. As a result, upon the improvement of contraction / relaxation, the generation of power and strength enhances the short-term intermittent running. Nitric oxide (NO) is a signaling molecule that is capable of improving vascular function, mitochondrial respiration, glucose homeostasis, and skeletal muscle contractions. However, the consumption of nitrate-rich vegetables (NO3-), such as lettuce, spinach, and beetroot (BR) have been identified as an alternative source and precursor of NO. Dietary NO3 is absorbed from the small intestine and then returned to saliva via the bloodstream and converted into NO2- by bacterial reductase. NO2- is converted into NO in the stomach and bowel. The remaining NO3- and NO2- molecules are absorbed by the intestine and increase the NO pool in the bloodstream. The consumption of NO3- and increase of NO production decrease oxidative stress in skeletal muscle, handle calcium, and increase contractile force and production capacity in type II muscle fibers, increase time to fatigue, and improve the exercise performance. BR is rich in foods such as sugar, phenolic compounds, and ascorbic acid. BR is a rich source of NO3- commonly consumed because it possesses high contents of betacyanin and polyphenol and it produces more NO  molecules than NO salts. The ergogenic effects of NO3-rich sources were first reported in metabolic adaptations following endurance training. Athletes in team or individual sports aim to increase performance in high-intensity interval training. High-intensity exercise results in a transition from low- to high-intensity and changes in metabolic conditions. In recent years, nitrate supplementation has been shown to have a significant effect on anaerobic exercise and high-intensity interval exercise. The effect of nitrate-rich BR juice support the improvement of the performance of high-intensity intermittent exercise in team sports; however, the length of the intake period and the time interval of nitrate-rich supplementation prior to the performance of the experiment are not completely clear. Based on these findings, we hypothesized that supplementation of BR in amateur trained soccer players could improve physiological and functional parameters. Therefore, we assessed the impact of a period of BR consumption on the performance of amateur trained soccer players following high-intensity intermittent exercise.
Materials & Methods: Forty-two male soccer players competing in the 2nd Iranian amateur league with the mean age of 20.50 ± 0.58, weight of 67.14 ± 2.35, body fat percent of 11.63 ± 1.44, and body mass index of 21.34 ± 0.48 voluntarily participate in the study. First off, all participants were informed about the nature of experimental procedures, including potential risks and benefits and then, received written informed consent. The experimental protocols were approved by the Ethical Committee of Shiraz University, Iran, according to Helsinki Declaration Guidelines. Participants were asked not to take any sport or medical supplements, or any ergogenic aids during the 4-week experiment period. The current study was randomized, placebo-controlled, cross-over, and double-blind that investigated the effect of BR supplementation on high-intensity intermittent exercise performance in soccer players. High- intensity intermittent running performance was assessed by the Yo-Yo IR1 test and Wingate test in two days. All subjects ingested beetroot juice nitrate- rich (2×70 ml/day; BR) or placebo (PLA) for six-days with seven-days of wash-out between trials. The experimental trials, which consisted of three sessions were performed outdoors in the running track of Shiraz University. Participants arrived at the facility 2.5 h after ingesting the last bolus of the supplement (8:30 A.M.). The heart rate was continuously monitored throughout the experiment (Polar Beat, Polar Electro, Kempele, Finland). The experimental protocols were carried out at the same time in every day. Subjects were asked to arrive to the laboratory 90 min before the experiment. They were also requested to be fully hydrated, and consume their least meal at least 3 h before the initiation of the exercise test. Besides, they had to avoid strenuous exercise 36 h before the experimental trials. Before the Yo-Yo test, warm-up was performed for each participant. The Yo-Yo test was carried out on running lanes with a width of 2 m and length of 20 m. The examination consisted of repeated 2 × 20 m runs that progressively increased the speed which was controlled by the audio bleeps from an audio system. Each 20 m running was interspersed by 5 m behind the finishing line marked the running distance that is 10-s active recovery period. Immediately after the termination of the Yo-Yo test, Subjective rating of perceived exertion was carried out in accordance with the Borgchr('39')s scale ranging from 6–20. Wingate test used for determine of power output and fatigue index. The heart rate and VO2max were measured continuously throughout the Yo-Yo test, and nitrate/nitrite plasma levels were collected prior and post of the six- days nitrate supplementation. Data are expressed as the means and standard deviation (mean ± SD). All statistical analyses were carried out by the SPSS software (version 19.0; IBM Corp, Armonk, NY, USA). The Shapiro-Wilk test was used to verify that the values are normally distributed. Independent t-test was used to calculate the differences between the experimental groups. Pearson correlation coefficients calculated to assess relationships between plasma levels of nitrate and nitrite with Yo-Yo performance and heart rate between in both groups. The level of statistical significance was set at p< 0.05.
Findings: Compared to PLA, six- days BR supplementation increased mean power (483.91 ± 23.60 vs. 468.77 ± 23.39, P<0.05) and low power (373.31 ± 22.03 vs. 340.41 ± 22.40, P<0.05) and also reduced fatigue index (37.66 ± 5.66 vs. 45.27 ± 7.94; P<0.05). High-intensity intermittent running performance (P= 0.034), VO2max (P= 0.043), nitrate and nitrite plasma levels (P<0.001) were significantly improved in subjects in the BR compared with the PLA.
Conclusion: The main finding of this study is that a 6-day period of BR supplementation led to a marked improvement in the performance of high-intensity intermittent exercise in soccer players. Such an improvement includes a decrease in the heart rate during high-intensity intermittent running tests, as well as an increase in VO2max. Our findings showed that BR supplementation enhanced the peak, mean and low power output, while it reduced the fatigue index. Additionally, there were a positive correlation between nitrate and nitrite with Yo-Yo performance and VO2max. On the other hand, there were a negative correlation between nitrate and nitrite with HRrest. Moreover, plasma levels of nitrate and nitrite were significantly increased after 6-days supplementation with BR in soccer players. We investigated the impact of a 6-day period of BR supplementation on nitrate/nitrite concentrations and performance during the speed and Yo-Yo tests in soccer players. After 6 days BR supplementation, the plasma levels of nitrate/ nitrite, peak power, mean power, low power, and performance in the Yo-Yo test were significantly increased. Also, the heart rate and fatigue index were significantly decreased in the BR compared with the PLA.
     
Type of Study: Research | Subject: Exercise Physiology

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