flavonoids comprise a large group of plant metabolites , 6,000 of which have been identified to date .
quercetin is a major natural flavonoid existing in the skin of many fruits and vegetables , as well as in leafy vegetables , berries , black tea , and various fruit juices .
since it can be found in many plant - derived foods , it is present in most people 's diet . having many antioxidant , anticarcinogenic , anti - inflammatory , and heart - protecting effects , quercetin decreases the risk of cancers and various chronic diseases .
thus , it is produced as a dietary supplement and is even added to some food and beverages . despite the large number of studies investigating the in vitro effects of quercetin , few have demonstrated its in vivo effects .
there might be differences between the in vivo and in vitro effects of quercetin owing to its digestion , absorption , and metabolism effects .
some animal studies have described the observed increased endurance performance and maximal oxygen consumption ( vo2max ) and therefore fitness following quercetin consumption as a result of elevated number of intracellular mitochondria caused by the flavonoid.[68 ] however , this association has not yet been proved in human studies . the improved physical performance caused by quercetin reported by some studies might be attributable to the decreased membranes in muscles , which in turn reduces the negative and exhaustive effects of excessive oxygen radicals during physical activity . proving this hypothesis to be right would mean quercetin to be able to reduce muscular damage and soreness , as well as neuromuscular dysfunction following exercise .
however , quercetin has been reported to have contrasting antioxidant effects . although some studies found improved neuromuscular function and decreased soreness , others only mentioned improved muscular strength as a result of long - term quercetin consumption .
however , they did not find quercetin to have significant effects on these indices . as mentioned previously ,
although in vitro and animal studies have suggested quercetin to have positive effects on athletic performance , inflammatory indices , and muscular damage , a definite judgment can not be made about its effects on athletes because of the fewer number of human studies and their contrasting findings .
on the other hand , there is a growing interest in supplement use among athletes .
therefore , this study evaluated the effects of supplementary quercetin on athletic performance , muscular damage , and body composition in male athlete students .
this double - blind clinical trial involved 60 male students at isfahan university of medical sciences having an athletic history of at least 3 years .
the subjects were excluded if they followed less than 70% of the study procedure or were unwilling to continue .
the trial was approved by the research and ethics committee , faculty of nutrition , isfahan university of medical sciences , isfahan , iran , and registered in irct .
the participants were first explained about the objectives and methods of the study . after obtaining written informed consents ,
height was measured to the nearest 0.5 cm by a tape meter in standing position without shoes .
weight was measured in light clothing without shoes by a scale with an accuracy of 100 g , following which body mass index ( bmi ) was calculated as weight divided by squared height ( kg / m ) .
a bioimpedence device was used to measure body water percentage and fat - free mass percentage . to evaluate body performance indices ,
exercise test was performed for all participants using the bruce protocol and hp cosmos treadmill ( mercury , germany ) . at the end of the test , vo2max and
the individuals were then assigned into four groups of 15 using permuted block randomization . the first to fourth groups received a 500 mg supplemental quercetin capsule plus a 250 mg vitamin c pill , a 500 mg supplemental quercetin capsule plus a 250 mg placebo vitamin c pill , a 500 mg placebo quercetin capsule plus a 250 mg vitamin c pill , and a 500 mg placebo quercetin capsule plus a 250 mg placebo vitamin c pill , respectively , daily for 8 weeks .
the participants were asked to continue their routine diet and physical activity during the study and they were monitored through phone calls or text messages . at the end of the intervention period , the remainder of the pills was evaluated to assess supplement intake .
due to the double - blind nature of the study , neither the researchers nor the participants were aware of the content of the capsules .
data were analyzed by paired t - test , analysis of covariance ( ancova ) , and repeated measure analysis of variance ( anova ) in spss15 .
data were analyzed by paired t - test , analysis of covariance ( ancova ) , and repeated measure analysis of variance ( anova ) in spss15 .
since four individuals were excluded due to unwillingness or other reasons , a total number of 56 participants were studied .
mean ages of subjects in groups 1 to 4 were 20.93  1.53 , 21.50  2.17 , 21.21  1.52 , and 20.46  1.18 years , respectively ( p > 0.05 ) .
table 1 shows the body composition indices among the four groups before and after the study .
as seen , lean body mass ( lbm ) , total body water ( tbw ) , basal metabolic rate ( bmr ) , and total energy expenditure ( tee ) increased significantly in the first group .
the comparison of body composition indices between four groups as presented in table 2 , body performance indices shows vo2max in group 1 significantly increased after the intervention .
in addition , as the results of ancova after excluding the initial effects of vo2max suggested , vo2max increased in the first and third groups following the intervention . however , repeated measure anova did not reveal the differences to be significant .
although the distance covered significantly increased in group 4 , ancova and repeated measure anova did not show significant differences .
this randomized clinical trial comprised four groups who were evaluated to determine the effects of quercetin intake on physical and body performance and muscle injury .
the results revealed significant differences in lactate dehydrogenase ( ldh ) , vo2max , tee , tbw , and lbm among the quercetin and vitamin c groups .
however , after eliminating confounding effects of initial variables , only vo2max changes remained significant .
our study is in line with the study of cureton et al . , who assessed the ergogenic effects of quercetin on 30 non - athletic men in a double - blind clinical trial .
during 7 to 16 days , they administered 1 g of daily quercetin to the intervention group and the same amount of placebo to the control group .
finally , they did not find significant changes either in ergogenic indices , such as phosphocreatine recovery time constant , vo2max , and perception of effort , during submaximal exercise test , or in the total work during a 10-min cycling with maximum power .
similarly , ganio et al . performed a double - blind clinical trial on 11 non - athletic inactive participants ( five males and six females ) .
although their intervention and control groups received , respectively , 1,000 mg of daily quercetin and placebo for 22 weeks , no significant differences were observed in terms of vo2max between the two groups .
utter et al . also compared the effects of 250 mg of daily quercetin for 3 weeks with placebo among marathon runners and cyclists .
they did not report any significant difference in the ratings of perceived exertion between the two groups .
a crossover clinical trial by macrae et al . compared the effects of quercetin and a combination of quercetin and vitamins on 11 male cyclists during a 6 week period .
although their results did not reveal significant differences in the total time of a 30 km ride and vo2max after the intervention , a significant increase was observed in peak power among the second group of cyclists . in a clinical trial , davis et al . evaluated the effects of quercetin on exercise performance among 12 volunteers .
they divided the participants into two groups of intervention ( 500 mg daily quercetin ) and control ( 500 mg daily placebo ) . unlike in other studies , they found significant improvements in time to fatigue , vo2max , and endurance among non - athletic individuals during a 30 km bicycle ride .
they performed a 12 week treatment with two doses of quercetin along with vitamin c and niacin on 941 male and female subjects aged 18 - 85 years .
the participants were randomly divided into three groups of 500 mg daily quercetin , 1,000 mg daily quercetin , and placebo .
their results did not show any significant differences between the intervention and placebo groups in terms of bmi or any other body composition indices .
egert et al . investigated the effects of quercetin consumption on 93 obese subjects aged 25 - 65 in a crossover study .
the participants received 6 weeks of 150 mg daily quercetin followed by a 5 week washout and a course of placebo .
however , crp and body composition indices , including weight , waist circumference , body fat mass , and fat - free mass , did not significantly change after the intervention period .
another study by egert et al . evaluated 35 healthy subjects in three groups of 50 , 100 , and 150 mg of daily quercetin .
the study did not indicate any significant difference in resting energy expenditure or weight after a 2 week quercetin supplementation .
similar to previous studies , the present study did not show any significant differences between the quercetin and placebo groups .
therefore , it might be concluded that quercetin alone does not affect body composition and body performance indices .
although different studies have used various doses of quercetin during various periods of time , we selected a dose within their range .
however , higher doses might be able to make significant differences in the above - mentioned indices .
since the findings of the present and previous studies are in contrast with in vitro and animal studies , a longitudinal research with long follow - up is suggested to evaluate the effects of quercetin .
moreover , studies assessing the effects of quercetin on cardiovascular disease risk factors , endothelial dysfunction , and atherosclerosis incidence might reveal beneficial effects of this flavonoid .
clinical trials with larger sample sizes of athletes and non - athletes are also recommended .
 background : flavonoids comprise a large group of plant metabolites , 6,000 of which have been identified to date . 
 some studies have shown the increased aerobic performance and maximal oxygen consumption ( vo2max ) and therefore fitness following quercetin intake as a result of elevated number of intracellular mitochondria caused by the flavonoid.methods:this double - blind clinical trial comprised 60 male students having an athletic history of at least 3 years . 
 body composition , exercise performance , and some blood biomarkers were analyzed . 
 the individuals were selected by convenient sampling , and then were assigned into four groups of equal number by using permuted block randomization . the first to fourth groups received a 500 mg supplemental quercetin capsule plus a 250 mg vitamin c pill , a 500 mg supplemental quercetin capsule plus a 250 mg placebo vitamin c pill , a 500 mg placebo quercetin capsule plus a 250 mg vitamin c pill , and a 500 mg placebo quercetin capsule plus a 250 mg placebo vitamin c pill , respectively , daily for 8 weeks . 
 the participants were asked to continue their routine diet and physical activity during the study and they were monitored through phone calls or text messages.results:lean body mass , total body water , basal metabolic rate , and total energy expenditure increased significantly in the quercetin group after intervention . on the other hand , vo2max increased in the  quercetin  and  quercetin + vitamin c  groups following the intervention , non-significantly.conclusion:our findings suggest that supplementation with quercetin in athletes may improve some indices of performance . 
INTRODUCTION
METHODS
Statistical analysis
RESULTS
DISCUSSION
CONCLUSION