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polyphenolic compounds , or polyphenols , are hydroxylated phytochemicals , of which the two main classes include flavonids and phenolic acids .
quercetin is a flavonol that constitutes the aglycone of the plant glycosides rutin and quercetin.[24 ] human subjects can absorb significant amounts of quercetin , with a reported half - life ranging from 3.5 to 28 h. high concentrations are found in apples , red wine , onions and tea .
a few recent studies have shown that quercetin may increase expression of mithochondrial and nuclear genes and effects on endurance performance and mitochondrial biogenesis similar to some other nutrients.[1315 ] recent studies have examined whether quercetin supplement enhances endurance exercise capacity .
one study of 11 elite male cyclists reported 1.7% performance enhancement above placebo after six weeks of quercetin supplementation .
another study using sedentary mice showed that quercetin feeding ( both 12.5 and 25 mg / kg ) increased treadmill run time to fatigue by 37% .
another study of trained cyclists showed no effect of 1000 mg of quercetin a day compared with placebo on cycling time trial performance .
quercetin also has non - selective anti - inflammatory actions that rely on a wide range of mechanisms of action .
for instance , quercetin may inhibit nuclear factor kappa - light - chain - enhancer of activated b cells ( nf - kb ) activity , inducible nitric oxide synthesis expression and lipoxygenase activity .
aerobic exercise elevates free radical generation in muscle and free radicals increase fatigue and muscle damage .
badminton is both an aerobic and anaerobic sport with emphasis on the aerobic aspect so this sport generates free radicals .
however , supplementation with an antioxidant may reduce oxidative stress , muscle damage and fatigue . in vitro studies
suggest that quercetin affects adipogenesis and basal metabolism , however , whether this metabolic effect translates into reductions in body mass or improvement in body composition in humans is unknown . as per our knowledge
, this is first time that the effect of quercetin on exercise performance , muscle damage and body muscle was investigated in male badminton players .
given the potential of quercetin to decrease body fat percent and mediate anti - oxidative and anti - inflammatory activity the purpose of this study was to measure the influence of eight weeks of quercetin supplementation on exercise performance , muscle damage and body muscle in male badminton players .
a randomized double - blind placebo - controlled clinical trial was conducted on 26 male badminton players .
the study was approved by the ethics committee , isfahan sport medicine association , iran .
anthropometric indices including weight , height and body mass index ( bmi ) were obtained through physical examination .
none of the participants had consumed quercetin , or any other dietary supplements , for a minimum of three months before the study .
athletes kept a record of their physical and dietary intakes and they did not have exhaustive exercise 24 h before the study .
subjects were randomly allocated to one of the two groups according to pre - arranged balanced block randomization to receive quercetin ( 1000 mg ) or placebo ( 1000 mg dextrose ) .
supplements and placebo had the same appearance and were supplied by solaray , usa , inc .
according to the findings of a previous study the supplementation procedure for quercetin was set at two capsules per day for two months  this amount provided a total daily dose of 1000 mg per day .
venous blood samples were taken from all participants between 5 and 6 pm , after intensive endurance exercising , before intervention and after intervention . at pre- and post - supplementation protocol
all participants performed a graded exercise test ( gtx ) on an electronically braked cycle ergometer ( lode , the netherlands ) to determine vo2 peak and time to exhaustion ( tte ) .
ped al cadence was maintained at 70 rpm , while the power output was initially set at 30 watts and increased by 30 watts every 2 min , until the participants could no longer maintain the required power output .
plasma samples were obtained for the determination of plasma lactate immediately prior to each gtx and 2 min post exercise .
we used a lactometer ( lactate pro lt-1710 , canada ) to analyze lactate and a body composition analyzer ( jawon ioi 353 , korea ) to determine body fat percent pre and post supplementation .
significant differences among and between the groups were determined by independent t - test and paired sample t - test .
general mean  sd for all study samples for age ( years ) , weight ( kg ) and body mass index ( bmi ) is shown in table 1 . as shown in table 1 there was no significant difference between the two groups in age , weight and bmi ( p > 0/05 ) .
table 2 shows the mean  sd values of time to exhaustion ( tte ) , lactate concentration , vo2 max and body fat percent pre and post supplementation . dietary intake before trial initiation was not similar ( p < 0.05 ) for energy and macronutrients between the two groups [ table 1 ] .
general characteristics and dietary intakes of study participants separately by case and control groups before intervention comparison of exercise performance indices , pre and post supplementation lactate concentration , body fat percent and vo2 did not show any significant difference ( p > 0/05 ) after eight weeks of supplementation with placebo and quercetin between the two groups and within one group .
there was a significant increase in tte after intervention in the quercetin group ( p < 0/05 ) but significant change was not observed in the placebo group ( p > 0/05 ) .
the finding of our study suggests that eight - week supplementation with quercetin may improve the endurance exercise performance as measured by tte .
dumke et al . , used a randomized crossover trial and showed that two weeks of supplementation with 1000 mg / day quercetin on 26 untrained men resulted in a significant increase in exercise performance . in the davis study ,
treadmill run time to exhaustion increased by 37% in sedentary mice that fed with quercetin ( 12.5 and 25 mgkg ) for 7 days .
the one mechanism for enhanced exercise performance that is followed by quercetin is quercetin ' potential to induce mitochondrial biogenesis and quercetin may increase vo2 max and endurance exercise performance .
our study showed no significant difference in vo2 max in the quercetin group after intervention .
tee and vo2 max are considered to be predictors of endurance exercise performance but subjects with already elevated mithochondrial density would be less likely to obtain benefit from quercetin , especially for vo2 max . in our study
fat may be oxidized as a preferential fuel source if mithochondrial biogenesis is stimulated by quercetin ingestion so bfp may decrease .
studies indicate that quercetin has beneficial effects on adipocytes in vitro and causes apoptosis of adipocytes through the adenosine monophosphate - activated protein kinase pathway ( ampk ) .
for example stewart et al . , found that quercetin supplementation for eight weeks in mice caused no difference in body mass or body composition between the quercetin group versus placebo .
, showed that two - week supplementation with low doses of quercetin did not alter bfp in healthy human subjects.[3133 ]
the current study shows that intake of quercetin may improve endurance exercise performance but may not reduce the body fat percent .
thus , more studies with longer periods of supplementation and larger doses that may increase quercetin bioactive effects are necessary .
background : quercetin is a bioflavonoid which occurs in many food items . 
 some previous studies on quercetin showed inconsistent results on exercise performance , muscle damage and body muscle in athletes . 
 the aim of this study was to determine the effects of eight weeks of quercetin supplementation on exercise performance , muscle damage indices and body muscle in badminton players.methods:this placebo - controlled , double - blind clinical trial was conducted on 26 badminton players for eight weeks . 
 the subjects were randomly assigned to one of two groups to receive quercetin ( 1000 mg ) or placebo ( 1000 mg dextrose ) . 
 vo2 and time to exhaustion ( tte ) for measuring performance and body fat percentage ( bfp ) were measured before and after intervention . 
 plasma sample swere obtained for the determination of plasma lactate before and after intervention.results:lactate concentration , body fat percentage and vo2 max did not show any significant difference ( p > 0/05 ) after eight weeks of supplementation with placebo and quercetin between two groups and within one group . 
 there was a significant increase in tte after intervention in the quercetin group ( p < 0/05 ) but a significant change was not observed in the placebo group ( p > 0/05).conclusions : the current study shows that intake of quercetin may improve endurance exercise performance but may not reduce the body fat percentage .