***TASK*** the task is to summarize an input biomedical literature in six sentences 
    ***INPUT*** the input is a biomedical literature 
    ***OUTPUT*** the output is the summary of an input biomedical literature in six sentences 
    ***DOCUMENTATION*** 
    ***EXAMPLES*** 
    Input: Previous investigations have determined that some individuals have minimal or even ergolytic performance effects after caffeine ingestion . The aim of this study was to analyze the influence of the genetic variations of the CYP1A2 gene on the performance enhancement effects of ingesting a moderate dose of caffeine . In a double-blind r and omized experimental design , 21 healthy active participants ( 29.3 ± 7.7 years ) ingested 3 mg of caffeine per kg of body mass or a placebo in testing sessions separated by one week . Performance in the 30 s Wingate test , visual attention , and side effects were evaluated . DNA was obtained from whole blood sample s and the CYP1A2 polymorphism was analyzed ( rs762551 ) . We obtained two groups : AA homozygotes ( n = 5 ) and C-allele carriers ( n = 16 ) . Caffeine ingestion increased peak power ( 682 ± 140 vs. 667 ± 137 W ; p = 0.008 ) and mean power during the Wingate test ( 527 ± 111 vs. 518 ± 111 W ; p < 0.001 ) with no differences between AA homozygotes and C-allele carriers ( p > 0.05 ) . Reaction times were similar between caffeine and placebo conditions ( 276 ± 31 vs. 269 ± 71 milliseconds ; p = 0.681 ) with no differences between AA homozygotes and C-allele carriers . However , 31.3 % of the C-allele carriers reported increased nervousness after caffeine ingestion , while none of the AA homozygotes perceived this side effect . Genetic variations of the CYP1A2 polymorphism did not affect the ergogenic effects and drawbacks derived from the ingestion of a moderate dose of caffeine INTRODUCTION Caffeine enhances performance of single bouts of endurance exercise , but its effects on repeated bouts typical of those in high-intensity team sports are unclear . PURPOSE To investigate effects of caffeine in a performance test simulating physical and skill dem and s of a rugby union game . METHODS The study was a double-blind , r and omized , crossover design in which nine competitive male rugby players ingested either caffeine ( 6 mg.kg(-1 ) body mass ) or placebo ( dextrose ) 70 min before performing a rugby test . Each test consisted of seven circuits in each of two 40-min halves with a 10-min half-time rest . Each circuit included stations for measurement of sprint time ( two straight-line and three agility sprints ) , power generation in two consecutive drives , and accuracy for passing balls rapidly . Interstitial fluid was sample d transdermally by electrosonophoresis before ingestion of caffeine or placebo and then before testing , at half-time , and immediately after testing ; sample s were assayed chromatographically for caffeine and epinephrine concentrations . RESULTS The effects of caffeine on mean performance ( + /-90 % confidence limits ) over all 14 circuits were : sprint speeds , 0.5 % ( + /-1.7 % ) through 2.9 % ( + /-1.3 % ) ; first-drive power , 5.0 % ( + /-2.5 % ) ; second-drive power , -1.2 % ( + /-6.8 % ) ; and passing accuracy , 9.6 % ( + /-6.1 % ) . The enhancements were mediated partly through a reduction of fatigue that developed throughout the test and partly by enhanced performance for some measures from the first circuit . Caffeine produced a 51 % ( + /-11 % ) increase in mean epinephrine concentration ; correlations between individual changes in epinephrine concentration and changes in performance were mostly unclear , but there were some strong positive correlations with sprint speeds and a strong negative correlation with passing accuracy . CONCLUSION Caffeine is likely to produce substantial enhancement of several aspects of high-intensity team-sport performance PURPOSE The objective of this study is to determine the effects of a caffeine-containing energy drink on female volleyball players ' performance . METHODS Thirteen elite female volleyball players ingested 3 mg·kg of caffeine with an energy drink or the same drink without caffeine ( placebo drink ) in a double-blind and r and omized study . Then , participants performed the following : st and ing spike , jumping spike , spike jump , blocking jump , squat jump , countermovement jump , manual dynamometry , and the agility t-test . A simulated volleyball game was played , videotaped , and notated afterward . RESULTS In comparison to the placebo drink , the ingestion of the caffeinated energy drink increased the ball velocity in the st and ing spike ( 19.2 ± 2.1 vs 19.7 ± 1.9 m·s , P = 0.023 ) and in the jumping spike ( 17.9 ± 2.2 vs 18.8 ± 2.2 m·s , P = 0.038 ) and the jump height in the squat jump ( 28.1 ± 3.2 vs 29.4 ± 3.6 cm , P = 0.028 ) , countermovement jump ( 32.0 ± 4.6 vs 33.1 ± 4.5 cm , P = 0.018 ) , spike jump ( 43.3 ± 4.7 vs 44.4 ± 5.0 cm , P = 0.025 ) , and block jump ( 35.2 ± 5.1 vs 36.1 ± 5.1 cm , P = 0.044 ) . Furthermore , the caffeinated energy drink decreased the time needed to complete the agility t-test ( 11.1 ± 0.5 vs 10.9 ± 0.3 s , P = 0.036 ) . During the game , the volleyball actions categorized as successful were more frequent with the caffeinated energy drink ( 34 % ± 9 % vs 45 % ± 9 % , P < 0.001 ) , whereas imprecise actions decreased ( 28 % ± 7 % vs 14 % ± 9 % , P < 0.001 ) when compared with the placebo drink . CONCLUSION Commercially available energy drinks can significantly improve physical performance in female volleyball players .  Increased physical performance led to improved accuracy during an actual volleyball match The purpose of the present study was to examine the duration of caffeine  's ergogenic effect and whether it differs between users and nonusers of the drug . Twenty-one subjects ( 13 caffeine users and 8 nonusers ) completed six r and omized exercise rides to exhaustion at 80 % of maximal oxygen consumption after ingesting either a placebo or 5 mg/kg of caffeine .  Exercise to exhaustion was completed once per week at either 1 , 3 , or 6 h after placebo or drug ingestion . Exercise time to exhaustion differed between users and nonusers with the ergogenic effect being greater and lasting longer in nonusers . For the nonusers , exercise times 1 , 3 , and 6 h after caffeine ingestion were 32.7 + /- 8.4 , 32.1 + /- 8.6 , and 31.7 + /- 12.0 min , respectively , and these values were each significantly greater than the corresponding placebo values of 24.2 + /- 6.4 , 25.8 + /- 9.0 , and 23.2 + /- 7.1 min . For caffeine users , exercise times 1 , 3 , and 6 h after caffeine ingestion were 27.4 + /- 7.2 , 28.1 + /- 7.8 , and 24.5 + /- 7.6 min , respectively . Only exercise times 1 and 3 h after drug ingestion were significantly greater than the respective placebo trials of 23.3 + /- 6.5 , 23.2 + /- 7.1 , and 23.5 + /- 5.7 min . In conclusion , both the duration and magnitude of the ergogenic effect that followed a 5 mg/kg dose of caffeine were greater in the nonusers compared with the users PURPOSE The purpose of this study was to determine the oral dose of caffeine needed to increase muscle force and power output during all-out single multijoint movements . METHODS Thirteen resistance-trained men underwent a battery of muscle strength and power tests in a r and omized , double-blind , crossover design , under four different conditions : ( a ) placebo ingestion ( PLAC ) or with caffeine ingestion at doses of ( b ) 3 mg · kg(-1 ) body weight ( CAFF 3 mg ) , ( c ) 6 mg · kg(-1 ) ( CAFF 6 mg ) , and ( d ) 9 mg · kg(-1 ) ( CAFF 9 mg ) . The muscle strength and power tests consisted in the measurement of bar displacement velocity and muscle power output during free-weight full-squat ( SQ ) and bench press ( BP ) exercises against four incremental loads ( 25 % , 50 % , 75 % , and 90 % one-repetition maximum [ 1RM ] ) . Cycling peak power output was measured using a 4-s inertial load test . Caffeine side effects were evaluated at the end of each trial and 24 h later . RESULTS Mean propulsive velocity at light loads ( 25%-50 % 1RM ) increased significantly above PLAC for all caffeine doses ( 5.4%-8.5 % , P = 0.039 - 0.003 ) . At the medium load ( 75 % 1RM ) , CAFF 3 mg did not improve SQ or BP muscle power or BP velocity  . CAFF 9 mg was needed to enhance BP velocity and SQ power at the heaviest load ( 90 % 1RM ) and cycling peak power output ( 6.8%-11.7 % , P = 0.03 - 0.05 ) . The CAFF 9 mg trial drastically increased the frequency of the adverse side effects ( 15%-62 % ) . CONCLUSIONS The ergogenic dose of caffeine required to enhance neuromuscular performance during a single all-out contraction depends on the magnitude of load used . A dose of 3 mg · kg(-1 ) is enough to improve high-velocity muscle actions against low loads , whereas a higher caffeine dose ( 9 mg · kg(-1 ) ) is necessary against high loads , despite the appearance of adverse side effects PURPOSE The purpose of this investigation was to assess the acute effects of caffeine ingestion on short-term , high-intensity exercise ( ST ) after a period of oral creatine supplementation and caffeine abstinence . METHODS Fourteen trained male subjects performed treadmill running to volitional exhaustion ( T(lim ) ) at an exercise intensity equivalent to 125 % VO(2max ) . Three trials were performed , one before 6 d of creatine loading ( 0.3 g x kg x d(-1 ) baseline ) , and two further trials after the loading period . One hour before the postloading trials , caffeine ( 5 mg x kg(-1 ) ) or placebo was orally ingested in a cross-over , double-blind fashion . Four measurements of rating of perceived exertion were taken , one every 30 s , during the first 120 s of the exercise . Blood sample s were assayed for lactate , glucose , potassium , and catecholamines , immediately before and after exercise . RESULTS Body mass increased ( P < 0.05 ) over the creatine supplementation period , and this increase was maintained for both caffeine and placebo trials . There was no increase in the maximal accumulated oxygen deficit between trials ; however , total VO(2 ) was significantly increased in the caffeine trial in comparison with the placebo trial ( 13.35 + /- 3.89 L vs 11.67 + /- 3.61 L ) . In addition , caffeine T(lim ) ( 222.1 + /- 48.9 s ) was significantly greater ( P < 0.05 ) than both baseline ( 200.8 + /- 33.4 s ) and placebo ( 198.3 + /- 45.4 s ) T(lim ) . RPE was also lower at 90 s in the caffeine treatment ( 13.8 + /- 1.8 RPE points ) in comparison with baseline ( 14.6 + /- 1.9 RPE points ) . CONCLUSION As indicated by a greater T(lim ) , acute caffeine ingestion was found to be ergogenic after 6-d of creatine supplementation and caffeine abstinence Purpose Many studies have examined the effect of caffeine on exercise performance , but findings have not always been consistent . The objective of this study was to determine whether variation in the CYP1A2 gene , which affects caffeine metabolism , modifies the ergogenic effects of caffeine in a 10-km cycling time trial . Methods Competitive male athletes ( n = 101 ; age = 25 ± 4 yr ) completed the time trial under three conditions : 0 , 2 , or 4 mg of caffeine per kilogram body mass , using a split-plot r and omized , double-blinded , placebo-controlled design . DNA was isolated from saliva and genotyped for the −163A > C polymorphism in the CYP1A2 gene ( rs762551 ) . Results Overall , 4 mg·kg−1 caff 
    Output:
    
The acute ingestion of a moderate dose of caffeine had a small but significant positive effect on several aspects related to physical performance in team sports