***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: This study compared the effects of a single and divided dose of caffeine on endurance performance and on  postexercise urinary caffeine and plasma paraxanthine concentrations .  Nine male cyclists and triathletes cycled for 90 min at 68 % of maximal oxygen uptake , followed by a self-paced time trial ( work equivalent to 80 % of maximal oxygen uptake workload over 30 min ) with three r and omized , balanced , and double-blind interventions : 1 ) placebo 60 min before and 45 min into exercise ( PP ) ; 2 ) single caffeine dose ( 6 mg/kg ) 60 min before exercise and placebo 45 min into exercise ( CP ) ; and 3 ) divided caffeine dose ( 3 mg/kg ) 60 min before and 45 min into exercise ( CC ) . Time trial performance was unchanged with caffeine ingestion ( P = 0.08 ) , but it tended to be faster in the caffeine trials ( CP : 24.2 min and CC : 23.4 min ) compared with placebo ( PP : 28.3 min ) . Postexercise urinary caffeine concentration was significantly lower in CC ( 3.8 micro g/ml ) compared with CP ( 6.8 micro g/ml ) . Plasma paraxanthine increased in a dose-dependent fashion and did not peak during exercise . In conclusion , dividing a caffeine dose provides no ergogenic effect over a bolus dose but reduces postexercise urinary concentration 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 UNLABELLED Both time-to-exhaustion ( TTE ) and time-trial ( TT ) exercise tests are commonly used to assess exercise performance , but no study has directly examined the reliability of comparable tests in the same subjects . PURPOSE To evaluate the reliability of comparable TTE and TT treadmill running tests of high and moderately high exercise intensity in endurance-trained male distance runners , and to vali date Hinckson and Hopkins TT prediction methods using log-log modeling from TTE results . METHODS After familiarization tests , eight endurance-trained male distance runners performed , in a r and omized , counterbalanced order , eight trials consisting of two 5-km TT and two 1500-m TT , and four TTE tests run at a speed equivalent to the average speed attained during both the 5-km and 1500-m TT distances . RESULTS Typical error of the estimate ( TEE ) expressed as a coefficient of variation for the 5-km TT , 5-km TTE , 1500-m TT , and 1500-m TTE were 2.0 , 15.1 , 3.3 , and 13.2 % , respectively . The st and ard error of the estimate for predicted TT running speed using log-log modeling from TTE results was 0.67 % , and the predicted versus criterion reliability of this method revealed TEE values of 1.6 % and 2.5 % for the prediction of 5-km and 1500-m TT , respectively . CONCLUSION The variability of 5-km and 1500-m TT tests was significantly less than for similar TTE treadmill protocol s. Despite the greater variability of the TTE tests , log-log modeling using the TTE test results reliably predicted actual TT performance This study analyzed the effect of caffeine ingestion on performance during a repeated- measures , 100-km , laboratory cycling time trial that included bouts of 1- and 4-km high intensity epochs ( HIE ) . Eight highly trained cyclists participated in 3 separate trials ' placebo ingestion before exercise with a placebo carbohydrate solution and placebo tablets during exercise ( Pl ) , or placebo ingestion before exercise with a 7 % carbohydrate drink and placebo tablets during exercise ( Cho ) , or caffeine tablet ingestion before and during exercise with 7 % carbohydrate ( Caf ) . Placebo ( twice ) or 6 mg.kg(-1 ) caffeine was ingested 60 min prior to starting 1 of the 3 cycling trials , during which subjects ingested either additional placebos or a caffeine maintenance dose of 0.33 mg.kg(-1 ) every 15 min to trial completion . The 100-km time trial consisted of five 1-km HIE after 10 , 32 , 52 , 72 , and 99 km , as well as four 4-km HIE after 20 , 40 , 60 , and 80 km . Subjects were instructed to complete the time trial and all HIE as fast as possible . Plasma ( caffeine ) was significantly higher during Caf ( 0.43 + /- 0.56 and 1.11 + /- 1.78 mM pre vs. post Pl ; and 47.32 + /- 12.01 and 72.43 + /- 29.08 mM pre vs. post Caf ) . Average power , HIE time to completion , and 100-km time to completion were not different between trials . Mean heart rates during both the 1-km HIE ( 184.0 + /- 9.8 Caf ; 177.0 + /- 5.8 Pl ; 177.4 + /- 8.9 Cho ) and 4-km HIE ( 181.7 + /- 5.7 Caf ; 174.3 + /- 7.2 Pl ; 175.6 + /- 7.6 Cho ; p < .05 ) was higher in Caf than in the other groups . No significant differences were found between groups for either EMG amplitude ( IEMG ) or mean power frequency spectrum ( MPFS ) . IEMG activity and performance were not different between groups but were both higher in the 1-km HIE , indicating the absence of peripheral fatigue and the presence of a central ly-regulated pacing strategy that is not altered by caffeine ingestion . Caffeine may be without ergogenic benefit during endurance exercise in which the athlete begins exercise with a defined , predetermined goal measured as speed or distance The ingestion of a combination of caffeine ( C ) and ephedrine ( E ) has been reported to prolong exercise time to exhaustion during cycle ergometry at 85 % VO2max . The present study was undertaken to investigate whether this enhancement would occur in a field setting and if drug ingestion on 1 d would affect performance 1 d later . Two hours after ingesting either a combination of 375 mg of C and 75 mg E ( C+E ) , or a placebo ( P ) , 9 healthy male recreational runners completed six balanced and double-blind trials of the Canadian Forces Warrior Test ( WT ) , a 3.2 km run wearing " fighting order " which weighed about 11 kg . The trials were performed in sets of two runs , i.e. , two runs were done 24 h apart , and these sets were separated by a minimum of 7 d. The sets were : C+E trial on day 1 ( D1 ) , placebo on day 2 ( P2 ) ; placebo first ( P1 ) , C+E second ( D2 ) ; and placebo first ( P3 ) , placebo second ( P4 ) . In addition , 1 wk before the treatment trials the subjects performed a control trial WT . During the WT , heart rates ( HR ) were recorded every minute . Plasma C and E levels immediately before the WT were similar for both C+E trials , but were undetectable for all P trials . Run times ( mean+/-SD ) were 15.3+/-0.6 , 15.4+/-0.9 , 15.5+/-1.2 , 15.4+/-0.9 , 15.4+/-0.9 , 14.8+/-0.7 , and 14.6+/-0.8 min for control , P1 , P2 , P3 , P4 , D1 , D2 trials , respectively . The two C+E trial run times were similar and both were significantly faster ( p < 0.05 ) than control and all placebo trials . HR during the WT was significantly higher ( p < 0.05 ) for the C+E trials compared with the other trials . WT performance was not impaired by C+E ingestion 24 h earlier . In conclusion , performance of the WT was improved by ingestion of BACKGROUND The ingestion of either caffeine ( C ) or ephedrine ( E ) has been shown to improve performance during high-intensity aerobic activity lasting 10 - 20 min , with an additive effect being found when the combination ( C + E ) was ingested . It was the purpose of this study to determine if the addition of E to C would improve performance in activity lasting longer than 20 min . METHODS One and one half hours after ingesting a placebo ( P ) , C ( 4 mg/kg ) , E ( 0.8 mg/kg ) , or C + E , 12 subjects performed a 10-km run while wearing a helmet and backpack weighing 11 kg . The trials were performed in a climatic suite at 12 - 13 degrees C , on a treadmill where the speed was regulated by the subject . VO(2 ) , VCO(2 ) , V(E ) , heart rate ( HR ) , and rating of perceived exertion ( RPE ) were measured during the run at 15 and 30 min , and again when the individual reached 9 km . Blood was sample d at 15 and 30 min and again at the end of the run and assayed for lactate , glucose , and catecholamines . RESULTS Run times ( mean + /- SD ) , in minutes , were for C ( 46.0 + /- 2.8 ) , E ( 45.5 + /- 2.9 ) , C + E ( 45.7 + /- 3.3 ) , and P ( 46.8 + /- 3.2 ) . The run times for the E trials ( E and C + E ) were significantly reduced compared with the non-E trials ( C and P ) . Pace was increased for the E trials compared with the non-E trials over the last 5 km of the run . VO(2 ) was not affected by drug ingestion . HR was elevated for the ephedrine trials ( E and C + E ) . RPE remained similar for all trails . Caffeine increased the epinephrine and norepinephrine response associated with exercise and also increased blood lactate , glucose , and glycerol levels .  Ephedrine reduced the epinephrine response but increased dopamine and FFA levels . CONCLUSION The previously seen additive nature of E and C was not evident in this study , with the primary ergogenic effect being attributed to The stimulatory effects of acute caffeine intake on choice reaction time , mood state , and visual vigilance are well established . Little research exists , however , on the effects of chronic caffeine ingestion on psychomotor tasks . Therefore , the purpose of this study was to evaluate the effects of 5 days of controlled caffeine intake on cognitive and psychomotor performance .  Three groups of 20 healthy males ( age=22+/-3 years , mass=75.4+/-7.9 kg , body fat percentage=11.2+/-5.1 % ) twice completed a battery of cognitive and psychomotor tasks : after 6 days of 3 mg.kg(-1 ) day(-1 ) caffeine equilibration ( Day 6 ) , and after 5 days of experimental ( 0 [ G0 ] , 3 [ G3 ] , or 6 [ G6 ] mg.kg(-1 ) day(-1 ) ) caffeine intake ( Day 11 ) . Groups were r and omized and stratified for age , mass , and body composition ; all procedures were double-blind . Cognitive analyses involved a visual four-choice reaction time test , a mood state question naire , and a visual vigilance task . Experimental chronic caffeine intake did not significantly alter the number of correct responses or the mean latency of response for either the four-choice reaction time or the visual vigilance tasks . The Vigor-Activity subset of the mood state question naire was 
    Output:
    
In conclusion , caffeine ingestion can be an effective ergogenic aid for endurance athletes when taken before and /or during exercise in moderate quantities ( 3 - 6 mg.kg body mass ) .
Abstaining from caffeine at least 7 days before use will give the greatest chance of optimizing the ergogenic effect