***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: PURPOSE To determine whether a dose-response relationship exists between caffeine and 2000-m rowing performance . METHODS In this r and omized , placebo-controlled , double-blind crossover study , 10 competitive male rowers ( mean + /- SD : age = 20.6 + /- 1.4 yr , body mass = 87.7 + /- 10.5 kg , height = 186.8 + /- 6.8 cm , (.)VO2peak = 5.1 + /- 0.6 L x min(-1 ) ) consumed 2 , 4 , or 6 mg x kg(-1 ) caffeine or a placebo 60 min before completing a 2000-m time trial on a rowing ergometer . The trials were preceded by a 24-h st and ardized diet ( including a light preexercise meal of 2 g x kg(-1 ) CHO ) , and subjects were tested preexercise for hydration , caffeine abstinence , and blood glucose concentrations . RESULTS Time trial performance was not significantly different across the three caffeine doses or placebo ( P = 0.249 ) . After the three caffeine trials , postexercise plasma glucose and lactate concentrations were higher compared with the placebo trial ( P < 0.05 ) . Plasma caffeine concentrations after 60 min of ingestion were lower than the values reported previously by others following the same dose , and there was considerable interindividual variation in plasma caffeine concentrations in response to the various caffeine doses . CONCLUSIONS The large interindividual response to the caffeine doses suggests that individual characteristics need to be considered when administering caffeine for performance enhancement . In addition , preexercise feeding may significantly affect plasma caffeine concentrations and the potential for caffeine to improve performance PURPOSE To investigate the effect of caffeine ingestion on short-term endurance performance in competitive rowers . METHODS In this r and omized double-blind crossover study , eight competitive oarsmen ( peak oxygen uptake [ VO2peak ] 4.7+/-0.4 L x min(-1 ) , mean + /- SD ) performed three familiarization trials of a 2000-m rowing test on an air-braked ergometer , followed by three experimental trials at 3- to 7-d intervals , each 1 h after ingesting caffeine ( 6 or 9 mg x kg(-1 ) body mass ) or placebo . Trials were preceded by a st and ardized warm-up ( 6 min at 225+/-39 W ; 75+/-7.7 % VO2peak ) . RESULTS Urinary caffeine concentration was similar before ingestion ( approximately 1 mg x L(-1 ) ) but rose to 6.2+/-3.6 and 14.5+/-7.0 mg x L(-1 ) for the low and high caffeine doses , respectively . Plasma free fatty acid concentration before exercise was higher after caffeine ingestion ( 0.29+/-0.17 and 0.39+/-0.20 mM for 6 and 9 mg x kg(-1 ) , respectively ) than after placebo ( 0.13+/-0.05 mM ) . Respiratory exchange ratio during the warm-up was also substantially lower with caffeine ( 0.94+/-0.09 and 0.93+/-0.06 for the low and high dose ) than with placebo ( 0.98+/-0.12 ) . Subjects could not distinguish between treatments before or after the exercise test . Both doses of caffeine had a similar ergogenic effect relative to placebo : performance time decreased by a mean of 1.2 % ( 95 % likely range 0.4 - 1.9 % ) ; the corresponding increase in mean power was 2.7 % ( 0.4 - 5.0 % ) . Performance time showed some evidence of individual differences in the effect of caffeine ( SD 0.9 % ; 95 % likely range 1.5 to -0.9 % ) . CONCLUSIONS Ingestion of 6 or 9 mg x kg(-1 ) of caffeine produces a worthwhile enhancement of short-term endurance performance in a controlled laboratory setting BACKGROUND AND PURPOSE Assessment of the quality of r and omized controlled trials ( RCTs ) is common practice in systematic review s. However , the reliability of data obtained with most quality assessment scales has not been established . This report describes 2 studies design ed to investigate the reliability of data obtained with the Physiotherapy Evidence Data base ( PEDro ) scale developed to rate the quality of RCTs evaluating physical therapist interventions . METHOD In the first study , 11 raters independently rated 25 RCTs r and omly selected from the PEDro data base . In the second study , 2 raters rated 120 RCTs r and omly selected from the PEDro data base , and disagreements were resolved by a third rater ; this generated a set of individual rater and consensus ratings . The process was repeated by independent raters to create a second set of individual and consensus ratings . Reliability of ratings of PEDro scale items was calculated using multirater kappas , and reliability of the total ( summed ) score was calculated using intraclass correlation coefficients ( ICC [ 1,1 ] ) . RESULTS The kappa value for each of the 11 items ranged from.36 to.80 for individual assessors and from.50 to.79 for consensus ratings generated by groups of 2 or 3 raters . The ICC for the total score was.56 ( 95 % confidence interval=.47-.65 ) for ratings by individuals , and the ICC for consensus ratings was.68 ( 95 % confidence interval=.57-.76 ) . DISCUSSION AND CONCLUSION The reliability of ratings of PEDro scale items varied from " fair " to " substantial , " and the reliability of the total PEDro score was " fair " to " good . This study examined the ergogenic effects in a 6 min maximal performance test ( PT ) on 12 elite rowers : 6 open-weight ( mean ± SD ; 25 ± 1 years , and 92 ± 3 kg ) and 6 light-weight ( 25 ± 3 years , and 73 ± 6 kg ) , following supplementation with caffeine ( CAF ) , sodium bicarbonate ( SB ) , and the combination of both , in a double-blind r and omized placebo ( PLA ) controlled design . PT was executed on 4 occasions , on separate days within a week , and in a non-fasted state , with st and ardized training being performed the day before PT . Protocol s were as follows : ( i ) CAF , 3 mg/kg , 45 min prior to PT + calcium as SB-PLA ; ( ii ) SB , 0.3 g/kg , 75 min prior to PT + dextrose as CAF-PLA ; ( iii ) CAF + SB ; and ( iv ) PLA ; CAF-PLA + SB-PLA . The total distance in the CAF ( 1878 ± 97 m ) and CAF + SB ( 1877 ± 97 m ) was longer than in the PLA ( 1865 ± 104 m ; P < 0.05 ) and SB ( 1860 ± 96 m ; P < 0.01 ) . The mean power in CAF ( 400 ± 58 W ) and CAF + SB ( 400 ± 58 W ) was higher than the PLA ( 393 ± 61 W ; P < 0.05 ) and SB ( 389 ± 57 W ; P < 0.01 ) . In CAF and CAF + SB , power was higher ( P < 0.05 ) relative to PLA in the last half ( 4 - 6 min ) of PT . Trials with CAF were more effective in light-weight rowers ( 1.0 % ± 0.8 % improvement in distance ; P < 0.05 ) than in open-weight rowers ( 0.3 % ± 0.8 % ; P > 0.05 ) . No difference between interventions was observed for readiness and stomach comfort before PT and perceived exertion during PT . This study demonstrates that caffeine ingestion does improve performance in elite rowing . In contrast sodium bicarbonate does not appear to be ergogenic , but it does not abolish the ergogenic effect of caffeine Eight competitive oarswomen ( age , 22 + /- 3 years ; mass , 64.4 + /- 3.8 kg ) performed three simulated 2,000-m time trials on a rowing ergometer . The trials , which were preceded by a 24-hour dietary and training control and 72 hours of caffeine abstinence , were conducted 1 hour after ingesting caffeine ( 6 or 9 mg á kg-1 body mass ) or placebo .  Plasma free fatty acid concentrations before exercise were higher with caffeine than placebo ( 0.67 + /- 0.34 vs. 0.72 + /- 0.36 vs. 0.30 + /- 0.10 mM for 6 and 9 mg á kg-1 caffeine and placebo , respectively ; p < .05 ) . Performance time improved 0.7 % ( 95 % confidence interval [ CI ] 0 to 1.5 % ) with 6 mg á kg-1 caffeine and 1 . 3 % ( 95 % CI 0.5 to 2.0 % ) with 9 mg á kg-1 caffeine . The first 500 m of the 2,000 m was faster with the higher caffeine dose compared with placebo or the lower dose ( 1.53 + /- 0.52 vs.1.55 + /- 0.62 and 1 . 56 + /- 0.43 min ; p = .02 ) . We concluded that caffeine produces a worthwhile enhancement of performance in a controlled laboratory setting , primarily by improving the first 500 m of a 2,000-m row 
    Output:
    
No significant differences between caffeine and placebo were found for the rating of perceived exertion , oxygen consumption , respiratory exchange ratio , and heart rate .
This meta- analysis found that acute caffeine ingestion improves 2000 m rowing ergometer performance by ~4 s. Our results support the use of caffeine pre-exercise as an ergogenic aid for rowing performance