***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: 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 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 We investigated changes in autonomic nerve activity following  caffeine intake by power spectral analysis of R-R intervals of heartbeats in humans . A beverage containing 240 mg of caffeine or a control beverage was given to 10 healthy volunteers , and R-R intervals were measured while subjects were sitting and controlling their respiration at a constant rate . After consumption of the caffeine-containing beverage , a transient and significant increase ( P < 0.001 ) in spectral integrated values ( areas under the curve ) of high frequency power ( high component , HC ) was observed , and at 30 min the value was significantly greater than in controls ( P < 0.02 ) , suggesting an increase in vagal autonomic nerve activity . The effect of caffeine was also examined using decaffeinated coffee supplemented with exogenous caffeine ( 2 mg/kg body wt ) . A transient and significant increase ( P < 0.0001 ) in HC was observed , and the value was significantly greater ( P < 0.02 ) than when subjects consumed decaffeinated coffee without supplemental caffeine . The ratio of HC to total integrated value ( which is also used as a selective indicator of vagal activity ) was also significantly higher ( P < 0.04 ) after caffeine consumption . Physiological variables accompanying the change in autonomic nerve activity ( i.e. , blood pressure , surface body temperature and heart rate ) were not significantly affected by caffeine intake . These results suggest that power spectral analysis of heartbeat R-R intervals is an effective and noninvasive method for detecting subtle changes in autonomic nerve activity in response to food intake INTRODUCTION Previous research has identified acute caffeine ingestion as an effective aid in counteracting the decline in vigilance experienced during sentry duty and sustained operations . However , further research is needed to clarify caffeine 's effects under various stressors and additional operational conditions . The purpose of the present study was to examine the effect of caffeine on target detection and rifle marksmanship during simulated combat operations . METHODS There were 12 reservists who ingested 5 mg x kg(-1 ) body mass of caffeine ( C ) or placebo ( P ) 1 h before beginning a 2.5-h loaded march and 1.0-h s and bag wall construction task . Following exercise , participants were given a re-dose of 2.5 mg x kg(-1 ) body mass of C or P. An hour after ingestion , participants commenced a 2.5-h shooting session on a small arms simulator , which included friend-foe discrimination ( FF ) and vigilance ( VIG ) tasks . Marksmanship performance measures included engagement time ( ET ) , the number of shots fired ( NS ) , accuracy , and precision . RESULTS C ingestion ( initial and /or redose ) did not affect shooting performance during the FF task . ET and NS improved during the VIG task with C ingestion ( mean + /- SD of 2.82 + /- 0.27 s and 29.2 + /- 1.9 shots out of 30 targets , respectively ) compared with the P trial ( 3.00 + /- 0.26 s and 28.0 + /- 3.0 shots ; p < 0.05 ) . CONCLUSION Caffeine ingestion improves target detection and engagement speed during vigilance situations , but is not effective during more complex operations requiring higher levels of cognitive processing and fine motor control and coordination Abstract We examined the influence of caffeine supplementation on cognitive performance and perceptual responses in female team-game players taking low-dose monophasic oral contraceptives of the same hormonal composition . Ten females ( 24 ± 4 years ; 59.7 ± 3.5 kg body mass ; 2–6 training sessions per week ) took part in a r and omised , double-blind , placebo-controlled crossover- design trial . A 90-min intermittent treadmill-running protocol was completed 60 min following ingestion of a capsule containing either 6 mg • kg−1 anhydrous caffeine or artificial sweetener ( placebo ) . Perceptual responses ( ratings of perceived exertion ( RPE ) , feeling scale ( FS ) , felt arousal scale ( FAS ) ) , mood ( profile of mood states ( POMS ) ) and cognitive performance ( Stroop test , choice reaction time ( CRT ) ) were completed before , during and after the exercise protocol , as well as after ~12 h post exercise . Caffeine ingestion significantly enhanced the ratings of pleasure ( P = 0.008 ) and arousal ( P = 0.002 ) during the exercise protocol , as well as increased vigour ( POMS ; P = 0.007 ) , while there was a tendency for reduced fatigue ( POMS ; P = 0.068 ) . Caffeine ingestion showed a tendency to decrease RPE ( P = 0.068 ) and improve reaction times in the Stroop ( P = 0.072 ) and CRT ( P = 0.087 ) tests . Caffeine supplementation showed a positive effect on perceptual parameters by increasing vigour and a tendency to decrease fatigue during intermittent running activity in female games players taking low-dose monophasic oral contraceptive steroids ( OCS ) The purpose of this study was to examine the acute effects of a caffeine-containing supplement on upper- and lower-body strength and muscular endurance as well as anaerobic capabilities . Thirty-seven resistance-trained men ( mean ± SD , age : 21 ± 2 years ) volunteered to participate in this study . On the first laboratory visit , the subjects performed 2 Wingate Anaerobic Tests ( WAnTs ) to determine peak power ( PP ) and mean power ( MP ) , as well as tests for 1 repetition maximum ( 1RM ) , dynamic constant external resistance strength , and muscular endurance ( TOTV ; total volume of weight lifted during an endurance test with 80 % of the 1RM ) on the bilateral leg extension ( LE ) and free-weight bench press ( BP ) exercises . Following a minimum of 48 hours of rest , the subjects returned to the laboratory for the second testing session and were r and omly assigned to 1 of 2 groups : a supplement group ( SUPP ; n = 17 ) , which ingested a caffeine-containing supplement , or a placebo group ( PLAC ; n = 20 ) , which ingested a cellulose placebo . One hour after ingesting either the caffeine-containing supplement or the placebo , the subjects performed 2 WAnTs and were tested for 1RM strength and muscular endurance on the LE and BP exercises . The results indicated that there was a significant ( p < 0.05 ) increase in BP 1RM for the SUPP group , but not for the PLAC group . The caffeine-containing supplement had no effect , however , on LE 1RM , LE TOTV , BP TOTV , PP , and MP . Thus , the caffeine-containing supplement may be an effective supplement for increasing upper-body strength and , therefore , could be useful for competitive and recreational athletes who perform resistance training Background Research has indicated that low-to-moderate dosages of caffeine supplementation are ergogenic for sustained endurance efforts as well as high-intensity exercise . The effects of caffeine supplementation on strength-power performance are equivocal , with some studies indicating a benefit and others demonstrating no change in performance . The majority of research that has examined the effects of caffeine supplementation on strength-power performance has been carried out in both trained and untrained men . Therefore , the purpose of this study was to determine the acute effects of caffeine supplementation on strength and muscular endurance in resistance-trained women . Methods In a r and omized manner , 15 women consumed caffeine  ( 6 mg/kg ) or placebo ( PL ) seven days apart . Sixty min following supplementation , participants performed a one-repetition maximum ( 1RM ) barbell bench press test and repetitions to failure at 60 % of 1RM . Heart rate ( HR ) and blood pressure ( BP ) were assessed at rest , 60 minutes post-consumption , and immediately following completion of repetitions to failure . Results Repeated measures ANOVA indicated a significantly greater bench press maximum  with caffeine ( p ≤ 0.05 ) ( 52.9 ± 11.1 kg vs. 52.1 ± 11.7 kg ) with no significant differences between conditions in 60 % 1RM repetitions ( p = 0.81 ) . Systolic blood pressure was significantly greater post-exercise , with caffeine ( p < 0.05 ) ( 116.8 ± 5.3 mmHg vs. 112.9 ± 4.9 mmHg ) . Conclusions These findings indicate a moderate dose of caffeine may be sufficient for enhancing strength performance in resistance-trained women Background The objective of this study was to analyze the effect of caffeine ingestion on the performance and physiological variables associated with fatigue in 20-km cycling time trials . Methods In a double-blind placebo-controlled crossover study , 13 male cyclists ( 26–10 y , 71–9 kg , 176–6 cm ) were r and omized into 2 groups and received caffeine ( CAF ) capsules ( 
    Output:
    
Supplementation with 3–6 mg/kg of caffeine was found to increase the glycolytic contribution to energy metabolism during the execution of real or simulated combats , as indicated by elevated blood lactate concentrations .
Caffeine intake was also noted to improve levels of strength , power and upper arm muscular endurance .
These effects were not paralleled by an increase in the exertion perceived by the athlete