***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: Background We examined the metabolic , performance and gastrointestinal ( GI ) effects of supplementation with a natural food product ( raisins ) compared to a commercial product ( sport chews ) . Methods Eleven male ( 29.3 ± 7.9 yrs ; mean and SD ) runners completed three r and omized trials  ( raisins , chews and water only ) separated by seven days . Each trial consisted of 80-min ( 75%VO2max ) treadmill running followed by a 5-km time trial ( TT )  . Heart rate ( HR ) , respiratory exchange ratio ( RER ) , blood lactate , serum free fatty acids ( FFA ) , glycerol and insulin , plasma glucose and creatine kinase , GI symptoms and rating of perceived exertion ( RPE ) were recorded every 20-min . We employed a within-subject two-way analysis of variance ( ANOVA ) for repeated measures with a Fisher ’s post hoc analysis to determine significant differences . Results VO2 , HR , lactate , glycerol and RPE did not differ due to treatment . Average plasma glucose was maintained at resting levels ( 5.3 ± 0.4 mmol·L-1 ) during the sub-maximal exercise bout ( 5.9 ± 0.6 , 5.7 ± 0.6 and 5.5 ± 0.5 mmol·L-1 for chews , raisins and water respectively ) , and was significantly higher with chews than water only . RER and % of non-protein macronutrient oxidation derived from carbohydrate was highest with chews , followed by raisins and water was the lowest ( 74.4 ± 6.4 , 70.0 ± 7.0 and 65.1 ± 8.7 % for chews , raisins and water respectively ) during the sub-maximal exercise period . Serum FFA was higher in the water treatment versus both raisins and chews at 80 min of sub-maximal exercise . Serum insulin was higher with the chews than both raisins and water ( 5.1 ± 2.0 , 3.1 ± 0.8 , 1.9 ± 0.6 uU·ml-1 for chews , raisins and water respectively ) . Plasma creatine kinase , corrected for baseline values , for the last 40 min of the sub-maximal exercise bout , was higher with raisins compared to other treatments . The TT was faster for both carbohydrate supplements ( 20.6 ± 2.6 , 20.7 ± 2.5 , 21.6 ± 2.7 min for raisin , chews and water respectively ) . GI disturbance was mild for all treatments . Conclusion Raisins and chews promoted higher carbohydrate oxidation and improved running performance compared to water only . Running performance was similar between the raisins and chews , with no significant GI differences On three occasions cyclists completed , as fast as possible , two exercise tasks ( T1 and T2 ) separated by 30 min rest . T1 and T2 were equivalent to the work performed during 2 h cycling at 75 % VO2max and 30 min at 75 % VO2max , respectively . Every 20 min subjects drank 275 mL of a 6 % ( MC ) or 2.5 % ( LC ) carbohydrate-electrolyte beverage or a water placebo ( P ) . The initial drink during both T1 and the rest period contained 20 g D2O as a marker for entry of ingested fluid into blood . No differences in drink effects were found for heart rate , sweat rate , change in plasma volume , rectal temperature , or D2O accumulation in blood . Blood glucose and respiratory exchange ratios were higher and T2 was performed faster with MC than with P. Ingestion of MC can help maintain blood glucose and enhance performance of prolonged cycling exercise without compromising fluid replenishment Summary The purpose of these experiments was to examine the influence of various fluid replacement drinks on exercise-induced disturbances in homeostasis during heavy exercise . Nine trained cyclists performed constant load exercise on a cycle ergometer to fatigue on three occasions with 1-week separating experiments . The work rate was set initially at ∼ 85 % of $ $ \dot V_{o_{2{\text { } } max } } $ $ ( range 82–88 % ) with fatigue being defined as a 10 % decline in power output below the initial value . During each experiment subjects consumed one of the following three beverages prior to and every 15 min during exercise : ( 1 ) non-electrolyte placebo ( NEP ; 31 mosmol · kg−1 ) ; ( 2 ) glucose polymer drink containing electrolytes ( GP ; 7 % CHO , 231 mosmol · kg−1 ) , and ( 3 ) electrolyte placebo drink without carbohydrate ( EP ; 48 mosmol · kg−1 ) . Both the GP and EP beverage contained sodium citrate/citric acid ( C ) as a flavoring agent while C was not contained in the NEP drink . Although seven of nine subjects worked longer during the GP and EP treatment when compared with the NEP trial , the difference was not significant ( P>0.05 ) . No differences ( P>0.05 ) existed between the GP and EP treatments in performance time . Exercise changes in rectal temperature , heart rate , Δ % plasma volume and plasma concentrations of total protein , free fatty acids , glucose , lactate , potassium , chloride , calcium , and sodium did not differ ( P>0.05 ) between trials . In contrast , blood hydrogen ion concentration [ H+ ] was significantly lower ( P<0.05 ) at 30 min of exercise during the GP and EP treatment when compared with the NEP run . These data provide evidence that electrolyte drinks do not minimize exercise-induced disturbances in blood-electrolyte concentrations during heavy execrcise when compared with nonelectrolyte drinks ; however , these results suggest that fluid replacement beverages containing buffers ( i.e. C ) and /or electrolytes may minimize blood alterations in [ H+ ] during intense exercise . Additional research is required to determine if the buffering influence of these beverages has an ergogenic benefit during heavy exercise In an effort to determine the effects of carbohydrate ( CHO ) feedings immediately before exercise in both the fasted and fed state , 10 well-trained male cyclists [ maximum O2 consumption ( VO2 max ) , 4.35 + /- 0.11 l/min ) ] performed 45 min of cycling at 77 % VO2 max followed by a 15-min performance ride on an isokinetic cycle ergometer . After a 12-h fast , subjects ingested 45 g of liquid carbohydrate ( LCHO ) , solid carbohydrate confectionery bar ( SCHO ) , or placebo ( P ) 5 min before exercise . An additional trial was performed in which a high-CHO meal ( 200 g ) taken 4 h before exercise was combined with a confectionery bar feeding ( M + SCHO ) immediately before the activity . At 10 min of exercise , serum glucose values were elevated by 18 and 24 % during SCHO and LCHO , respectively , compared with P. At 0 and 45 min no significant differences were observed in muscle glycogen concentration or total use between the four trials . Total work produced during the final 15 min of exercise was significantly greater ( P less than 0.05 ) during M + SCHO ( 194,735 + /- 9,448 N X m ) , compared with all other trials and significantly greater ( P less than 0.05 ) during LCHO and SCHO ( 175,204 + /- 11,780 and 176,013 + /- 10,465 N X m , respectively ) than trial P ( 159,143 + /- 11,407 N X m ) . These results suggest that , under conditions when CHO stores are less than optimal , exercise performance is enhanced with the ingestion of 45 g of CHO 5 min before 1 h of intense cycling . ( ABSTRACT TRUNCATED AT 250 WORDS It is presently unclear whether the reported ergogenic effect of a carbohydrate ( CHO ) mouth rinse on cycling time-trial performance is affected by the acute nutritional status of an individual . Hence , the aim of this study was to investigate the effect of a CHO mouth rinse on a 60-min simulated cycling time-trial performance commenced in a fed or fasted state . Twelve competitive male cyclists each completed 4 experimental trials using a double-blinded Latin square design . Two trials were commenced 2 h after a meal that contained 2.5 g·kg(-1 ) body mass of CHO ( FED ) and 2 after an overnight fast ( FST ) . Prior to and after every 12.5 % of total time during a performance ride , either a 10 % maltodextrin ( CHO ) or a taste-matched placebo ( PLB ) solution was mouth rinsed for 10 s then immediately expectorated . There were significant main effects for both pre-ride nutritional status ( FED vs. FST ; p < 0.01 ) and CHO mouth rinse ( CHO vs. PLB ; p < 0.01 ) on power output with an interaction evident between the interventions ( p < 0.05 ) . The CHO mouth rinse improved mean power to a greater extent after an overnight fast ( 282 vs. 273 W , 3.4 % ; p < 0.01 ) compared with a fed state ( 286 vs. 281 W , 1.8 % ; p < 0.05 ) . We concluded that a CHO mouth rinse  improved performance to a greater extent in a fasted compared with a fed state ; however , optimal performance was achieved in a fed state with the addition of a CHO mouth rinse Summary The availability of carbohydrate ( CHO ) as a substrate for the exercising muscles is known to be a limiting factor in the performance of prolonged cycle exercise , and provision of exogenous CHO in the form of glucose can increase endurance capacity . The present study examined the effects of ingestion of fluids and of CHO in different forms on exercise performance .  Six male volunteers exercised to exhaustion on a cycle ergometer at a workload which required approximately 70 % of $ $ \dot V_{O_2 \max } $ $ . After one preliminary trial , subjects performed this exercise test on six occasions , one week apart . Immediately before exercise , and at 10-min intervals throughout , subjects ingested 100 ml of one of the following : control ( no drink ) , water , glucose syrup , fructose syrup , glucose-fructose syrup or a dilute glucose-electrolyte solution . Each of the syrup solutions contained approximately 36 g CHO per 100 ml ; the isotonic glucose-electrolyte solution contained 4 g glucose per 100 ml . A r and omised Latin square order of administration of trials was employed . Expired air sample s for determination of $ $ \dot V_{O_2 } $ $ , respiratory exchange ratio and rate of CHO oxidation were collected at 15-min intervals . Venous blood sample s were obtained before and after exercise . Subjects drinking the isotonic glucose-electrolyte solution  exercised longer ( 90.8 ( 12.4 ) min , mean ( SEM ) ) than on the control test ( 70.2 ( 8.3 ) min ; p<0.05 ) . Endurance capacity was not affected by any of the other drinks . Blood glucose concentration at exhaustion was higher when concentrated sugar solutions were given , but no instance of hyperglycaemia or hypoglycaemia was observed in any trial . Neither the rate of CHO oxidation nor the total amount of CHO oxidised was influenced by the ingestion of large quantities of glucose or fructose The effects of a commercial sports drink on performance in  high-intensity cycling  was investigated . Nine well-trained subjects were asked to complete a set amount of work as fast as possible ( time trial ) following 24 h of dietary ( subjects were provided with food , energy 57.4+/-2.4 kcal/kg and carbohydrate 9.1+/-0.4 g/kg ) and exercise control . During exercise , subjects were provided with 14 mL/kg of either 6 % carbohydrate-electrolyte ( CHO-E ) solution or carbohydrate-free placebo ( P ) . Results showed that subjects ' performances did not greatly improve ( time , 62:34+/-6:44 min : sec ( CHO-E ) vs. 62:40+/-5:35 min : sec ( P ) ; average power output , 283.0+/-25.0 W ( CHO-E ) vs. 282.9+/-29.3 W ( P ) , P > 0.05 ) while consuming the sports drink . It was concluded that CHO-E consumption throughout a 1-h time trial , following a pre-exercise dietary regimen design ed to optimize glucose availability , did not improve time or power output to a greater degree than P in well-trained cyclists Solutions containing multiple carbohydrates utilizing different intestinal transporters ( glucose and fructose ) show enhanced absorption , oxidation , and performance compared with single-carbohydrate solutions , but the impact of the ratio of these carbohydrates on outcomes is unknown . In a r and omized double-blind crossover , 10 cyclists rode 150 min at 50 % peak power , then performed an incremental test to exhaustion , while ingesting artificially sweetened water or one of three carbohydrate-salt solutions comprising fructose and maltodextrin in the respective following concentrations : 4.5 and 9 % ( 0.5-Ratio ) , 6 and 7.5 % ( 0.8-Ratio ) , and 
    Output:
    
While not mutually exclusive , the primary mechanism(s ) for performance enhancement likely differs depending on the duration of the exercise .
In short duration exercise situations ( ∼1 h ) , oral receptor exposure to CHO , via either mouthwash or oral consumption ( with enough oral contact time ) , which then stimulates the pleasure and reward centers of the brain , provide a central nervous system-based mechanism for enhanced performance .
Thus , the type and ( or ) amount of CHO and its ability to be absorbed and oxidized appear completely irrelevant to enhancing performance in short duration exercise situations .
For longer duration exercise ( > 2 h ) , where muscle glycogen stores are stressed , the primary mechanism by which carbohydrate supplementation  enhances performance is via high rates of CHO delivery ( > 90 g/h ) , result ing in high rates of CHO oxidation .