de medicina del deporte - femede

ARCHIVOS DE MEDICINA DEL DEPORTEPALACIOS GIL-ANTUÑANO, Net al.– The limit of use of glucose by the sportsman,which stands at 60 g/h 25 .– The limit of gastric emptying and of intestinalabsorption of the solution, which determinethe assimilation of the liquid drunk 26 .As regards the limit of use of glucose, the maximumamount of it that should be supplied whendoing sport can be achieved by drinking 1200ml in an hour of a solution containing 8% ofcarbohydrates in the form of glucose, sucroseand/or maltodextrins. Glucose absorption issubject (to begin with) to an active transportmechanism mainly dependent on the sodiumion, and on the paracellular route when highluminal concentrations are present. Fructose isabsorbed by facilitated diffusion (in a transportsystem linked with disaccharidases) and by glucosefacilitated transport. These different andcomplementary absorption routes make the mixof carbohydrates recommendable. There areactually no conclusive data on the type of carbohydratethat gives the best result in beverages.Some authors argue slightly in favour of usingpolysaccharides (maltodextrin) due to the lowerrise in osmolality that they produce, togetherwith glucose and fructose 27 . Glucose increasesthe activity of the Na + -K + -ATPasa, at least invitro, which is a good reason for including it inthese formulations 28 . For other authors, sucrose,because it tastes better, is the most suitablecarbohydrate.The American College of Sports Medicine(ACSM) 29 recommends that the beverage shouldhave a high glycemic index (better still, a highglycemic load) and maintains that greater use ofcarbohydrates is achieved by a mixture of them(i.e. glucose, sucrose, fructose, maltodextrin). Ofthe carbohydrates used, glucose, with 97, is theone with the highest glycemic index, followed bysucrose (glucose plus fructose), with an index of65 30 .As regards gastric emptying, the following factorshave to be taken into account:– Circumstances that stimulate emptying:- The increase in gastric volume: it producesdistension of the wall of this organ, provokingmyenteric reflexes which increase theactivity of the pyloric pump, speeding upgastric emptying.- The presence of gastrin, which stimulatesthe pyloric pump slightly.– Factors that inhibit emptying:- The degree of distension of the duodenum.- Irritation of the duodenal mucose.- The degree of acidity of the duodenal chyme.- The degree of osmality of the chyme.- Excessive amount of proteins or fats in thestomach.- The presence of hypotonic or hypertonicliquids (particularly the latter), as theytrigger enterogastric reflexes which slowdown or inhibit gastric emptying.- Prior dehydration.- Exercise intensity of over 80% of theV02max.The time it usually takes the stomach to empty 1litre of liquid varies from 1-1.5 h. but this gastricemptying rate depends on a broad set of factors,among which the determining factors are thenature of the solutes and the energy value of thebeverage 31 . As of the approximate quantity of600 ml, the greater the gastric content volume,the faster the emptying. As the volume decreases,evacuation slows down. For that reason, to keepit at an adequate rate is it advisable to replace theamounts eliminated by the repeated ingestion ofliquids.The absorption of carbohydrates, water andelectrolytes takes place in the first portions of thethin intestine (duodenum and yeyunum). It iscalculated that optimum quantities of intestinalabsorption are between 600-800 ml for water,and some 60 grams for glucose. When morethan a litre of liquids per hour are drunk, thesurpluses can accumulate and produce intestinaldiscomfort.248A M D