Tag Archives: mouth rinse

Carbohydrate ingestion during exercise of relatively short duration and high intensity

Intermittent high intensity exercise and carbohydrate ingestion

High Intensity: During-Exercise Nutrition
Fig. 1- During-Exercise Nutrition

Carbohydrate ingestion during intermittent high intensity or prolonged (>90 min) sub-maximal exercise can:

  • increase exercise capacity;
  • improve exercise performance;
  • postpone fatigue.

The intake of very small amounts of carbohydrates or carbohydrate mouth rinsing (for example with a 6% maltodextrin solution) may improve exercise performance by 2-3% when the exercise is of relatively short duration (<1 h) and high intensity (>75% VO2max), that is, an exercise not limited by the availability of muscle glycogen stores, given adequate diet.
The underlying mechanisms for the ergogenic effect of carbohydrates during this type of activity are not metabolic but may reside in the central nervous system: it seems that carbohydrates are detected in the oral cavity by unidentified receptors, promoting an enhanced sense of well-being and improving pacing.
These effects are independent of taste or sweet and non-sweet of carbohydrates but are specific to carbohydrates.

It should be noted that performance effects with drink ingestion are similar to the mouth rinse; therefore athletes, when they don’t complain of gastrointestinal distress when ingesting too much fluid, may have an advantage taking the drink (in endurance sports, dehydration and carbohydrate depletion are the most likely contributors to fatigue).

Conclusion

It seems that during exercise of relatively short duration (<1 h) and high intensity (>75% VO2max) it is not necessary to ingest large amounts of carbohydrates: a carbohydrate mouth rinsing or the intake of very small amounts of carbohydrates may be sufficient to obtain a performance benefit.

References

Carbohydrate mouth rinse and endurance exercise performance

Carbohydrate mouth rinse and performance responses

The importance of carbohydrates as an energy source for exercise is well known: one of the first study to hypothesize and recognize their importance was the study of Krogh and Lindhardt at the beginning of the 20th century (1920); later, in the mid ‘60’s, Bergstrom and Hultman discovered the crucial role of muscle glycogen on endurance capacity.
Nowdays, the ergogenic effects of carbohydrate supplementation on endurance performance are well known; they are mediated by mechanisms such as:

  • a sparing effect on liver glycogen;
  • the maintenance of glycemia and rates of carbohydrate oxidation;
  • the stimulation of glycogen synthesis during low-intensity exercise ;
  • a possible stimulatory effect on the central nervous system.

However, their supplementation, immediately before and during exercise, has an improving effect also during exercise (running or cycling) of a shorter and more intense nature: >75% VO2max (maximal oxygen consumption) and ≤1 hour, during which euglycaemia is rarely challenged and adequate muscle glycogen store remains at the cessation of the exercise.

Hypothesis for carbohydrate mouth rinse

In the absence of a clear metabolic explanation it was speculated that ingesting carbohydrate solutions may have a ‘non-metabolic’ or ‘central effect’ on endurance performance. To explore this hypothesis many studies have investigated the performance responses of subjects when carbohydrate solutions (about 6% carbohydrate, often maltodextrins) are mouth rinsed during exercise, expectorating the solution before ingestion.
By functional magnetic resonance imaging and transcranial stimulation it was shown that carbohydrates in the mouth stimulate reward centers in the brain and increases corticomotor excitability, through oropharyngeal receptors which signal their presence to the brain.
Probably salivary amylase releases very few glucose units from maltodextrins which is probably what is needed in order to activate the purported carbohydrate receptors in the oropharynx (no glucose transporters in the oropharynx are known).
However, the performance response appears to be dependent upon the pre-exercise nutritional status of the subject: most part of the studies showing an improving effect on performance was conducted in a fasted states (3- to 15-h fasting).
Only one study has shown improvements of endurance capacity   in both fed and fasted states by carbohydrate mouth rinse, but in non-athletic subjects.

References

Beelen M., Berghuis J., Bonaparte B., Ballak S.B., Jeukendrup A.E., van Loon J. Carbohydrate mouth rinsing in the fed state: lack of enhancement of time-trial performance. Int J Sport Nutr Exerc Metab 2009;19(4):400-9 [Abstract]

Bergstrom J., Hultman E. A study of glycogen metabolism during exercise in man. Scand J Clin Invest 1967;19:218-28 [Abstract]

Bergstrom J., Hultman E. Muscle glycogen synthesis after exercise: an enhancing factor localized in muscle cells in man. Nature 1966;210:309-10 [Abstract]

Painelli V.S., Nicastro H., Lancha A. H.. Carbohydrate mouth rinse: does it improve endurance exercise performance? Nutrition Journal 2010;9:33 [Abstract]

Fares E.J., Kayser B. Carbohydrate mouth rinse effects on exercise capacity in pre- and postprandial States. J Nutr Metab 2011;385962. doi: 10.1155/2011/385962. Epub 2011 Jul 27 [Abstract]

Krogh A., Lindhard J. The relative value of fat and carbohydrate as sources of muscular energy. Biochem J 1920;14:290-363 [PDF]

Rollo I. Williams C. Effect of mouth-rinsing carbohydrate solutions on endurance performance. Sports Med. 2011;41(6):449-61 [Abstract]