Wednesday, October 19, 2011

Carbohydrate ingestion in training and game: why is needed?

A large amount of research suggests carbohydrate (CHO) ingestion either in liquid or solid form prior to and during prolonged exercise that lasts more than 1 hour. Limited information exists regarding the role of this strategy on performance in intermittent exercise such as football. From these studies, it appears that carbohydrate ingestion before and during exercise improves intermittent endurance capacity. Although there are no scientific data, I speculate that total distance covered and distance covered at moderate/high intensity should be improved with carbohydrate ingestion. From published research, it seems that sprint performance remains unaffected by CHO ingestion.

It is noteworthy that football skills seem to be affected by CHO ingestion. Ajmol Ali and Clyde Williams from the University of Loughborough asked 17 players to perform a football-specific intermittent test and also evaluated skill performance under two experimental conditions: 1) following ingestion of a CHO-electrolyte solution before and every 15min during the test, 2) following ingestion of a placebo solution of equivalent taste and volume. Their results showed a 17% reduction in skill performance during the control trial. This reduction was only 3% in the CHO trial. Thus, it seems that carbohydrate ingestion during exercise may maintain football skill performance during the game.

What is the mechanism behind performance improvement?
Football skill maintenance with carbohydrate ingestion could be due to direct effect of CHO in the central nervous system. Indeed, recent studies show that CHO when in the mouth may activate brain regions that are involved in reward and motor control (Chambers et al., 2009). There are two more explanations for the positive effect of CHO ingestion on intermittent running performance:  a) the sparing of muscle glycogen, b) the maintenance of blood glucose, although hypoglycemia is not usually presented in running.

Table. Effect of carbohydrate ingestion prior and during exercise that simulates football on performance.

Endurance capacity
No effect
Level of evidence
Level of evidence ranges from 1 (very low) to 5 (very strong)

Is it safe for youth players?
Yes, it is. There is no study to suggest that youth players should not ingest carbohydrate solutions. Recent studies show that carbohydrate ingestion either in a beverage or gel improves intermittent endurance capacity in young players (Phillips et al., 2011a; Phillips et al., 2011b).

What to drink, how much and at what time?
-You can drink carbohydrate solutions before (150-250ml for 80kg body weight) and during exercise (at regular intervals when it is possible). Players should try to consume 50-60 g CHO per hour.
-It is better to drink solutions than contain 2-7% CHO or 20-70 gr CHO per liter.
-Commercially available carbohydrate drinks contain electrolytes. Electrolytes a) improve the drink’s taste, b) speed glucose entry into the bloodstream.
-Recent studies suggest that adding some protein may improve more endurance capacity compared with the CHO-electrolyte solution (Alghannam, 2011).
-Choose the drink temperature you like. Drink temperature must be mild and not too low (<5oC)
-It is not easy for the players to ingest beverages or solid CHO before a game or at half-time. EXPERIMENT YOUR STRATEGY BEFORE USING IT IN THE GAME.
-Do not overdo it. If you drink too much you might get stomach discomfort.

For additional reading
Ali and Williams (2009). Carbohydrate ingestion and soccer skill performance during prolonged intermittent exercise. J Sports Sci 27(14):1499-1508.

Alghannam (2011). Carbohydrate-protein ingestion improves subsequent running capacity towards the end of a football-specific intermittent exercise. Appl Physiol Nutr Metab 36(5):748-57.

Chambers et al. (2009). Carbohydrate sensing in the human mouth: effects on exercise performance and brain activity. J Physiol 587:1779-94.

Nassis et al (1998). Effect of a carbohydrate-electrolyte drink on endurance capacity during prolonged intermittent high intensity running. Br J Sports Med 32(3):248-252.

Phillips et al. (2011). Carbohydrate ingestion during team games exercise: current knowledge and areas for future investigation. Sports Med 41(7):559-585.

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