The ingestion of combined carbohydrates does not alter metabolic responses or performance capacity during soccer-specific exercise in the heat compared to ingestion of a single carbohydrate

Journal Title (Medline/Pubmed accepted abbreviation): J. Sports Sci.
Year: 2012
Page numbers: 699-708
doi: 10.1080/02640414.2012.665941

Summary of background and research design

Background: Ingestion of fluid during exercise in the heat is essential to prevent dehydration.  Energy in beverages that contain more than one type of carbohydrate (ex. glucose and fructose) is absorbed at a faster rate because there are multiple transporters that are involved in carbohydrate uptake.  Additionally, a beverage that contains multiple carbohydrates may increase the rate of fluid uptake.

Hypothesis: Consumption of a beverage that contains multiple types of carbohydrates will improve soccer performance compared to a beverage with only glucose or a placebo.

Subjects: 11 male soccer players, age 27 ± 2 y

Experimental design: randomized, counter-balanced, double-blinded, placebo-controlled

Treatments: The participants consumed 228 ± 6 mL every 15 min throughout the protocol to equal 1337 ± 124 mL.  This was equivalent to 1.0 g carbohydrate/min.  Beverages also included several B-vitamins and other ingredients that were the same for all treatments.
GLU- glucose + maltodextrin + sodium
MIX- fructose + dextrose + maltodextrin + sodium (2:1 glucose:fructose)
PLA- placebo – less than 0.5 g carbohydrate/100 mL + sodium + color and flavor to mimic the other beverages

Protocol: The participants were first assessed for VO2max and familiarized with the soccer-specific, treadmill-based training protocol.  They then reported to the laboratory three times, one for each treatment.  The exercise protocols were completed in an exercise chamber that was held at 30.2 ± 0.5°C (about 86°F) and 45 ± 4% relative humidity.  The protocol included 2 × 45 min halves with a 15 min half time.  One of the treatment beverages was consumed throughout the protocol.  After the second half, the participants ran at a 20% gradient at 12.8 km/hr (8 mph) to exhaustion, their time noted.  This is the Cunningham and Faulkner test to assess fatigue resistance.  Respiratory gases were analyzed every 15 min.  Blood samples were collected before, half-way through, and after exercise.  A muscle biopsy was acquired before and after exercise.

Summary of research findings
Key practice applications
For soccer-like exercise (a combination of high and low intensity of exercise for about 1.5 hrs) in the heat, there appears to be a slight advantage to ingesting beverages with different types of carbohydrates compared to a single type of carbohydrate.  This is evidenced by a slightly higher concentration of glycogen at the end of the trial and slightly better performance on the exercise capacity evaluation.  With that said, results were not statistically significant and more research should be done to optimize the composition of a sports beverage for maximal performance of soccer players.
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