Ingesting a high-dose carbohydrate solution during the cycle section of a simulated Olympic-distance triathlon improves subsequent run performance


Journal Title (Medline/Pubmed accepted abbreviation): Appl. Physiol. Nutr. Metab.
Year: 2012
Volume: 37
Page numbers: 664-671
doi: 10.1139/H2012-040
Summary of background and research design:
Background: Olympic distance triathlons, which include a 1500-m swim followed by a 40-km cycle then a 10-km run, are gaining popularity.  Due to the large amounts of energy required, close to optimal nutrition is essential.  Because different types of sugars are taken up in the intestines by different protein transporters, a carbohydrate beverage that contains fructose and glucose can be absorbed more quickly than an equicaloric beverage containing either sugar alone.

Hypothesis: A sports beverage delivering 1.8 g sugar/min at a 2:1 ratio of glucose:fructose will improve performance during a triathlon compared to a sugar-free beverage.

Subjects:  Ten amateur triathletes, 4 females and 6 males, age 25 ± 7 y

Experimental design: randomized, single-blind, placebo-controlled, crossover study

Treatments:
CHO: 1.2 g/min maltodextrin + 0.6 g/min fructose
Placebo: sugar-free, fruit flavored beverage

Protocol: On the first visit to the laboratory, participants were evaluated for individual swimming race pace by completing a 1500-m swim time trial.  About 60 min later, VO2max and maximal aerobic power (MAP) were determined by completing a cycling session with increasing resistance until exhaustion.  The participants then completed 2 Olympic distance triathlons, one with each of the experimental beverages.  Diets and exercise schedules were mirrored the day and morning before the triathlons.  After a 2 min warm-up (swim) and a 2 min rest, the triathlon began.  The participants were paced for the swim to within ± 0.5% of the time set in the initial visit.  There were 3 min in between the swim and the cycling session, which was performed on a stationary bicycle.  Participants cycled at 75% of their MAP and aimed to maintain a rate of 85 rotations per minute.  Approximately 2 min before they completed each 25% of the cycling distance (10 m), the participants ingested 25% of their allotted experimental beverage (808 ± 81 mL).  Blood samples were collected throughout the cycling session for analysis of blood glucose and lactate concentrations.  Heart rate and feelings of gastrointestinal discomfort were also noted periodically.  Finally, after a 3 min transition, participants ran 5 × 2-km loops around University of Bath (UK) campus.  Immediately after the run, participants reported any gastrointestinal discomfort.  A final blood sample was also collected.  The participants repeated the triathlon 5-12 days later with the other treatment.
Summary of research findings: 
  • Swim times did not differ between groups, which is consistent with the researchers’ expectations since no beverage had been consumed yet.  Times were about 24:51 ± 3:27 min:sec.
  • Heart rate, ratings of perceived exertion, and perceived stomach upset were not different between trials.
  • Blood glucose concentrations were greater during most of the CHO trial compared to the placebo trial.
  • Blood lactate concentrations also tended to be greater during the carbohydrate trial compared to the placebo trial.
  • The run was about 1:40 ± 0.34 min:sec (4.0 ± 1.3%) faster during the carbohydrate trial compared to the placebo trial.

Key practice applications: Consuming a beverage composed of 2:1 glucose:fructose at 1.8 g/min improved performance compared to a calorie-free beverage and did not upset the participants’ stomachs.   This is important because it shows that triathletes can safely consume carbohydrates during the race without experiencing nausea or flatulence and also improve their race time.  A limitation of this study is that there was no other carbohydrate treatment with which to compare this treatment.

Key search terms for this article (5-7 terms): triathlons, triathletes, marathon, Ironman, carbohydrates, nausea
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