Conger, S. A., Warren, G. L., & Millard-Stafford, M. L. (2010). Addition of caffeine to carbohydrate: improved ergogenic effect for endurance exercise? Presentation 926 at the 2010 Annual Meeting of the American College of Sports Medicine, Baltimore, Maryland; June 2-5.

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The effects of caffeine co-ingested with carbohydrate on endurance exercise performance were compared to carbohydrate alone by using a meta-analytic systematic literature review. PubMed, SportDiscus, and ProQuest databases were searched using key words: caffeine, endurance, exercise, carbohydrate, and performance. Criteria for inclusion were studies utilizing human subjects performing endurance exercise that included a performance task (at least 10 minutes in duration), a carbohydrate condition, and a carbohydrate plus caffeine condition.

One-hundred and forty studies were identified with 20 meeting the criteria. Effect sizes ranged from -0.08 (trivial effect favoring carbohydrate) to 0.81 (large effect favoring carbohydrate plus caffeine). Carbohydrate plus caffeine provided a greater performance benefit (~6%) over carbohydrate. Effect sizes were not significantly related to caffeine dosage, exercise duration, or method used to assess performance. To determine whether adding caffeine to carbohydrate was different from adding caffeine to water (placebo), a subgroup meta-analysis comparing 33 "caffeine vs. placebo" studies against the 20 "carbohydrate plus caffeine vs. carbohydrate" studies was conducted; the overall effect size for the former group of studies (0.51) was nearly two-fold greater than for "carbohydrate plus caffeine vs. carbohydrate" studies.

Implication. Adding caffeine to carbohydrate provides a significant but small effect that improves endurance exercise performance compared to carbohydrate alone; however, the performance benefit of adding caffeine to carbohydrate is less than when caffeine is added to water.

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