Luden, N. D., Acker, T. L., Shafer, B. M., Saunders, M. J., Womack, C. J., & Goh, Q. (2011). Carbohydrate and caffeine improve high-intensity aerobic cycling performance only when combined. Medicine and Science in Sports and Exercise, 43(5). Supplement abstract 2370.

This study examined the independent and combined effects of carbohydrate and caffeine ingestion on performance and various physiological parameters during one hour of high-intensity aerobic cycling. Cyclists (N = 10) performed 20 minutes of steady-state cycling (60% Wmax) followed by a simulated 20-km time-trial under the following four treatment conditions: placebo, carbohydrate, caffeine, and combined carbohydrate and caffeine. Prior to exercise, cyclists consumed a standardized breakfast (-2 hours) and a placebo/caffeine capsule (-1 hour). Beverages (250 ml; placebo or 8% CHO) were consumed prior to 20-minutes of steady-state activity, prior to the time-trial, and at 20 minutes into the time-trial.

Combined carbohydrate and caffeine improved time-trial performance by 3.4% and power output by 5% compared to the placebo condition. No differences were detected among carbohydrate, caffeine, and placebo. Steady-state RER was elevated in carbohydrate, caffeine, and carbohydrate-caffeine conditions when compared to placebo. Post-steady-state and post-time-trial blood glucose levels were elevated in carbohydrate-caffeine condition when compared to placebo. Treatment conditions did not differentially impact ventilation, oxygen uptake, heart rate, peak quadriceps muscle strength, rating of perceived exertion, or blood lactate.

Implication. Caffeine and carbohydrate improve cycling time-trial performance when taken together but not independently. No obvious physiological mechanisms were evident. It is worth noting that despite higher workloads and faster time-trial performance, carbohydrate-caffeine elicited rating of perceived exertion levels similar to those exhibited in the placebo condition. Carbohydrate-caffeine was also the only condition in which blood glucose was elevated over placebo. Cyclists in a fed state should ingest carbohydrate and caffeine together to improve high-intensity time-trial performance.

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