Rauk, E., Connor, D., Brumet, A., Strubeck, E., Brown, K. M., & Seifert, J. G. (2013). The influence of caffeine on power output and response time. Medicine & Science in Sports & Exercise, 45(5), Supplement abstract number 1106.

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This study compared the ingestion of a commercially available liquid caffeine product with a flavored, non-caloric placebo during endurance cycling. Ss (N = 14) completed a 120-minute work bout divided into 8 x 15-minute intervals (13 minutes at 70% VO2max; 2 minutes at 90% VO2max), and ended with a six-minute power output performance task. Caffeine was ingested at a dose of 256 mg caffeine/hour. Water (200 mL/hr) was co-ingested with the caffeine and placebo supplements. Blood glucose, heart rate, rating of perceived exertion, respiratory exchange ratio, and auditory reaction time were measured throughout the 120-minute exercise. The power output task required Ss to cycle at their highest sustainable power output for six minutes. Cycling resistance was set at 5% body-weight. The caffeine and placebo treatments were administered in a double blind, randomly assigned protocol.

No statistical differences between treatments were observed for mean power output, auditory reaction time, heart rate, rating of perceived exertion, respiratory exchange ratio, or blood glucose.

Implication. Ingestion of a moderate dose of caffeine (~6.8 mg/kg BW) did not result in significant improvements in reaction time or power output when compared to a non-caloric placebo. Additionally, caffeine ingestion did not change substrate utilization, as measured by blood glucose and respiratory exchange ratio during exercise. The caffeine dose used in this study had minimal influence on physiological function and performance under the given conditions.

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