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00005768-200909000-0000800005768_2009_41_1743_coker_performance_9miscellaneous< 24_0_2_0 >Medicine & Science in Sports & Exercise©2009The American College of Sports MedicineVolume 41(9)September 2009p 1743Caffeine, Cycling Performance and Exogenous, CHO Oxidation: A Dose-Response Study-Comment[BASIC SCIENCES]Coker, Robert H.Department of Geriatrics, University of Arkansas for Medical Sciences, and the Central Arkansas Veterans Healthcare System, Little Rock, ARIngestion of relatively high amounts of caffeine (i.e., ∼350 mg) has been shown to produce significant improvements in endurance exercise performance (1), and concomitant ingestion of glucose may provide even greater enhancement of this effect (2). Thus, it is important to mention that 350 mg of caffeine would be roughly equivalent to three cups of generic coffee and would likely exceed the reasonable range of caffeine intake for most athletes. Recognizing this point, Desbrow et al. (3) completed an interesting study designed to evaluate the influence of low to moderate levels of caffeine ingestion on time trial performance and carbohydrate oxidation. Surprisingly, neither low (∼125 mg) nor moderate (∼250 mg) doses of caffeine promoted increased time trial performance or fuel metabolism, even in the presence of ad libitum carbohydrate supplementation.This study was strengthened by a randomized, double-blind, placebo-controlled design as well as familiarization sessions that eliminated a potential "learning" effects. In addition, all volunteers were provided with well-controlled diets before performance of each time trial. This represents a significant strength because nutritional intake may have a substantial influence on substrate metabolism or exercise (4), and studies of this nature do not normally address this important issue. The scientific rigor of these studies was also enhanced by the use of 14C glucose that enabled the derivation of exogenous glucose oxidation, and this variable was not influenced by either low or moderate doses of caffeine ingestion.Although the factors discussed above represent important strengths of the study, there are a few important issues that should be mentioned. First, the primary limitation of this study was the lack of a caffeine dose that demonstrated a positive effect on endurance performance. Based upon results from other studies (5), it was indeed surprising that the moderate dose did not boost performance. Although it is understood that previous studies have already shown an ergogenic effect at high doses (2), the lack of a high-dose group that demonstrates a significant effect does limit interpretation of the data. In addition, there was a wide range of habitual caffeine consumption among the subjects. This may have contributed to variable caffeine sensitivity and could have potentially influenced the results of the study. It would have been interesting to determine whether low consumers of caffeine respond more favorably when caffeine is used to elicit increased endurance performance. Unfortunately, the limited number of volunteers in this study precluded this opportunity.Nevertheless, this manuscript used several familiarization sessions, randomized experimental trials, and standardized nutritional intake along with caffeine doses that may be more representative of those actually used in endurance competition. Under this experimental paradigm, this manuscript supports the contention that low to moderate levels of caffeine intake along with modest carbohydrate supplementation has a negligible impact on endurance performance.Robert H. CokerDepartment of GeriatricsUniversity of Arkansas for Medical Sciencesand the Central Arkansas Veterans Healthcare SystemLittle Rock, ARREFERENCES1. Cohen B, Nelson A, Prevost M, Thompson G, Marx B, Morris G. Effects of caffeine ingestion on endurance racing in heat and humidity. Eur J Appl Physiol. 1996;73:358-63. [CrossRef] [Medline Link] [Context Link]2. Cox G, Desbrow B, Montgomery P, et al. Effect of different protocols of caffeine intake on metabolism and endurance performance. J Appl Physiol. 2002;93:990-9. [Medline Link] [Context Link]3. Desbrow B, et al. Caffeine, cycling performance, and exogenous CHO oxidation: a dose-response study. Med Sci Sports Exerc. 2009;41(9):1744-1751. [CrossRef] [Full Text] [Medline Link] [Context Link]4. Rodriguez NR, DiMarco NM. Position of the American Dietetic Association, Dietitians of Canada, American College of Sports Medicine. Nutrition and athletic performance. J Am Diet Assoc. 2009;109(3):509-27. [Context Link]5. Yeo S, Jentjens R, Wallis G, Jeukendrup A. Caffeine increase exogenous carbohydrate oxidation during exercise. J Appl Physiol. 2005;99(3):844-50. 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