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Jaworski, Carrie A.

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Current Sports Medicine Reports: September 2009 - Volume 8 - Issue 5 - p 218-218
doi: 10.1249/JSR.0b013e3181b7d332
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In the 2009, Volume 41, Number 9, issue of Medicine & Science in Sports & Exercise®, researchers investigated the effects of low and moderate caffeine doses on exogenous carbohydrate (CHO) oxidation and endurance exercise performance in fed subjects. While it is well documented that a high dose of caffeine has an ergogenic effect on endurance performance, little to no data exist describing the smallest caffeine dose required to elicit optimal performance during long-duration (>60 min) endurance exercise. Investigating the lowest threshold of caffeine required for ergogenic benefit has implications in the sporting world, as it could assist athletes in the safe use of this supplement. This study investigated the effect of 1.5 and 3 mg·kg−1 body weight (BW) on endurance exercise metabolism and performance in a group of nine trained male cyclists. The subjects undertook three trials, with training and CHO diet being controlled. One hour before exercise, the subjects ingested capsules containing placebo, 1.5 mg·kg−1 BW of caffeine, or 3 mg·kg−1 BW of caffeine, using a double blind protocol. The trials consisted of 120 min of steady-state (SS) cycling at approximately 70% V˙O2max, followed by a 7 kJ·kg−1 BW time trial (TT). Subjects were provided with fluids containing 14C glucose every 20 min during exercise to determine exogenous CHO oxidation. The results demonstrated no significant TT performance improvements in the caffeine-containing trials. Additionally, caffeine failed to have a significant effect on altering maximal exogenous CHO oxidation. Despite other studies that demonstrate the contrary, the findings of this study indicate no significant ergogenic effect when either a 1.5 or 3 mg·kg−1 BW caffeine dose was provided to endurance trained athletes 1 h before an endurance cycling task where CHO was readily available.

The authors hypothesize that perhaps the ergogenic potential of caffeine was changed based on the ample availability of CHO, citing other studies with similar results. Because endurance athletes typically consume CHO containing sports drinks during competitive endurance events, the authors suggest that further studies looking at the interaction between CHO availability and caffeine should be undertaken. Bottom line: No significant effects were observed on substrate utilization or performance following administration of either a 1.5 or a 3 mg·kg−1 BW dose of caffeine in a group of fed, trained male cyclists.


The 2009, Volume 13, Number 5, issue of ACSM's Health & Fitness Journal® provides readers with a review of common, and often incredible, claims made by exercise equipment manufacturers and suggestions as to how exercise professionals can use their knowledge of exercise physiology and peer-reviewed literature to assess these claims. Several examples given by the author are claims such as "burns twice as many calories as a treadmill," "get fit in four minutes," and "lose four inches from your waist in two weeks." Each example is accompanied by a thorough review of the exercise physiology that helps the reader see the truth behind the advertising. For example, the "burns twice as many calories as a treadmill" claim is physiologically near impossible, based on the fact that running uphill on a treadmill generally elicits the highest V˙O2 of any mode of exercise, due to the large amounts of muscle mass being engaged, and even the most highly trained athletes have a difficult time exceeding their treadmill V˙O2 values by more than 3% to 5%. If one looks closer at the claim, the manufacturer of one such device claims "twice as many calories as the treadmill at the same speed" but fails to indicate that the new machine was set at a much harder resistance, while the treadmill was set on an easy grade. The author also cautions readers to research any "studies" that product manufacturers state were conducted on their equipment. Using PubMed as one's search engine is recommended, as it indexes only reputable scientific journals. Additionally, commonly found features on exercise machines, such as the "fat burning" versus "cardio" workout modes, and reported versus actual caloric expenditures are discussed. Bottom line: The claims made by manufacturers of exercise equipment need to be scrutinized highly. Exercise professionals need to rely on their knowledge of exercise physiology and experience to provide accurate assessments of what a piece of exercise equipment can and cannot do for their clients.

© 2009 American College of Sports Medicine