Effects of caffeine on time trial performance in sedentary men

Journal Title (Medline/Pubmed accepted abbreviation): J. Sports Sci.
Year: 2012
Volume: 30
Issue: 12
Page numbers: 1235-1240
doi: 10.1080/02640414.2012.693620
Summary of background and research design:
Background: Caffeine is one of the most widely used supplements among athletes and non-athletes.  There is incontrovertible evidence that caffeine can improve performance among athletes.  However, it is unknown if caffeine has similar performance-enhancing properties in sedentary individuals.  If caffeine can decrease pain and perceived effort associated with exercise and increase motivation, it may encourage sedentary individuals to partake in exercise and increase their overall health status.

Hypothesis: Consumption of caffeine will increase the amount of work performed in half an hour on a self-paced stationary bicycle in sedentary individuals.  The increase in exercise performed will be accompanied by a decrease in perceived exertion, an increase in energy expenditure, and an increase in oxygen consumption.

Subjects:  Sedentary males who typically consume less than 120 mg of caffeine per day (n = 12), age 25.5 ± 2.2 y

Experimental design: randomized, double-blind, placebo-controlled, cross-over study

Caffeine- 6 mg/kg body weight in the form of an opaque gelatin capsule (ex. 510 mg for an 85 kg or 187 lb. person, or about 3 cups of coffee)
Placebo- saccharin, delivered in the same gelatin capsules

Protocol: The participants were first familiarized with the equipment and the testing protocol.  They then reported to the facility two times, separated by one week.  They arrived at the facility in the morning after a 12 hr fast.  One hour before exercise, they consumed one of the two treatments.  After a warm-up on the exercise bicycle, they cycled for 30 min at a self-set pace with the goal of cycling as hard as possible.  Respiratory gases (oxygen and carbon dioxide), heart rate, and perceived exertion were assessed during the test.
Summary of research findings: 
  • Caffeine increased the amount of work performed during the 30 min exercise session (3646 ± 799 J/kg with caffeine vs. 3465 ± 718 J/kg without caffeine, p < 0.001).
  • Ratings of perceived exertion did not differ between groups.
  • Heart rate was greater with caffeine (168 ± 19 beats per minute, bpm) than without caffeine (161 ± 17 bpm).
  • Oxygen consumption and energy expenditure were greater when the participants consumed caffeine compared to the placebo.
  • Respiratory exchange ratios were similar between trials, suggesting that the participants were burning a similar ratio of carbohydrate:fat during the exercise session.
  • Only one participant reported a negative side effect; he reported being marginally agitated.

Key practice applications: In men who don’t typically exercise, caffeine ingestion increased the amount of work performed by during a 30 min, self-paced exercise session without increasing their perceived exertion.   This is important because it may increase the rate at which overweight men lose weight, and therefore fuel motivation to exercise.  One limitation is that the dose of caffeine was relatively large-it would have been interesting to see if a smaller dose would have had the same effects.

Key search terms for this article (5-7 terms): caffeine, weight loss, motivation, energy expenditure, weight management
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