Bethesda, MD (July 15, 2002) -- The late author Anne Morrow Lindberg observed, "Good communication is as stimulating as black coffee, and just as hard to sleep after." While the art of conversation may have had its down periods, coffee has remained a renowned stimulant since its first appearance, circa 1,000 A.D.
The first recorded users of coffee are the Galla tribe in Ethiopia who noticed that they received an energy boost when they ground up the coffee bean and mixed it with animal fat. One thousand years later, many in the tribe known as the American labor force swear that a strong cup of coffee erases the effects of too little sleep. Witness, for example, the fact that the thousands of Americans who protect our country rely on coffee for the stimulation to fly an aircraft, stand a watch at sea, or stay awake for long hours while planning combat operations.
Americans having their morning coffee refer to the caffeine effect as a "charge" or "jolt." Physiologists, the scientists who study what makes the body "tick," call that effect "ergogenic." But are those caffeine drinkers in military uniform, white collar shirts, blue collar overalls and no-collar t-shirts, correct in thinking that coffee consumption will assist them in "making it through the day?"
Numerous studies have already demonstrated that caffeine ingested before physical activity causes rapid and significant improvement in performance, especially in aerobic exercise capacity. Most researchers believe that caffeine's ergogenic effect is related to the circulating level of the drug in the bloodstream, creating an assumption that the maximum effects are found one hour after consumption.
Two physiologists, affiliated with the Canadian research and defense establishment, recently set out to clarify several issues: whether the ergogenic effect achieved following the ingestion of 5 mg.kg-1 is related to the circulating concentration of caffeine; the duration of the ergogenic effect following the ingestion of a 5 mg.kg-1 dose of caffeine; and whether these effects are different for users and non-users of caffeine.
The authors of "Exercise Endurance 1, 3, and 6 Hours After Caffeine Ingestion in Caffeine Users and Non-users," are Douglas G. Bell and Tom M. McLellan, both from the Operation Medicine Section, Defence R&D Canada, Toronto, Ontario, Canada. Their findings appeared in the Journal of Applied Physiology, articles in press, a journal of the American Physiological Society (APS).
Nineteen civilian and two military subjects (15 males and six females) with a mean age of 32 +/- 7 years, height 179 +/- 9.5 cm, and body mass 74.8 +/- 12.6 kg participated in the study. All subjects were active in aerobic events, 13 were regular caffeine users (ingesting greater than or equal to 00 mg/day) and eight were considered non-users (ingesting less than or equal to 50 mg/day).
Caffeine was primarily ingested in the form of coffee. Subjects were asked to refrain from heavy exercise and alcohol for 24 hours before each trial. Caffeine consumption was halted 12 hours before the events.
The subjects completed six randomized exercise rides to exhaustion at 80 percent of maximal oxygen consumption on a cycle ergometer after ingesting either a placebo or 5 mg/kg of caffeine. Exercise to exhaustion was completed once per week at either one three, three or six hours after placebo or drug ingestion. Blood samples were taken from each subject.
Key findings of the study were that:
* For all subjects, caffeine improved the time to exhaustion from 24.0 +/- 6.5 minutes during the placebo trials to 28.8 +/- 8.6 minutes. Improvement was found to be greater in the non-users of caffeine.
* The effect of caffeine was still found in non-users six hours after ingestion but not in the users.
* Heart rates were higher for non-users throughout the trials. The values increased over time and were further increased following caffeine consumption.
* Caffeine produced a small but significant increase in oxygen consumption after 15 minutes of exercise for users and non-users.
* Non-users had higher glucose levels prior to exercise. Caffeine consumption elevated the levels at a slight but significant rate.
* The change of caffeine concentration in plasma above the baseline value was the same for users and non-users following caffeine intake. For the one-hour trial, however, caffeine concentration increased significantly throughout exercise, whereas it remained constant in trials conducted at three and six hours after ingestion. Generally, the concentration increased one and three hours after caffeine intake was greater than that after six hours.
Non-users demonstrated a greater ergogenic benefit or "boost" from caffeine consumption than regular users. Regular users may benefit from that first cup of coffee but non-users can derive additional energy. But neither group is aided by too many trips to the coffee pot.
The American Physiological Society (APS) was founded in 1887 to foster basic and applied science, much of it relating to human health. The Bethesda, MD-based Society has more than 10,000 members and publishes 3,800 articles in its 14 peer-reviewed journals every year.
Materials provided by American Physiological Society. Note: Content may be edited for style and length.
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