QUESTION:
WHAT ARE YOUR THOUGHTS ON THE USE OF CAFFEINE?
ANSWER: Research suggests that caffeine influences positive endurance results in those who do not consume it on a regular basis. It takes only four days of regular caffeine ingestion to cause the body to develop a tolerance, reducing the overall stimulant-like effects. Though caffeine increases blood pressure and pulse the first time, a regular caffeine-user does not experience the same increased rate change.
Like most xanthines, caffeine is rapidly absorbed and distributed in all body tissues and fluids. Hepatic biotransformation prior to excretion results in about equal amounts of 1-methyl-xanthine and 1-methyluric acid. Of the 70% of the dose that is recovered in the urine, only 3% is unchanged drug. In other words, 97% of the caffeine consumed is metabolically active. Its final metabolic fate is excretion via urine. Plasma half-life is about three hours. Caffeine is well-absorbed by the stomach and intestine, and peak blood levels occur about 45-60 minutes after ingestion. Caffeine's stimulant properties create increased blood pressure, pulse rate, and stomach acid. Fat stores breakdown, releasing an increase in fatty acid blood levels, which produces an energy "high" sensation. These effects generally last from 2-3 hours to as long as 12 hours. This does not mean that the best way to utilize caffeine for a performance boost is to take it 45-60 minutes prior, however. Let me explain . . .
Muscle glycogen is generally the predominant fuel for the first 70-90 minutes of exercise, depending on pace. After that, body fat, an abundant secondary energy source, becomes the torque-for-energy "fuel of choice," converted to ATP by working muscle mitochondria cells. Glycogen is the principal fuel for muscles, and exhaustion occurs when it is depleted. As long as there is still glycogen available—be it from muscle store supplies at the onset of exercise, or exogenously supplied as exercise duration increases—working muscles can utilize fat. Caffeine mobilizes fat stores and encourages working muscles to use fat as a fuel. This process delays the depletion of muscle glycogen and allows for a prolongation of exercise.
The most critical time period for reducing the amount of glycogen used appears to occur during the first 15 minutes of exercise, where caffeine has been shown to decrease glycogen utilization by as much as 50%. The less glycogen depleted at the beginning means more available during the later stages of exercise. Caffeine causes sparing in all of the human studies where muscle glycogen levels were measured. The effect on performance, which was observed in most experimental studies, was that subjects were able to exercise longer before exhaustion occurred. If you are going to take caffeine-enhanced fuels, research has reported that the best effects are gained by ingesting it three hours before the competition. Though blood levels of caffeine peak much sooner, the maximum caffeine effect on fat stores appears to occur several hours after peak blood levels.
In addition, caffeine may alter the perception of how hard you are working. During testing, athletes are asked to judge their effort, which is referred to as the rating of perceived exertion (RPE). Some studies have shown significantly lower RPE's and less fatigue when using caffeine. As a word of precaution, too much of this drug may cause gastric upset in some athletes.
While the International Olympic Committee (IOC) regards caffeine as a banned-substance positive drug, urinary levels up to a concentration of 12 mg/liter are acceptable, representing casual use. Levels above this are viewed as an athlete’s deliberate attempt at doping. Approximately 1,000 mg of caffeine (about 8 cups of coffee) would be required to exceed the current IOC limit, but it is very important to note that people can metabolize caffeine at very different rates. Differences in metabolism, medications, and certain diseases may significantly alter the rate at which caffeine is cleared from the body. Some athletes have come close to flunking the drug test after ingesting only 350 mg! It would be wise to reconsider the science of caffeine before using it as an ergogenic aid. It is argued that caffeine is not healthly nor ideal for one who is concerned about their optimal health outcome. Many of the arguments for the stimulant drug, caffeine, have an opposing argument, which should be considered in equal light. For every sports scientist who argues pro-caffeine, there are a few who attempt to discourage use. Reading Dr. Jenky's website article [ http://www.rice.edu/~jenky/sports/caffeine.html] on caffeine would be beneficial.
Misner, Bill. "ASK DR. BILL From the Archives of Bill Misner, Ph.D."
ENDURANCE NEWS: Issue 78 1 Feb. 2012: 34. Web.
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