Caffeine and Exercise
Caffeine has three main effects on the body as it relates to exercise. Caffeine acts: (1) as a stimulus to the central nervous system, (2) to decrease the contractile threshold of a muscle, allowing a smaller stimulus to elicit a muscle contraction, and (3) to increase the mobilization of free fatty acids in the blood stream.2
Free fatty acids are the portion of fat that can be burned as fuel by the muscles, and as an energy resource they are of major importance to marathoners and other distance runners.
Caffeine's Benefits to Distance Runners
Due to the increase of free fatty acids that occurs as a result of caffeine ingestion, caffeine was seen as beneficial to long distance runners, especially marathoners.
Physiologically speaking, as you run, your muscles use both fat and glycogen as fuel. Theoretically, the body has an unlimited supply of fat for distance running purposes. However, the natural tendencies of our bodies are to use mostly muscle glycogen as fuel in the first 90 minutes of running.
Caffeine increases the use of fat as fuel, thus sparing our bodies' limited supply of muscle glycogen.
After about 90 minutes, the glycogen stores can become depleted, causing you to slow down (also known as "hitting the wall") as your body switches to fat as the primary fuel.
By performing extra long runs (more than 90 minutes in duration), not only will you be able to (1) build thick, new networks of oxygen-carrying capillaries, (2) increase the number and energy-producing capacity of your muscle cells' mitochondria, (3) safely recruit and train fast-twitch muscle fibers to gain greater endurance potential, but you will also be able to (4) teach your body to begin using more fat as a fuel earlier in your runs, thereby delaying the depletion of your muscle glycogen and ultimately increasing your endurance (your ability to run for a longer period of time).
Therefore, if you could further increase the body's use of fat as a fuel earlier in your training runs (through caffeine ingestion), you could benefit from being able to train longer distances and race farther before slowing down. This is because delaying the use of glycogen will allow you to maintain a given pace longer before fatigue sets in.3
Early Research on Caffeine
With these concepts in mind in the mid- to late-1970's, several research studies were performed to examine the effects of caffeine on endurance performance. In 1978, Dr. David Costill and associates studied the effects of caffeine on the time to exhaustion for nine competitive cyclists.
The cyclists were divided into two groups. One group drank 2.5 cups of decaffeinated coffee and one group drank 2.5 cups of caffeinated coffee, 60 minutes prior to riding to exhaustion at 80 percent of their VO2max (an effort equivalent to a marathon race for the average, well-trained runner).
The results showed that the cyclists' time to exhaustion was increased by a remarkable 19.5 percent for the cyclists who ingested the caffeinated coffee. In addition, the "caffeinated" cyclists perceived their ride to be less strenuous, even though the time to exhaustion was increased. As a result, Costill's team concluded that caffeine did, in fact, increase the use of fat by the muscles, sparing limited glycogen stores, and improving performance.4
One year later, another similar study was prepared which analyzed the effect of caffeine compared to carbohydrate drinks on distance covered in a two-hour bike ride.
This time, the "caffeinated" cyclists actually rode significantly farther in the two-hour trial than those using a non-caffeinated, glucose-polymer, carbohydrate drink. Like Costill's study, these researchers also found that the cyclists who used caffeine perceived the exercise to be easier than those who used the decaffeinated carbohydrate drinks.5
A third study performed in 1980 provided additional evidence that glycogen sparing occurred with caffeine intake when it was shown to decrease muscle glycogen use by 42 percent.6
Together, the three studies we've discussed seemed to offer what was seen as conclusive evidence that caffeine increased fat usage and delayed the use of muscle glycogen. However, since the time of these early studies, many other reports have documented conflicting results.
In fact, present-day critics have indicated that these early studies on caffeine failed to take into account a number of critical factors, such as prior caffeine usage, dosage size, and diet in the subjects tested.
In order to clear up some of the inconsistent conclusions of these studies, a team of researchers from the University of Florida met in January 1993 to review the scientific literature on the effects of caffeine.
In this review, the researchers concluded that the majority of evidence supports caffeine as an enhancer of endurance exercise as a result of caffeine's ability to increase fat mobilization and spare glycogen use.
However, these experts concluded that caffeine is beneficial only for short-term, high-intensity exercise in animals or isolated muscle studies, but not for humans.
More recently it has been documented that extremely high doses of caffeine are required to obtain any performance improvements, and doses in such quantities would be toxic and possibly fatal in humans.7
Side Effects and Bans
While caffeine may be considered a performance enhancer, the possible side effects from its use must also be considered. Prolonged and frequent caffeine intake (about 10 cups per day) can lead to excessive nervousness, and can result in a condition known as "caffeinism" - causing restlessness, anxiety, diarrhea, headaches, and heart palpitations.8
Furthermore, caffeine has a diuretic effect (causing the body to urinate), which can rob the body of its precious water supply that is so essential during hot and humid race conditions.9
Because of caffeine's potential side effects as well as benefits to performance, extremely high bodily concentrations of caffeine have been banned by both the International Olympic Committee (IOC) and the U.S.'s National Collegiate Athletic Association (NCAA). However, in order to attain the banned levels of caffeine concentrations in the body, an athlete would probably have had to have an injection or have used a suppository.10
Among the growing body of scientific research, there exists evidence both in support of and opposed to, caffeine intake as a performance enhancer for endurance exercise.
Extremely high caffeine usage can cause several health concerns and is restricted by two important governing athletic organizations. Nevertheless, caffeine can be legally used in small amounts in events governed by the IOC and NCAA and without any legal limit on training runs as well as in most road races and track meets.
Except for the legal restrictions and health concerns that should be heeded, caffeine can be used as a performance enhancer depending on (1) the individual runner's physical responsiveness, (2) the race distance, and (3) weather conditions. Test it on your next long run in cool weather to see if it works for you.
1, 2, 3, 7 S. Dodd, et. al., "Caffeine and Exercise Performance: An Update," Sports Medicine, 1993, Vol. 15, No. 1, pp.14-23.
4 D. Costill, et. al., "Effects of Caffeine Ingestion on Metabolism and Exercise Performance," Medicine and Science in Sports and Exercise, 1978, Vol. 10, No. 3, pp. 155-58.
5 J. Ivy, et. al., "Influence of Caffeine and Carbohydrate Feedings on Endurance Performance," Medicine and Science in Sports and Exercise, 1979, Vol. 11, No. 1, pp. 6-11.
6 D. Essig, et. al., "Effects of Caffeine Ingestion on Utilization of Muscle Glycogen and Lipid During Leg Ergometer Cycling," International Journal of Sports Medicine, 1980, Vol. 1 pp. 86-90.
8 D. Sawyer, et. al., "Caffeine and Human Behavior," Journal of Behavioral Medicine, 1982, Vol. 5, pp. 415-39.
9, 10 B. Jacobson, et. al., "Health and Ergogenic Effects of Caffeine." British Journal of Sports Medicine, 1989, Vo. 23, No. 1, pp. 34-40