Caffeine and Endurance Performance - Triathlon Week

Robert G. · 02-07-2003, 01:18 AM

Caffeine holds a unique position in the athletic world. The use of caffeine is restricted by the International Olympic Committee in that urinary caffeine levels above 12 micrograms/ml are considered illegal. However, caffeine is an integral part of many athletes' diets and moderate caffeine doses (3-6 mg/kg) can enhance performance in certain exercise situations. Thus, caffeine has the potential to be a "legal" ergogenic aid.

How does caffeine enhance exercise performance? Since caffeine enters the central nervous system and skeletal muscle, it isn't possible to separate caffeine's central effects from it's peripheral effects. It's also possible that different mechanisms are responsible for performance improvement in different exercise situations (1).

Three major theories have been proposed for the ergogenic effects of caffeine (1). First, as a central nervous system stimulant, caffeine increases alertness and decreases the perception of fatigue. Caffeine may reduce the perception of effort by lowering the neuron activation threshold, making it easier to recruit the muscles for exercise.

Second, caffeine may increase the force of muscle contractions by positively influencing calcium kinetics and the sodium-potassium pump activity within the exercising muscles.

Third, caffeine may increase fat utilization and decrease carbohydrate utilization. This is the classic or "metabolic" hypothesis. Caffeine mobilizes free fatty acids from adipose or intramuscular triglyceride by increasing circulating epinephrine levels. The increased availability of free fatty acids increases fat metabolism and decreases carbohydrate utilization. This delays glycogen depletion and so enhances endurance performance.

The interest in caffeine as an endurance aid and the metabolic hypothesis were initiated by work from Costill's laboratory. In an 1978 study (2), competitive cyclists consumed 330 mg of caffeine (5 mg/kg) one hour prior to cycling at 80% of VO2max and were able to ride 19 percent longer (90 minutes compared to 75 minutes) prior to reaching exhaustion. A second study in 1979 demonstrated that consuming 250 mg of caffeine was associated with a 20% increase in the amount of work that could be performed in two hours (3). These two studies suggested that the utilization of fat for energy increased by about 30% in the caffeine trials. A third study in 1980 found that consuming 5 mg of caffeine/kg reduced muscle glycogen usage by 42% and increased muscle triglygeride usage by 150% during 30 minutes of cycling at 7O% of VO2max (4).

Following these studies, there was limited well-controlled research on caffeine and exercise performance and the results were inconsistent. However, since 1990 an impressive body of research has established that caffeine can improve endurance performance.

In 1991, Graham and Spriet evaluated the performance effects of caffeine in a study of competitive distance runners who were given 9 mg caffeine/kg one hour prior to cycling and running to exhaustion at intensities of about 85% VO2max (5). The average increase in endurance for the running test was 44%; for the cycling test it was 51%. However, the urine caffeine levels in 4 of the 12 caffeine trials resulted in levels near or above the IOC threshold.

Graham and Spriet have recently reviewed the effects of varying doses of caffeine on endurance performance. They concluded that the ingestion of 3-13 mg of caffeine/kg can improve endurance performance by 20-50% in elite and recreationally trained athletes who run or cycle at 80-90% of VO2Max. The authors noted that the 3,5, and 6 mg/kg doses produced an ergogenic effect with urinary caffeine levels below the IOC doping threshold.

Although the higher doses also improved performance, about one-fourth of the athletes consuming 9 mg of caffeine/kg exceeded the IOC limit, and two-thirds of those consuming 13 mg of caffeine/kg exceeded the IOC limit. Side effects of caffeine consumption (dizziness, headache, insomnia, and gastrointestinal distress) were common at the 9 and 13 mg/kg doses, but infrequent with doses at or below 6 mg/kg.

Graham and Spriet also noted that caffeine produced a two-fold increase in plasma epinephrine (at rest and during exercise) and in plasma free fatty acids at rest. The elevation in free-fatty acids only lasted for the first 15-20 minutes of exercise. Muscle glycogen usage was reduced following caffeine consumption, but this "glycogen sparing" effect was limited to the initial 15 minutes of exercise at 80% of VO2Max. Although these metabolic findings partly explain how caffeine improves endurance, the other proposed mechanisms cannot be ruled out.

The fact that caffeine has ergogenic effects when urinary levels are well below the IOC's limit raises serious ethical issues regarding the use of caffeine to improve performance. Even when caffeine is used in "legal" amounts, this may be considered a form of doping. thereby violating the ethics of sports performance.

1. Graham TE, Spriet LL. Caffeine and exercise performance. Sports Sci. Exch. Vol. 9, No.1:1-6, 1996.

2. Costill DL, Dalsky G, Fink W. Effects of caffeine ingestion on metabolism and exercise performance. Med. Sci. Sports 10:155-158, 1978.

3. Ivy JL, Costill DL, Fink WJ, Lower RW. Influence of caffeine and carbohydrate feedings on endurance performance. Med. Sci. Sports 11:6-11, 1979.

4. Essig D, Costill Dl, VanHandel PJ. Effects of caffeine ingestion on utilization of muscle glycogen and lipid during leg ergometer cycling. Int. J. Sports Med. 1: 86-90, 1980.

5. Graham, T.E. and L.L. Spriet. Performance and metabolic responses to a high caffeine dose during prolonged exercise. J. Appl. Physiol. 71: 2292, 1991.

Ellen Coleman, RD, MA, MPH // www.cruciblefitness.com

quadmaster96 · 02-27-2003, 06:09 AM

I am training for the Navy Seals. I need to build up the endurance and Strength (not get built). I run, swim, and work out 6-7 days a week. I somtimes don't have the energy. What are some things (drinks/food/whatever) that i can use, that has alot of caffinee or energy suppliment (no pop/cofffee).

Thankz,

Joshua Poe