Caffiene and exercise

American Fitness, Jan-Feb, 2003 by Scott O. Roberts

Surveys show that approximately 90 percent of Americans consume caffeine daily. In fact, more than half of American adults ingest over 300 milligrams of caffeine every day (i.e., approximately two and a half cups of regular coffee). Most people consume caffeine to give them a daytime boost or keep them awake longer at night. How concerned should fitness professionals be regarding caffeine's influence on exercise? This column will try to shed some light on that question.

More About Caffeine

Caffeine is not synonymous with coffee. It comes in various forms, including coffee, tea, cola, chocolate, medications, etc. According to the National Soft Drink Association, most 12-ounce cans of soda contain approximately 45 milligrams of caffeine. By comparison, a seven-ounce cup of coffee has approximately 100 milligrams of caffeine.

A cardiovascular stimulant, caffeine affects the heart directly by causing andrenergic nerve terminals in the heart and adrenal medulla to release more catecholamines. It has both positive inotropic (i.e., strength of contraction) and chronotropic (i.e., increased heart rate) effects. Caffeine is also a powerful central nervous system stimulant, acting particularly on the brain and skeletal muscles. It also delays fatigue and acts as a smooth muscle relaxant and vasodilator. Blood concentrations of caffeine peak within 15 to 45 minutes of ingestion. However, its metabolic effects may last over an hour. The liver metabolizes almost 100 percent of caffeine, but some residual may appear in the urine.

No solid evidence indicates moderate caffeine consumption is a risk factor for any type of cancer, cardiovascular disease or decreased fertility in women. In 1987, the FDA affirmed that moderate quantities of caffeine have no adverse effects. However, studies have shown caffeine can cause high blood pressure and increase heart rate. At least one study concluded that long-term coffee consumption decreased bone mineral density in women.

Probably the most important long-term health side-effect is caffeine's effect on sleep. Studies have shown that as little as one strong cup of coffee (150 to 200 milligrams of caffeine), consumed 30 to 60 minutes before sleeping, can cause restlessness, difficulty falling asleep, increased body movements, decreased quality of sleep and a tendency to be awakened by sudden noises. Ceasing caffeine consumption five to six hours prior to sleeping, thus allowing more time for the body to metabolize the caffeine, will lessen these side-effects.

Caffeine's Effect on Exercise

Numerous studies have researched the effect of caffeine ingestion on exercise performance. Most of them generally conclude that caffeine consumption prior to working out seems to extend endurance performance during moderately strenuous aerobic exercise. The main proposed mechanism for this improvement is the increased use of fat as fuel. However, there seems to be benefit discrepancies between habitual caffeine users and non-habitual users. Once a certain level of tolerance is reached, the ergogenic effect of caffeine may be reduced.

Another commonly reported benefit of caffeine ingestion prior to exercise is a decreased sense of overall exertion (i.e., reduced RPE), which may lead to improved enjoyment of exercise. However, since caffeine is often used as an appetite suppressant, some individuals may not consume the calories needed to sustain exercise. Keep in mind, caffeine's effects vary from person to person. Following caffeine ingestion, some might notice tremendous benefits during exercise, while others may not.

Conclusion

Caffeine ingestion prior to exercise seems to have metabolic, musculoskeletal and central nervous system stimulant effects. However, there is no consistent evidence on its ability to delay fatigue. Caffeine appears to offer ergogenic benefits during prolonged exercise, but not during short-burst, high-intensity activities.

However, caffeine ingestion in the range of 400 to 500 milligrams may cause nausea, abdominal discomfort and irritability. It elevates heart rate and blood pressure, which may affect the ability to accurately monitor training intensity. Withdrawal from regular caffeine ingestion also produces an array of negative side effects, including headaches, irritability and drowsiness.

Many people do not realize how much caffeine they ingest daily. Some people drink coffee in the morning, sodas throughout the day and a piece of chocolate here and there. It could take all day and part of the night for the body to rid its systems of caffeine. It is important to ask clients about their current caffeine habits to get an indication of their daily caffeine intake.

Exercise sessions may need to be modified for clients who consume too much caffeine prior to exercise and those withdrawing from caffeine. For example, a decrease in the intensity or duration of exercise may be necessary following changes in caffeine consumption patterns. If a client has consumed too much caffeine, the intensity and duration may need to be lowered for that day. If a client is withdrawing from caffeine use, his or her training heart rate should be re-evaluated and exercise duration modified since the client may not have the same level of energy or motivation as before. In addition, it is important to reevaluate resting heart rates prior to exercise to see if they have changed due to any changes in caffeine consumption.