Special thanks to Ryan for contributing this great review to the blog. Much appreciated!
The Effects of Caffeine on Physical Activity and Athletic Performance
Introduction
Caffeine, a central nervous system and cardiac stimulant, is the most popular and most readily available drug in the world (Bramstedt 2007). Athletes of all ages and abilities are exposed to caffeine on a regular basis and make a choice of whether or not to use the drug. Many athletes, regardless of age or ability, do not know the specifics of the drug in relation to the physiology and biochemistry of their bodies. This lack of knowledge can hinder performance in some cases, and lead to serious illness or injury in others.
There are many aspects of fitness including cardiorespiratory endurance, muscular strength, muscular endurance, flexibility, and body composition. The effects of caffeine ingestion related to these aspects of fitness have been documented in research studies. However, many studies are restricted to a small population with a specific gender, degree of athletic ability, and socio-economic status. In order for an athlete to understand the effects of caffeine on their particular body they must find studies performed on populations similar to his or her particular gender, age, and athletic ability.
Through careful analysis of current research, caffeine has been positively correlated to benefit athletic performance in regards to upper body strength and endurance, cardiorespiratory endurance, hydration, thermoregulation, and mental concentration. Countless sports are highly dependent on the previously stated characteristics of physical performance. Upper body strength and endurance plays a large role in football, baseball, lacrosse, swimming, and basketball. Cardiorespiratory endurance, hydration, thermoregulation, and mental concentration are cornerstones of track and field, Nordic skiing, and cycling, amongst many other sports. With that being said, caffeine supplementation in a regulated amount, such as mg of caffeine per kg of body weight, will enhance athletic performance. In today’s athletic competition, winners and losers are determined by fractions of a second. Even if caffeine’s effects are miniscule in comparison to illegal drugs such as EPO and steroids, the small difference may be enough to push an athlete just enough to win a competition they otherwise would not have.
Review of Literature
As a central nervous system and cardiac stimulant caffeine is easily tied to cardiovascular athletic performance. However, the link relating caffeine’s effects to resistance training is less obvious. Beck, Housh, Schmidt, Johnson, Coburn, and Malek (2006) concluded that a supplement containing caffeine allowed participants to increase upper body strength as determined by a one-repetition maximum (1RM) bench press. Thirty-seven men with a mean age of 21 participated in the study; all having previous resistance training experience. 48 hours following the subjects’ initial visits to the laboratory where they performed the baseline 1RM bench press they returned and were randomly assigned to a caffeine supplement group or a placebo group. After ingesting the caffeine or placebo pill the participants waited one hour before retesting his 1RM bench press. There was a significant (p<0.05) style="">
Astorino, Rohmann, and Firth (2007) provide further validation of caffeine positively affecting upper body strength and endurance in a study consisting of 22 resistance trained men with a mean age of 23.4, ranging from 18 to 29 years old. Previous resistance training experience of at least two total-body workouts a week was a prerequisite for participating in the study. The men’s previous training history ranged from 1.5 years to 12 years, with a mean of 6 years. Prior to testing the participants were required to have no caffeine intake for 48 hours and refrain from exercise for 24 hours immediately before visiting the laboratory. During the first visit to the laboratory the participants were given either a 6 mg/kg dose of caffeine or the placebo and then performed a 1RM bench press. Immediately following the 1RM test, 60% of the 1RM was placed on the bar and the participants pressed that weight until complete failure as a means of measuring muscular endurance. Even though statistically insignificant (p>0.05), an increase in muscular endurance (11-12%) was shown in the participants who ingested the caffeine supplement when compared to those who ingested the placebo.
Many studies investigating the relationship between caffeine and exercise use pharmaceutical caffeine in capsules. However, Forbes, Candow, Little, Magnus, and Chilibeck (2007) examined the effects of Red Bull Energy Drink on exercising participants performing three sets of bench press to determine muscular endurance. This study also differed from others investigating caffeine and muscular strength or endurance in the fact that it included women. 11 men and 4 women who are physically active two to three days a week were selected for the study. Subjects were randomly assigned to ingest Red Bull at 2 mg/kg or placebo 60 minutes prior to performing the bench press endurance test. One week after the initial testing the participants revisited the laboratory and ingested the opposite supplement. After determining the participants’ 1RM on the bench press they were instructed to complete three sets of bench press repetitions to complete fatigue. The weight used for the trials was 70% of the participants’ 1RM, and the trails were separated by a one-minute rest period. There was a significant increase in the number of repetitions achieved over the three sets by those who ingested Red Bull (34 ± 9) versus the placebo (32 ± 8).
Caffeine is not only a cardiac stimulant, but also a central nervous system stimulant as well. The central nervous system controls cognitive functions that are essential to athletic performance.
McLellan, Kamimori, Voss, Tate, and Smith (2007) hypothesized that soldiers who received a dose of caffeine during overnight periods of no sleep would physically and cognitively function better in the morning hours when compared to soldiers given a placebo. Twenty male Special Forces soldiers with a mean age of 28.6 and a mean body mass of 81.2 kg participated in the study. The soldiers were randomly separated into groups of four. Two soldiers within each group received caffeine, while the other two soldiers received the placebo. Instead of using caffeine supplemented in a pill form, the soldiers were given pieces of Stay Alert caffeine gum with 100 mg of caffeine in each piece. The placebo pieces of gum matched Stay Alert in taste, color, and texture. McLellan et al. opted to use gum instead of pills for this study because it is shown that the caffeine in the gum is more quickly absorbed into circulation. The soldiers’ physical skills were assessed through an obstacle course run and marksmanship, while cognitive skills were assessed in analyzing their communication and vigilance. The vigilance test consisted of soldiers sitting 175-200 meters away from a building. The soldiers were then asked to record the “where, when, and what” of any activity that occurred in their field of vision. The caffeine group maintained vigilance at a mean of 60.2%, while the placebo group scored only a mean of 33.6% in the vigilance tests. McLellan et al. suggests that the use of 800 mg of caffeine given throughout overnight periods maintained cognitive alertness and vigilance better than the placebo group. However, the physical obstacle course test did not show significant differences between the two groups.
As with any other drug used for performance enhancement caffeine has a perceived benefit to many athletes. Desbrow and Leveritt (2007) investigated the perceptions, knowledge, and experiences of caffeine use by competitors in the 2005 Ironman Triathlon World Championships. 105 men and 35 women from both the elite and age-group levels of competitor participated in the study. The mean length of experience competing in triathlons was 10.2 ± 7 years. The participants were required to complete a questionnaire exploring his or her knowledge, attitudes, use history, planned consumption, and caffeine-related side effects. The athletes’ attitudes regarding caffeine use included the effect of caffeine on endurance, speed, power, strength, concentration, and fat loss. The section of the questionnaire regarding the athletes’ knowledge of caffeine sources included categorizing foods and beverages into groups of “contains no caffeine,” “contains caffeine but only a small amount,” or “contains caffeine in a larger amount.” Finally, the athletes were asked to provide information regarding the dosage they would consume if they wanted to improve their Ironman triathlon performance and the severity of common side effects related to caffeine consumption, such as tremors, shakes, headaches, elevated heart rate, and abdominal discomfort. Through statistical analysis, Desbrow and Leveritt (2007) concluded that it is the perception of the 2005 Ironman Triathlon participants that caffeine is ergogenic to their performance. The athletes were able to identify sources of caffeine in mainstream products such as coffee, tea, cola, and energy drinks, but were not accurate in their ability to quantify the amount of caffeine in those products. The top three ways of obtaining knowledge regarding information on caffeine’s effectiveness were self-research/experimentation, fellow athletes, and magazine articles.
Caffeine’s physical effects on exercise are well documented; however, a relationship between caffeine and the mental aspect of exercise is less studied. As heart rate is a physical measure of exercise intensity a rating of perceived exertion (RPE) is a subjective mental measure of exercise intensity. Ahrens, Lloyd, and Walker (2006) investigated the relationship between caffeine and cardiorespiratory fitness in women, with RPE being one of the criterions to determine the results. 20 women ranging in age from 19 to 28 participated in the study. The women were of average fitness level and were not habitual caffeine users. The women participated in three trials of stead-state treadmill walking at 3.5mph. The three trials consisted of each woman being randomly assigned a 3-mg/kg caffeine, 6-mg/kg caffeine, or placebo dosage. Test subjects made four separate visits to the laboratory, two to seven days apart. During each visit the subject participated in an eight minute walk at 3.5mph exactly one hour after ingesting the given capsule. Analysis of data determined that RPE was not significantly different between the 3-mg/kg caffeine, 6-mg/kg caffeine, or placebo dosages. The results led Ahrens et al. to state “it would not be prudent for a trainer to recommend caffeine in order to increase a woman’s energy expenditure or to decrease perception of effort during mild exercise. Caffeine intake should not interfere with monitoring walking intensity by tracking exercise heart rate in women.”
Ahrens et al. (2006) gives insight into how caffeine would affect cardiorespiratory training in a low intensity setting as the subjects were not pushed past a 3.5mph pace. Contrarily, McClaran and Wetter (2007) performed tests that pushed the participants to absolute exhaustion on a cycle ergometer. The nine male subjects that participated in the study were randomly assigned to perform the bicycle test after ingesting 1.5 mg/kg caffeine, 3.0 mg/kg caffeine, or a placebo. The participants took part in three separate tests so that they could be given all three variations in the supplement prior to performing the test. As most studies previously stated, there was a one hour time period between the participants ingesting the given supplement and performing the test. However, in the study performed by McClaran and Wetter (2007) the subjects were only allowed to rest for thirty minutes prior to partaking in the cycle test. The subjects endured three separate warm-up sessions of 60 watts, 120 watts, and 180 watts, with each session lasting five minutes. After receiving a two-minute rest off of the bike the subjects once again cycled at 180 watts for one minute, which was then increased 30 watts every minute until complete exhaustion. Measurements taken during the tests included heart rate, systolic blood pressure, tidal volume of breathing, rating of perceived exertion, and oxygen consumption (VO2). After analyzing the data McClaran and Wetter (2007) concluded that caffeine doses of 1.5 mg/kg and 3.0 mg/kg of body weight significantly lowered heart rate during the submaximal testing, ranging from four to seven beats per minute lower. However, the heart rates were not found to be lower as the participant’s gave their maximal effort in the exhaustion phase of the test. Also, McClaran and Wetter (2007) stated that neither dose of caffeine had any effect on blood pressure during the exercise portion of the test. Further validation of the findings in Ahrens et al. (2006) were provided as McClaran and Wetter (2007) stated that caffeine had no effect on the subject’s rating of perceived exertion during the test.
In a similar manner to the study performed by Forbes et al. (2007) in which the widely available product Red Bull Energy Drink was used as the supplement in the study Roberts, Taylor, Wismann, Wilborn, Kreider, and Willoughby (2007) used JavaFit Energy Extreme coffee as the supplement provided to test subjects. JavaFit Energy Extreme coffee is described as “a functional gourmet coffee that contains a proprietary blend of caffeine, garcinia cambogia, chromium polynicotinate, and aurantium” and claims to increase energy expenditure. In hopes of determining if the claim of increased energy expenditure was valid, Roberts et al. (2007) goal for the study was to determine if post-exercise fat metabolism was enhanced by use of JavaFit Energy Extreme coffee. Study participants performed baseline testing in a graded treadmill test to determine peak VO2 and also a Wingate test for peak power. Three to four days following the baseline testing the subjects returned and went through the same testing after ingesting 354 mL of JavaFit Energy Extreme coffee or decaffeinated coffee. One week after the first round of testing the participants returned to the laboratory where they once again performed the graded treadmill test and Wingate test, but after consuming the remaining type of coffee. Roberts et al. (2007) discovered that JavaFit Energy Extreme coffee significantly increased VO2 readings three minutes after the exercise stopped when compared to baseline readings. The increase post-exercise VO2 led Roberts et al. to state that enhanced post-exercise fat metabolism may be obtained by consuming JavaFit Energy Extreme coffee prior to aerobic exercise.
An athlete’s hydration level can be the determining factor if he or she performs up to their greatest potential. Millard-Stafford, Cureton, Wingo, Trilk, Warren, and Buyckx (2007) investigated the affect a caffeinated sports drink had on the fluid delivery and hydration process during exercise. The conditions of the experiment were warm and humid, with a temperature of 28.5* Celsius (83.3* Fahrenheit) and 60% relative humidity at an indoor environmental chamber. A group of 16 highly trained male cyclist participated in the study. The cyclists performed three tests, separated by at least five days rest. They were given the carbohydrate-electrolyte drink Gatorade for one test, Gatorade with caffeine for one test, and a placebo for the remaining test. The cycling test included two portions. First the cyclist would perform two hours of steady state cycling at 60%-75% of their VO2max. After completing the initial two hours of cycling the subjects immediately performed a 15-minute maximal effort ride. Prior to performing the two-hour ride the cyclist drank 6mL/kg body weight of the selected beverage for that day. During the experiment the subjects were given 3mL/kg body weight of the beverage at 15-minute intervals. For those ingesting the caffeinated beverage the caffeine was given at a volume of 5.3 mg/kg body weight. Millard-Stafford et al. (2007) measured the sweat rate, urine output, and fluid retention of each participant to determine his hydration level throughout the test. As there were no significant differences found among the three types of beverages administered Millard-Saffort et al. (2007) concluded that a caffeinated carbohydrate-electrolyte sustains hydration and thermoregulatory function as well as a normal carbohydrate-electrolyte drink. Even though caffeine is considered a diuretic the effects are not shown when it is consumed during exercise.
Discussion
The research studies discussed investigated the effect of caffeine on different areas of fitness such as cardiorespiratory endurance, muscular strength, power, and endurance, and mental concentration. The studies were designed in such a way that they measured only one particular area of fitness at a time. Even though the studies differed in purpose and design there were common themes throughout that collectively limited the studies. The first common theme throughout the studies is that they all used a small number of participants. On average, the researchers limited the number of participants to 10-20. Also further limiting the results of some studies was the use of only males or females. Studies conducted by Millard-Safford et al. (2007), McClaran and Wetter (2007), Ahrens et al. (2006), McLellan et al. (2007), and Astorino et al. (2007) only used one gender of participants. By only including a very distinct population in the studies the results are only applicable to a small group of people. In many instances only middle-aged males will receive information regarding how caffeine affects their performance in the athletic world.
Another limiting factor in the research is regarding the length of the studies performed. Many of the studies including Astorino et. al. (2007), Roberts et al. (2007), Ahrens et al. (2006), Beck et al. (2006), and Forbes et al. (2007) investigated the acute effects of caffeine on exercise. The participants in these studies would go to the laboratory, ingest caffeine or placebo, and perform the given exercise within one and a half hours after ingestion. The design of these studies would then send the participant home, and only see them once more as they were tested for the remaining dosage (caffeine or placebo). The design of these studies limits the available knowledge regarding the long-term effects of caffeine and exercise. Granted availability of both researchers and participants for a chronic caffeine prior to exercise study would be difficult, the results would be interesting.
A final limiting factor in the research was ethically how much caffeine the participants could be given. Roberts et al. (2007) limited the pre-exercise caffeine consumption to 354 ml of coffee. Forbes et al. only gave the participants 2 mg/kg body mass of caffeine. Ahrens et al. (2006) and Astorino et al. (2007) did give an increased amount of 6 mg/kg body mass, yet this amount of caffeine has been shown to be a safe level of caffeine. A research approval board would not allow participants to be given such a large amount of caffeine that could possibly have detrimental health effects. However, in reality athletes do not measure their caffeine consumption by the mg per kg of body mass, and may have taken far greater amounts of caffeine prior to exercise so the research would be interesting to see how higher levels of caffeine affected performance.
As a certified personal trainer the knowledge obtained through this research has a very practical application. The improvements that caffeine gives athletes would also be beneficial to the less elite average personal training client. The increase in VO2max and possible post-exercise fat metabolism as described by Roberts et al. (2007) would give the greatest benefit as many clients are overweight and looking for any advantage that they can obtain in their fight against obesity. Additionally, the correlation between pre-exercise ingestion of caffeine and increase in muscular strength would be beneficial for the vast number of clients in a more strength and conditioning aspect.
Unfortunately, accompanying the many benefits that are associated with caffeine and exercise are ethical issues regarding the possibility of adverse side effects that a client could experience. Unlike a controlled laboratory setting, a personal trainer would not be able to account for many of the variables that researchers are able to eliminate. For instance, researchers often used pharmaceutical grade caffeine that was precisely measured. The average personal trainer and their client would not likely have the money or means of obtaining pharmaceutical grade caffeine and would settle for other forms of caffeine such as coffee, soda, or supplements, which could do more harm than good. Supplements are not regulated by the Food and Drug Administration, thus leaving both the training and client wondering if the amount of caffeine on the label is actually the amount in the supplement. Additionally, the carbonation in many beverages like soda and energy drinks would affect the client’s physiology during exercise. With all of these variables to account for the practice of a personal trainer telling a client to ingest caffeine prior to exercise may be risky. Without proper equipment to detect and monitor certain cardiac functions throughout exercise many personal trainers should not be willing to risk their certification and a possible lawsuit if there were an adverse side affect related to the caffeine consumption.
Future research regarding the effect of caffeine on athletic performance should attempt to lessen some of the limitations of the current research studies. For starters, the participants of future studies should be larger in number and more diverse in age and gender. In order to perform similar tests such as a cycle ergometer, graded treadmill tests, or maximum bench presses on a large number of people the process could be both costly and time consuming. However, the valuable information received from such a large study could be related to a greater number of people. Also, the larger studies should test males and females side by side for ease of comparison. Forbes et al. (2007) and Roberts et al. (2007) did test males and females together in the same study, however, the number of males and females were uneven in the study performed by Forbes (11 male, 4 female) and the total number of participants in the study conducted by Roberts was very small (10). A large study consisting of both males and females at a relatively close ratio would eliminate the variables when comparing similar studies. Even if two studies had very similar methods and procedures the results cannot be accurately lumped into one general correlation. Factors such as the environment of the testing facility and attitude of the researchers can factor in to how the participant performs regardless of the methods and procedures of the studies.
Research performed using participants varying in age would also increase the knowledge regarding caffeine use during exercise. Studies conducted by Beck et al. (2006), Forbes et al. (2007), Roberts et al. (2007), and Ahrens et al. (2006) all used participants with an average age ranging from 20-29. This is a small window of people that use caffeine, exercise, or a combination of the two. Information regarding the use of caffeine on the changing metabolisms and physiologies of an aging population would be interesting to compare to the current studies focusing on a young to middle-aged healthy population.
Conclusion
A critical review of literature pertaining to the ingestion of caffeine prior to physical activities and athletics shows that caffeine does in fact have a positive effect on performance in some areas of fitness. Specifically, athletes participating in events that depend heavily on aerobic endurance, muscular strength and endurance, and/or sustained mental concentration could improve their performance by ingesting caffeine prior to an event. However, there is no dosage that is applicable to every athlete. Each athlete would need to relate the findings in of the research studies to themselves. A common theme from many of the research articles suggests that a dose equal to 3-6 mg/kg of the athlete’s body weight ingested 30-60 minutes prior to exercise would be most beneficial in enhancing performance. Even with that recommendation the athlete must weigh the risks versus the perceived benefits. Prior to combining caffeine with exercise the athlete should see a physician to ensure they do not have an underlying cardiovascular disease that could be aggravated by caffeine’s stimulus of the central nervous system and cardiorespiratory system. If the athlete experiences headaches, tremors, unnecessary nervousness, or tachycardia, they should immediately refrain from combining caffeine and exercise. Hopefully in the future athletes will be better educated on the subject of how caffeine affects the physiology of their exercising bodies. In doing so they will be able to more precisely determine the amount of caffeine that will be beneficial to their performance.
Ryan will graduate in May 2009 with a B.S. degree in Kinesiology, with an
emphasis in exercise science. He is personal trainer, certified through the
American Council on Exercise (ACE) and hopes to obtain a more advanced
certification such as ACSM upon graduating. Ryan will always have passion
for performance training athletes, but he hopes to broaden his health and
fitness knowledge base and work in a clinical setting in the future.
If someone wishes to apply for his personal training services please visit
http://www.recsports.umn.edu/fitness/index.html for further information.
References
Ahrens, J. N., Lloyd, L. K., & Walker, J. L. (2006). The physiological effects of caffeine in women during treadmill walking. The Journal of Strength and Conditioning Research, 21(1), 164-168.
Astorino, T. A., Rohmann, R. L., & Firth, K. (2007). Effect of caffeine ingestion on one-repetition maximum muscular strength. European Journal of Applied Physiology, 102, 127-132.
Beck, T. W., Housh, T. J., Schmidt, R. J., Johnson, G. O., Coburn, J. W., & Malek, M. H. (2006). The acute effects of a caffeine-containing supplement on strength, muscular endurance, and anaerobic capabilities. The Journal of Strength and Conditioning Research, 20(3), 506-510.
Bramstedt, K. A. (2007). Caffeine use by children: The quest for enhancement. Substance use & Misuse, 42, 1237-1251.
Desbrow, B., & Leveritt, M. (2007). Well-trained endurance athletes' knowledge, insight, and experience of caffeine use. International Journal of Sport Nutrition and Exercise Metabolism, 17, 328-339.
Forbes, S. C., Candow, D. G., Little, J. P., Magnus, C., & Chilibeck, P. D. (2007). Effect of red bull energy drink on repeated wingate cycle performance and bench-press muscle endurance. International Journal of Sport Nutrition and Exercise Metabolism, 17, 433-444.
McClaran, S. R., & Wetter, T. J. (2007). Low doses of caffeine reduce heart rate during submaximal cycle ergometry. Journal of International Society of Sports Nutrition, 4(11)
McLellan, T. M., Kamimori, G. H., Voss, D. M., Tate, C., & Smith, S. J. (2007). Caffeine effects on physical and cognitive performance during sustained operations. Aviation, Space, and Environmental Medicine, 78(9), 871-877.
Millard-Stafford, M. L., Cureton, K. J., Wingo, J. E., Trilk, J., Warren, G. L., & Buyckx, M. (2007). Hydration during exercise in warm, humid conditions: Effect of a caffeinated sports drink. International Journal of Sport Nutrition and Exercise Metabolism, 17, 163-177.
Roberts, M. D., Taylor, L. W., Wismann, J. A., Wilborn, C. D., Kreider, R. B., & Willoughby, D. S. (2007). Effects of ingesting JavaFit energy extreme functional coffee on aerobic and anaerobic fitness markers in recreationally-active coffee consumers. Journal of the Internation Society of Sports Nutrition, 4(25)
