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Downing, Jason J.
Effects of a commercially available energy drink on anaerobic performance
h [electronic resource] /
by Jason J. Downing.
[Tampa, Fla] :
b University of South Florida,
Title from PDF of title page.
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Thesis (M.A.)--University of South Florida, 2009.
Includes bibliographical references.
Text (Electronic thesis) in PDF format.
ABSTRACT: In an attempt to improve aerobic and anaerobic performance, athletes and fitness enthusiasts consume a variety of supplements. Because of this, energy drinks are quickly becoming more and more popular every day. Despite its highly addictive nature, caffeine, which is the main active ingredient in energy drinks, is gaining recognition as an ergogenic aid. However, due to the many factors that affects the action of caffeine, and because the research on caffeine and anaerobic performance is limited, the potential for studying energy drinks and anaerobic performance is quite large. PURPOSE: To determine if a commercially available energy drink has any ergogenic effects on lower body and upper body resistance exercise performance. METHODS: In a block randomized, double-blind, placebo-controlled, crossover study thirteen recreationally trained male and female volunteers (mean SD age = 22.5 3.4 years) performed 4 sets of the leg press and 4 sets of the bench press exercises (at 80% of 1 RM with all sets separated by 2 minutes). Acting as their own controls, participants were tested on each dependent variable (i.e., bench press total volume, leg press total volume and total workout volume) twice, after ingesting a Venom Energy Drink and after ingesting a placebo drink. RESULTS: Data were tested via a dependent samples t-test with p value set at < 0.05. No significant differences were found for any of the three dependent variables. DISCUSSION: The major finding of this study is that consumption of a Venom Energy Drink does not produce an ergogenic effect by improving anaerobic exercise performance when the exercises are performed forty-five minutes following ingestion. Future studies should focus more on examining the factors behind the actions of caffeine. More specifically, the exercise performed, the training status of the participants, individual differences of the participants, and the dose of caffeine.
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Advisor: Bill Campbell, Ph.D.
x Physical Education and Exercise Science
t USF Electronic Theses and Dissertations.
Effects of a Commercially Available Energy Drink on Anaerobic Performance by Jason J. Downing A thesis submitted in partial fulfillment of the requirements for the degree of Master of Arts Department of Physical Education and Exercise Science College of Education University of South Florida Major Professor: Bill Campbell, Ph.D. Marcus Kilpatrick, Ph.D. Candi Ashley, Ph.D. Date of Approval: July 17, 2009 Keywords: Venom, caffeine, ergogenic, endurance, bench press, leg press Copyright 2009, Jason J. Downing
i Table of Contents List of Tables ................................ ................................ ................................ ..................... iii List of Figures ................................ ................................ ................................ .................... iv Abstract ................................ ................................ ................................ ................................ v Chapter One : Introduction ................................ ................................ ................................ ... 1 Purpose of the Study ................................ ................................ ................................ 2 Independent and Dependent Variables ................................ ................................ .... 2 Hypotheses ................................ ................................ ................................ ............... 3 Chapter Two : Review of Literature ................................ ................................ ..................... 4 ................................ ........... 4 Caffeine and Aerobic Exercise Performance ................................ ........................... 6 Caffeine and Anaerobic Exercise Performance ................................ ....................... 7 Caffeine and Resistance Exercise Performance ................................ ..................... 10 Energy Drinks and Bench Press and Leg Press Exercise Performance ................. 11 Dose, Side Effects, and Health Implications ................................ ......................... 1 2 Caffeine, Exercise, and the Menstrual Cycle ................................ ......................... 1 3 Summary ................................ ................................ ................................ ................ 1 5 Chapter Three : Methodology ................................ ................................ ............................. 1 7 Study Design ................................ ................................ ................................ .......... 1 7 Participants ................................ ................................ ................................ ............. 1 7 Entry and Physician Clearance Session ................................ ................................ 1 8 Familiarization and Baseline Testing Session ................................ ....................... 18 Testing Protocol ................................ ................................ ................................ ..... 2 0 Supplementation Protocol ................................ ................................ ...................... 2 0 Methods and Materials ................................ ................................ ........................... 2 1 Body Weight and Height ................................ ................................ ........... 2 1 Heart Rate and Blood Pressure ................................ ................................ .. 2 1 Caffeine Consumption Status Evaluation ................................ .................. 2 2 Resistance Exercise Tests ................................ ................................ .......... 2 2 Research Design and Data Analysis ................................ .......................... 2 3 Chapter Four : Results ................................ ................................ ................................ ........ 24 Bench Press Total Volume ................................ ................................ ..................... 27 Leg Press Total Volume ................................ ................................ ......................... 27
ii Total Workout Volume ................................ ................................ .......................... 28 Chapter Five : Discussion ................................ ................................ ................................ ... 2 9 References Cited ................................ ................................ ................................ ................ 36 Appendices ................................ ................................ ................................ ......................... 42 Appendix 1: Typical Caffeine Content of Common Foods and Medications ....... 43
iii List of Tables Table 1 Description of Laboratory Visits 18 Table 2 Characteristics of Study Participants ( N = 13) 25 Table 3 One Repetition Maximum in the Bench Press and Leg Press Exercises (Expressed as Absolute and Relative) 25 Table 4 Repetitions Completed per Set and Repetition Range per Set 26 Table 5 Test Comparisons for Dependent V ariables 27
iv List of Figures Figure 1 Outline of Sessions 3 and 4 (resistance exercise sessions) 2 0
v Effects of a Commercially Available Energy Drink on Anaerobic Performance Jason J. Downing A BSTRACT In an attempt to improve aerobic and anaerobic performance, athletes and fitness enthusiasts consume a variety of supplements. Because of this, energy drinks are quickly becoming more and more popular every day. Despite its highly addictive nature, caffe ine, which is the main active ingredient in energy drinks, is gaining recognition as an ergogenic aid. However, due to the many factors that affects the action of caffeine, and because the research on caffeine and anaerobic performance is limited, the pot ential for studying energy drinks and anaerobic performance is quite large. PURPOSE: T o determine if a commercially available energy drink has any ergogenic effects on lower body and upper body resistance exercise performance. METHODS: In a block randomi zed, double blind, placebo controlled, crossover study thirteen recreationally trained male and female volunteers ( mean + SD age = 22.5 + 3.4 years ) perform ed 4 sets of the leg press and 4 sets of the bench press exercises ( at 80% of 1 RM with all sets separated by 2 minutes) Acting as their own controls, participants w er e tested on each dependent variable (i.e., bench press total volume, leg press total volume and total workout volume) twice after ingesting a Venom Energy Drink and after ingesting a placebo drink RESULTS: Data were tested via a dependent samples t test with p value set at < 0.05. No significant differences were found for any of the three dependent
vi variables. DISCUSSION: The major finding of this study is that consumption of a Ve nom Energy Drink does not produce an ergogenic effect by improving anaerobic exercise performance when the exercises are performed forty five minutes following ingestion. Future studies should focus more on examining the factors behind the actions of caf feine. More specifically, the exercise performed, the training status of the participants, individual differences of the participants, and the dose of caffeine.
1 C hapter One I ntroduction Athletes and fitness enthusiasts are always looking for ways to improve their edge on performance. In doing so they consume different types of supplements in an attempt to improve aerobic and anaerobic performance. One of the most popular supplements today is energy drinks. Th is popularity can be seen by the number of energy drinks currently on the market today and by the consistent influx of new drinks into the market. The active ingredient in these commercially available energy drinks is caffeine and the range of dosage is quite large Caffeine is one of the mo st common drugs used in America, and possibly worldwide 1 7 ,3 6 p opularity, as an ergogenic aid. An ergogenic aid is any substance that can increase physical or mental performance, usually by reducing symptoms of fatigue. The potential for investigations into caffeine as an ergogenic aid especially in the form of energy drinks, is quite large becaus e caffeine action depends on many factors such as: the exercise performed (type, intensity, and duration) individual differences, the environment, nutritional status, and the dose of caffeine. 9 Although there is still some debate among the literature as to the specific ergogenic effects of caffeine and the physiological factors behind these effects, most researchers do agree that 1) caffeine does enhance aerobic endurance performance (i.e.,
2 prol onged, submaximal intensity) 3,9 ,1 6 and 2) that the literature on the effects of caffeine on anaerobic performance (i.e., short term, near maximal or maximal intensities) is quite limited. 3,6 9 Purpose of the Study The purpose of the present study will be to determine if a commercially available energy drink (Venom ) has any ergogenic effects on upper body and lower body r esistance exercise endurance performance. Independent and Dependent Variables The indepe ndent variables will be Venom supplementation a commercially available energy drink produced and marketed by Dr. Pepper / S even Up and containing 160 mg of caffeine (80 mg/8 oz of liquid), and placebo supplementation. Ingredients in the Venom Energy Drink are very similar to Red Bull Energy Drink: carbonated water, sugar, glucose, citric acid, maltodextrin, taurine, sodium citrate, glucuronolactone, natural and artificial flavors, ginseng extract, L carnitine, inositol, caffeine, sodium benzo ate (preservative), caramel color, potassium sorbate (preservative), niacinamide (vitamin B3), guarana, sucralose, pyridoxine hydrochloride (vitamin B6), riboflavin (vitamin B2), and cyanocobalamin (vitamin B12). Dependent variables will include: upper bo dy resistance exercise endurance performance lower body resistance exercise endurance performance and whole body total lifting volume.
3 Hypotheses Ho 1 : There will be no difference in bench press total lifting volume between the energy drink group and the placebo group. Ho 2 : There will be no difference in leg press total lifting volume between the energy drink group and the placebo group. Ho 3 : There will be no difference in whole body total lifting volume between the energy drink group and the placeb o group.
4 C hapter Two R eview of Literature A multitude of clinical studies have investigated the effects of caffeine on exercise performance. The majority of these investigations have focused on aerobic exercise performance, with limited attention investigating anaerobic exercise performance. The following review of literature will summarize the potential provide an overview of caffeine ingestion and its effects on: Aerobic exercise performance Anaerobic exercise performance Resistance exercise performance Following this, the effects of energy drinks (a caffeine containing beverage) on resistance training performance will be summarized Finally, a discussion of common doses, side effects, and menstrual cycle issues in conjunction with c affeine ingestion will be presented. It is believed that caffeine a ffects performance by arousal of the c entral n ervous s ystem (CNS), mobilization of FFA for use by the muscles (which has a glycogen sparring effect), enhancement of neuromuscular transmission, and enhancement (possibly) of the strength of muscle contractions. 2 5 ,2 7 ,3 8 Studies have shown that during
5 long term, submaximal aerobic exercise caffeine does stimulate the CNS (sympath omimetic effect), improve neuromuscular transmission, and increase skeletal muscle contractility. 10,13,2 5 ,3 0 ,3 6 ,3 7 ,3 8 However, some of these same studies showed no improvements in these same parameters during short term, intense exercise (such as muscular strength exercises or high intensity endurance exercise). Tarnopolsky & Cupido 37 looked at low frequency potentiation of skeletal muscle in habitual and non habitual caffeine users. They found no difference between habitual and non habitual caffeine con sumption on any of the dependent variables. In addition, they found that during aerobic endurance activity, a portion of the ergogenic effect of caffeine comes directly from skeletal muscle activity due to an increase in the release of calcium from the sa rcoplasmic reticulum, increased sensitivity of the skeletal muscles to calcium, and improvements in neuromuscular transmission (and possibly motor unit recruitment and firing rates). One of the primary mechanisms responsible for the ergogenic effects of c affeine is its inhibition of adenosine receptors. 10 Caffeine appears to improve our ability to handle mental and physical tasks, mainly through this inhibition of the adenosine receptor. Stimulation of these receptors (more specifically the A1 receptors) inhibits nerve cells and has a profound effect on the heart by lowering heart rate and slowing atrioventricular nodal conduction (a parasympathetic action). On the other hand, if these receptors are inhibited as seen with caffeine ingestion, nerve cells are stimulated and heart rate is increased. Therefore, caffeine provides a sympathomimetic effect on the CNS and neuromuscular transmission by inhibiting adenosine receptor activity. Although studies are lim ited, the inhibition of adenosine receptor activity that caffeine
6 possesses may also help in force production (strength and power) by increasing motor unit recruitment and firing rates. 6 While it is not considered the primary mechanism behind the ergogenic effects of caffeine on submaximal endurance performance, 16 there is quite a bit of evidence suggesting that caffeine consumption increases plasma FFA for skeletal muscle to use as an energy substrate. 10,16,2 7 ,2 8 ,3 0 ,3 1 ,3 2 ,3 5 ,3 6 Caffeine promotes the break down of fat tissue during endurance exercise which increases FFA in the blood. With the increased availability of this energy substrate for the skeletal muscles, there is a reduced reliance on glycogen stores allowing the sparing of glycogen to be used la ter, thereby, improving during prolonged, submaximal exercise. In addition, research shows that caffeine consumption before performing prolonged, submaximal exercise incre ases VO 2 (and fat oxidation) post exercise as well. 16,2 8 ,3 0 Caffeine and Aerobic Exercise Performance Graham & Spriet 15 demonstrated that low to moderate doses (3 6 mg/kg of body weight) of caffeine produced a greater effect on endurance performance that is time to exhaustion (TTE) at 85% of their maximum aerobic capacity (VO 2MAX ), than high doses (9 mg/kg of body weight) In addition, acute caffeine consumption prior to exercise has been shown to improve aerobic performance and fitness parameters, whereas, prolonged consumption (along with aerobic training) has no effect on aerobic performance and fitness 2 3 While most studies agree that moderate amounts of caffeine improve s aerobic performance (endurance and speed) and enhance s fat mobilization (r esulting in an
7 increase in plasma free fatty acids, or FFA) for use as energy, 10 1 3 1 4 1 6 2 7 3 1 ,3 3 3 5 ,3 6 ,3 7 some studies disagree and show no ergogenic effects. 1 4 1 6 19 ,2 7 29 3 2 In these studies that disagree caffeine showed no significant effect on aerobic endurance performance, VO 2MAX heart rate, respiratory exchange ratio (RER) and substrate utilization (i.e. FFA), or ratings of perceived exertion (RPE). In a very recent study, Beck et al (2008) examined the effects of a caffeine supplement on time to running exhaustion (TRE) at 85% VO 2PEAK in thirty one untrained and moderately trained men. They concluded that, status (i.e., provides more of an ergogenic effect in trained individuals) and the relative intensity of the task being performed (i.e., provides more of an ergogenic effect at low to moderate intensities) their results failed to validate caffeine as having an ergogenic effect on running performan ce. This supports what was previously mentioned about the actions o n caffeine depending of several factors including dose and training status. In addition, the time lapse (acute vs. chronic) from ingestion of caffeine to the testing protocol may have had an impact on the ergogenic effects of caffeine. Caffeine and Anaerobic Exercise Performance Research on whether or not caffeine produces an effect on anaerobic performance is still in its infancy Research does seem to lean in favor of caffeine improving muscular endurance (dynamic and specific), but not muscular power, and it is still in disagreement for caffeine improving maximal muscular strength. 2,3,5 7,1 2 1 7 ,1 8 19 ,3 8 Lopes et al. 22 and Tarnopolsky & Cupido 37 reported similar findings relative to the effects caffeine has on the tension developed within skeletal muscle during maximal voluntary contraction
8 (MVC) and tetanic stimulation (Hz) at different frequencies. Low frequency tetanic stimulation (20, 30, and 40 Hz) produced g reater tension during the caffeine trials after ingesting 6 mg of caffeine/kg of body weight (i.e., a moderate dose of caffeine 15 ), than the placebo trials due to an increase in calcium release from the sarcoplasmic reticulum and an increase in the sensit ivity of the skeletal muscles to calcium The same was not true for peak twitch stimulation (100 Hz) or MVC. Therefore, caffeine directly stimulates skeletal muscle during endurance events (dynamic and specific), but not during events that require maxima l strength. This has been shown to be true during anaerobic endurance cycling events where caffeine improves time to exhaustion (TTE) and allows one to maintain max speed for a set period of time (20 second sprints), even at intensities as high as 125% VO 2PEAK, 2,7 ,2 0 but it may not be true during anaerobic endurance running events, i.e., time to running exhaustion (TRE at 85% VO 2MAX ). 6 Caffeine may also have the potential to improve jumping endurance, which could be important for athletes such as basketball p layers and volleyball players. Low doses (2 mg/kg) of caffeine have been shown to increase the number of jumps performed at various heights in rats. 4 0 Possible limitations to the studies on anaerobic performance and caffeine that could explain the conflicting results of previous studies a re the doses of caffeine used, time lapse from ingestion to test, the use of mostly men, and the tests chosen Most studies have used only low to moderate doses of caffeine (2mg/kg 6mg/kg). One study stated their reason for using 6mg/kg was that it is strong enough to elicit an effect without violating the limits set by the International Olympic Committee (IOC). 1 7 It may be possible that stronger doses of caffeine are needed to improve anaerobic perf ormance
9 however, the results of these studies would not benefit athletes and coaches. The time lapse from ingestion of caffeine to the test trials may also be responsible for conflicting results. All but one of the studies reported exercise testing 45 100 minutes after caffeine ingestion with the majority at 60 minute s post ingestion The study with the shortest time lapse had only 30 minutes from ingestion to test (i.e., ability to maintain max speed during 20 second cycle sprints) and successful ly demonstrated an increase in the ability to maintain max imum speed with caffeine. 2 The final limitation in these studies is the limited variability of tests chosen for testing maximal muscular strength ( i.e., 1RM in the bench press and leg press) and l ower body anaerobic power ( i.e., standard 30s Wingate Anaerobic Test, or WAnTs and 20s cycle sprints). Stickley, Hetzler, and Kimura 3 4 found that a 20 second WAnT protocol produced the same results without the ill effects that come with the standard 30 second WAnT protocol. Perhaps in the current studies the ill effects of the 30 second protocol outweighed the ergogenic effects of caffeine. More research into the effects of caffeine on anaerobic performance, especially upper and lower body resistance exercise endurance performance, maximal muscular strength and lower body power, is needed. Future studies should focus on including more females, investigating consu mption of caffeine through common methods (i.e., commercially available energy drinks), use other durations in time from ingestion to test that have not been reported in the literature, and look at using different anaerobic tests Also, more studies on ca receptor antagonist action and motor unit recruitment and firing rates are needed to possibly explain the mechanism of action responsible for improve anaerobic performance.
10 Caffeine and Resistance Exercise Performance In addition to dynamic muscular endurance, specific muscular endurance is also improved through the ingestion of caffeine. However, the research thus far only supports improvements in upper body muscular endurance, specifically the bench press exercise. 3 1 2 39 While not all investigations have reported significant improvements in muscular endurance for the bench press, one such investigation reported an 11 12% increase in repetitions to failure during the caffeine trial (using a dose of 6 mg/kg) 3 as compared to the placebo condition Despite these studies showing no significant improvements in the leg press exercises, more total weight was still lifted during the caffeine trials. 3 39 Therefore, caffeine allows one to perform more total repetitions during benc h press exercises, and possibly during leg press exercises, at moderate intensity (approximately 70% 1RM). Equivocal data limit the conclusions that can be made relative to caffe on bench press and leg press 1RM 3,6,7 In fact, two studies reported conflicting results despite the use of the same dose of caffeine and same exercise protocol. 6,7 Beck et al. 5 and Beck et al. 6 used the same 1RM be nch press equipment and protocol and administered the same dose of caffeine (201 mg) to their participants. The difference between the two studies was the training background of t he participants. In the first study 5 the participants regularly engaged in resistance training (at least four sessions per week), whereas, in the second study 6 participants were untrained and not experi enced with resistance training. It was the former study that demonstrated an ergogenic effect of caffeine o n 1RM bench press while the latter study did not The researchers concluded that a possible explanation for this may have be en the differences in training status and
11 experience of the participants This reinforces the hypothesis that the ergogenic effects of caffeine depend s on training status (favoring trained over untrained) and it demonstrates the need for further investigation into caffeine, training status, and maximal muscular strength. Energy Drinks and Bench Press and Leg Press Exercise Performance Studies that have examined the effec ts of energy drinks (which contain caffeine as the primary ergogenic ingredient) on anaerobic exercise performance have shown conflicting results. Forbes et al. 12 looked at the effects of Red Bull Energy Drink on bench press muscle endurance performance. Sixty minutes following ingestion of a Red Bull Energy Drink (with a caffeine dose of 2.0 mg/kg of body mass) or placebo drink, sixteen men and women performed three sets of the bench press exercise at 70% of their one repetition maximum (with 1 minute rest between sets). The study demonstrated a significant improvement in upper body muscle endurance during the bench press exercise. Woolf, Bidwell, and Carlson 39 studied the effects of a caffeine containing leg press and bench press exercises. Nineteen male athletes consumed a caffeine containing shake (with a caffeine dose of 5 mg/kg of body mass), or a placebo shake, 60 minutes prior to performing the exercise tests. After a ten minute dynamic and static warm up, all participants performed the bench press and leg press exercises in a block randomized order. Results showed si gnificant increases in the total weight lifted during the bench press exercise but not during the leg press exercise.
12 Both of these energy drink studies utilized a block randomized double blind, placebo controlled, cross over design. The main difference between the energy drink and the placebo drink was caffeine content (i.e., caffeine vs. no caffeine). In addition, all participants in these studies were either physically active or were athletes. Therefore, it is possible that the improvement in anaerob ic performance was likely do to caffeine (12,39) Dose, S ide E ffects, and H ealth I mplications There is still much debate as to the dose, the side effects, and health implications of chronic and acute caffeine consumption 1 6 When considering caffeine dose, important questions to be asked (and studied) include: W hat amount is the optimal (& safe) amount? How is it delivered? What are the correct method s mode s and pattern s of administration ? The dose of caffeine in the Venom E nergy Drink that will be used in the current study is similar to Red Bull Energy Drink (i.e., 80 mg / 8 oz of liquid). The common side effects of excessive intake of caffeine (i.e., > 9mg/kg of body weight or > 500 mg total), especially for non habitual consumers, are dependence, tolerance, diuresis, tremors, irritability, mood shifts, and agitation. 1 6 ,2 6 These side effects are especially important in competitive settings and why caffeine has been banned by some sport governing bodies The debate concerning health imp lications revolve around insulin resistance (which can lead to Type II Diabetes Mellitus) and potential cardiovascular risks (especially if combined with ephedrine). 1 6
13 Caffeine, E xercise, and the Menstrual C ycle There are t wo phases to the menstrual cycle that are determined by the concentrations of estrogen and progesterone: 1) follicular phase (first 2 weeks of the cycle ) where both hormone levels are low however, near the end of this phase (right before ovulation) estrogen levels become high; and 2) luteal phase (final 2 weeks of cycle ) where both hormone levels are high. 2 1 Due to the differences in the concentration levels of these hormones throughout the cycle, inter and intra individual differences within the study sample, and the variability in effect of the interaction between the two hormones (i.e., opposing vs. synergistic) timing of study tests may be important during aerobic exercise 2 1 Altho ugh most research has found no differences, d uring the luteal phase both body temperature and cardiovascular strain increase possibly creating a negative effect on prolonged exercise performance. 2 1 Research that has examined maximal strength and muscle contractile characteristics of women during their menstrual cycle show conflicting results. 2 1 Some show increased strength mid cycle (i.e., near the end of the follicular phase) with a subsequent decrease in strength at, or around, ovulation claiming a positive effect of estrogen followed by an opposing effect of the interaction between estrogen and progesterone. However, other studies show negative effects of e strogen on strength. Research has also claimed a positive effect of progesterone, and possibly a synergistic effect of the interaction between estrogen and progesterone on strength by demonstrating increased strength during the luteal phase. Still, other studies show no differences in strength during the entire menstrual cycle. 2 1
14 Two major limitations in these studies are: 1) most did not use true tests of maximal muscular strength (i.e., superimposed electrical stimulus) and 2) most did not provide ve rification of hormone levels by testing their participants. The measurement and verification of estrogen and progesterone levels is important in research that involves women who are eumenorrheic. 2 1 The majority of the studies that did measure and provide verification of hormone levels saw no change in strength, muscle contractile characteristics, or lactate response (fatigability) in eumenorrheic women. Therefore, it would be unnecessary to adjust for the menstrual cycle when studying muscular strength a nd/or endurance of women experiencing normal menstruation. Nor would it be necessary to make adjustments for competition or while training normal eumenorrheic women who are involved in strength specific, intense anaerobic or intense aerobic sport. The men strual cycle, as well as gender or exercise, has not been shown to effect how caffeine is absorbed, metabolized, distributed, or eliminated 2 4 H owever, caffeine intake may affect the length Fenster et al. 11 looked at habitual caffeine consumption and menstrual function in healthy premenopausal women. They found that habitual caffeine consumption affected the length of the menstrual cycle. Women who consumed more than 300 mg of caffeine a day (considered heavy consump tion) were a third less likely to have a long cycle and, in fact, actually increased (doubled) their risk for a short er cycle. Researchers believe that there are two reasons behind these findings. First, caffeine affects luteinizing hormone and follicle stimulating hormone by inhibiting adenosine. These two hormones are involved in the menstrual cycle and may affect the length of the cycle. Second, caffeine is a vasoconstrictor,
15 therefore high consumption would be expected to constrict the uterine blood vessels thereby reducing blood flow and possibly shortening the menstrual cycle. 1 1 Summary Energy drinks are becoming very popular among athletes and fitness enthusiast s as a way of giving them an edge on performance. The main active ingredient in energy drinks is caffeine. While research supports the theory that caffeine ingestion improve s aerobic endurance performance research on the effects of caffeine on an aerobic performance is limited. Research has provided much insight as to the possible mechanisms behind the ergogenic effects of caffeine mainly for aerobic performance First, inhibition of adenosine receptors appears to be the most important during aerobic activity Inhibition of these receptors improves nerve cell function (improving neuromuscular transmission and possibly motor unit recruitment and firing rates ) and provides a sympathomimetic effect on the body (stimulates the CNS). Second, caffeine increases the strength of ske letal muscle contraction by stimulating the release of calcium from the sarcoplasmic reticulum and increases Finally, and to a lesser effect, caffeine promotes increases in FFA in the blood to be used by the ske letal muscles for energy during prolonged, submaximal activity allowing the musc ores All of these mechanisms have been shown to improve aerobic endurance performance. Tolerance to the effects of caffeine has been observe d in the literature demonstrating that c affeine consumption status (i.e., habitual vs. non habitual) does not affect aerobic performance. 3 7
16 Research on caffeine and anaerobic performance is somewhat limited Therefore, potential for future studies into the effects of caffeine ingestion on anaerobic performance is high, especially with focus on direct testing of muscular endurance, strength, and power as well as on adenosine receptor antagonist action and force production (i.e., motor unit recruitment and firing rates). When taken in moderate amounts, caffeine can be used by athletes and non athle tes as a way of improving their time to exhaustion (i.e. performance) during prolonged, s ubmaximal exercise but data is conflicting on more intense, short term exercise. There is also evidence indicating that moderate amounts of caffeine enhance dynamic and specific muscular endurance. However, more research needs to be conducted in relation to caffeine ingestion and its effects on muscular endurance, strength and power.
17 C hapter Three M ethodology Study Design The study was consistent with previous studies in that utilized a block randomized double b lind, placebo controlled, cross over design Participants Thirteen recreationally trained (physically active at least three times a week) volunteers, 18 to 35 years of age, participated in the study. The sample consisted of 8 males (body mass index, or BMI = 25.0 + 3.0 kg/m 2 ) and 5 females ( BMI = 21.4 + 1.9 kg/m 2 ) Sin ce the menstrual cycle does not affect anaerobic exercise, we did not control for women who were eumenorrheic Participants were randomly assigned to one of two groups: an energy drink group (ENE) a nd a placebo drink group (PLA). Each participant visited the lab oratory for four separate sessions (Table 1).
18 Table 1 Description of Laboratory Visits Session Description 1 Screening that included a physical exam, informed consent, and personal / medical history questionnaires 2 Familiarization and baseline testing that included bench press and leg press 1RM testing, a run through of the testing protocol to be used, and verbal/written pre testing session rules 3 Random assignment to either ENE or PLA group and testing session 1 4 Testing session 2 Entry and Physician Clearance Session Participants were recruited by word of mouth from the University of South Florida and the surrounding Tampa Community P articipants, 18 to 3 5 years of age, who we re apparently healthy and who participate in some form of physical activity at least three times per week were invited to attend Session 1 at th Performance Nutrition Laboratory. Durin g this session participants 1) complete d per sonal and medical history questionnaires, 2) sign ed an infor med consent statement, and 3) were cleared to participate by a licensed p hysician.
19 Familiarization and Baseline Testing Session Participants who me t the entry criteria and who we re cleared to participate were invited back to the lab to attend Session 2. They were also instructed to refrain from resistance training for 4 days prior to attending Session 2 This instruction was given at the time they accept ed the offer to participate. Session 2 consist ed of four parts. First, participants were familiarized to the study via a verbal and written explanation outlining the study design. Next, participants ha d their one repetition maximum (1RM) tested in both th e bench press ( BP ) and le g press ( LP ) exercises using standar d procedures 1 For both exercises, 1RM was determined within 6 sets with 2 minute rests between set s. Participants warm ed up by completing 2 sets of 10 repetitions at 50% of their perceived cap acity for each exercise. Participants then perform ed successive 1RM lifts of both exercises starting with a weight that is within their perceived capacity (approximately 70% of capacity). For the BP weight was increased by 10 20 pounds and for the LP weight was increased by 30 40 pounds. The final weight successfully lifted one time, for each exercise, was were familia rized with the testing protocol by having them complete all sets and rest periods in the order to be used during the testing sessions, as outlined in the Methods and Materials section. F inally, participants were instructed to refrain from resistance training during the course of the study ( < 2 weeks) as well as refrain from any exhaustive exercise for 48 hours prior to each testing session They were also instructed to refrain from ingesting caffeine 48 hours prior to each testing session. To help facilitate this, participants were instr ucted verbally and in writing to 1) avoid consuming caffeine containing foods and medications ( Appendix 1 ) 2) to read nutrition labels of any food item to see if caffeine is
20 an ingredient and 3) try to eat the same foods the day prior to each training session Testing took place in the morning; therefore, p articipants were also i nstructed to f ast for 1 0 hours prior to each testing session. Testing Protocol Sessions 3 and 4 consist ed of the participants performing the BP and LP exercises in a back to back fashion, as outlined in the Methods and Materials section, to ok take place approxima tely 7 days following Session 2. Initially, participants were randomly assigned to either the ENE group or the PLA group. During Session 3 the ENE group consume d the ener gy drink and the PLA group consume d the place bo drink. S even days later, at the same time of the day, all participants return ed to attend Session 4 This time, however, the ENE group from Session 3 bec a me the PLA group and the PLA group bec a me the ENE group. Figure 1 displays the outline of S essions 3 and 4 Figure 1 Outline of Sessions 3 and 4 (resistance exercise sessions).
21 Supplementation Protocol Participants were randomly assigned to one of two groups: ENE group or PLA group. Upon arriving at the laboratory for each session, participants s a t and rest ed in a chair for 5 minutes. Then, in a double blind manner, one group consume d a shake that contained Venom Energy Drink a 16 oz energy drink containing 160 mg of caffeine ( ENE group ; approximately 2 3 mg of caffeine/kg of body weight ) while the other group consu med a placebo shake of similar volume texture and carbohydrate content as the energy drink sh ake (PLA group). Supplements were prepared by a third party. The beverages were transferred to a Styrofoam cup with a straw and were label ed with the Before ingestion, each participant was blindfolded and a clip was placed on the ir nose Forty five minutes following ingestion participants bega n the Methods and Materials section. Methods and Materials Body w eight and h eight and height were obtained using the O height and weight scale. Heart r ate and b lood p ressure All heart rate measurements were determined by palpation of the radial a rtery using standard procedures 1 All blood pressure measurements were determined in the seated position using a mercurial sphygmomanometer using standard procedu res. 1 After arriving at the lab and resting for 5 minute s and prior to ingesting the energy or placebo drink, resting heart rate and blood pressure were recorded. Heart rates and b lood pressures were again recorded pre test at
22 20 and 4 0 minutes post ingestion. A final heart rate an d blood pressure were recorded 5 minute s post test. Caffeine c onsumption s tatus e valuation history (i.e., habitual versus non habitual caffeine consumption) has been shown to not affect aerobic performance 3 7 e ach participant in the current study was surveyed, as part of their personal history questionna ire, as to the status of their current caffeine intake On a scale of 1 5 [ 1 = never ( < 1 day /week) 2 = rarely (1 2 days/week), 3 = sometimes (3 4 days/week), 4 = often (5 6 days/week), or 5 = daily ( > 7 days/week)] t he questionn aire (17 questions) ask ed the participants how often they consume /take the caffeine containing foods and medications listed in Table 1 8 A score of 59 was used as the cutoff point between habitual and non habitual caffeine consumption. Therefore, a score of 59 or less (which equated to < 3 days of caffeine consumption per week) mean t the participant i s a non habitual caffeine consumer and a score of 60 or higher (which equated to > 4 days of caffeine consumption per week) meant the participant i s a habitual caffeine consumer. After reviewing all questionnaires, it was determined that all participants were non habitual caffeine consumers (t he highest score was a 32) Resistance e xercise t ests The L P and B P exercises were performed back to back in a rotated fashion as follows: L P set 1, 2 minute rest, B P set 1, 2 minute rest, L P set 2, 2 minute rest, B P set 2, 2 minute rest, L P set 3, 2 minute rest, B P set 3 2 minute rest, L P set 4, 2 minute rest, and B P set 4 For both exercises, participants perform ed all 4 sets to volitional fatigue at 8 0% of their 1RM
23 Research d esign and d ata a nalysis Each participant serve d as his or her own control and was tested on each dependent variable two times (after ingesting the en ergy drink shake and after ingesting the placebo shake ). Null hypotheses were t ested via a dependent samples t test and the criterion for significance for all tests was set at p < 0.05. Effect sizes were calculated by subtracting mean one from mean two and dividing by the d ).
24 C hapter Four R esults Thirteen physically active volunteers participated in the study (8 males and 5 females). Descriptive statistics for age, weight, height, and BMI are presented in Table 2 descriptive statistics for 1 RM in both exercises are presented in Table 3, and descriptive statistics for repetitions completed per set (and the range of repetitions) are presented in Table 4 To test the null hypotheses, dependent samples t tests were conducted to determine if there were significant differences in bench press total volume (kg) between the two groups, in leg press total volume (kg) between the two groups, and in total workout volume (kg) between the two groups. d ) for each dependent variable were also calculated to determine if there is any significance in the outcomes of the t tests These values are summarized and listed in Table 5
25 Table 2 Characteristics of Study Participants (N = 13) Variable Mean Standard Deviation Age (yrs) 22.5 3.4 Height (total; cm) 174.9 11.2 Height (males; cm) 181.8 6.2 Height (females; cm) 163.7 7.3 Weight (total; kg) 73.2 17.9 Weight (males; kg) 83.3 15.4 Weight (females; kg) 57.1 4.1 BMI (total; kg/m 2 ) 23.6 3.1 BMI (males; kg/m 2 ) 25.0 3.0 BMI (females; kg/m 2 ) 21.4 1.9 Table 3 One Repetition Maximum in the Bench Press and Leg Press Exercises (Expressed as Absolute and Relative). Variable Mean Standard Deviation Absolute BP 1 RM (total; kg) 79.0 38.5 Absolute BP 1 RM (males; kg) 106.3 17.5 Absolute BP 1 RM (females; kg) 35.5 7.1 Relative BP 1 RM (total) 1.0 0.4 Relative BP 1 RM (males) 1.3 0.2 Relative BP 1 RM (females) 0.6 0.1 Absolute LP 1 RM (total; kg) 268.9 117.4 Absolute LP 1 RM (males; kg) 346.9 72.0 Absolute LP 1 RM (females; kg) 144.1 25.5 Relative LP 1 RM (total) 3.6 1.0 Relative LP 1 RM (males) 4.2 0.5 Relative LP 1 RM (females) 2.6 0.6 Note. RM = repetition maximum. Relative was calculated by dividing the absolute 1
26 Table 4 Repetitions Completed per Set and Repetition Range per Set Variable Males (Mean + SD) Range Females (Mean + SD) Range ENE Group BP Set 1 repetitions 8.5 + 2.7 10 10.0 + 3.1 9 BP Set 2 repetitions 6.6 + 2.3 8 8.4 + 1.1 4 BP Set 3 repetitions 5.8 + 2.3 8 5.8 + 0.4 2 BP Set 4 repetitions 4.3 + 1.4 5 5.0 + 1.0 3 LP Set 1 repetitions 12.5 + 6.2 20 15.8 + 7.5 21 LP Set 2 repetitions 9.8 + 3.2 12 13.6 + 6.0 16 LP Set 3 repetitions 7.1 + 2.5 8 11.0 + 5.1 15 LP Set 4 repetitions 5.8 + 2.1 6 9.4 + 5.3 15 PLA Group BP Set 1 repetitions 9.6 + 2.3 8 11.8 + 1.3 4 BP Set 2 repetitions 7.0 + 1.7 6 8.2 + 0.8 3 BP Set 3 repetitions 5.0 + 1.5 5 6.4 + 0.5 2 BP Set 4 repetitions 4.6 + 1.6 6 5.2 + 1.1 4 LP Set 1 repetitions 12.1 + 6.2 20 13.2 + 6.4 17 LP Set 2 repetitions 8.8 + 4.0 12 9.2 + 3.3 9 LP Set 3 repetitions 7.0 + 1.8 5 8.2 + 2.9 9 LP Set 4 repetitions 4.8 + 1.4 5 8.4 + 4.7 14 Note. ENE Group = energy drink group; PLA Group = placebo drink group; BP = bench press; LP = leg press.
27 Table 5 Test Comparisons for Dependent Variables Variable ENE (mean + SD; kg) PLA (mean + SD; kg) p Value Effect Size d ) BP TV LP TV TWV 1,639 + 89 1 8,09 9 + 3,29 3 9,73 8 + 3,74 4 1,71 1 + 83 2 7,13 9 + 3,19 7 8,849 + 3,5 60 .314 .108 .150 .08 .3 .2 Note. Data were analyzed using Dependent Samples t Test s BP TV = Bench Press Total Volume (kg x reps); LP TV = Leg Press Total Volume (kg x reps); TWV = Total Workout Volume (BP TV + LP TV). B ench Press Total Volume Ho 1 stated t here will be no difference in bench press total lifting volume between the energy drink group and the placebo group. No statistically significant differences were found in bench press total volume between the energy drink trials and the placebo drink trials (ENE = 1,639 + 89 1 kg; PLA = 1,71 1 + 83 2 kg; p = .314 ; effect size = .08 ). Therefore, based on the non significant results, we fail to reject the null hypothesis (Ho 1 ). Leg Press Total Volume Ho 2 stated t here will be no difference in leg press total lifting volume between the energy drink group and the placebo group. No statistically significant differences were found in leg press total volume between the energy drink trials and the placebo drink
28 trials (ENE = 8,09 9 + 3,29 3 kg; PLA = 7,13 9 + 3,19 7 kg; p = .108 ; effect size = .3 ). Therefore, based on the non significant results, we fail to reject the null hypothesis (Ho 2 ). Total Workout Volume Ho 3 stated there will be no difference in whole body total lifting volume between the energy drink group and the placebo group. No statistically significant differences were found in total workout volume between th e energy drink trials and the placebo drink trials (ENE = 9,73 8 + 3,74 4 kg; PLA = 8,849 + 3,5 60 kg; p = .150 ; effect size = .2 ). Therefore, based on the non significant results, we fail to reject the null hypothesis (Ho 3 ).
29 C hapter Five D iscussion The major statistical finding of this study is that consumption of a commercially available energy drink does not produce an ergogenic effect by improving anaerobic exercise performance in regards to resistance exercise lifting volume (i.e., bench press tot al volume, leg press total volume or total workout volume ) when the exercises are performed forty five minutes following ingestion. However, due to the small effect size of each t test, the non significant results of this study do not necessarily imply that there is no diff erence between the two groups. T here was a 13% increase in leg press total volume and a 10% increase in total workout volume during the energy drink trials. Therefore, from a practical sense, consumption of a commercially available e nergy drink does produce an ergogenic effect by improving anaerobic exercise performance in regards to resistance exercise lifting volume A n interesting finding was that for bench press total volume the placebo drink group lifted more total volume (9% mor e) than the energy drink group Previous studies that have examined energy drink consumption (containing caffeine) on bench press performance have demonstrated improvements in bench press endurance performance 3,12, 39 Both Forbes et al. 12 and Woolf, Bidwell, and Carlson 39 demonstrated statistically significant increases in bench press endurance performance after participants who participated in moderate physical a ctivity 2 3 days per week, consumed a Red Bull
30 energy drink (approximately 2.0 mg of caffeine/kg of body weight) 60 minutes before performing the bench press exercise on a lever chest press machine. Participants performed 3 sets, to volitional fatigue, a t 70% of their one repetition maximum (1RM) with 1 minute rests between sets. In the latter study, participants were athletes who participated in at least 1 2 hours per week of some type of programmed physical activity that included 2 4 hours per week of s trength, endurance, and movement training. Sixty minutes after ingesting a caffeine (ap proximately 5 mg of caffeine/ kg of body weight), participants completed 1 set each, to volitional fatigue, of the bench press exercise and leg press exercise, on Keiser Exercise Equipment, with 1 minute rest between the two exercises. Perce ntage of 1RM for each exercise was not reported. Although the results of one of these previous studies that showed improvement in bench press endurance perf ormance, A storino, Rohman, and Firth 3 were not significant, the caffeine trials did show an 11 12% increase in repetitions to failure ( using a sample size of 22, the statistical power was .2 for the bench press and .1 for the leg press) In this study, p articipants (who were experienced with resistance training) consumed pharmaceutical grade caffeine anhydrous (app roximately 6 mg of caffeine/ kg of body weight), rested for 60 minutes, and then completed (on separate days) the bench press exercise and leg press exercise on standard free weight equipment (i.e., a barbell and horizontal bench and a 45 o plate loaded sled, respectively). The exercises were completed immediately after they were test ed for their 1RM and the protocol called for 1 set of eac h, to volitional fatigue, at 60 % of their 1 RM. Of the previous studies that demonstrated improvements in bench press endurance performance 3,12, 39 only one had similar participants ( men and women who were
31 physically active 2 3 days/week ; N = 15 ), similar suppl ementation (2.0 mg of caffeine /kg 3 mg/kg of body weight), and a similar lifting scheme (3 sets to volitional fatigue). 12 The major differences were the time from ingestion to testing (60 minutes compare d to the 45 minutes in the current study), the equipment used (a lever chest press machine compared to a standard barbell and bench in the current study), and the intensity used (70% of 1RM compared to the 80% of 1RM in the current study). The other bench press studies share no similarities to the current study, 3, 39 except one that used the same equipment (i.e., a barbell and standard bench). 3 The current study used men and women (compared to just men ; N = 22 and N = 8 ), used 45 minutes from ingestion of the energy drink to testing (compared to 60 minutes), only screened for participants who were physically active (compared to athletes or individuals who were experienced with resistance exercise), used an energy drink with a caffeine dose of approximat ely 2 or a caffeine pill with a caffeine dose of approximately 6 mg/kg of body weight), had participants complete 3 sets to volitional fatigu e (compared to 1 set to volitional fatigue), and used an exercise intensity of 80% of 1RM (compared to 60% of 1RM) After examining the similarities and differences between the bench press endurance studies, there are two possible reasons for the failur e of the current study to demonstrate an ergogenic effect of Venom Energy Drink on bench press endurance performance . First, it is possible that the 80% o f 1RM used was too heavy to allow for more volume to be lifted. the body depends on several factors, one of which is the relative intensity of the task being performed. 9 The previous
32 studies that reported the percentage of 1RM used had participants lift 10 20% less (than the 80% used in the current study) of their 1R M. Second, it is possible that the 45 minutes from ingestion to testing was not long enough to allow for peak caffeine absorption. S ixty minutes is the approximate time it takes for caffeine to reach its peak concentration in the blood 12 which was the time from ingestion to testing used in the previous studies. 3,12, 39 Th erefore, since Forbes et al. 12 was similar to the current study in so many aspects except for the intensity used and the time from ingestion to testing these are plausi ble conclusions to the current findings regarding the effects on an energy drink on bench press performance. The results of the current study relating to leg press endurance performance does agree with previous studies that have examined caffeine o r energy drink consumption and leg press exercise performance. 3, 39 Although these previous studies, as well as the current study, showed no significant improvements in the leg press exercise, the data trended towards significance. Previous studies that examined caffeine/energy drinks and leg press endurance performance share no similarities to the current study, 3, 39 except one that used the same equipment (i.e., a standard 45 o plate loaded sled ). 3 After examining these differences, which are the same a s the differences noted previously in the discussion on bench press endurance performance, it is believed that the failure of the current study to demonstrate an ergogenic effect of Venom Energy Drink on leg press endurance performance is related to the d ose of caffeine and one of the possible reasons behind As mentioned in the literature review, a portion of the ergogenic effect of caffeine comes directly from skeletal muscle activity due to an increase in the release of calcium from the sarcoplasmic reticulum, increased
33 sensitivity of the skeletal muscles to calcium, improvements in neuromuscular transmission and possibly motor unit recruitment and firing rates). 3 7 In addition, inhibition of adenosine receptor activity may also help in force production by increasing motor unit recruitment and firing rates. 6 I f caffeine has the potential to increase force production by increasing motor unit recruitment, individuals w ith larger muscle mass (e.g., athletes and r esistance trained individuals ) and exercises that involve the larger muscles/muscle groups in the body (e.g., legs versus the chest) would require larger doses of caffeine to activate the greater number of motor units that come with larger muscle mass Therefore, because the upper leg is composed of such a large amount of muscle fibers that a caffeine dose as high as 6 mg/kg of body weight may not be enough to produce an ergogenic effect. current study is simply the sums of the total volumes for the bench press and leg press exercises, and given that there were no signifi cant differences in total volume for each exercise separately, it is no surprise that there were no significant differences in total workout volume between the energy drink trials and the placebo trials. There are some limitations to the current study th at could possibly explain the results for the bench press trials conflicting with the results of previous studies. First as mentioned above, the time frame from ingestion of the energy drink to performing the bench press exercise may not have been long e nough to allow for peak absorption of caffeine into the blood. Second, also mentioned above, the percentage of the may have been too much Lastly, the training background (i.e., experi ence with resistance training) may partially explain the lack of improvement in bench press performance. The current study
34 used recreationally trained participants, meaning that they only needed to be physically active at least three times a week. While conducting the study, it was apparent to the researchers that some of the participants were not experienced in the bench press exercise. Two previous studies, Beck et al. 5 and Beck et al. 6 investigated caffeine and one repetition maximum (1 RM) bench press performance. The major difference between the two studies was the training background of the participants. In one study the participants regularly participated in resistance exercise (and demonstrated a significant improvement in bench press 1 RM) 5 while those in the other study 6 were not experienced with resistance exercise (and did not demonstrate an improvement in 1 RM) The two noteworthy strengths of the current study are: 1) its block randomized double blind, placebo controlled, cross over design which is consistent with previous studies and 2) its inclusion of female research participants. In conclusion, the current study does not support the use of a commercially available energy drink to increase bench press exercise or leg press exercise endurance performance. Our findings, in regards to the leg press exercise, share two aspects with pre vious studies: 1) that there were no statistically significant improvements in total leg press performance and 2) the energy drink trials lifted more total volume. On the other hand, our findings regarding bench press performance is in contrast to other s tudies. Previous studies 3,12, 39 have demonstrated that the ingestion of caffeine and/or energy drinks may allow one to perform more total repetitions during bench press exercises, and possibly during leg press exercises, at moderate intensity (approximate ly 70% 1RM). However, r esults from the current study cannot be used to support this statement.
35 In light of these findings, more research on the effects of energy drinks and resistance training performance is recommended. These future studies need to fo cus on the factors behind the actions of caffeine. Specifically, the exercises performed (i.e., the type, intensity, and duration), the training status of the participants, individual differences of the participants (i.e., specific caffeine consumption st atus), and the dose of caffeine. For exercises performed, future studies should include other common exercise and not just the bench press and leg press. In addition, the duration of the exercise session should be lengthened by having participants perfor m more than just two exercises, possibly focusing on a full workout to see if the effects of caffeine wear off. The intensities used should also be varied, since not everyone uses an intensity of 80% of their 1 RM. As for the participants themselves, future research should focus on examining trained versus untrained participants in the same study. This would allow for comparison in training status of the participants, that is, those experienced with resistance exercise and those with no experience. I n addition, including participants based on a more specific analysis of their caffeine consumption status (i.e., the actual mg of caffeine they consume each week) may provide a different insight into the ergogenic effects of caffeine/energy drinks on anaer obic exercise performance. Last l y, the dose of caffeine needs to be increased in future studies. The current research primarily has focused on low to moderate doses of caffeine (2 mg/kg of body wei g h t 6 mg/kg of body weight). For some exercises, and muscle groups, higher doses of caffeine may be needed to produce significant increases in performance. Since caffeine and anaerobic exercise performance is still in its infancy, and due to the many diff erent factors behind caffeine action, the future research potential is quite large.
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43 Appendix 1 Typical Caffeine Content of Common Foods and Medications. 8 Substance Serving Size Caffeine Content Caffeine Content (volume or weight) (range) (typical) Coffee: Brewed/Drip 6 oz 77 150 mg 100 mg Coffee: Instant 6 oz 20 130 mg 70 mg Coffee: Espresso 1 oz 30 50 mg 40 mg Coffee: Decaffeinated 6 oz 2 9 mg 4 mg Tea: Brewed 6 oz 30 90 mg 40 mg Tea: Instant 6 oz 10 35 mg 30 mg Tea: Canned or Bottled 12 oz 8 32 mg 20 mg Caffeinated Soft Drinks 12 oz 22 71 mg 40 mg Caffeinated Water 16.9 oz 50 125 mg 100 mg Cocoa/Hot Chocolate 6 oz 2 10 mg 7 mg Chocolate Milk 6 oz 2 7 mg 4 mg Coffee Ice Cream or Yogurt 8 oz 8 85 mg 50 mg Milk Chocolate Candy Bar 1.5 oz 2 10 mg 10 mg Dark Chocolate Candy Bar 1.5 oz 5 35 mg 30 mg Caffeinated Gum 1 stick 50 mg 50 mg Analgesics (e.g., Excedrin, Midol) 2 tablets 64 130 mg 64 or 130 mg Stimulants (e.g., NoDoz, Vivarin) 1 tablet 75 350 mg 100 or 200 mg Caffeine Pills 2 3 tablets 80 200 mg 80 200 mg Energy Drinks 8 16 oz 50 400 mg 80 160 mg