Posted: July 17, 2006

Science of Sport: Caffeine and Endurance

Reviewed by Robert Kunz MS

Intro: Caffeine continues to be one of the most studied ergogenic ingredients. Researchers are constantly re-designing studies to get a clear indication how caffeine improves performance. In 2004-2005 over a dozen studies have been published on the effects of caffeine as an ergogenic aid. This newsletter reviews five of those studies.

For years athletes have been using caffeine in various doses to improve their performance. Everyone knows that a strong cup of Java gives you that alertness and sense of extra energy. Drink three cups of leaded Starbucks coffee and you'll feel like you want to run a marathon! So….does the caffeine just make you want to run that marathon or do you actually run it and run it faster? Many professional endurance athletes use caffeine to enhance their performance. Prior to 2004, Caffeine was banned by the US Olympic Committee, World Anti-Doping Association (WADA) and US Anti-doping association. This decision was reversed in 2004, allowing the use of caffeine in sports, though this reversal may be short lived. Research published in 2004 and 2005 continues to indicate that caffeine does elicit an ergogenic boost. Prior to 2004, Caffeine was banned at a level of 12mcg/ml in urine, which requires about 1,200 mg of pure caffeine or 8 cups of strong coffee. WADA has lifted this ban starting in January of 2004, although it comes with some controversy since caffeine does have some ergogenic properties and can be dangerous if abused. Back to that marathon: you can run it faster, but only if done correctly, so let's talk about who can benefit from caffeine and how it can be properly used.

Caffeine stimulates the central nervous system (CNS), increases the release of adrenaline, increases the use of body fat as fuel and spares glycogen. Adrenaline release is accomplished through caffeine's effect on epinephrine and nor-epinephrine. This CNS excitatory response is used by many athletes to give them that alertness and sense of extra 'energy' needed for their workouts. More importantly, caffeine mobilizes free fatty acids (FFA) in the blood. Increased FFA in the blood allows the body to use fat as a fuel source. The use of fat as fuel allows the body to spare glycogen (carbohydrates) for later use in exercise.

Notes to consider:

Caffeine is classified as a diuretic.* This can complicate an athlete's water balance, which determines how efficient he/she will perform. Diuretics not only dehydrate the body, they can cause bowel movements and gastric distress which would obviously be detrimental to your exercise bout.

*Recently some experts and publications have reversed their viewpoint of caffeine's diuretic properties. The current literature is contradictory in respect to caffeine's classification as a diuretic.-see Diuretic effects of caffeine below

Habitual caffeine users will not see any ergogenic effects from caffeine prior to a race. Your body has an intricate natural defense mechanism (builds a tolerance) which over time compensates for high doses of most nutrients and chemicals you put in your body. In other words, if you habitually use caffeine you can expect your body to reduce all the beneficial endurance and performance effects. *So recent publications have also shown this may not necessarily be true.

Caffeine is also a thermogenic. This means it will raise your heartbeat and core body temperature. As you can guess, this may not be wise when exercising in heat.

Caffeine has not shown any benefit on power.

The previous four points may lead you to believe that caffeine should not be used by anyone as an ergogenic aid. In fact, the majority of the research on sedentary individuals does not support the use of caffeine as an ergogenic aid. However, the research done on trained athletes showed no detrimental diuretic effect and no increased body temperature. Trained athletes who are also habitual caffeine users can get benefit from caffeine if they abstain at least three days prior to the event. Caffeine has been shown to increase power, reduce the perceived effort at a given workload, e.g., cycling at 24mph may seem easier when loading with caffeine.

Diuretic Effects of Caffeine Depending on several factors, the diuretic effects caused by caffeine can be considered weak to negligible under normal caffeine consumption and for people without urinary tract problems. However, it is difficult to measure the effects, even in a laboratory situation. A study by Nussberger et al. (1) does not show a significant increase of urine excretion when comparing intake of drinks containing caffeine to the water control intake. Transitory effects have been reported by Neuhäuser-Berthold et al. (2) when passing from abstinence to an elevated dose or when a chronic intake is followed by massive absorption. Such transitory imbalances disappear after less than an hour. A study by Martof and Knox (3) concluded that there is no evidence to recommend that xanthines should be omitted when forcing fluids. Even in a recent epidemiological study attempting to classify alcohol and caffeine as diuretic substances (4) , the author admits that there are no estimates of the chronic effect of caffeine on diuresis under variable free-living conditions. Caffeine also causes smooth muscle relaxation particularly in relation to the function of lungs and the blood vessels. Its effect on the detrusor muscle, which is involved in bladder function, has been studied. A control study (5) showed that consumption of caffeine led to a rise in pressure on the detrusor muscle upon bladder filling but not to a diuretic effect as such. Women with normal bladder function were not significantly affected by caffeine. A more recent study (6) confirmed an association between high caffeine intake and detrusor instability in a population of women with symptoms of urinary incontinence. The beneficial effects of caffeine on endurance exercise performance were discussed in an earlier section. However, there has been concern that use of caffeine during exercise might exacerbate dehydration induced by exercise. Consequently, it has usually been accepted that beverages containing caffeine should not be used to promote fluid replacement during prolonged exercise. Wemple and collaborators (7) , however, demonstrated that the presence of caffeine in drinks, taken before moderate endurance exercise, did not compromise hydration of the body, even though it did cause weak diuresis during rest. In a study aimed at assessing the effects of caffeine on endurance Graham and collaborators (8) did not observe differences among their trials in the volume of urine produced during preexercise and postexercise when comparing different fluids, decaffeinated coffee, placebo capsules, decaffeinated coffee with caffeine added, regular coffee and caffeine capsules. 1. Nussberger, J. et al. Journal of cardiovascular Pharmacology, 15, 685-691, 1990. 2. Neuhäuser-Berthold, M. et al. Annals of Nutrition & Metabolism, 41, 29-36, 1997. 3. Martof, M.T. and Knox, D.K., Clinical Nursing Research, 6, 186-196, 1997. 4. Stookey, J.D., European Journal of Epidemiology, 15, 181-188, 1999 5. Creighton, S.M. and Stanton, S.L. British Journal of Urology, 66, 613-614, 1990. 6. Arya, L.A. et al. Obstetrics & Gynecology, 96, 85-89, 2000. 7. Wemple, R.D. et al. International Journal of Sports Medicine, 18, 40-46, 1997. 8. Graham, T.E. et al. Journal of Applied Physiology, 85, 883-889, 1998. The above excerpt was borrowed from The Coffee Science Information Center.

Abstracts supporting use of caffeine with trained athletes:

A study using well-trained cyclists also supports the use of caffeine during competition to improve performance. In this study, 15 cyclists ingested different levels of caffeine in addition to a carbohydrate-electrolyte drink during a time trial. The highest caffeine doses (225 and 320 mg) resulted in a 5% increase in power relative to the control trials without caffeine (308 + 9 and 309 + 10W versus 295 + 9W, respectively). The amount of caffeine ingested during this study were relatively small, and yielded caffeine concentrations in the urine of less than 5 mg/L for the participants.(Kovacs)

Another recent study supported the use of caffeine both before and during performance. This study involved a cycling time trial which occurred after 2 hours of steady state cycling at 70% of VO2 max. They used several different patterns of caffeine ingestion, including different levels of before and during trial caffeine intake. None of the methods caused an increase of urine caffeine concentrations to exceed 12ug/ml. Their results also demonstrated that ingestion of 1-3 mg/kg of caffeine produced the same level of performance enhancement (~3%) as did the higher levels of caffeine intake (6 mg/kg). (Cox)

NEW Studies (2004-2005):

A recent study performed by Dr. Yeo at the University of Birmingham, UK looked at the effects of Cafffeine ingestion on carbohydrate oxidation. Eight male cyclists exercised at for 120 min on three occasions. During exercise subjects ingested either a 5.8% glucose solution (Glu; 48 g/h), glucose with caffeine (Glu+Caf, 48 g/h + 5 mg x kg(-1) x h(-1)), or plain water (Wat). Average exogenous CHO oxidation over the 90- to 120-min period was 26% higher (P < 0.05) in Glu+Caf (0.72 +/- 0.04 g/min) compared with Glu (0.57 +/- 0.04 g/min). Total CHO oxidation rates were higher (P < 0.05) in the CHO ingestion trials compared with Wat, but they were highest when Glu+Caf was ingested (1.21 +/- 0.37, 1.84 +/- 0.14, and 2.47 +/- 0.23 g/min for Wat, Glu, and Glu+Caf, respectively; P < 0.05). There was also a trend (P = 0.082) toward an increased endogenous CHO oxidation with Glu+Caf (1.81 +/- 0.22 g/min vs. 1.27 +/- 0.13 g/min for Glu and 1.12 +/- 0.37 g/min for Wat). In conclusion, compared with glucose alone, 5 mg x kg (approximately 350mg caffeine for a 150lb athlete) caffeine coingested with glucose increases exogenous CHO oxidation, possibly as a result of an enhanced intestinal absorption.

A Meta-Analysis of the use of caffeine ingestion on rate of perceived exertion (RPE) proved the value of caffeine as an ergogenic aid. Twenty-one studies were reviewed. In comparison to placebo, caffeine reduced RPE during exercise by 5.6% (95% CI (confidence interval). These values were significantly greater (P<0.05) than RPE obtained at the end of exercise (RPE % change, 0.01%; 95%). In addition, caffeine improved exercise performance by 11.2% (95% CI; 4.6 17.8%). Regression analysis revealed that RPE obtained during exercise could account for 29% of the variance in the improvement in exercise performance. The results demonstrate that caffeine reduces RPE during exercise and this may partly explain the subsequent ergogenic effects of caffeine on performance.

The aim of this study was to determine the effects of caffeine ingestion on a 'preloaded' protocol that involved cycling for 2 min at a constant rate of 100% maximal power output immediately followed by a 1-min 'all-out' effort. Eleven male cyclists completed a ramp test to measure maximal power output. On two other occasions, the participants ingested caffeine (5 mg. kg(-1)or placebo. Ratings of perceived exertion (RPE; 6-20 Borg scale) were lower in the caffeine trial by approximately 1 RPE point at 30, 60 and 120 s during the constant rate phase of the preloaded test (P <0.05). The mean power output during the all-out effort was increased following caffeine ingestion compared with placebo (794+/-164 vs 750+/-163 W; P=0.05). Blood lactate concentration 4, 5 and 6 min after exercise was also significantly higher by approximately 1 mmol. l(-1) in the caffeine trial (P <0.05). These results suggest that high-intensity cycling performance can be increased following moderate caffeine ingestion and that this improvement may be related to a reduction in RPE and an elevation in blood lactate concentration.

Dr. Mclellan looked at the ergogenic role of ingesting coffee (COF) prior to the subsequent ingestion of anhydrous caffeine (CAF). Thirteen subjects performed 6 rides to exhaustion at 80 % VO2max 1.5 h after ingesting combinations of COF, decaffeinated coffee (DECOF), CAF, or placebo. Times to exhaustion were significantly greater for all trials with CAF versus placebo. In conclusion, the prior consumption of COF did not decrease the ergogenic effect of the subsequent ingestion of anhydrous CAF.

This study determined the physiological effects of caffeine on cross-country runners during submaximal exercise. Ten college-age subjects (5 women; 5 men) volunteered to participate in this study. After completing a VO2max test, each subject completed 2 30-minute runs at 70% VO2max on the treadmill, 1 after ingesting caffeine and the other after ingesting a placebo. Tidal volume (TV), alveolar ventilation (VA), and rating of perceived exertion (RPE) were significantly different (p < 0.05) between treatment and control groups. The results suggest that the ingestion of caffeine at 7 mg.kg(-1) of body weight prior to submaximal running might provide a modest ergogenic effect via improved respiratory efficiency and a psychological lift.

BEWARE: caffeine content in energy drinks is often not listed so be aware of the presence of guarana extracts (an herbal caffeine source included in un-standardized amounts) as well as many other unknown ingredients

LATEST CAFFEINE RECOMMENDATIONSAN ERGOGENIC AID
FORM	tablets, coffee, with a sports drink
TIMING	ingest 60-75 minutes before event ingest small amount during event (if carbonated, should be flat) ingest small amount late in endurance event (if carbonated, should be flat)
CONCERNS	rehydration post exercise compared to a carbohydrate electrolyte drink slowed large variability between athletes responses
SIDE EFFECTS	anxiety, jitters, insomnia, inability to focus, GI unrest, irritability, dependency with withdrawal side effects mild side effects common with high doses (> 6 mg/kg) minimal side effects with low to moderate doses (3-6 mg/kg)
NOTE: CAFFEINE HAS BEEN REMOVED FROM WORLD ANTI-DOPING AGENCY'S (WADA) 2004 LIST OF PROHIBITED SUBSTANCES AND METHODS

Discussion: It was previously thought that Caffeine's ergogenic effect was limited to endurance events lasting greater than 2 hours. Based on the latest clinical research, evidence now suggests that short bouts of exercise may also benefit from Caffeine's use. The mechanism of action appears to be quite different and varied depending on the length of activity.

For activities >1 hour: Caffeine stimulates the use of stored fat (free fatty acids). This in-turn spares carbohydrates and allows athletes to exercise longer.

For high Intensity activities: Caffeine improves the athletes rate of perceived exertion, oxidation of ingested carbohydrates and allows for higher lactate levels. These physiological changes allows the athlete to push a little harder and may elicit improved performance

Recommendations: :Using caffeine as an ergogenic aid should be done with extreme caution. Caffeine's stimulatory effect on the central nervous system can pose harm to individuals at risk. Limit your caffeine intake for 3-4 days leading up to an event. Start 3 to 4 hours prior to your event and consume 1mg - 6mg of caffeine per kg body weight (that's 70mg to 420mg for a 150lb athlete). This can be a large amount of caffeine, so be sure to experiment before you do this with incremental levels of caffeine. If you are not trained, then you are better off not using caffeine at all. Excess caffeine can cause anxiety, irritability, delirium and hallucinations. Caffeine increases core body temperature and heart rate. Consult a physician before using caffeine prior to exercise.

If you choose to load with caffeine prior to training or an event, be sure to use products which clearly list total caffeine content. Many energy drinks list caffeine, green tea or guarana on the label but do not list total caffeine content. Most of these drinks offer minimal levels of caffeine (5mg-40mg).

WADA's removal of caffeine from its banned substance list does raise some serious concerns. If abused, caffeine can be detrimental and dangerous. Caffeine's actions on the CNS, excitory response and potential as a diuretic can all cause serious damage if abused. We strongly urge all athletes wanting to use caffeine to do so under extreme caution.

Typical Caffeine amounts:

Soda: 35 - 90mg caffeine
Cup of Coffee: 50 - 150mg caffeine
Cup of tea: 10 - 80mg caffeine
Guarana: active ingredient is caffeine (8% to 15%)
Green tea herb: active ingredient is caffeine (0% to 15%) 
I.E. 100mg of Green Tea extract provides between 0mg and 15mg total caffeine content. 

References:
Costill DL, Dalsky GP, Fink WJ. Effects of caffeine ingestion on metabolism and exercise performance. Med Sci Sports Exercise. 1978; 10: 155-158

Cox GR, Desbrow B, Montgomery PG, Anderson ME, Bruce CR, Macrides TA, Martin DT, Moquin A, Roberts A, Hawley JA, Burke LM. Effect of different protocols of caffeine intake on metabolism and endurance performance. J Appl Physiol. 2002; 93(3):990-9.

Essig D, Costill DL, Van Handel RJ. Effects of caffeine ingestion on utilization of muscle glygogen and lipid during leg ergometer cycling. International Journal of Sports Med. 1980; 1:86-9

Fisher SM, McMurray RG, Berry M, et al. Influence of caffeine on exercise performance in habitual caffeine users. International Journal of Sports Med 1986;7:276-280

Greer F, Friars D, Graham TE; Comparison of caffeine and theophylline ingestion: exercise metabolism and endurance.J Appl Physiol 2000 Nov;89(5):1837-44 Department of Human Biology and Nutritional Sciences, University of Guelph, Guelph, Ontario, Canada N1G 2W1.

Ivy JL, Costill DL, Fink WJ, et al. Influence of caffeine and carbohydrate feedings on endurance performance Med Science Sports and Exercise. 1979; 11;6-1

Kovacs EMR, Stegen JHCH, Brouns F. Effect of caffeinated drinks on substrate metabolism, caffeine excretion, and performance. J Appl Physiol 1998; 85: 709-715.

World Anti-Doping Association http://www.wada-ama.org

Caffeine Drug Info: www.nlm.nih.gov

NEW:
Yeo SE, Jentjens RL, Wallis GA, Jeukendrup AE. Caffeine increases exogenous carbohydrate oxidation during exercise. J Appl Physiol. 2005 Sep;99(3):844-50. Epub 2005 Apr 14.

M. Doherty, P. M. Effects of caffeine ingestion on rating of perceived exertion during and after exercise: a meta-analysis. Smith Scandinavian Journal of Medicine & Science in Sports. Volume 15 Issue 2 Page 69 - April 2005

Doherty M, Smith P, Hughes M, Davison R. Caffeine lowers perceptual response and increases power output during high-intensity cycling. J Sports Sci. 2004 Jul;22(7):637-43. Department of Sport, Exercise and Biomedical Sciences, University of Luton, Luton LU1 3JU.

McLellan TM, Bell DG. The impact of prior coffee consumption on the subsequent ergogenic effect of anhydrous caffeine. Int J Sport Nutr Exerc Metab. 2004 Dec;14(6):698-708.

Birnbaum LJ, Herbst JD. Physiologic effects of caffeine on cross-country runners. J Strength Cond Res. 2004 Aug;18(3):463-5.

The Endurance Research Board's (ERB) objective is to offer a broad perspective on both innovative and long-standing endurance nutrition. In addition to having advance science degrees, each member of our ERB races at an elite level. Our scientists are professional mountain bikers, professional triathletes and Cat 1 cyclists. Members of the Endurance Research Board include: Sally Warner MA Ph.D., Neal Henderson MS CSCS, Shawn Dolan Ph.D., Bob Seebohar, MS, RD, CSCS

* The ERB is a resource of First Endurance Nutrition

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