Ergogenic Aids: Caffeine

1. Ergogenic Aids: Caffeine

2. Caffeine • Characterization • Member of methylxanthine group of compounds • Mild stimulant that affects multiple organ systems • Absorbed rapidly from the gastrointestinal tract • Blood half-life of 3 to 6 hours • Sources • Found in many food, beverage, and pharmaceutical sources • Occurs naturally in coffee beans, tea leaves, cocoa, and cola nuts

3. Caffeine Sources Table 1. Caffeine Content (mg) of Some Common Foods, Beverages, and Over-the-Counter and Prescription Medications Data from product labels and manufacturers, and National Soft Drink Association. 1997.aBrewing tea or coffee for longer periods slightly increases the caffeine content. bPrescription, 1 oz; 30 mL.Reprinted from Mc Ardle WD, et al. Sports and Exercise Nutrition, 3rd ed. Philadelphia, PA: Lippincott Williams & Wilkins; 2009:338.

4. Caffeine and General Health • No consistent evidence for adverse effects on the cardiovascular system • Pre-existing heart arrhythmias or high blood pressure should limit consumption • Potential interactions with other compounds (eg, ephedrine) may increase risk of side effects • Sleeplessness and jitters are well-recognized side effects, especially in people not used to caffeine • Stomach irritation may occur with caffeinated beverages that increase stomach acid • No convincing links between caffeine and cancer or osteoporosis • Stimulant effects of caffeine on metabolic rate are minor and should not greatly affect weight control • Coffee may help to protect against type 2 diabetes and diseases such as Parkinson’s • Data are mainly observational and the relationships are not exceedingly strong • Abstinence or moderation of intake (≤ 2 cups per day) is advisable during pregnancy and lactation Williams MH. Nutrition for Health, Fitness, & Sport. 9th ed. New York, NY: McGraw Hill; 2010:539-542.

5. Why Is Caffeine Possibly Ergogenic? • Increased free fatty acids, glycogen sparing • Associated with higher levels of cAMP in adipose cells • Adenosine receptor antagonism • Phosphodiesterase inhibition (at high doses) • Inhibition of glycogen phosphorylase enzyme • Less breakdown of glycogen • Links excitation to contraction in muscle cells • Via release of Ca++ • Direct stimulation of central nervous system • Endorphin release causes decreased perception of effort • Stimulation of sodium/potassium pumps • Increased nutrient entry into cells by secondary active transport • Inhibition of phosphoinositide metabolism • Less signaling effects of insulin • Possibly other mechanisms as well Abbreviation: cAMP, cyclic adenosine monophosphate. Magkos F, Kavouras SA. Caffeine use in sports, pharmacokinetics in man, and cellular mechanisms of action. Crit Rev Food Sci Nutr. 2005;45(7-8):535-562.

6. Effects of Caffeine on Substrate Oxidation During Exercise Caffeine trial .30 Decaffeinated trial .24 .20 SE Subjects: • 2 female, 7 male cyclists Exercise: • Cycle to exhaustion at 80% VO2max Design: • Crossover Caffeine: • Decaffeinated or caffeinated coffee (330 mg caffeine) 1 hour before cycling .16 Glycerol, mM .12 .08 .04 .00 0.5 0.4 FFA, mM 0.3 0.2 1.0 Time to exhaustion was nearly 15 min longer for caffeine vs placebo 0.9 R, VCO2/VO2 0.8 0 10 20 30 40 50 60 70 80 90 Exercise time, minutes Abbreviations: FFA, free fatty acid; SE, standard error; VO2max, maximal oxygen consumption; R, ratio; VCO2, carbon dioxide production. Reprinted from Costill DL, et al. Med Sci Sports. 1978;10(3):155-158.

7. Effect of Caffeine on 500-m Split Times During a 1,500-m Swim 448 Placebo Caffeine 444 440 Subjects swam faster after caffeine consumption and reported lower perceived exertion 436 432 Time, seconds/500 m 428 424 420 416 412 408 0 500 1000 1500 Distance, meters Subjects: • 7 male (72.3 kg), 4 female (57.9 kg) swimmers • Capable of swimming 1,500 m in < 25 minutes • All subjects consumed < 300 mg caffeine/week • All subjects abstained from caffeine for 48 hours before study Design: • Randomized, double-blind, crossover Caffeine: • 6 mg/kg body weight (BW) administered in a fruit juice drink 2.5 hours before the swim • Placebo was fruit juice drink alone Reprinted from MacIntosh BR, et al. Can J Appl Physiol. 1995;20(2):168-177.

8. Effects of Different Doses of Caffeine on Performance *P < 0.05 placeboversus caffeine 80 * * * Subjects: • 9 well-trained cyclists • Caffeine users (100 to 250+ mg/day) • Abstained from caffeine for 3 days prior to exercise Exercise:• Cycle to exhaustion at 80% VO2max Caffeine:• 0, 5, 9, or 13 mg/kg BW • Caffeine given by capsule 70 60 59 min 58 min 58 min 50 47 min Endurance time, minutes 40 30 20 There was no dose response observed for the dose range evaluated 10 0 0 5 9 13 mg caffeine/kg BW Abbreviations: BW, body weight; VO2max, maximal oxygen consumption. Reprinted from Pasman WJ, et al. Int J Sports Med. 1995;16(4):225-230.

9. Urinary Caffeine Levels With Different Doses of Caffeine Only the 5-mg/kg BW dose always resulted in urine concentrations below previous IOC limits 30 Subjects 25 1 2 20 3 Previous IOC limit> 12 doping limit Urinary caffeine, µg/mL 15 4 5 10 6 7 5 8 0 9 5 9 13 0 mg caffeine/kg BW Abbreviations: BW, body weight; IOC, International Olympic Committee. Reprinted from Pasman WJ, et al. Int J Sports Med. 1995;16(4):225-230.

10. What Is the Ergogenic Dose of Caffeine? • 3 to 6 mg/kg BW associated with ergogenic benefits for endurance exercise • No further benefits with higher doses • May have more pronounced effects on non-users or regular users who abstain from caffeine for several days • These data are not always consistent • There are potential adverse effects in athletes who don’t regularly use caffeine • Recommended to try caffeine in practice before competition conditions Abbreviation: BW, body weight. Mc Ardle WD, et al. Sports and Exercise Nutrition, 3rd ed. Philadelphia, PA: Lippincott Williams & Wilkins; 2009:340-341.

11. Is Caffeine Permissible as an Ergogenic Aid? • No longer listed by the World Anti-Doping Agency as a prohibited substance • Remains on their Monitoring List • Still on the National Collegiate Athletic Association (NCAA) Banned Substance List at a dose that results in a urine concentration of 15 μg/mL • Equivalent to 9 to 13 mg/kg BW consumed 1 hour before event • Equals 630 to 910 mg caffeine/day for a 70-kg person • Roughly 6 to 9 cups of coffee Abbreviations: BW, body weight; NCAA, National Collegiate Athletic Association.

12. Position of the International Society of Sports Nutrition • Caffeine is effective as an ergogenic aid at 3 to 6 mg/kg BW • More effective when consumed in anhydrous state • Caffeine may • Enhance vigilance during extended exhaustive exercise or sleep deprivation • Be beneficial for sustained maximal endurance exercise, such as time trial performance • Be beneficial for high-intensity exercise with intermittent activity occurring over a long period of time (eg, team sports such as soccer or rugby) • Data are equivocal regarding effects of caffeine on strength and power • Scientific literature does not support the notion that caffeine is a diuretic during exercise Abbreviation: BW, body weight. Goldstein ER, et al. J Int Soc Sports Nutr. 2010;7(1):5.