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CAFFEINE & SPORTS.
Term Paper ID:22985
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Essay Subject:
Physiological & psychological effects of drug on athletic performance, regulation, cellular process involved, effectiveness, endurance, metabolism.... More...
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10 Pages / 2250 Words
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Paper Abstract:
Physiological & psychological effects of drug on athletic performance, regulation, cellular process involved, effectiveness, endurance, metabolism.
Paper Introduction:
Effects of Caffeine in Sports-Related Performance
The drug, caffeine (1,3,7-trimethylxanthine), is consumed worldwide. It is found in tea, coffee, and soft drinks. Caffeine is also a common ingredient in headache medications and appetite suppressants. The drug's primary physiologic effects involve the central nervous system: Caffeine is a stimulant. In addition, over the past several decades, the compound's influence on sports-related performance has also been investigated. Various studies indicate that caffeine may improve endurance performance during long-term, low-to-moderate intensity aerobic exercise. It is thought that this effect may result from an increase in metabolic efficiency. Some investigators believe that caffeine enhances the utilization of blood borne free fatty acids. Unfortunately though, such factors as a lack of
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5. Jacobson & Edwards (1991) tested subjects for maximal strength andendurance using a Cybex II Isokinetic Dynomometer (7:147-152). Whilemany researchers believe that caffeine decreases reaction and movementtimes, some studies have concluded otherwise (12:481-489). For instance, they contribute to such criticalprocesses as glycogenolysis, glucose uptake, gluconeogenesis, muscle andadipose lipolysis, contractility, inotropic and chronotropic responses ofthe heart, and circulatory system adjustments (8:139-155). Adenosinereceptor inhibition, however, occurs at physiologic caffeine concentrations(8:139-155). (1986), for example, foundthat small doses of caffeine had no ergogenic effect on muscle function(3:188-193). Theprecise physiologic mechanisms by which caffeine mediates these effects,however, have yet to be unambiguously delineated. Inaddition, people generally become more sensitive to caffeine as they getolder. For example, the drug could act directly on the centralnervous system and stimulate the release of such perception-modifyingcompounds as ß-endorphins. Nehlig, A.; Daval, J.; Debry, G. Then, soon afterward, Sutherland and his coworkers observedthat methylxanthine inhibits cyclic nucleotide phosphodiesterase, andthereby prevents cAMP's breakdown. Metabolic, catecholamine, and exercise performance responses to various doses of caffeine. Acute caffeine ingestion does notincrease either maximal voluntary contractions or maximal power output(12:481-498). For any given steadystate caffeine intake, there is considerable variability among differentindividuals as far as both urine and plasma concentrations (1:4 7).Nonetheless, it is generally accepted that about 8 milligrams of caffeinewill elicit a urine level of 12 micrograms per milliliter in a 7 -kilogramathlete. All three drugsproduce similar physiologic effects (11:435-436). At concentrations of between 1 and 2millimolar, caffeine lowers the muscle's excitability threshold andprolongs the duration of the active period of muscle contraction. The Journal of Sports Medicine and Physical Fitness 31:425-432; 1991, September. Caffeine and the central nervous system: Mechanism of action, biochemical, metabolic and psychostimulant effects. 4. For instance, the drug's effect onskiing was found to be more pronounced at an altitude of 29 meters (9425feet) than it was at 3 meters (975 feet). Ergogenic drugs are employed primarily to "bestow energy orotherwise enhance athletic performance (2:2 5)." Although most drugs with ergogenic potential are banned fromcompetition, caffeine is allowed in moderate amounts. In relation to athleticperformance, it may be defined as "any means to enhance energy utilization,including energy production, control, and efficiency (13:S344-S347)."There are at least five categories of ergogenic aids. Eichner, R. The research evidence does suggest though that caffeineenhances endurance exercise performance. Some investigators believe that caffeine enhances theutilization of blood borne free fatty acids. French, C.; McNaughton, L.; Davies, P.; Tristram, S. Thus, the exact effects of caffeine on athletic performanceremain largely unknown. Of the three mechanisms of caffeine action, perhaps the mostimportant is the drug's antagonistic action on the adenosine receptors.The mobilization of intracellular calcium and the inhibition ofphosphodiesterases occurs only at high caffeine concentrations. H. In addition, caffeine appearsto significantly prolong time to exhaustion in athletes not acclimated tohigh altitudes (9:215-219). A.; Jeukendrup, A. Graham & Spriet (1995), for instance, demonstrated that low andmoderate doses of caffeine enhance endurance performance (5:867-873). Suchstudies, therefore, do not provide any evidence of a change in substrateutilization in humans (11:435-436). Researchers have observed thatcaffeine can improve physical performance or work output during prolongedexercise at submaximal intensity (e.g., cross-country skiing, running, andcycling). The investigators noted thattheophylline reduces the accumulation of cAMP in cerebral slices. Peak blood levels usually occur within approximately 3 to 6 minutes (11:435-436). Thisobservation was opposite that which would have been expected from aphosphodiesterase inhibitor. For the most part, the effects of caffeine vary greatly from oneindividual to another. Theresearchers observed that maximal strength was not affected by twodifferent levels of caffeine treatment. Despite the ongoing debatethough, many athletes are convinced of caffeine's positive effects.Therefore, urine caffeine concentrations are currently monitored andcontrolled. L. Brain Research Reviews 17:139-17 ; 1992. This enhanced capacity for lipolysis may thereforefacilitate a shift in substrate utilization (9:215-219). The beneficial effects of caffeine on endurance have also beenassociated with variations in altitude. Birkett, D. Caffeine is also a commoningredient in headache medications and appetite suppressants. W. W. Moderate doses of caffeine act as a "mild stimulant (8:139-155)."The drug is primarily used for the relief of minor fatigue. The mobilization of intracellular calcium by caffeine was firstdemonstrated in skeletal muscle. These effects may be related to differences in such things asintestinal absorption, gastric evacuation, and variations in caffeine'smetabolic half-life (8:139-155). Moreover, their results concurredwith those of other researchers. Literature Cited 1. The main threetheories--in chronological order of their discovery--include the following: (1) the intracellular mobilization of calcium from the sarcoplasmicreticulum of skeletal muscle; (2) the inhibition of phosphodiesterases invarious tissues including muscles and adipocytes; and (3) the antagonism ofcentral nervous system adenosine receptors (8:139-155). The compound achieved this interference by blocking the nervoussystem's adenosine receptors (8:139-155). L. A number of hypotheses have been advanced to explain caffeine'seffect on endurance performance. Caffeine may also alter the"perception of the effort required" for prolonged athletic activities(8:139-155). 3. H. Other studies on plasmacatecholamines, however, have provided contradictory results (9:215-219). (199 ) observed that theingestion of a 1 milligram per kilogram dose of caffeine three hours priorto an incremental work test enabled recreational cyclists to work for alonger period of time (3:188-193). While it is known that the drug stimulates the central nervoussystem, promotes neuromuscular transmission, and improves skeletal musclecontractility, there is considerable disagreement over whether or not itenhances activities requiring quick reactions and rapid movements. 2. Although some studies have shown that the drug improvesendurance, the hypotheses remain controversial. International Journal of Sports Medicine 11:194-197; 199 . J.; Van Baak, M. Influence of two levels of caffeine on maximal torque at selected angular velocities. (198 ), other researchershave been unable confirm the metabolic effects of caffeine (1 :225). In addition, the xanthine derivatives arehighly lipid soluble, and readily cross the blood-brain barrier. LeBlanc et al. Medicine and Science in Sports and Exercise 24(9 Supplement):S344-S348; 1992, September.----------------------- 3 Ergolytic drugs in medicine and sports. In addition, investigators have more recently suggested that thepsychological stimulant effects of caffeine may be related to increasedepinephrine levels (13:S344-S347). The American Journal of Medicine 94:2 5-211; 1993, February. Moreover,while there are few adverse effects associated with caffeine, ingestion ofexcessive quantities can result in death. First they identified theregulatory role of cyclic-3',5'-adenosine monophosphate (cAMP) in theseprocesses. Costill et al. The brain concentration of caffeine may then remainstable for at least an hour (8:139-155). R.; Tristram, S.; Davies, P. The use of caffeine to improve athletic performance was suggestedduring the 195 s. In addition, variousinvestigators have been unable to find any increase in free fatty acidoxidation associated with increased blood free fatty acid levels. Perhaps the most important theory explaining caffeine's effect onendurance though, involves the utilization of blood borne free fatty acidsand the sparing of muscle glycogen. Effects of Caffeine in Sports-Related Performance The drug, caffeine (1,3,7-trimethylxanthine), is consumed worldwide.It is found in tea, coffee, and soft drinks. Recently though, caffeine has been shown to "increase the levels ofexcess post-exercise oxygen consumption in untrained female subjects bothduring and after 9 minutes of exercise (9:215-219)." Apparently, thisincrease in oxygen consumption results from a corresponding increase inmetabolic rate. That is approximately equal to between six and eight cups ofcoffee (9:215-219). At the cellular level, numerous mechanisms of action have beendescribed to account for caffeine's physiologic effects. Such wide-ranging effects may partly explain the controversyassociated with caffeine's influence on short duration, high intensityactivities. Williams, M. J.; Miners, J. The other two, theobromine andtheophylline, are found in cocoa and tea, respectively. Finally, both diet and ergogenic aids can additionallyinfluence sports-related performance (13:S344-S347). Caffeine hasbeen found to increase levels of plasma catecholamines both during and atthe end of exercise. Caffeine, neuromuscular function and high-intensity exercise performance. In addition, caffeine alsoenhances the tension of nerve-muscle preparations by indirect stimulation.This effect is only obtained at very high caffeine concentrations though.Furthermore, the increases in contractility do not appear to translate intoimproved in vivo muscle strength. These includemechanical, psychological, physiological, pharmacological, and nutritionalaids. E.; Spriet, L. A.; Thein, J. Forinstance, studies involving rodent models have found that caffeine neithermodifies the plasma concentration of free fatty acids, nor alters theutilization of glycogen from muscle or liver. Caffeine renal clearance and urine caffeine concentrations during steady state dosing. 9. Unfortunately, various other studies havefound contradictory effects for caffeine with regard to maximal oxygenconsumption and delay before exhaustion (8:139-155). Journal of Applied Physiology 78:867-874; 1995, March. Over 2 decades ago, Calhoun (1971)suggested that performance enhancements may simply be related to the moodaltering effects of caffeine (9:215-219). International Journal of Sports Medicine 15:215-223; 1994.1 . Unfortunately though, suchfactors as a lack of standardization between studies and individualdifferences in response to caffeine have resulted in contradictory researchfindings. It isthought that this effect may result from an increase in metabolicefficiency. Bond et al. The exact physiologic mechanisms by which this increaseoccurs, however, remain unclear (9:215-219). The lethal acute dose for anadult is between 5 and 1 grams (i.e., the amount found in about 75 cups ofcoffee) (8:139-155). This isthought to occur both by diffusion and also by a saturable transport system(8:139-155). Flinn, S.; Gregory, J.; McNaughton, L. The term, "ergogenic," is of Greek origin. Caffeine ingestion during exercise to exhaustion in elite distance runners. Inaddition, French et al. In vitro analyseshave shown that caffeine increases the release of calcium from thesarcoplasmic reticulum, and also inhibits its uptake. M.; Landry, G. Costill et al. For instance, Bachrach (1966) found that the peakplasma concentration of caffeine measured in nine subjects given 25 milligrams of the drug ranged from 4.2 to 26 milligrams per liter. Catecholamines help the body adjust tothe stress of exercise. (1991) observed that a large dose of caffeine (1 milligrams per kilogram) administered immediately prior to the start of anexhaustive exercise also increases the ability of "elite distance runners"to perform work (4:425-432). Suchobservations suggest that caffeine's effects result from selectiveactivation of the adrenal medulla (4:425-432). Caffeine and sports activity: A review. Since the depletion of muscle glycogen is thought to belargely responsible for fatigue during endurance tests, the caffeine-induced modification of substrate utilization could conceivably increaseendurance (13:S344-S347). Unfortunately though, while similar observations were subsequentlymade by both Ivy et al. In addition, over the past several decades, the compound'sinfluence on sports-related performance has also been investigated.Various studies indicate that caffeine may improve endurance performanceduring long-term, low-to-moderate intensity aerobic exercise. For one, their genetic complement is very important.Second, morphological, physiological, and psychological training are alsoessential. With regard to short-term, high intensityactivities like weightlifting or sprinting such ideas are probablyincorrect. For instance,Jacobson & Edwards (199 ) found that a moderately high dose of caffeine (6milligrams per kilogram) causes a significant increase in the monosynapticreflex response time. The effect of different dosages of caffeine on endurance performance time. (1978) concluded that "caffeinestimulates the mobilization of free fatty acids thus increasing free fattyacid oxidation and therefore sparing muscle glycogen during exercise at aconstant work rate (4:425)." Thus, it appears that caffeine may improveendurance performance by stimulating lipolysis. Sattin & Rall (197 ) eventually concludedthat theophylline interfered with the stimulation of cAMP by endogenousadenosine. Ergogenic aids. Implications for monitoring caffeine intake during sports events. (1979) and Essig et al. Theresearchers used theophylline and caffeine during their investigations ofglycogen metabolism and peripheral lipolysis. The researchers therefore postulatedthat the physiologic effects of caffeine result from the accumulation ofcAMP and the "potentialization of its effects in order to stimulate theaction of substances such as catecholamines (9:215-219)." The third cellular mechanism of action for the xanthine derivativeswas proposed by Sattin & Rall (197 ). As aresult of intensive training, the muscles of such athletes have moremitochondria. Several studies have found that the drugpotentiates the tension of isolated muscle contraction by directstimulation both at rest and after fatigue. In fact, Jacobson & Edwards (199 ) concluded thatcaffeine retards the "initiation of muscle contraction (6:194-197)." There does appear, however, to be consensus on the fact that caffeineincreases muscle contractility. They then diffuse throughout the entireorganism; their distribution correlates closely with that of body water.In particular, the compounds achieve their highest concentrations withinskeletal muscle (9:215-219). Jacobson, B. 7. International Journal of Sports Medicine 16:225-23 ; 1995.11. E.; De Haan, A. 8. Caffeine ingestion prior to incremental cycling to exhaustion in recreational cyclists. H.; Edwards, S. The maximal concentration allowed by the International OlympicCommittee is 12 micrograms per milliliter (1 :225). Thein, L. Theseeffects result primarily from the enhancement of calcium translocationthrough the plasma membrane and sarcoplasmic reticulum. O. 6. While studies involving in vivo caffeine have not shown anysignificant improvement in high-intensity, short-term exercise, the drugmay have beneficial effects on endurance. Therefore, it may be of somebenefit to long-distance runners, cross-country skiers, and cyclists. Effects of ingested doses of caffeine on neuromuscular reflex response time in man. Pasman, W. E. Upon consumption, xanthine derivatives are completely absorbed fromthe gastrointestinal tract. Caffeine is one ofthree different xanthine derivatives. Thus, the use of caffeine to improve performance inactivities requiring strength and short-term endurance--e.g.,weightlifters, throwers, sprinters, etc.--may be inappropriate (12:481-489). Graham, T. (1978) found elevatedplasma free fatty acid levels in 7 cyclists who ingested 33 milligrams ofcaffeine. (1985) showed that decreased restingmetabolic rates associated with ingestion of the drug were associated witha fall in norepinephrine, and a rise in epinephrine levels. Moreover, the study found that these elevated free fatty acidlevels were associated with a 4 percent decrease in the athletes' rates ofmuscle glycogen depletion. Nehlig, A.; Debry, G. Ergogenic and ergolytic substances. Jacobson, B. Obviously, there is a strong belief that caffeine is an ergogenic aidto sports-related performance. The Journal of Sports Medicine and Physical Fitness 31:481-489; 1991, September.13. British Journal of Clinical Pharmacology 31:4 5-4 8; 1991, April. Similarly, caffeine neither delays fatigue, increases workoutput, or increases work capacity (8:139-155). Williams, J. Physical Therapy 75:426-439; 1995, May.12. The Journal of Sports Medicine and Physical Fitness 31:147-153; 1991, June. The drug'sprimary physiologic effects involve the central nervous system: Caffeineis a stimulant. Certain authors have even suggestedthat only well-trained athletes can benefit from the use of caffeine. This generally makesthe ion more available for muscle contraction, and thus "facilitates thecoupling of excitation and contraction in striated muscles (9:215-219)." In addition, Sutherland's group (1962; 197 ) discovered that themethylxanthines inhibit the cyclic nucleotide phosphodiesterases. The hydrolysis of fattytissue triglycerides increases the blood concentration of fatty acids.During exercise, free fatty acids are then utilized by the muscle insteadof glycogen. Last, Flinn et al. International Journal of Sports Medicine 11:188-193; 199 . H.; Edwards, S. An athlete's success in any particular sport typically depends onmany factors.
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