This investigation determined if 3 levels of controlled caffeine consumption affected fluid-electrolyte balance and renal function differently. Fifty-nine active males (mean + SD; age, 21.6 + 3.3 y) consumed 3 mg caffeine·kg-1·d-1 on days 1-6 (equilibration phase). On days 7-11 (treatment phase), subjects consumed either 0 mg (G0; placebo; n=20), 3 mg (G3; n=20), or 6 mg (G6; n=19) caffeine·kg-1·d-1 in capsules; no other dietary caffeine intake was allowed. Subjects maintained detailed records of food and fluid intake. These variables were measured on days 1, 3, 6, 9 and 11: body mass, urine osmolality, urine specific gravity, urine color, 24-hour urine volume, 24-hour Na+ and K+ excretion, 24-hour creatinine, blood urea nitrogen, serum Na+ and K+, serum osmolality, hematocrit, and total plasma protein. No significant differences were detected between groups G0, G3 and G6 (P>0.05) for any of the hydration-relevant variables, including urine volume. Although a few significant differences occurred between days (P<.05), indicating acute within-group perturbations, all hydration indices were within the normal clinical range. In conclusion, no evidence of hypohydration was observed in G3 or G6 during 11 d of controlled caffeine consumption. These findings question the widely accepted notion that caffeine acts chronically as a diuretic.
Nutritional strategies to influence adaptations to training. Spriet LL, Gibala MJ. J Sports Sci. 2004 Jan;22(1):127-41.
Department of Human Biology and Nutritional Sciences, University of Guelph, Guelph, Ontario, Canada.
This article highlights new nutritional concerns or practices that may influence the adaptation to training. The discussion is based on the assumption that the adaptation to repeated bouts of training occurs during recovery periods and that if one can train harder, the adaptation will be greater. The goal is to maximize with nutrition the recovery/adaptation that occurs in all rest periods, such that recovery before the next training session is complete. Four issues have been identified where recent scientific information will force sports nutritionists to embrace new issues and reassess old issues and, ultimately, alter the nutritional recommendations they give to athletes. These are: (1) caffeine ingestion; (2) creatine ingestion; (3) the use of intramuscular triacylglycerol (IMTG) as a fuel during exercise and the nutritional effects on IMTG repletion following exercise; and (4) the role nutrition may play in regulating the expression of genes during and after exercise training sessions. Recent findings suggest that low doses of caffeine exert significant ergogenic effects by directly affecting the central nervous system during exercise. Caffeine can cross the blood-brain barrier and antagonize the effects of adenosine, resulting in higher concentrations of stimulatory neurotransmitters. These new data strengthen the case for using low doses of caffeine during training. On the other hand, the data on the role that supplemental creatine ingestion plays in augmenting the increase in skeletal muscle mass and strength during resistance training remain equivocal. Some studies are able to demonstrate increases in muscle fibre size with creatine ingestion and some are not. The final two nutritional topics are new and have not progressed to the point that we can specifically identify strategies to enhance the adaptation to training. However, it is likely that nutritional strategies will be needed to replenish the IMTG that is used during endurance exercise. It is not presently clear whether the IMTG store is chronically reduced when engaging in daily sessions of endurance training or if this impacts negatively on the ability to train. It is also likely that the increased interest in gene and protein expression measurements will lead to nutritional strategies to optimize the adaptations that occur in skeletal muscle during and after exercise training sessions. Research in these areas in the coming years will lead to strategies designed to improve the adaptive response to training.
Fluid and fuel intake during exercise. Coyle EF. J Sports Sci. 2004 Jan;22(1):39-55.
Human Performance Laboratory, Department of Kinesiology and Health Education, The University of Texas at Austin, Austin, TX.
The amounts of water, carbohydrate and salt that athletes are advised to ingest during exercise are based upon their effectiveness in attenuating both fatigue as well as illness due to hyperthermia, dehydration or hyperhydration. When possible, fluid should be ingested at rates that most closely match sweating rate. When that is not possible or practical or sufficiently ergogenic, some athletes might tolerate body water losses amounting to 2% of body weight without significant risk to physical well-being or performance when the environment is cold (e.g. 5-10 degrees C) or temperate (e.g. 21-22 degrees C). However, when exercising in a hot environment ( > 30 degrees C), dehydration by 2% of body weight impairs absolute power production and predisposes individuals to heat injury. Fluid should not be ingested at rates in excess of sweating rate, thus body water and weight should not increase during exercise. Fatigue can be reduced by adding carbohydrate to the fluids consumed so that 30-60 g of rapidly absorbed carbohydrate are ingested throughout each hour of an athletic event. Furthermore, sodium should be included in fluids consumed during exercise lasting longer than 2 h or by individuals during any event that stimulates heavy sodium loss (more than 3-4 g of sodium). Athletes do not benefit by ingesting glycerol, amino acids or alleged precursors of neurotransmitter. Ingestion of other substances during exercise, with the possible exception of caffeine, is discouraged. Athletes will benefit the most by tailoring their individual needs for water, carbohydrate and salt to the specific challenges of their sport, especially considering the environment's impact on sweating and heat stress.
Central nervous system effects of caffeine and adenosine on fatigue.
Davis JM, Zhao Z, Stock HS, Mehl KA, Buggy J, Hand GA. Am J Physiol Regul Integr Comp Physiol. 2003 Feb;284(2):R399-404.
Department of Exercise Science, Schools of Public Health and Medicine, University of South Carolina, Columbia, SC.
Caffeine ingestion can delay fatigue during exercise, but the mechanisms remain elusive. This study was designed to test the hypothesis that blockade of central nervous system (CNS) adenosine receptors may explain the beneficial effect of caffeine on fatigue. Initial experiments were done to confirm an effect of CNS caffeine and/or the adenosine A(1)/A(2) receptor agonist 5'-N-ethylcarboxamidoadenosine (NECA) on spontaneous locomotor activity. Thirty minutes before measurement of spontaneous activity or treadmill running, male rats received caffeine, NECA, caffeine plus NECA, or vehicle during four sessions separated by approximately 1 wk. CNS caffeine and NECA (intracerebroventricular) were associated with increased and decreased spontaneous activity, respectively, but caffeine plus NECA did not block the reduction induced by NECA. CNS caffeine also increased run time to fatigue by 60% and NECA reduced it by 68% vs. vehicle. However, unlike the effects on spontaneous activity, pretreatment with caffeine was effective in blocking the decrease in run time by NECA. No differences were found after peripheral (intraperitoneal) drug administration. Results suggest that caffeine can delay fatigue through CNS mechanisms, at least in part by blocking adenosine receptors.
Caffeine, body fluid-electrolyte balance, and exercise performance.
Armstrong, LE. Int J Sport Nutr Exerc Metab 2002, 12:189-206.
Recreational enthusiasts and athletes often are advised to abstain from consuming caffeinated beverages (CB). The dual purposes of this review are to (a) critique controlled investigations regarding the effects of caffeine on dehydration and exercise performance, and (b) ascertain whether abstaining from CB is scientifically and physiologically justifiable. The literature indicates that caffeine consumption stimulates a mild diuresis similar to water, but there is no evidence of a fluid-electrolyte imbalance that is detrimental to exercise performance or health. Investigations comparing caffeine (100 – 680 mg) to water or placebo seldom found a statistical difference in urine volume. In the ten studies reviewed, consumption of a CB resulted in 0 - 84 % retention, whereas consumption of water resulted in 0 - 81 % retention, of the initial volume ingested. Further, tolerance to caffeine reduces the likelihood that a detrimental fluid-electrolyte imbalance will occur. The scientific literature suggests that athletes and recreational enthusiasts will not incur detrimental fluid-electrolyte imbalances if they consume CB in moderation and eat a typical U.S. diet. Sedentary members of the general public should be at less risk than athletes because their fluid losses via sweating are smaller.
Ergogenic aids in aerobic activity. Juhn MS. Curr Sports Med Rep. 2002 Aug;1(4):233-8.
Hall Health Sports Medicine, University of Washington, Seattle, WA.
There are many products that are potentially ergogenic for aerobic exercise, although evidence-based support varies. The most popular supplements or ergogenic aids for the endurance athlete are caffeine, antioxidants, erythropoietin, and the dietary practice of carbohydrate loading. Caffeine and carbohydrate loading have the most evidence-based support of being both ergogenic and safe. Erythropoietin is ergogenic but unsafe, and is banned by all major sport-sanctioning bodies, and antioxidants have potential but warrant further study.
Caffeine and exercise: metabolism, endurance and performance. Graham TE. Sports Med. 2001;31(11):785-807.
Human Biology and Nutritional Sciences, University of Guelph, Ontario, Canada.
Caffeine is a common substance in the diets of most athletes and it is now appearing in many new products, including energy drinks, sport gels, alcoholic beverages and diet aids. It can be a powerful ergogenic aid at levels that are considerably lower than the acceptable limit of the International Olympic Committee and could be beneficial in training and in competition. Caffeine does not improve maximal oxygen capacity directly, but could permit the athlete to train at a greater power output and/or to train longer. It has also been shown to increase speed and/or power output in simulated race conditions. These effects have been found in activities that last as little as 60 seconds or as long as 2 hours. There is less information about the effects of caffeine on strength; however, recent work suggests no effect on maximal ability, but enhanced endurance or resistance to fatigue. There is no evidence that caffeine ingestion before exercise leads to dehydration, ion imbalance, or any other adverse effects. The ingestion of caffeine as coffee appears to be ineffective compared to doping with pure caffeine. Related compounds such as theophylline are also potent ergogenic aids. Caffeine may act synergistically with other drugs including ephedrine and anti-inflammatory agents. It appears that male and female athletes have similar caffeine pharmacokinetics, i.e., for a given dose of caffeine, the time course and absolute plasma concentrations of caffeine and its metabolites are the same. In addition, exercise or dehydration does not affect caffeine pharmacokinetics. The limited information available suggests that caffeine non-users and users respond similarly and that withdrawal from caffeine may not be important. The mechanism(s) by which caffeine elicits its ergogenic effects are unknown, but the popular theory that it enhances fat oxidation and spares muscle glycogen has very little support and is an incomplete explanation at best. Caffeine may work, in part, by creating a more favourable intracellular ionic environment in active muscle. This could facilitate force production by each motor unit.
Dose-dependent effect of caffeine on reducing leg muscle pain during cycling exercise is unrelated to systolic blood pressure. O'Connor PJ, Motl RW, Broglio SP, Ely MR. Pain. 2004 Jun;109(3):291-8.
Department of Exercise Science, University of Georgia, Athens, GA.
This double-blind, within-subjects experiment examined the effects of ingesting two doses of caffeine on perceptions of leg muscle pain and blood pressure during moderate intensity cycling exercise. Low caffeine consuming college-aged males ingested one of two doses of caffeine (5 or 10mg.kg(-1) body weight) or placebo and 1h later completed 30 min of moderate intensity cycling exercise (60%). The order of drug administration was counter-balanced. Resting blood pressure and heart rate were recorded immediately before and 1h after drug administration. Perceptions of leg muscle pain as well as work rate, blood pressure, heart rate, and oxygen uptake were recorded during exercise. Caffeine increased resting systolic pressure in a dose-dependent fashion but these blood pressure effects were not maintained during exercise. Caffeine had a significant linear effect on leg muscle pain ratings. The mean (+/-SD) pain intensity scores during exercise after ingesting 10mg.kg(-1) body weight caffeine, 5mg.kg(-1) body weight caffeine, and placebo were 2.1+/-1.4, 2.6+/-1.5, and 3.5+/-1.7, respectively. The results support the conclusion that caffeine ingestion has a dose-response effect on reducing leg muscle pain during exercise and that these effects do not depend on caffeine-induced increases in systolic blood pressure during exercise.
Dry mouth:
Cappuccino coffee treatment of xerostomia in patients taking tricyclic antidepressants: preliminary report (In Polish) Chodorowski Z. Przegl Lek. 2002;59(4-5):392-3.
I Klinika Chorob Wewnetrznych Akademii Medycznej w Gdansku, Poland.
Ten patients underwent a trial treatment with cappuccino coffee. All of them (8 university lecturers and 2 clerks) aged from 60 to 69 (average 63) years old, used tricyclic antidepressants because of insomnia as a monosymptomatic type of depression or insomnia as a dominant symptom in the course of depression. One evening dose of doxepin was from 150 to 250 mg (average 225), causing xerostomia the following day, usually between 9-15 o'clock. The five-minute chewing [drinking?] of 15.0 g of cappuccino coffee increased the amount of saliva, decreased xerostomia, and improved the ability of speech. The beneficial effect of coffee lasted from 0.5 to 4 (average about 2) hours. To the best of our knowledge there are no publications dealing with the positive effect of coffee in xerostomia.
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