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Research Articles
Caffeine
Can J Appl
Physiol 2001;26 Suppl:S103-19 |
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Caffeine, coffee and ephedrine: impact on exercise
performance and metabolism.
Graham TE.
Department of Human Biology and Nutritional Sciences, University of
Guelph Guelph, ON.
This paper addresses areas where there is controversy regarding
caffeine as an ergogenic aid and also identifies topics that have
not been adequately addressed. It is clear that caffeine, in
moderate amounts, can be used orally as an ergogenic aid in aerobic
activity lasting for more than 1 min. It increases endurance and
speed, but not maximal VO2 and related parameters. While there are
fewer well-controlled studies for resistance exercise, the
literature would suggest similar improvements: increased endurance
at submaximal tension and power generated in repeated contractions
and no change in maximal ability to produce force. It is likely that
theophylline (a related methylxanthine) has similar actions and it
has been suggested that the combination of caffeine and
sympathomimetics may be a more potent erogenic aid. The voids in our
understanding of caffeine include the dose (what amount is optimal,
what vehicle is used to deliver the drug as well as method, pattern,
and mode of administration), the potential side effects
(particularly in competitive settings), health implications (insulin
resistance and if combined with ephedrine, cardiovascular risks) and
mechanisms of action. It appears unlikely that increased fat
oxidation and glycogen sparing is the prime ergogenic mechanism.
J Appl Physiol
1998 Sep;85(3):883-9
http://jap.physiology.org/cgi/content/full/85/3/883 |
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Metabolic and exercise endurance effects of coffee
and caffeine ingestion.
Graham TE, Hibbert E, Sathasivam P.
Human Biology and Nutritional Sciences, University of Guelph, Guelph,
Ontario, Canada N1G 2W1. tgraham.ns@aps.uoguelph.ca
Caffeine (Caf) ingestion increases plasma epinephrine (Epi) and
exercise endurance; these results are frequently transferred to
coffee (Cof) consumption. We examined the impact of ingestion of the
same dose of Caf in Cof or in water. Nine healthy, fit, young adults
performed five trials after ingesting (double blind) either a
capsule (Caf or placebo) with water or Cof (decaffeinated Cof,
decaffeinated with Caf added, or regular Cof). In all three Caf
trials, the Caf dose was 4.45 mg/kg body wt and the volume of liquid
was 7.15 ml/kg. After 1 h of rest, the subject ran at 85% of maximal
O2 consumption until voluntary exhaustion (approximately 32 min in
the placebo and decaffeinated Cof tests). In the three Caf trials,
the plasma Caf and paraxanthine concentrations were very similar.
After 1 h of rest, the plasma Epi was increased (P < 0.05) by Caf
ingestion, but the increase was greater (P < 0.05) with Caf capsules
than with Cof. During the exercise there were no differences in Epi
among the three Caf trials, and the Epi values were all greater (P <
0.05) than in the other tests. Endurance was only increased (P < 0.
05) in the Caf capsule trial; there were no differences among the
other four tests. One cannot extrapolate the effects of Caf to Cof;
there must be a component(s) of Cof that moderates the actions of
Caf.
Med Sci Sports
Exerc 2000 Nov;32(11):1958-63 |
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Enhancement of 2000-m rowing performance after caffeine ingestion.
Bruce CR, Anderson ME, Fraser SF, Stepto NK, Klein R,
Hopkins WG, Hawley
JA.
Department of Human Biology and Movement Science, RMIT University,
Bundoora, Victoria Australia.
PURPOSE: To investigate the effect of caffeine ingestion on
short-term endurance performance in competitive rowers. METHODS: In
this randomized double-blind crossover study, eight competitive
oarsmen (peak oxygen uptake [VO2peak] 4.7+/-0.4 L x min(-1), mean
+/- SD) performed three familiarization trials of a 2000-m rowing
test on an air-braked ergometer, followed by three experimental
trials at 3- to 7-d intervals, each 1 h after ingesting caffeine (6
or 9 mg x kg(-1) body mass) or placebo. Trials were preceded by a
standardized warm-up (6 min at 225+/-39 W; 75+/-7.7% VO2peak).
RESULTS: Urinary caffeine concentration was similar before ingestion
(approximately 1 mg x L(-1)) but rose to 6.2+/-3.6 and 14.5+/-7.0 mg
x L(-1) for the low and high caffeine doses, respectively. Plasma
free fatty acid concentration before exercise was higher after
caffeine ingestion (0.29+/-0.17 and 0.39+/-0.20 mM for 6 and 9 mg x
kg(-1), respectively) than after placebo (0.13+/-0.05 mM).
Respiratory exchange ratio during the warm-up was also substantially
lower with caffeine (0.94+/-0.09 and 0.93+/-0.06 for the low and
high dose) than with placebo (0.98+/-0.12). Subjects could not
distinguish between treatments before or after the exercise test.
Both doses of caffeine had a similar ergogenic effect relative to
placebo: performance time decreased by a mean of 1.2% (95% likely
range 0.4-1.9%); the corresponding increase in mean power was 2.7%
(0.4-5.0%). Performance time showed some evidence of individual
differences in the effect of caffeine (SD 0.9%; 95% likely range 1.5
to -0.9%). CONCLUSIONS: Ingestion of 6 or 9 mg x kg(-1) of caffeine
produces a worthwhile enhancement of short-term endurance
performance in a controlled laboratory setting.
Diabetes 2002
Mar;51(3):583-90 |
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Caffeine-induced impairment of insulin action but not
insulin signaling in human skeletal muscle is reduced by exercise.
Thong FS, Derave W, Kiens B, Graham TE, Urso B, Wojtaszewski JF,
Hansen BF, Richter EA.
Department of Human Biology and Nutritional Sciences, University of
Guelph, Guelph, Canada. fthong@uoguelph.ca
We investigated the effects of caffeine ingestion on skeletal muscle
glucose uptake, glycogen synthase (GS) activity, and insulin
signaling intermediates during a 100-min euglycemic-hyperinsulinemic
(100 microU/ml) clamp. On two occasions, seven men performed 1-h
one-legged knee extensor exercise at 3 h before the clamp. Caffeine
(5 mg/kg) or placebo was administered in a randomized, double-blind
fashion 1 h before the clamp. During the clamp, whole-body glucose
disposal was reduced (P < 0.05) in caffeine (37.5 +/- 3.1 micromol x
min(-1) x kg(-1)) vs. placebo (54.1 +/- 2.9 micromol x min(-1) x
kg(-1)). In accordance, the total area under the curve over 100 min
(AUC(0--100 min)) for insulin-stimulated glucose uptake in caffeine
was reduced (P < 0.05) by approximately 50% in rested and exercised
muscle. Caffeine also reduced (P < 0.05) GS activity before and
during insulin infusion in both legs. Exercise increased insulin
sensitivity of leg glucose uptake in both caffeine and placebo.
Insulin increased insulin receptor tyrosine kinase (IRTK), insulin
receptor substrate 1-associated phosphatidylinositol (PI) 3-kinase
activities, and Ser(473) phosphorylation of protein kinase B (PKB)/Akt
significantly but similarly in rested and exercised legs.
Furthermore, insulin significantly decreased glycogen synthase
kinase-3alpha (GSK-3alpha) activity equally in both legs. Caffeine
did not alter insulin signaling in either leg. Plasma epinephrine
and muscle cAMP concentrations were increased in caffeine. We
conclude that 1) caffeine impairs insulin-stimulated glucose uptake
and GS activity in rested and exercised human skeletal muscle; 2)
caffeine-induced impairment of insulin-stimulated muscle glucose
uptake and downregulation of GS activity are not accompanied by
alterations in IRTK, PI 3-kinase, PKB/Akt, or GSK-3alpha but may be
associated with increases in epinephrine and intramuscular cAMP
concentrations; and 3) exercise reduces the detrimental effects of
caffeine on insulin action in muscle.
Sports Med
2001;31(11):785-807 |
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Caffeine and exercise: metabolism, endurance and
performance.
Graham TE.
Human Biology and Nutritional Sciences, University of Guelph,
Ontario, Canada. terrygra@uoguelph.ca
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.
Metabolic, catecholamine, and exercise performance
responses to various doses of caffeine.
Graham TE, Spriet LL.
School of Human Biology, University of Guelph, Ontario, Canada.
This study examined the exercise responses of well-trained endurance
athletes to various doses of caffeine to evaluate the impact of the
drug on exercise metabolism and endurance capacity. Subjects (n = 8)
withdrew from all dietary sources of caffeine for 48 h before each
of four tests. One hour before exercise they ingested capsules of
placebo or caffeine (3, 6, or 9 mg/kg), rested quietly, and then ran
at 85% of maximal O2 consumption to voluntary exhaustion. Blood
samples for methylxanthine, catecholamine, glucose, lactate, free
fatty acid, and glycerol analyses were taken every 15 min. Plasma
caffeine concentration increased with each dose (P < 0.05). Its
major metabolite, paraxanthine, did not increase between the 6 and 9
mg/kg doses, suggesting that hepatic caffeine metabolism was
saturated. Endurance was enhanced with both 3 and 6 mg/kg of
caffeine (increases of 22 +/- 9 and 22 +/- 7%, respectively; both P
< 0.05) over the placebo time of 49.4 +/- 4.2 min, whereas there was
no significant effect with 9 mg/kg of caffeine. In contrast, plasma
epinephrine was not increased with 3 mg/kg of caffeine but was
greater with the higher doses (P < 0.05). Similarly only the highest
dose of caffeine resulted in increases in glycerol and free fatty
acids (P < 0.05). Thus the highest dose had the greatest effect on
epinephrine and blood-borne metabolites yet had the least effect on
performance. The lowest dose had little or no effect on epinephrine
and metabolites but did have an ergogenic effect. These results are
not compatible with the traditional theory that caffeine mediates
its ergogenic effect via enhanced catecholamines.
Relationship between basal metabolic rate,
thermogenic response to caffeine, and body weight loss following
combined low calorie and exercise treatment in obese women.
Yoshida T, Sakane N, Umekawa T, Kondo M.
First Department of Internal Medicine, Kyoto Prefectural University
of Medicine, Japan.
To clarify whether there were any differences in basal metabolic
rate (BMR) and thermogenic response to caffeine in individual obese
women, and if so, whether such differences affected weight loss, the
basal and resting metabolic rates at 30 min after a caffeine loading
test (4 mg/kg ideal body weight, per os) were measured in 136 obese
women and ten lean age-matched controls. The obese subjects were
then asked to follow a combined low calorie diet and exercise
regimen. There were no differences in the BMR and thermogenic
responses to caffeine between the obese and lean groups. However,
the BMR and the thermogenic responses to caffeine varied widely in
obese subjects. After two months of treatment, body weight and
percentage body fat in obese women were significantly (P < 0.001)
reduced. There were significant correlations between the BMR and
body weight loss (r = 0.3621, P < 0.001), between BMR/lean body mass
and body weight loss (r = 0.3196, P < 0.001) and between the
thermogenic response to caffeine and body weight loss (r = 0.6943, P
< 0.001). When the criterion of a BMR less than 3.10 kJ/min (less
than two standard deviations below the mean of the age-matched lean
control) was used to define an obese group with reduced BMR, there
were 30 obese subjects in this group, and their body weight was
significantly decreased by treatment.(ABSTRACT TRUNCATED AT 250
WORDS)
Int J Sports Med
1999 Aug;20(6):354-61 |
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Caffeine improves cognitive performance after
strenuous physical exercise.
Hogervorst E, Riedel WJ, Kovacs E, Brouns F, Jolles J.
Department of Psychiatry and Neuropsychology, Brain & Behaviour
Institute, European Graduate School for Neurosciences, The
Netherlands.
The effects of three carbohydrate electrolyte solutions (CES)
containing different amounts of caffeine on cognitive function and
the combined effects of these drinks and exercise on cognitive
functions were investigated in a double-blind, cross-over study. On
five separate occasions, fifteen endurance trained male athletes
(23.3 years) received water placebo, CES placebo (68.8 g/l), and
three CES drinks containing low, medium and high dosages of caffeine
(150, 225 and 320 mg/l). Each occasion, 8 ml/kg of the drink was
consumed before -- and 6 ml/kg of the drink was consumed during an
all-out 1 hour time trial on a bicycle ergometer. Cognitive (attentional,
psychomotor, and memory) tests were carried out immediately before
and immediately after exercise. Before exercise, long term memory
was improved by CES plus low dose caffeine compared to both
placebos. Immediately after exercise, all cognitive functions were
improved by CES plus low- and medium-dose caffeine compared to
placebo. These results comprise the first practical demonstration of
the cognition improving effects of low amounts of caffeine in CES
after strenuous physical exercise.
Can J Physiol
Pharmacol 1990 Jul;68(7):889-92 |
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Effects of caffeine ingestion on body fluid balance
and thermoregulation during exercise.
Falk B, Burstein R, Rosenblum J, Shapiro Y, Zylber-Katz E, Bashan
N.
Faculty of Health Sciences, McMaster University, Hamilton, Ont.,
Canada.
This study investigated the effects of caffeine supplementation on
thermoregulation and body fluid balance during prolonged exercise in
a thermoneutral environment (25 degrees C, 50% RH). Seven trained
male subjects exercised on a treadmill at an intensity of 70-75% of
maximal oxygen consumption to self-determined exhaustion. Subjects
exercised once after caffeine and once after placebo ingestion,
given in a double-blind crossover design. Five milligrams per
kilogram body weight of caffeine followed by 2.5 mg.kg-1 of caffeine
were given 2 and 0.5 h before exercise, respectively. Rectal
temperature was recorded and venous blood samples were withdrawn
every 15 min. Water loss and sweat rate were calculated from the
difference between pre- and post-exercise body weight, corrected for
liquid intake. Following caffeine ingestion, when compared with
placebo, no significant difference in final temperature or in
percent change in plasma volume were found. No significant
differences were observed in total water loss (1376 +/- 154 vs. 1141
+/- 158 mL, respectively), sweat rate (12.4 +/- 1.1 vs. 10.9 +/- 0.7
g.m-2.min-1, respectively), rise in rectal temperature (2.1 +/- 0.3
vs. 1.5 +/- 0.4 degrees C, respectively), nor in the calculated rate
of heat storage during exercise (134.4 +/- 17.7 vs. 93.5 +/- 22.5 W,
respectively). Thus, in spite of the expected rise in oxygen uptake,
caffeine ingestion under the conditions of this study does not seem
to disturb body fluid balance or affect thermoregulation during
exercise performance.
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