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Carbohydrate mouth rinse and caffeine improves high-intensity interval running capacity when carbohydrate restricted

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We tested the hypothesis that carbohydrate mouth rinsing, alone or in combination with caffeine, augments high-intensity interval (HIT) running capacity undertaken in a carbohydrate-restricted state. Carbohydrate restriction was achieved by performing high-intensity running to volitional exhaustion in the evening prior to the main experimental trials and further refraining from carbohydrate intake in the post-exercise and overnight period. On the subsequent morning, eight males performed 45-min steady-state (SS) exercise (65% [Formula: see text]) followed by HIT running to exhaustion (1-min at 80% [Formula: see text]interspersed with 1-min walking at 6 km/h). Subjects completed 3 trials consisting of placebo capsules (administered immediately prior to SS and immediately before HIT) and placebo mouth rinse at 4-min intervals during HIT (PLACEBO), placebo capsules but 10% carbohydrate mouth rinse (CMR) at corresponding time-points or finally, caffeine capsules (200 mg per dose) plus 10% carbohydrate mouth rinse (CAFF + CMR) at corresponding time-points. Heart rate, capillary glucose, lactate, glycerol and NEFA were not different at exhaustion during HIT (P > 0.05). However, HIT capacity was different (P < 0.05) between all pair-wise comparisons such that CAFF + CMR (65 ± 26 min) was superior to CMR (52 ± 23 min) and PLACEBO (36 ± 22 min). We conclude that carbohydrate mouth rinsing and caffeine ingestion improves exercise capacity undertaken in carbohydrate-restricted states. Such nutritional strategies may be advantageous for those athletes who deliberately incorporate elements of training in carbohydrate-restricted states (i.e. the train-low paradigm) into their overall training programme in an attempt to strategically enhance mitochondrial adaptations of skeletal muscle.
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Carbohydrate mouth rinse and caffeine improves high-intensity interval
running capacity when carbohydrate restricted
Research Institute for Sport and Exercise Sciences, Liverpool John Moores University, Liverpool, UK
We tested the hypothesis that carbohydrate mouth rinsing, alone or in combination with caffeine, augments
10 high-intensity interval (HIT) running capacity undertaken in a carbohydrate-restricted state. Carbohydrate
restriction was achieved by performing high-intensity running to volitional exhaustion in the evening prior to
the main experimental trials and further refraining from carbohydrate intake in the post-exercise and overnight
period. On the subsequent morning, eight males performed 45-min steady-state (SS) exercise (65% .
followed by HIT running to exhaustion (1-min at 80% .
VO2maxinterspersed with 1-min walking at 6 km/h).
15 Subjects completed 3 trials consisting of placebo capsules (administered immediately prior to SS and
immediately before HIT) and placebo mouth rinse at 4-min intervals during HIT (PLACEBO), placebo
capsules but 10% carbohydrate mouth rinse (CMR) at corresponding time-points or finally, caffeine capsules
(200 mg per dose) plus 10% carbohydrate mouth rinse (CAFF + CMR) at corresponding time-points. Heart
rate, capillary glucose, lactate, glycerol and NEFA were not different at exhaustion during HIT (P> 0.05).
20 However, HIT capacity was different (P< 0.05) between all pair-wise comparisons such that CAFF + CMR
(65 ± 26 min) was superior to CMR (52 ± 23 min) and PLACEBO (36 ± 22 min). We conclude that
carbohydrate mouth rinsing and caffeine ingestion improves exercise capacity undertaken in carbohydrate-
restricted states. Such nutritional strategies may be advantageous for those athletes who deliberately incorporate
elements of training in carbohydrate-restricted states (i.e. the train-low paradigm) into their overall training
25 programme in an attempt to strategically enhance mitochondrial adaptations of skeletal muscle.
Keywords:Train-low, HIT, fatigue, mouth rinse
Traditional nutritional approaches for endurance
30 training have typically promoted high carbohydrate
availability before, during and after training sessions
so as to fuel the energy requirements of high daily
training intensities and volumes (Burke, Hawley,
Wong, & Jeukendrup, 2011). However, during the
35 past decade, data from our laboratory and others
have demonstrated that deliberately training in con-
ditions of reduced carbohydrate availability can pro-
mote training-induced adaptations of human skeletal
muscle (Bartlett, Hawley, & Morton, 2015), as demon
40 strated by increased maximal mitochondrial enzyme
activities and mitochondrial content (Morton et al.,
2009;Yeo et al., 2008 AQ4
), increased rates of lipid oxida
tion (Hulston et al., 2010) and in some instances,
improved exercise capacity (Hansen et al., 2005).
Such data have led to the concept of training-
low, but competing-highwhereby selected training
sessions are completed in conditions of reduced
carbohydrate availability (so as to promote training
adaptation) but competition is supported with high
carbohydrate availability (Bartlett et al., 2015).
The augmented adaptive responses of skeletal
muscle observed with training-low strategies are
likely regulated by enhanced activation of key cell
Correspondence: J. Morton, Research Institute for Sport and Exercise Sciences, Liverpool John Moores University, Tom Reilly Building,
Byrom St. Campus, Liverpool, L3 3AF, UK. E-mail:
European Journal of Sport Science, 2015
Vol. 00, No. 00, 19,
© 2015 Taylor & Francis
signalling kinases (e.g. AMPK, p38MAPK), tran-
55 scription factors (e.g. p53, PPARδ) and trans
criptional co-activators (e.g. PGC-1α) such that
a co-ordinated up-regulation of both the nuclear
and mitochondrial genomes occur (Bartlett et al.,
2013; Cochran, Little, Tarnopolsky, & Gibala, 2010;
60 Psilander, Frank, Flockhart, & Sahlin, 2013; Yeo
et al., 2010). It is noteworthy, however, that an up-
regulation of the above cell signalling pathways
cannot be considered as proxy markers of improved
exercise performance given that actual changes in
65 performance (despite increases in mitochondrial en
zymes and alterations to substrate metabolism during
exercise) have not always been observed. None-
theless, the capacity of altered carbohydrate availab-
ility to enhance activation of the aforementioned
70 signalling pathways forms the theoretical basis for
incorporating periods of train-low into an athletes
overall training programme (Hawley & Morton,
2014). Despite the premise promoting train-low, its
practical application is limited by potential pertur
75 bations to immune function (Gleeson, Nieman, &
Pedersen, 2007), increased muscle protein break-
down (Howarth, Moreau, Phillips, & Gibala, 2009)
and of course, an inability to maintain the desired train
ing intensity and/or duration (Hulston et al., 2010;
80 Yeo et al., 2008AQ5 ). For this reason, it is therefore
essential that sessions of training-low are carefully in
tegrated into a periodised training programme whereby
sessions of deliberately training-high provide the plat
form for those training sessions where training
85 intensity is priority.
In those instances when training-low is the goal,
however, it is prudent to implement strategies that
attempt to maintain or indeed rescue the capacity to
perform the desired training workloads. One strategy
90 may be to target nutritional interventions to the
central nervous system so as to potentially restore
training capacity. In this regard, Lane, Bird, Burke,
and Hawley (2013b) demonstrated that carbohyd-
rate mouth-rinsing (a strategy known to activate
95 reward regions in the brain) improved cycling exer-
cise performance to a greater extent when fasted
as opposed to the fed state. Furthermore, the same
researchers also observed that caffeine ingestion can
partially restore power outputs during cycling based
100 training sessions undertaken in a low glycogen state
to that observed when in glycogen loaded conditions
(Lane et al., 2013a). Taken together, these data
suggest that the combination of both pre-exercise
caffeine ingestion and carbohydrate mouth-rinsing
105 during exercise may therefore have additive effects in
augmenting measures of training performance dur-
ing those sessions that are deliberately commenced
in conditions of reduced carbohydrate availability.
Such a strategy may also be particularly pertinent
110 for running exercise given that running is more
dependent on carbohydrate utilisation than when cyc
ling at the same relative exercise intensities (Arkinstall
et al., 2004 AQ6).
Accordingly, the aim of the present study was
to therefore test the hypothesis that carbohydrate
mouth rinsing, alone or in combination with caffeine
intake, augments high-intensity interval (HIT) run-
ning capacity undertaken in carbohydrate restricted
states. To achieve our model of carbohydrate restric-
tion, we utilised a sleep-low, train-lowdietary and
exercise protocol recently studied in our laboratory,
whereby subjects performed a morning training ses
sion after an overnight fast and having also com-
pleted a prolonged and exhaustive exercise protocol
in the evening prior (Bartlett et al., 2013).
Eight recreationally active males who regul AQ7arly
engaged in running exercise (35 times per week)
volunteered to participate in the study (mean ± SD:
age, 22 ± 2 years; body mass, 70.8 ± 8.1 kg; height,
1.78 ± 0.09 m, .
VO2max, 57 ± 5
). All
subjects gave written and informed consent after
details of the study procedures were fully explained.
No subject had a history of smoking or cardio-
vascular and metabolically related disease and none
were under any pharmacological treatment during
the course of the study. All subjects refrained from
exercise and consuming alcohol and common caf-
feine containing substances for 2448 h before each
trial. The study was approved by the Ethics Com-
mittee of Liverpool John Moores University.
Experimental design
In a randomised, repeated measures and double
blind design, subjects performed an exhaustive run-
ning exercise protocol in the evening prior to arriving
in the laboratory on the subsequent morning in a
fasted state where they then performed a steady-state
(45 min at 65% .
VO2max) running exercise protocol
followed by a HIT running protocol to exhaustion
(1-min bouts at 80% .
VO2max interspersed with 1-min
bouts walking at 6 km/h). Subjects ingested a stan
dardised caffeine dose (200 mg) or placebo (in cap
sule format) immediately prior to commencing the
steady-state exercise protocol and a further standar-
dised caffeine dose (200 mg) or placebo immediately
prior to commencing the HIT protocol. During
HIT, subjects also rinsed a 10% carbohydrate mouth
rinse or taste matched placebo (for 10-second
periods) at 4-min intervals during exercise. In this
way, each subject therefore completed three experi-
mental trials consisting of both placebo capsules and
2A. M. Kasper et al.
placebo mouth rinse (PLACEBO), placebo capsules
but carbohydrate mouth rinse (CMR) or caffeine
165 capsules plus carbohydrate mouth rinse (CAFF +
CMR). Our primary outcome variable was exercise
capacity during the HIT protocol. Heart rate, ratings
of perceived exertion and fingertip capillary blood
samples were also obtained at regular intervals during
170 the steady-state exercise protocol so as to assess for
physiological, metabolic and perceptual responses to
exercise. An overview of the experimental design is
shown in Figure 1.
Assessment of maximal oxygen uptake
175 At least 710 days prior to the first familiarisation
trial, subjects performed a continuous incremental
treadmill protocol run to volitional exhaustion on a
motorised treadmill (h/p/cosmos Pulsar, Nussdorf-
Traunstein, Germany) for the determination of max-
180 imal oxygen uptake ( .
VO2max). The test protocol
commenced with a 2 min stage at a treadmill speed
of 10 km
followed by 2 min stages at 12, 14, 16
and 18 km
. After completion of the 18 km
stage, the treadmill inclined by 2% every 2 min
185 thereafter until volitional exhaustion. Breath-by-breath
measurements were obtained throughout exercise
using a CPX Ultima series online gas analysis system
(Medgraphics, Minnesota, USA) and .
VO2max was
stated as being achieved by the following end point
190 criteria (1) heart rate within 10 b
of age
predicted maximum, (2) RER > 1.1 and (3) plateau
of oxygen consumption despite increasing workload.
The .
VO2max relationship with running speed was
used to determine the appropriate running speeds for
195 the experimental trials described below.
Carbohydrate restriction protocol
Subjects reported to the laboratory at approximately
1900 h to perform 90-min of HIT running (or to
exhaustion if this occurred first) where the aim was
to reduce muscle glycogen stores. Following a 5 min
self-selected warm-up, participants commenced run-
ning for 2 min bouts at a velocity corresponding
to 100% .
VO2max interspersed with 2 min recovery
periods at 60% .
VO2max. When subjects were unable
to complete 2 min work bouts at 100% .
VO2max, the
work-rest ratio was reduced to 1.5 min2 min and
finally, 1 min2 min. When participants were unable
to complete 1-min work bouts at 100% .
VO2max, the
running velocity was reduced to 90% .
VO2max and
the same pattern of work-rest ratio was completed as
described above. The glycogen depletion protocol
was performed for 90 min or until the point of
exhaustion, the latter defined as inability maintain
1-min work bouts at 70% .
The pattern of
exercise completed in subjects initial trial was
replicated for their remaining two experimental
trials. Subjects were also permitted to consume
water ad libitum during exercise with the pattern of
ingestion replicated for all trials. At 15-min after
completion of each trial, subjects ingested 25 g of
whey protein isolate (Myprotein®Inc, Northwich,
UK) mixed with 500 ml of water.
Steady-state (SS) exercise protocol and HIT exercise
capacity test
Subjects arrived in the laboratory at 0700 h on the
subsequent morning after an overnight fast of
approximately 10 h. Subjects were immediately pro
vided with an additional 25 g of whey protein isolate
(Myprotein®Inc, Northwich, UK) mixed with 500 ml
of water at 45 min prior to completing the SS
exercise protocol, the latter consisting of 45 min at
65% .
VO2max. Subjects also consumed 200 mg of
caffeine (Myprotein®Inc, Northwich, UK) or visu-
ally identical placebo capsules (Whey Protein Isolate,
Myprotein®Inc, Northwich, UK) immediately prior
to and immediately upon completion of the SS
Figure 1. Overview of the experimental design
Carbohydrate mouth rinse and caffeine improves HIT AQ13
exercise protocol. Given that peak plasma caffeine
typically occurs 45 min post-ingestion (Graham &
Spriet, 1995), we deliberately chose to administer
240 caffeine immediately prior to SS exercise so that
peak plasma caffeine levels would be observed im
mediately prior to commencing the HIT protocol.
Furthermore, this standardised dose of caffeine of
200 mg corresponds to approximately 3 mg/kg for
245 the body mass of our subjects and is therefore
commensurate with known doses that are ergogenic
(Spriet, 2014). Additionally, given that caffeine con
sumed during prolonged exercise is also ergogenic
(Cox et al., 2002) and on the basis of our exercise
250 capacity observed during familiarisation trials, we
also chose to administer a further 200 mg dose
immediately prior to the HIT protocol in an attempt
to further augment ergogenic effects. Measurements
of heart rate (Polar, S610i, Finland) and ratings of
255 perceived exertion (RPE, Borg, 1973) were also
obtained at 15-min intervals during SS exercise.
After completion of the SS protocol, subjects walked
for 2 min at 6 km/h and subsequently commenced a
HIT exercise capacity test consisting of 1-min bouts
260 at 80% .
VO2max interspersed with 1-min bouts walk-
ing at 6 km/h until volitional exhaustion. Subjects
rinsed 25 ml of a 10% CHO beverage or a taste
matched (orange) and visually identical placebo solution
(Robinsons Squash, Britvic Orange Soft Drinks
265 PLC, Hertfordshire, UK) with/without maltodextrin
(Myprotein®Inc, Northwich, UK), respectively, for
10-second periods every 4-min during exercise
before expectorating. Capillary blood samples were
also collected at 15-min intervals during the SS
270 protocol and at the point of exhaustion during the
HIT capacity test. Water ingestion was permitted
ad libitum during both exercise protocols with the
pattern of ingestion replicated across all experi-
mental trials. Immediately after completion of the
275 third main experimental trial, each subject was asked
to identify the sequence of treatments they had
received. Only one subject from the eight studied
was able to correctly identify the sequence of their
treatments administered.
280 Familiarisation
All eight subjects completed the full experimental
protocol described above whilst adhering to the
PLACEBO conditions at least 57 days prior to
commencing their first experimental trial, thereby
285 serving as a familiarisation trial (FAM). Upon comp
letion of all three experimental trials, we compared
each subjects exercise capacity during the FAM trial
and the PLACEBO trial of the main experimental
trials and observed no significant difference between
290 trials, as evidenced by students-t-test for paired
samples (FAM = 33 ± 15, PLACEBO = 36 ± 22,
P= 0.67).
Blood analyses
Blood glucose and lactate concentrations were
obtained via finger prick capillary sampling using a
1.8 mm safety lancet (Sarstedt, Aktiengesellschaft &
Co., Sweden) after sterilisation using a pre-injection
medical swab (Medlock Medical Ltd., Oldham).
Five µl of whole blood was immediately analysed for
glucose and lactate concentration using an auto-
mated glucose analyser (HemoCue Glucose 201
Analyser, Ängelholm, Sweden) and lactate analyser
(Lactate Pro, Arkray, Shiga, Japan), respectively.
Additionally, approximately 200 µl of capillary blood
was collected in EDTA tubes, centrifuged at 1500 g
for 10 min at 4°C and plasma was stored at 80°C
until later analysis. Plasma glycerol and NEFA were
determined using commercially available kits (Ran-
dox, Daytona, UK).
Statistical analyses
Data were analysed by one-way and/or two-way
within subject General Linear Models (GLMs) with
repeated measures (version 18 for Windows, SPSS
Inc, Chicago, IL, USA). Prior to analysis, all data
were analysed for normal distribution using the
Shapiro-Wilks test. Differences in exercise related
variables (i.e. physiological, perceptual and metabolic
variables) were analysed using a two-way repeated
measures GLM where the within factors were time (i.
e. exercise) and condition (i.e. PLACEBO v CMR v
CAFF + CMR). Differences in exercise capacity (i.e.
time to exhaustion) between conditions were analysed
using a one-way repeated measures GLM. Where
there was a significant difference, a paired t-test using
Bonferonni corrections for multiple comparisons
was employed for post hoc analysis. All values are
expressed as means and SD, with the statistical level of
significance established at P< 0.05. In relation to our
primary outcome variable of exercise capacity, we also
report uncertainty of outcomes as 95% confidence
intervals (95% CI) and make probabilistic magnitude
based-inferences about the true (large sample) values
of outcomes by qualifying the likelihood that the true
effect represents a substantial change, according to
Batterham and Hopkins (2006).
Physiological and perceptual responses during SS exercise
and HIT capacity test
Subjectsheart rate and RPE during the SS and HIT
protocols are displayed in Table I. Both heart rate
4A. M. Kasper et al.
and RPE increased during exercise (both P< 0.01)
though neither variable was different between trials
(P= 0.42 and 0.94, respectively). Subjectsrunning
velocity corresponding to 80 and 65% .
VO2max was
345 14.2 ± 1.7 and 11.6 ± 0.3 km.h
, respectively.
Metabolic responses during SS exercise and HIT
capacity test
Blood glucose, blood lactate, plasma glycerol and
plasma NEFA are displayed in Table II. Glucose,
350 lactate, glycerol and NEFA all displayed significant
changes during exercise (all P< 0.01) though there
were no significant differences between trials (P=
0.41, 0.24, 0.18 and 0.56, respectively). Specifically,
glucose significantly decreased from pre-exercise
355 following completion of the SS protocol (P= 0.04)
and at the point of exhaustion during the HIT pro
tocol (P< 0.01). In contrast, changes in blood lactate
were only significant at the point of exhaustion upon
completion of the HIT capacity test (P< 0.01).
Plasma glycerol and NEFA showed progressive in
creases during exercise such that each time-point
was significantly different from the preceding time-
point, after the point at which significance from pre-
exercise values were first detected (all P< 0.05).
Exercise capacity during HIT test
Exercise capacity during the HIT test is displayed in
Figure 2a,b AQ9where both group means and individual
responses are shown, respectively. There was a
significant main effect between trials (P< 0.01)
where both CMR (52 ± 23 min; P= 0.06) and
CAFF + CMR (65 ± 26 min; P< 0.01) were
different from PLACEBO (36 ± 22 min). Seven of
the eight subjects ran longer in both the CMR (95%
CI for differences = 1.6 to +33 min, possibly
beneficial) and CAFF + CMR conditions (95% CI
for differences = +10 to +46 min, beneficial) versus
the PLACEBO trial. Furthermore, all eight subjects
ran longer in the CAFF + CMR trial (95% CI for
differences = +8 to +17 min, beneficial) compared
with the CMR only trial (P< 0.01).
Confirming our hypothesis, we provide novel data by
demonstrating that carbohydrate mouth rinsing im
proves HIT running capacity undertaken in conditions
of carbohydrate restriction when compared with
rinsing a placebo solution. We further demonstrate
that carbohydrate mouth rinsing with co-ingestion of
caffeine before and during exercise augments exer-
cise capacity compared to carbohydrate mouth rinse
Table I. Heart rate and RPE during the SS exercise protocol and
at exhaustion following the HIT capacity test in the PLACEBO,
CMR and CAFF + CMR experimental trials
Time (min)
15 30 45 Exhaustion
Heart rate (b.min
PLACEBO 141 ± 16 149 ± 20 151 ± 23* 159 ± 11*
CMR 144 ± 16 153 ± 15 153 ± 14* 166 ± 9*
CAFF + CMR 138 ± 21 148 ± 21 155 ± 16* 166 ± 12*
PLACEBO 12 ± 3 14 ± 2 14 ± 3* 19 ± 1*
CMR 12 ± 2 14 ± 2 14 ± 2* 19 ± 1*
CAFF + CMR 12 ± 1 13 ± 1 14 ± 1* 19 ± 1*
*denotes significant difference from 15, P< 0.05.
Table II. Blood glucose, blood lactate, plasma glycerol and plasma NEFA during the SS exercise protocol and at exhaustion following the
HIT capacity test in the PLACEBO, CMR and CAFF + CMR experimental trials
Time (min)
Pre AQ8
15 30 45 Exhaustion
Glucose (mmol.L1)
PLACEBO 4.5 ± 0.7 3.9 ± 0.7 4.0 ± 0.7 3.7 ± 0.7 3.6 ± 0.6*
CMR 4.4 ± 0.5 4.2 ± 0.5 4.2 ± 0.3 3.9 ± 0.4 3.7 ± 0.6*
CAFF + CMR 4.5 ± 0.4 4.1 ± 0.3 4.3 ± 0.2 4.3 ± 0.3 3.7 ± 0.5*
Lactate (mmol.L1)
PLACEBO 0.9 ± 0.2 1.0 ± 0.3 1.1 ± 0.3 1.3 ± 0.4 1.8 ± 0.7*
CMR 1.0 ± 0.2 1.0 ± 0.2 1.1 ± 0.3 1.1 ± 0.2 1.7 ± 0.5*
CAFF + CMR 1.0 ± 0.3 1.1 ± 0.3 1.2 ± 0.4 1.2 ± 0.4 2.4 ± 0.9*
Glycerol (μmol.L1)
PLACEBO 58 ± 51 173 ± 52* 309 ± 102* 351 ± 87* 444 ± 127*
CMR 46 ± 33 181 ± 102* 288 ± 141* 288 ± 77* 456 ± 116*
CAFF + CMR 75 ± 81 216 ± 70* 360 ± 109* 337 ± 96* 541 ± 171*
NEFA (mmol.L1)
PLACEBO 0.81 ± 0.31 1.00 ± 0.28 1.48 ± 0.41* 1.98 ± 0.38* 2.42 ± 0.48*
CMR 0.80 ± 0.25 1.14 ± 0.47 1.32 ± 0.53* 1.49 ± 0.32* 2.43 ± 0.53*
CAFF + CMR 0.80 ± 0.23 1.00 ± 0.35 1.63 ± 0.38* 1.67 ± 0.57* 2.69 ± 0.91*
*denotes significant difference from pre-exercise, P< 0.05.
Carbohydrate mouth rinse and caffeine improves HIT AQ15
390 per se. Given that the capacity to perform HIT
exercise was enhanced with this feeding protocol, we
therefore consider our data to have obvious practical
implications for those athletes who deliberately train in
carbohydrate restricted states in an attempt to stra-
395 tegically enhance mitochondrial related adaptations.
To achieve our model of carbohydrate restriction,
we employed a sleep-low, train-lowdietary and
exercise protocol recently studied in our laboratory,
whereby subjects perform a morning training session
400 after refraining from carbohydrate intake and having
also completed a glycogen depletion training proto-
col in the evening prior (Bartlett et al., 2013).
Although we did not directly quantify muscle glyco-
gen levels, our observation of capillary metabolite
405 data (e.g. glucose, lactate, NEFA and glycerol) are
consistent with that previously observed in our
laboratory when exercising in conditions of severe
carbohydrate restriction (Bartlett et al., 2013; Taylor
et al., 2013). In an attempt to prevent excessive pro
410 tein breakdown and promote muscle protein
synthesis, we also fed 25 g of protein prior to sleep
(Res et al., 2012) and at 45 min prior to commen-
cing the SS exercise bout (Coffey et al., 2011). We
have recently reported that this approach is asso-
ciated with positive modulation of those molecular
pathways purported to regulate both mitochondrial
biogenesis (e.g. AMPK, p53 activation) and protein
synthesis (eEF2 activation) (Bartlett et al., 2013;
Taylor et al., 2013). As such, this protocol repre-
sents a model of exercising with reduced carbohyd-
rate but high protein availability and is a nutritional
approach to fuelling training sessions recently
reported to be adopted by elite endurance athletes
(Walsh, 2014).
Despite the theoretical rationale for adopting this
dietary approach to training, its practical application
is often limited by the inability to maintain the re
quired training intensity and/or duration. To this end,
we observed that rinsing a 10% carbohydrate solution
for 10-second periods at 4-min intervals during
exercise significantly improved HIT capacity when
compared with rinsing a placebo solution. These data
therefore extend a growing body of literature demon-
strating the carbohydrate mouth rinsing improves
endurance performance during both cycling (Carter,
Jeukendrup, & Jones, 2004a; Carter, Jeukendrup,
Mann, & Jones, 2004b) and running exercise (Rollo,
Cole, Miller, & Williams, 2010), an effect likely medi
ated via direct effects on the CNS (Chambers, Bridge,
& Jones, 2009). Indeed, using functional magnetic
resonance imaging, the latter authors observed that
oral taste receptors in the mouth appear receptive
to carbohydrate (independent of sweetness) that, in
turn, activates a multitude of brain regions including
the anterior cingulate cortex and ventral striatum
thereby inducing emotional, cognitive and behavi-
oural responses (Rolls, 2007). Importantly, this is also
the first report to demonstrate a positive effect of
carbohydrate mouth rinsing when simultaneously
exercising in both a glycogen reduced and overnight
fasted state as opposed to the latter per se. Indeed,
seven of our eight subjects displayed substantial
improvements in exercise capacity when compared
with placebo rinsing (95% CI for differences of 2
to +33 min), a magnitude of improvement which was
typically larger than when subjects commenced an
exercise capacity test in the fed state (Fares & Kayser,
2011). As such, these data appear consistent with
emerging data demonstrating that the ergogenic
effects of carbohydrate mouth rinsing are more
prominent when the duration of the pre-exercise
fasting period increases (Beelen et al., 2009 AQ10; Lane
et al., 2013a). Support for this hypothesis was pro
vided by Haase, Cerf-Ducastel, and Murphy (2009)
who reported that greater brain activity was observed
in the ventral striatum, amygdala and hypothalamus
when sucrose was ingested in conditions of hunger
Figure 2. (a) Exercise capacity during the HIT capacity test
(undertaken immediately after completion of the 45-min SS
exercise protocol) in the PLACEBO, CMR and CAFF + CMR
experimental trials. Data are expressed as groups means where +
denotes difference from PLACEBO (P= 0.06) and * denotes
signicant difference from both PLACEBO and CMR (P< 0.01).
(b) Individual subjects exercise capacity during the HIT capacity
test in the PLACEBO, CMR and CAFF + CMR experimental
6A. M. Kasper et al.
(i.e. after a 12 h fast) versus conditions of satiety (i.e.
the post-prandial state).
470 In an attempt to further augment HIT exercise
capacity, we also conducted an experimental trial in
which subjects performed the carbohydrate mouth
rinsing protocol but also consumed 200 mg of
caffeine immediately priorto SS and a further 200 mg
475 immediately prior to the HIT test. We deliber
ately chose to administer a standardised dose of
caffeine (i.e. 2 ×200 mg) based on feedback from
athletes that tend to adopt a standardised caffeine
feeding protocol (as based on the dose inherent
480 to commercially available products) as opposed to
prescribing to body mass. Nevertheless, in relation to
the body mass of the current subjects, this dose
corresponds to 56 mg/kg body mass and is therefore
consistent with the upper range of the dose that is
485 now well documented to be ergogenic to perform-
ance (Burke, Desbrow, & Spriet, 2013). Accord-
ingly, we observed that co-ingestion of caffeine
improved HIT capacity when compared with carbo-
hydrate mouth rinsing per se, an effect that was
490 apparent in all 8 subjects (95% CI for differences of
+8 to +17 min).
It should be noted, however, that the ergogenic
proprieties of caffeine observed here are likely to
have been observed with less aggressive forms of
495 caffeine supplementation. For example, although we
chose a 2448 h withdrawal period from habitual
caffeine intake prior to the main experimental trial,
caffeine has also been shown to enhance endurance
performance in the absence of a withdrawal period,
500 an effect that is evident in both moderate (240 ± 162
) and high (761 ± 12
) habitual
users (Irwin et al., 2011; Van Soeren & Graham,
1998). Furthermore, a much smaller absolute dose
of caffeine (3
) ingested 6090 min before
505 an acute exercise protocol undertaken in conditions
of both high (Irwin et al., 2011) and low carbohyd-
rate availability (Lane et al., 2013a) has also proven
ergogenic. When taken together, it is therefore
apparent that a dosing strategy prescribed without
510 prior withdrawal and according to body mass (and
not on the basis of the absolute caffeine dose present
in commercial products) may be a more practically
applicable protocol. This is especially relevant for
those athletes who are smaller in stature (e.g. <60 kg),
515 given that negative side effects may actually be
observed with the high absolute dose adopted here
(Graham & Spriet, 1995).
We also acknowledge that our data are limited in
that we did not also study caffeine only trial and
520 hence, our observed performance effects may be due
to the effects of caffeine per se as opposed to additive
effects when combined with carbohydrate mouth
rinsing. Nevertheless, we extend recent data from cycl
ing based training sessions commenced in glycogen
depleted states (Lane et al., 2013b) and demonstrate
that caffeine ingestion is also a highly practical inges-
tion to improve HIT capacity when running is the
exercise modality and exercise is also completed in
conditions of reduced carbohydrate availability. Given
that we observed no differences in plasma NEFA or
glycerol availability, the observed ergogenic effect is
likely to be due to the now well-documented effects of
caffeine on the CNS (Meeusen, 2014)asopposedto
alterations in substrate utilisation. Indeed, caffeine is
readily transported across the blood-brain barrier and
can act as an adenosine antagonist thereby opposing
the action of adenosine. As such, caffeine can increase
concentrations of important neurotransmitters such
as dopamine (Fredholm, 1995), the result of which
manifests itself as increased motivation (Maridakis,
Herring, & OConnor, 2009)andmotordrive(Davis
et al., 2003). Alternatively, our observed performance
effect may also be due, in part, to an additional mech
anism related to maintenance of muscle membrane
excitability (Mohr, Nielsen, & Bangsbo, 2011). For
example, the latter authors observed improved per-
formance on Yo-Yo Intermittent Recovery Test 2
following caffeine supplementation (using a 6 mg/kg
dose similar to that employed here) that was associated
with reduced muscle interstitial accumulation of pot-
assium (K
) during intense intermittent exercise. The
latter observation is consistent with the notion that
extra-cellular accumulation of potassium is a contrib-
uting cause of fatigue during very high-intensity exercise.
In summary, we provide novel data by demon-
strating that both pre-exercise caffeine ingestion and
carbohydrate mouth rinsing during exercise aug-
ments HIT running capacity in conditions of car
bohydrate restriction, when compared with either
mouth-rinseor placebo conditions. As such, we consider
our data to have practical applications for those ath
letes who deliberately incorporate periods of carbo-
hydrate restriction into their training programmes
in an attempt to strategically enhance mitochondrial
related adaptations of skeletal muscle. Future studies
should now test whether the improved physical
performance observed during acute training sessions
translates to improvements in training adaptations
and endurance performance when performed chro
nically as part of a periodised endurance training
Disclosure statement
No potential conflict of interest was reported by the
authors AQ11.
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Carbohydrate mouth rinse and caffeine improves HIT AQ19
... Ingesting CHO during a training session has been shown to have the strongest effect on high-intensity exercise capacity in a low-glycogen state (Hargreaves et al. 1984;O'Brien et al. 2013). Even a mouth rinse with a CHO solution and caffeine supplementation has been shown to enhance power output and performance when a demanding exercise bout is started with reduced muscle glycogen (Lane et al. 2013;Kasper et al. 2016). Such effects of CHO availability on HIIT performance could potentially be explained through the maintenance of gross efficiency (Cole et al. 2018), reduction of perceived effort (Lane et al. 2013), altered oxygen uptake kinetics (Carter et al. 2004;Krustrup et al. 2004), and changes in muscle deoxygenation. ...
... Descriptive statistics were used to define participant characteristics (mean ± SD). A priori sample size estimation using freely available study power calculator (G*Power, Version 3.1) indicated a sample size of eight participants was deemed sufficient to detect large effects in HIIT performance change given the statistical power (α = 0.05, β = 0.8) (Kasper et al. 2016). Two-way ANOVA (type of experimental drink vs time or exercise intensity) was used to determine differences between the conditions. ...
... The performance benefit of CHO intake during exercise with reduced glycogen availability would be explained through several mechanisms as follows: (1) providing energy substrate for ATP resynthesis when muscle and liver glycogen stores are low and allowing to maintain blood glucose levels (Coyle et al. 1986), (2) acting through central mechanisms; the performance-enhancing effect is reported after a mouth rinse with carbohydrate solution (Kasper et al. 2016) and caffeine (Lane et al. 2013), or even perception of CHO intake (Waterworth et al. 2020) and (3) potentially acting on other performance-related factors, such as work efficiency (Cole et al. 2018). ...
Full-text available
Muscle glycogen state and carbohydrate (CHO) supplementation before and during exercise may impact responses to high-intensity interval training (HIIT). This study determined cardiorespiratory, substrate metabolism, muscle oxygenation, and performance when completing HIIT with or without CHO supplementation in a muscle glycogen depleted state. On two occasions, in a cross-over design, eight male cyclists performed a glycogen depletion protocol prior to HIIT during which either a 6% CHO drink (60⁻¹) or placebo (%CHO, PLA) was consumed. HIIT consisted of 5 × 2 min at 80% peak power output (PPO), 3 × 10-min bouts of steady-state (SS) cycling (50, 55, 60% PPO), and a time-to-exhaustion (TTE) test. There was no difference in SS V˙O2\documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$${\dot{\text{V}}\text{O}}_{{2}}$$\end{document}, HR, substrate oxidation and gross efficiency (GE %) between CHO and PLA conditions. A faster rate of muscle reoxygenation (%. s⁻¹) existed in PLA after the 1st (Δ − 0.23 ± 0.22, d = 0.58, P < 0.05) and 3rd HIIT intervals (Δ − 0.34 ± 0.25, d = 1.02, P < 0.05). TTE was greater in CHO (7.1 ± 5.4 min) than PLA (2.5 ± 2.3 min, d = 0.98, P < 0.05). CHO consumption before and during exercise under reduced muscle glycogen conditions did not suppress fat oxidation, suggesting a strong regulatory role of muscle glycogen on substrate metabolism. However, CHO ingestion provided a performance benefit under intense exercise conditions commenced with reduced muscle glycogen. More research is needed to understand the significance of altered muscle oxygenation patterns during exercise.
... Several studies have evaluated the effects of various types of mouth rinsing solutions during exercise performance (Beaven et al., 2013;Kasper et al., 2015;Mundel and Jones, 2010). Mundel and Jones (2010) investigated if menthol solution mouth rinse would increase the endurance capacity in time to exhaustion (TTE) cycling exercise. ...
... Kizzi et al. (2016) revealed that caffeine mouth rinses increased peak power output during repeated cycling sprint bout when compared to CHO. Caffeine mouth rinse could enhance performance during high-interval running when compared to PLA (Kasper et al., 2015). Meanwhile, guarana mouth rinses improved cognitive functions and decreased subjective perception of effort during submaximal cycling exercise (Pomportes et al., 2017). ...
... Sinclair et al., (2014) concluded that the improvement in exercise performance when mouth rinsing a CHO solution for 10 s as compared to 5 s would suggest a dose-response relationship to the duration of mouth rinse. Improvement in exercise performance with 10 s duration of mouth rinse motivated several researchers to apply this regime in their studies (Chambers et al., 2009;Fraga et al., 2015;Kasper et al., Malaysian Journal of Movement, Health and Exercise | Volume 11 | Issue 2 | July-December 2022 2015; Lane et al., 2013). Although the finding reported by Sinclair et al. (2014) promotes the use of 10 s mouth rinse duration during 30 min cycling event, this may be impractical during the competition that demands a higher breathing rate. ...
... In these studies, the doses of caffeine administered ranged from 3 to 9 mg/kg. A total of three studies [34,44,47] provided absolute doses of caffeine in the form of caffeine powder, gum, and mouth strips with doses ranging from 200 to 300 mg. The general data of the experiments included in this systematic review are depicted in Table 2. ...
... In the 21 studies included in this systematic review [7,[23][24][25][26]30,34,35,[42][43][44][45][46][47][48][49][50][51][52][53][54], there was a total sample of 254 participants, including 220 men, 19 women and 15 participants with no information about gender. The participants were all runners, of which 167 were categorized as amateur and 87 were categorized as trained runners. ...
... In these studies, the doses of caffeine administered ranged from 3 to 9 mg/kg. A total of three studies [34,44,47] provided absolute doses of caffeine in the form of caffeine powder, gum, and mouth strips with doses ranging from 200 to 300 mg. The general data of the experiments included in this systematic review are depicted in Table 2. Figure 2 displays the categorization for each RoB 2 item for each included study. ...
Full-text available
Caffeine (1,3,7-trimethylxanthine) is one of the most widely consumed performance-enhancing substances in sport due to its well-established ergogenic effects. The use of caffeine is more common in aerobic-based sports due to the ample evidence endorsing the benefits of caffeine supplementation on endurance exercise. However, most of this evidence was established with cycling trials in the laboratory, while the effects of the acute intake of caffeine on endurance running performance have not been properly reviewed and meta-analyzed. The purpose of this study was to perform a systematic review and meta-analysis of the existing literature on the effects of caffeine intake on endurance running performance. A systematic review of published studies was performed in four different scientific databases (Medline, Scopus, Web of Science, and SportDiscus) up until 5 October 2022 (with no year restriction applied to the search strategy). The selected studies were crossover experimental trials in which the ingestion of caffeine was compared to a placebo situation in a single- or double-blind randomized manner. The effect of caffeine on endurance running was measured by time to exhaustion or time trials. We assessed the methodological quality of each study using Cochrane’s risk-of-bias (RoB 2) tool. A subsequent meta-analysis was performed using the random effects model to calculate the standardized mean difference (SMD) estimated by Hedges’ g and 95% confidence intervals (CI). Results: A total of 21 randomized controlled trials were included in the analysis, with caffeine doses ranging between 3 and 9 mg/kg. A total of 21 studies were included in the systematic review, with a total sample of 254 participants (220 men, 19 women and 15 participants with no information about gender; 167 were categorized as recreational and 87 were categorized as trained runners.). The overall methodological quality of studies was rated as unclear-to-low risk of bias. The meta-analysis revealed that the time to exhaustion in running tests was improved with caffeine (g = 0.392; 95% CI = 0.214 to 0.571; p < 0.001, magnitude = medium). Subgroup analysis revealed that caffeine was ergogenic for time to exhaustion trials in both recreational runners (g = 0.469; 95% CI = 0.185 to 0.754; p = 0.001, magnitude = medium) and trained runners (g = 0.344; 95% CI = 0.122 to 0.566; p = 0.002, magnitude = medium). The meta-analysis also showed that the time to complete endurance running time trials was reduced with caffeine in comparison to placebo (g = −0.101; 95% CI = −0.190 to −0.012, p = 0.026, magnitude = small). In summary, caffeine intake showed a meaningful ergogenic effect in increasing the time to exhaustion in running trials and improving performance in running time trials. Hence, caffeine may have utility as an ergogenic aid for endurance running events. More evidence is needed to establish the ergogenic effect of caffeine on endurance running in women or the best dose to maximize the ergogenic benefits of caffeine supplementation.
... to be ergogenic, but complement existing carbohydrate swilling literature of similar exercise durations [44][45][46]. ...
... This suggests that during extended self-paced exercise in the heat, fuel availability and associated oral sensing may be a more dominant signal than thermal perception when swills are applied at regular intervals throughout the exercise bout. These findings are contrary to previous research in shorter duration [22,40] and fixedpaced exercise [41][42][43] in the heat, where menthol administration has been shown to be ergogenic, but complement existing carbohydrate swilling literature of similar exercise durations [44][45][46]. ...
Full-text available
The current study compared mouth swills containing carbohydrate (CHO), menthol (MEN) or a combination (BOTH) on 40 km cycling time trial (TT) performance in the heat (32 • C, 40% humidity, 1000 W radiant load) and investigates associated physiological (rectal temperature (Trec), heart rate (HR)) and subjective measures (thermal comfort (TC), thermal sensation (TS), thirst, oral cooling (OC) and RPE (legs and lungs)). Eight recreationally trained male cyclists (32 ± 9 y; height: 180.9 ± 7.0 cm; weight: 76.3 ± 10.4 kg) completed familiarisation and three experimental trials, swilling either MEN, CHO or BOTH at 10 km intervals (5, 15, 25, 35 km). The 40 km TT performance did not differ significantly between conditions (F 2,14 = 0.343; p = 0.715; η 2 = 0.047), yet post-hoc testing indicated small differences between MEN and CHO (d = 0.225) and MEN and BOTH (d = 0.275). Subjective measures (TC, TS, RPE) were significantly affected by distance but showed no significant differences between solutions. Within-subject analysis found significant interactions between solution and location upon OC intensity (F 28,196 = 2.577; p < 0.001; η 2 = 0.269). While solutions containing MEN resulted in a greater sensation of OC, solutions containing CHO experienced small improvements in TT performance. Stimulation of central CHO pathways during self-paced cycling TT in the heat may be of more importance to performance than perceptual cooling interventions. However, no detrimental effects are seen when interventions are combined.
... Nonetheless, carbohydrate mouth rinse has been shown to attenuate reductions in 20-km cycle time trial performance when in a glycogen depleted state (Ataide-Silva et al., 2016), while Kasper et al. (2016) demonstrated a ~45% increase in the number of 1-minute high-intensity (80% VO2max) running repetitions completed to failure after glycogen-depleting exercise with carbohydrate mouth rinse. As such, carbohydrate availability may have a moderating effect on the ergogenic effect of carbohydrate mouth rinse. ...
... The number of repetitions was greater with CHO mouth rinse in squat exercises, but not in the bench press exercise. This is likely due to the enhanced efficacy of CHO mouth rinse to alleviate fatigue and improve performance when in a state of low-carbohydrate availability, as has been observed in previous studies (Ataide-Silva et al., 2016;Fares & Kayser, 2011;Kasper et al., 2016;Kizzi et al., 2016;Lane et al., 2013). Of interest, Bastos-Silva, Prestes & Geraldes (2019) observed enhanced fed-state performance with carbohydrate mouth rinse in upper-body, but not lower-body resistance exercise, contrasting the findings of the present study. ...
Ageing is associated with reductions in appetite and food intake leading to unintentional weight loss. Such weight loss, particularly through muscle mass reduction, is associated with muscle weakness and functional decline, which represent predictors of poor health outcomes and contribute to frailty in older adults. Exercise-induced anorexia is an established phenomenon in young adults; however appetite and energy intake (EI) responses to resistance exercise are unknown in older adults. Twenty healthy older adults (68 ± 5 years, BMI 26.2 ± 4.5 kg.m-2) undertook two 5-hour experimental trials. Participants rested for 30 minutes before being provided with a standardised breakfast (196 kcal, 75.2% carbohydrate, 8.9% protein and 15.9% fat). Participants then rested for 1-hour before completing: 1-hour resistance exercise bout followed by 2-hour of rest (RE) or, a control condition (CON) where participants rested for 3 hours, in a randomised crossover design. Appetite perceptions were measured throughout both trials and on cessation, an ad libitum meal was provided to assess EI. A repeated-mesures ANOVA revealed no significant condition x time interaction for subjective appetite (p = 0.153). However, area under the curve for appetite was significantly lower in the RE compared with CON (49 ± 8mm•hour-1 vs. 52 ± 9mm•hour-1, p = 0.007, d = 0.27). There was no difference in EI (RE = 681 ± 246 kcal; CON = 673 ± 235 kcal; p = 0.865), suggesting that resistance exercise does not affect EI 2 hours post-exercise in older adults despite a significant but modest reduction in appetite over a 5-h period. In conclusion, resistance exercise may be an appropriate means for optimising muscle mass adaptations without attenuating acute EI of older adults.
... This may explain the decline in training intensity seen in the 'train low' studies of Yeo et al. (2008) and Hulston et al. (2010). However, periodisation of 'train low' to solely lowintensity sessions (Jeukendrup, 2017), CHO mouth rinse (Kasper et al., 2016) and caffeine supplementation (Silva-Cavalcante et al., 2013) have been recommended to counteract this performance deficit. ...
... immunosuppression and disproportionate protein metabolism) (Gleeson et al., 2001;Howarth et al., 2010), and to ensure that central adaptations are not compromised (Impey et al., 2018). Lastly, athletes should also implement nutritional strategies during 'train low' by ingesting caffeine (Silva-Cavalcante et al., 2013) and/or utilising CHO mouth rinse (Kasper et al., 2016) to offset decreases in exercise intensity, consuming added protein to counteract heightened protein oxidation (Burke et al., 2011;Taylor et al., 2013) and supplementing with vitamin D and/or zinc to negate immunosuppression (Rondanelli et al., 2018). ...
Full-text available
Due to the importance of glycogen for energy production, research has traditionally recommended sufficient carbohydrate (CHO) availability to maximise exercise performance. However, recent evidence has suggested that undertaking some training sessions with low CHO availability may bring about greater physiological adaptations. This strategy has commonly been termed as 'train low'. Although desirable adaptations in gene expression related to mitochondrial biogenesis and the activity of enzymes related to aerobic metabolism have been observed, research is conflicted towards the ergogenic impact this technique has on exercise performance. Additionally, this strategy may produce maladaptations such as reduced training intensity, immunosuppression, protein oxidation and reduced pyruvate dehydrogenase (PDH) activity. Therefore, if athletes are to adopt this strategy, it is suggested that they periodise 'train low' to solely low-intensity sessions which won't be impaired by a drop in work rate, but otherwise maintaining sufficient daily CHO intake. Also, athletes could negate potential maladaptations by using caffeine and/or CHO mouth rinse to maintain exercise intensity, and increasing protein ingestion to counteract increased protein oxidation. Future research should directly compare the effect of 'train low' between use in all sessions and solely low-intensity sessions within one comprehensive study to better understand the mechanisms behind the apparent superiority of the latter strategy.
... To circumvent this, attempts have been made to rescue the reduction in training capacity by utilization of ingestion of ergogenic aids. In line with this, carbohydrate and caffeine mouth rinsing have been shown to improve high-intensity exercise performance when conducted under a carbohydraterestricted state [156]. Whether training adaptation can be enhanced with this approach has not been studied. ...
Full-text available
The importance of carbohydrate as a fuel source for exercise and athletic performance is well established. Equally well developed are dietary carbohydrate intake guidelines for endurance athletes seeking to optimize their performance. This narrative review provides a contemporary perspective on research into the role of, and application of, carbohydrate in the diet of endurance athletes. The review discusses how recommendations could become increasingly refined and what future research would further our understanding of how to optimize dietary carbohydrate intake to positively impact endurance performance. High carbohydrate availability for prolonged intense exercise and competition performance remains a priority. Recent advances have been made on the recommended type and quantity of carbohydrates to be ingested before, during and after intense exercise bouts. Whilst reducing carbohydrate availability around selected exercise bouts to augment metabolic adaptations to training is now widely recommended, a contemporary view of the so-called train-low approach based on the totality of the current evidence suggests limited utility for enhancing performance benefits from training. Nonetheless, such studies have focused importance on periodizing carbohydrate intake based on, among other factors, the goal and demand of training or competition. This calls for a much more personalized approach to carbohydrate recommendations that could be further supported through future research and technological innovation (e.g., continuous glucose monitoring). Despite more than a century of investigations into carbohydrate nutrition, exercise metabolism and endurance performance, there are numerous new important discoveries, both from an applied and mechanistic perspective, on the horizon.
... Descriptive statistics (mean ± SD) were used to define participants' characteristics. A-priori sample size estimation, using a freely available study power calculator (G*Power, Version 3.1), indicated a sample size of 8 participants was deemed sufficient to detect previously observed (Kasper et al., 2016) large effects (β = 0.8, α = 0.05) of carbohydrate-restriction on HIIT performance. Data were assessed for normal distribution using Shapiro-Wilk test and visually assessing QQ-plots. ...
Highlights: Acute manipulation of muscle glycogen availability using an exercise and dietary manipulation protocol did not affect subsequent high intensity running performance across a range of running distances.Reduced muscle glycogen resulted in a marked increase in fat oxidation in low glycogen condition but no changes in running economy or critical speed.Individual factors should be considered when prescribing high intensity sessions with restricted carbohydrate availability.
... Prior to higher intensity sessions, the athlete may decide to consume a relatively greater dose of caffeine (~3 mg/kg) to optimise performance in their "key" sessions, and mediate some of the general fatigue and soreness that may be accumulating [24,51]. Caffeine may also be utilised to augment other nutritional interventions, such as training with low carbohydrate availability [95,96]; here, caffeine may support performance when training a carbohydrate-depleted state [97,98]. ...
Caffeine is a well-established ergogenic aid, with its performance-enhancing effects demonstrated across a variety of sports and exercise types. As a result of caffeine's ergogenic properties, it is widely utilised by athletes at all levels around both competition and training. Caffeine exerts its performance benefits through a variety of mechanisms, each of which may be of increased importance at a given stage of training or competition. In addition, regular caffeine use may diminish the performance enhancing effects of a subsequent dose of caffeine. Recently, interest in the concept of nutritional periodization has grown; here we propose a framework for the periodization of caffeine through the sporting year, balancing its training and competition performance-enhancing effects, along with the need to mitigate any negative effects of habituation. Furthermore, the regular use of caffeine within training may support the development of positive beliefs towards caffeine by athletes—potentially serving to enhance future performance through placebo and expectancy mechanisms—as well as allowing for the optimisation of individual athlete caffeine strategies. Whilst future work is required to validate some of the suggestions made, the framework proposed here represents a starting point for athletes to maximise caffeine's performance benefits across the sporting year.
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No presente estudo, foram investigados através de uma revisão sistemática, os efeitos da utilização de cafeína sobre o indivíduo nas sessões de HIIT. A seleção de artigos foi realizada nas bases de dados Medline/PubMed, Science Direct, Scholar Google e Scielo, e encontraram-se 2301 estudos. Após aplicar os critérios de inclusão e exclusão foram considerados elegíveis apenas cinco artigos para a revisão sistemática. Entre esses estudos, o total de participantes foi de 80 indivíduos, sendo 24 mulheres e 56 homens, com idades entre 18 e 30 anos. Os protocolos utilizados consistiram em dois tipos: agudos e crônico, avaliando parâmetros antropométricos e/ou metabólicos. Nos experimentos que utilizaram uma abordagem crônica, foram encontrados resultados favoráveis à perda de gordura corporal e melhora de índices metabólicos. Por outro lado, os estudos com abordagem aguda observaram melhora na performance através do retardo da fadiga muscular, embora, sem diferença significativa de massa corporal ao final da sessão. Ainda, um dos estudos com intervenção crônica não observou diferença significativa entre os grupos. A cafeína associada ao HIIT é capaz de trazer benefícios ao indivíduo, independentemente de seu condicionamento físico. Entretanto, ainda é preciso mais estudos para um melhor entendimento da extensão e condição desses benefícios.
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Caffeine is a popular work-enhancing supplement that has been actively researched since the 1970s. The majority of research has examined the effects of moderate to high caffeine doses (5-13 mg/kg body mass) on exercise and sport. These caffeine doses have profound effects on the responses to exercise at the whole-body level and are associated with variable results and some undesirable side effects. Low doses of caffeine (<3 mg/kg body mass, ~200 mg) are also ergogenic in some exercise and sport situations, although this has been less well studied. Lower caffeine doses (1) do not alter the peripheral whole-body responses to exercise; (2) improve vigilance, alertness, and mood and cognitive processes during and after exercise; and (3) are associated with few, if any, side effects. Therefore, the ergogenic effect of low caffeine doses appears to result from alterations in the central nervous system. However, several aspects of consuming low doses of caffeine remain unresolved and suffer from a paucity of research, including the potential effects on high-intensity sprint and burst activities. The responses to low doses of caffeine are also variable and athletes need to determine whether the ingestion of ~200 mg of caffeine before and/or during training and competitions is ergogenic on an individual basis.
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Abstract Traditional nutritional approaches to endurance training have typically promoted high carbohydrate (CHO) availability before, during and after training sessions to ensure adequate muscle substrate to meet the demands of high daily training intensities and volumes. However, during the past decade, data from our laboratories and others have demonstrated that deliberately training in conditions of reduced CHO availability can promote training-induced adaptations of human skeletal muscle (i.e. increased maximal mitochondrial enzyme activities and/or mitochondrial content, increased rates of lipid oxidation and, in some instances, improved exercise capacity). Such data have led to the concept of 'training low, but competing high' whereby selected training sessions are completed in conditions of reduced CHO availability (so as to promote training adaptation), but CHO reserves are restored immediately prior to an important competition. The augmented training response observed with training-low strategies is likely regulated by enhanced activation of key cell signalling kinases (e.g. AMPK, p38MAPK), transcription factors (e.g. p53, PPARδ) and transcriptional co-activators (e.g. PGC-1α), such that a co-ordinated up-regulation of both the nuclear and mitochondrial genomes occurs. Although the optimal practical strategies to train low are not currently known, consuming additional caffeine, protein, and practising CHO mouth-rinsing before and/or during training may help to rescue the reduced training intensities that typically occur when 'training low', in addition to preventing protein breakdown and maintaining optimal immune function. Finally, athletes should practise 'train-low' workouts in conjunction with sessions undertaken with normal or high CHO availability so that their capacity to oxidise CHO is not blunted on race day.
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Accumulating evidence suggests that diet and lifestyle can play an important role in delaying the onset or halting the progression of age-related health disorders and can improve cognitive function. Exercise has been promoted as a possible prevention for neurodegenerative diseases. Exercise will have a positive influence on cognition and it increases the brain-derived neurotrophic factor, an essential neurotrophin. Several dietary components have been identified as having effects on cognitive abilities. In particular, polyphenols have been reported to exert their neuroprotective actions through the potential to protect neurons against injury induced by neurotoxins, an ability to suppress neuroinflammation, and the potential to promote memory, learning, and cognitive function. Dietary factors can affect multiple brain processes by regulating neurotransmitter pathways, synaptic transmission, membrane fluidity, and signal-transduction pathways. Flavonols are part of the flavonoid family that is found in various fruits, cocoa, wine, tea and beans. Although the antioxidant effects of flavonols are well established in vitro, there is general agreement that flavonols have more complex actions in vivo. Several cross-sectional and longitudinal studies have shown that a higher intake of flavonoids from food may be associated with a better cognitive evolution. Whether this reflects a causal association remains to be elucidated. Several studies have tried to 'manipulate' the brain in order to postpone central fatigue. Most studies have clearly shown that in normal environmental circumstances these interventions are not easy to perform. There is accumulating evidence that rinsing the mouth with a carbohydrate solution will improve endurance performance. There is a need for additional well controlled studies to explore the possible impact of diet and nutrition on brain functioning.
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It is presently unclear whether the reported ergogenic effect of a carbohydrate (CHO) mouth rinse on cycling time-trial performance is affected by the acute nutritional status of an individual. Hence, the aim of this study was to investigate the effect of a CHO mouth rinse on a 60-min simulated cycling time-trial performance commenced in a fed or fasted state. Twelve competitive male cyclists each completed 4 experimental trials using a double-blinded Latin square design. Two trials were commenced 2 h after a meal that contained 2.5 g·kg(-1) body mass of CHO (FED) and 2 after an overnight fast (FST). Prior to and after every 12.5% of total time during a performance ride, either a 10% maltodextrin (CHO) or a taste-matched placebo (PLB) solution was mouth rinsed for 10 s then immediately expectorated. There were significant main effects for both pre-ride nutritional status (FED vs. FST; p < 0.01) and CHO mouth rinse (CHO vs. PLB; p < 0.01) on power output with an interaction evident between the interventions (p < 0.05). The CHO mouth rinse improved mean power to a greater extent after an overnight fast (282 vs. 273 W, 3.4%; p < 0.01) compared with a fed state (286 vs. 281 W, 1.8%; p < 0.05). We concluded that a CHO mouth rinse improved performance to a greater extent in a fasted compared with a fed state; however, optimal performance was achieved in a fed state with the addition of a CHO mouth rinse.
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The mechanisms that regulate the enhanced skeletal muscle oxidative capacity observed when training with reduced carbohydrate (CHO) availability are currently unknown. The aim of the present study was to test the hypothesis that reduced CHO availability enhances p53 signalling and expression of genes associated with regulation of mitochondrial biogenesis and substrate utilisation in human skeletal muscle. In a repeated measures design, muscle biopsies (vastus lateralis) were obtained from eight active males before and after performing an acute bout of high-intensity interval running with either high (HIGH) or low CHO availability (LOW). Resting muscle glycogen (HIGH, 467 ± 19; LOW, 103 ± 9 dw) was greater in HIGH compared with LOW (P<0.05). Phosphorylation (P-) of ACC(Ser79) (HIGH, 1.4 ± 0.4; LOW, 2.9 ± 0.9) and p53(Ser15) (HIGH, 0.9 ± 0.4; LOW, 2.6 ± 0.8) was higher in LOW immediately post- and 3 h post-exercise, respectively (P<0.05). Before and 3 h post-exercise, mRNA content of PDK4, Tfam, COXIV and PGC-1α were greater in LOW compared with HIGH (P<0.05) whereas CPT1 showed trend towards significance (P=0.09). However, only PGC-1α expression was increased by exercise (P<0.05) where 3-fold increases occurred independent of CHO availability. We conclude that the exercise-induced increase in p53 phosphorylation is enhanced in conditions of reduced CHO availability which may be related to upstream signalling through AMPK. Given the emergence of p53 as a molecular regulator of mitochondrial biogenesis, such nutritional modulation of contraction-induced p53 activation has implications for both athletic and clinical populations.
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The aim of the present study was to test the hypothesis that consuming protein does not attenuate AMPK signalling when exercise is commenced in a glycogen-depleted state. After performing a glycogen-depleting protocol the evening before, the subsequent morning ten active men performed 45 min steady-state cycling at 50 % of peak power output (PPO) followed by an exercise capacity test (1-min intervals at 80 % PPO interspersed with 1-min periods at 40 % PPO). In a repeated measures design, subjects consumed 20 g of a casein hydrolysate solution (PRO) 45 min before exercise, 10 g during and a further 20 g immediately post-exercise, or an equivalent volume of a non-calorie taste matched placebo (PLA). Resting (PRO = 134 ± 29; PLA = 136 ± 28 mmol kg(-1)) and post-exercise muscle glycogen (PRO = 43 ± 16; PLA = 47 ± 18 mmol kg(-1)) was not different (P > 0.05) between trials nor was exercise capacity (PRO = 26 ± 9; PLA = 25 ± 10 min, P > 0.05). Phosphorylation of AMPK(Thr172) increased threefold immediately post-exercise (P < 0.05) and PGC1-mRNA increased sixfold at 3 h post-exercise (P < 0.05), though there were no differences between conditions (P > 0.05). In contrast, there was a trend (P = 0.08) for a divergent response in eEF2(Thr56) phosphorylation such that 1.5 fold increases post- and 3 h post-exercise in PLA were blunted with PRO, thus indicative of greater eEF2 activation. We conclude that athletes who deliberately incorporate training phases with reduced muscle glycogen into their training programmes may consume protein before, during and after exercise without negating signalling through the AMPK cascade.
Mitochondrial biogenesis in skeletal muscle results from the cumulative effect of transient increases in mRNA transcripts encoding mitochondrial proteins in response to repeated exercise sessions. This process requires the coordinated expression of both nuclear and mitochondrial (mt) DNA genomes and is regulated, for the most part, by the peroxisome proliferator-activated receptor γ coactivator 1α. Several other exercise-inducible proteins also play important roles in promoting an endurance phenotype, including AMP-activated protein kinase, p38 mitogen-activated protein kinase and tumour suppressor protein p53. Commencing endurance-based exercise with low muscle glycogen availability results in greater activation of many of these signalling proteins compared with when the same exercise is undertaken with normal glycogen concentration, suggesting that nutrient availability is a potent signal that can modulate the acute cellular responses to a single bout of exercise. When exercise sessions are repeated in the face of low glycogen availability (i.e. chronic training), the phenotypic adaptations resulting from such interventions are also augmented.
Purpose: Commencing selected workouts with low muscle glycogen availability augments several markers of training adaptation compared with undertaking the same sessions with normal glycogen content. However, low glycogen availability reduces the capacity to perform high-intensity (>85% of peak aerobic power (VO2 peak)) endurance exercise. We determined whether a low dose of caffeine could partially rescue the reduction in maximal self-selected power output observed when individuals commenced high-intensity interval training with low (LOW) compared with normal (NORM) glycogen availability. Methods: Twelve endurance-trained cyclists/triathletes performed four experimental trials using a double-blind Latin square design. Muscle glycogen content was manipulated via exercise-diet interventions so that two experimental trials were commenced with LOW and two with NORM muscle glycogen availability. Sixty minutes before an experimental trial, subjects ingested a capsule containing anhydrous caffeine (CAFF, 3 mg · kg(-1) body mass) or placebo (PLBO). Instantaneous power output was measured throughout high-intensity interval training (8 × 5-min bouts at maximum self-selected intensity with 1-min recovery). Results: There were significant main effects for both preexercise glycogen content and caffeine ingestion on power output. LOW reduced power output by approximately 8% compared with NORM (P < 0.01), whereas caffeine increased power output by 2.8% and 3.5% for NORM and LOW, respectively, (P < 0.01). Conclusion: We conclude that caffeine enhanced power output independently of muscle glycogen concentration but could not fully restore power output to levels commensurate with that when subjects commenced exercise with normal glycogen availability. However, the reported increase in power output does provide a likely performance benefit and may provide a means to further enhance the already augmented training response observed when selected sessions are commenced with reduced muscle glycogen availability.