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ORIGINAL ARTICLEAQ2
Carbohydrate mouth rinse and caffeine improves high-intensity interval
running capacity when carbohydrate restricted
AQ1
5ANDREAS M. KASPER, SCOTT COCKING, MOLLY COCKAYNE, MARCUS BARNARD,
JAKE TENCH, LIAM PARKER, JOHN MCANDREW, CARL LANGAN-EVANS,
GRAEME L. CLOSE, & JAMES P. MORTON
AQ3
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% .
VO2max)
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
Introduction
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).
45
Such data have led to the concept of ‘training-
low, but competing-high’whereby selected training
sessions are completed in conditions of reduced
carbohydrate availability (so as to promote training
adaptation) but competition is supported with high
50
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: J.P.Morton@ljmu.ac.uk
European Journal of Sport Science, 2015
Vol. 00, No. 00, 1–9, http://dx.doi.org/10.1080/17461391.2015.1041063
© 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 athlete’s
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
115
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-
120
tion, we utilised a ‘sleep-low, train-low’dietary 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
125
in the evening prior (Bartlett et al., 2013).
Methods
Subjects
Eight recreationally active males who regul AQ7arly
engaged in running exercise (3–5 times per week)
130
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 ml.kg
−1
.min
−1
). All
subjects gave written and informed consent after
details of the study procedures were fully explained.
135
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-
140
feine containing substances for 24–48 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
145
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
150
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
155
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
160
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 7–10 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
.
h
−1
followed by 2 min stages at 12, 14, 16
and 18 km
.
h
−1
. After completion of the 18 km
.
h
−1
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
.
min
−1
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
200
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
205
to complete 2 min work bouts at 100% .
VO2max, the
work-rest ratio was reduced to 1.5 min−2 min and
finally, 1 min−2 min. When participants were unable
to complete 1-min work bouts at 100% .
VO2max, the
running velocity was reduced to 90% .
VO2max and
210
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% .
VO2max
.
The pattern of
215
exercise completed in subject’s 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
220
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
225
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
230
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,
235
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 5–7 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 subject’s 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
295
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
300
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
305
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).
310
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
315
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.
320
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
325
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
330
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
335
Batterham and Hopkins (2006).
Results
Physiological and perceptual responses during SS exercise
and HIT capacity test
Subjects’heart rate and RPE during the SS and HIT
340
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). Subjects’running
velocity corresponding to 80 and 65% .
VO2max was
345 14.2 ± 1.7 and 11.6 ± 0.3 km.h
−1
, 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).
360
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).
365
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)
370
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
375
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
380
with the CMR only trial (P< 0.01).
Discussion
Confirming our hypothesis, we provide novel data by
demonstrating that carbohydrate mouth rinsing im‐
proves HIT running capacity undertaken in conditions
385
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
−1
)
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*
RPE (AU)
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.L−1)
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.L−1)
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.L−1)
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.L−1)
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-low’dietary 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-
415
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-
420
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).
425
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
430
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
435
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,
440
& 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
445
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
450
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
455
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
460
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)
465
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
significant difference from both PLACEBO and CMR (P< 0.01).
(b) Individual subject’s exercise capacity during the HIT capacity
test in the PLACEBO, CMR and CAFF + CMR experimental
trials.
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 5–6 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 24–48 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
mg.day
−1
) and high (761 ± 12 mg.day
−1
) habitual
users (Irwin et al., 2011; Van Soeren & Graham,
1998). Furthermore, a much smaller absolute dose
of caffeine (3 mg.kg
−1
) ingested 60–90 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
525
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
530
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
535
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
540
manifests itself as increased motivation (Maridakis,
Herring, & O’Connor, 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
545
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
550
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.
555
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
560
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
565
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‐
570
nically as part of a periodised endurance training
programme.
Disclosure statement
No potential conflict of interest was reported by the
authors AQ11.
575
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Carbohydrate mouth rinse and caffeine improves HIT AQ19
