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Skeletal muscle adaptation: Training twice every second day vs. training once daily


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Low muscle glycogen content has been demonstrated to enhance transcription of a number of genes involved in training adaptation. These results made us speculate that training at a low muscle glycogen content would enhance training adaptation. We therefore performed a study in which seven healthy untrained men performed knee extensor exercise with one leg trained in a low-glycogen (Low) protocol and the other leg trained at a high-glycogen (High) protocol. Both legs were trained equally regarding workload and training amount. On day 1, both legs (Low and High) were trained for 1 h followed by 2 h of rest at a fasting state, after which one leg (Low) was trained for an additional 1 h. On day 2, only one leg (High) trained for 1 h. Days 1 and 2 were repeated for 10 wk. As an effect of training, the increase in maximal workload was identical for the two legs. However, time until exhaustion at 90% was markedly more increased in the Low leg compared with the High leg. Resting muscle glycogen and the activity of the mitochondrial enzyme 3-hydroxyacyl-CoA dehydrogenase increased with training, but only significantly so in Low, whereas citrate synthase activity increased in both Low and High. There was a more pronounced increase in citrate synthase activity when Low was compared with High. In conclusion, the present study suggests that training twice every second day may be superior to daily training.
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doi: 10.1152/japplphysiol.00163.2004
98:93-99, 2005. First published 10 September 2004;J Appl Physiol
Saltin and Bente Klarlund Pedersen
Anne K. Hansen, Christian P. Fischer, Peter Plomgaard, Jesper Løvind Andersen, Bengt
day vs. training once daily
Skeletal muscle adaptation: training twice every second
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Skeletal muscle adaptation: training twice every second day
vs. training once daily
Anne K. Hansen, Christian P. Fischer, Peter Plomgaard,
Jesper Løvind Andersen, Bengt Saltin, and Bente Klarlund Pedersen
Department of Infectious Diseases and The Copenhagen Muscle Research Centre,
Rigshospitalet, University of Copenhagen, Copenhagen, Denmark
Submitted 13 February 2004; accepted in final form 7 September 2004
Hansen, Anne K., Christian P. Fischer, Peter Plomgaard, Jes-
per Løvind Andersen, Bengt Saltin, and Bente Klarlund Ped-
ersen. Skeletal muscle adaptation: training twice every second day vs.
training once daily. J Appl Physiol 98: 93–99, 2005. First published
September 10, 2004; doi:10.1152/japplphysiol.00163.2004.—Low
muscle glycogen content has been demonstrated to enhance transcrip-
tion of a number of genes involved in training adaptation. These
results made us speculate that training at a low muscle glycogen
content would enhance training adaptation. We therefore performed a
study in which seven healthy untrained men performed knee extensor
exercise with one leg trained in a low-glycogen (Low) protocol and
the other leg trained at a high-glycogen (High) protocol. Both legs
were trained equally regarding workload and training amount. On day
1, both legs (Low and High) were trained for 1 h followed by2hof
rest at a fasting state, after which one leg (Low) was trained for an
additional 1 h. On day 2, only one leg (High) trained for 1 h. Days 1
and 2 were repeated for 10 wk. As an effect of training, the increase
in maximal workload was identical for the two legs. However, time
until exhaustion at 90% was markedly more increased in the Low leg
compared with the High leg. Resting muscle glycogen and the activity
of the mitochondrial enzyme 3-hydroxyacyl-CoA dehydrogenase in-
creased with training, but only significantly so in Low, whereas citrate
synthase activity increased in both Low and High. There was a more
pronounced increase in citrate synthase activity when Low was
compared with High. In conclusion, the present study suggests that
training twice every second day may be superior to daily training.
substrate availablity; 3-hydroxyacyl-CoA dehydrogenase; citrate syn-
area within exercise physiology for many years. When relating
to the effect on performance, e.g., running time in a marathon
race, it is clear that carbohydrate loading the days before to
rebuild muscle glycogen as well as carbohydrate intake during
the race enhance performance (28, 31, 37). In analogy, a
common belief is that carbohydrate intake during training at
high amounts will allow the athlete to train harder and longer
and thus achieve a superior training response. However, this
argument does not consider the unsolved longstanding question
of whether it is a lack or a surplus of a substrate that triggers
the training adaptation (14).
In endurance exercise, adaptation includes systemic changes
such as improved maximal oxygen uptake (V
2 max
). Adapta
tion also includes prolonged time until exhaustion at a given
workload, which is linked to maximal aerobic power but may
also be linked to local factors within the muscle (46). The
multitude of adaptations that occur with training that allow for
greater performance also includes an increased number of
capillaries (2, 3), an increased density of mitochondria with the
activity of enzymes such as 3-hydroxyacyl-CoA dehydroge-
nase (HAD) and citrate synthase (CS) being elevated, an
increased concentration of transport proteins, greater glycogen
concentration (24, 27, 30, 46), and a relative increase in the
occurrence of type IIA fibers at the expense of type IIX fibers
(2, 3). As a result, the ability to metabolize fat is enhanced (24).
When a more molecular view on training adaptation is taken,
it is obvious that adaptation is a consequence of accumulation
of specific proteins. The gene expression that allows for these
changes in protein concentration is pivotal to the training
adaptation. Recent studies have demonstrated that exercise
induces transcription of several genes (43). Furthermore, it has
been demonstrated that muscle glycogen is a determining
factor for the transcription of some genes. Exercising when
muscle glycogen concentration was low resulted in a greater
transcriptional activation of interleukin-6 (32), pyruvate dehy-
drogenase kinase 4 (23, 42), hexokinase (42), and heat shock
protein 72 (22) compared with when muscle glycogen concen-
tration was high or normal at the start of exercise. The role of
glycogen could be explained by the fact that several transcrip-
tion factors include glycogen-binding domains. When muscle
glycogen is low, these factors are released and become free to
associate with different targeting proteins (4, 18, 44, 48, 49).
Helge and Kiens (29) studied the role of substrate availabil-
ity on muscle enzyme activity and found that HAD increased
with training after adaptation to a fat-rich diet but not a
carbohydrate-rich diet. Transcriptional activities of HAD and
CS are only markedly influenced by acute muscle contractions
(43). However, it is possible that the accumulation of mRNA
for these genes peaks late in the recovery from the exercise and
that a low muscle glycogen level may enhance the transcription
of these genes.
On this molecular background, we have formulated the
overall hypothesis that training on a low muscle glycogen level
will improve training adaptation (21). In the present study, we
specifically tested the hypothesis that training at a low muscle
glycogen content would enhance levels of HAD and CS.
Moreover, performance defined as time until exhaustion at a
given power output would be more pronounced by training
twice every second day compared with training once daily.
Address for reprint requests and other correspondence: B. K. Pedersen,
Dept. of Infectious Diseases M7641, and The Copenhagen Muscle Research
Centre, Rigshospitalet, Blegdamsvej 9, DK-2100 Copenhagen, Denmark
The costs of publication of this article were defrayed in part by the payment
of page charges. The article must therefore be hereby marked advertisement
in accordance with 18 U.S.C. Section 1734 solely to indicate this fact.
J Appl Physiol 98: 93–99, 2005.
First published September 10, 2004; doi:10.1152/japplphysiol.00163.2004.
8750-7587/05 $8.00 Copyright
2005 the American Physiological Societyhttp://www. 93
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We therefore designed a protocol of two different training
regimens in which the cycling of muscle glycogen differed.
Critical would be to have direct comparison between legs on
the same individual, where one leg has trained markedly more
with low glycogen than the other. This can be accomplished by
having one leg train twice every second day, whereas the other
only trains once daily.
When a subject exercises, muscle glycogen declines and is
slowly restored over the following 24 h if carbohydrate intake
is normal (14, 26, 34). Therefore, when two exercise sessions
of1hisseparated by 2 h, the second bout of exercise is
undertaken with low muscle glycogen at its start, whereas
muscle glycogen is restored before each exercise bout when the
exercise is separated by 24 h.
Seven healthy untrained young men were recruited with a mean age
of 26 yr (range 24 –29 yr), a mean weight of 86.7 kg (range 53–129
kg), mean height of 180.1 cm (range 171–189 cm). The subjects were
exposed to a highly demanding and intensive training program lasting
10 wk with one- and/or two-legged knee extensor exercise (Fig. 1).
The study was opposed by the local Ethical Committee of Copenha-
gen and Frederiksburg Communities and was performed in accor-
dance with the Declaration of Helsinki. The two legs were trained
after different schedules. By randomization, all subjects trained one
leg twice every second day [low-glycogen training (Low)], whereas
the other leg was trained once daily [high-glycogen training (High)].
Each bout of exercise lasted 1 h. On day 1, both legs trained
simultaneously for1hat75%ofmaximal power output (P
followed by2hofrecovery. Thereafter, the Low leg trained for 1 h
at 75% of P
.On day 2, the High leg trained alone for1hat75%
of P
. This 2-day training cycle was repeated for 10 wk. Every
week, subjects trained 5 days and then rested 2 days. The training
sessions were performed in the morning after an overnight fast, the
first exercise bout being undertaken between 6:00 and 9:00 AM. The
subjects were fasting until the training session was finished. Water
intake was ad libitum. The workload of the 10-wk training was
initially 75% of P
before the training started. Workload was
increased individually by 5–10% depending on the progress of each
individual. The workload was identical for the two legs. Before and
after the 10 wk of training, a P
test was obtained for each leg
separately using the same cycle ergometer-knee extensor exercise
apparatus (Monark, Varberg, Sweden). Thereafter, a 90% P
durance test was performed for each leg.
In the first trial, the subjects performed a V
2 max
test on each leg
to determine the individual knee P
. Both legs were tested on the
same day with at least 30 min of rest in between. The test began with
a 10-min warm-up at 20 W followed by a stepwise increase of 10 W
in workload every 2 min. Subjects worked until exhaustion.
Diet. The subjects consumed a mixed Western diet throughout the
study (16 MJ per day, 70% carbohydrate, 15% protein, 15% fat).
Subjects were asked to adhere to the diet and to refrain from strenuous
exercise other than that included in the training protocol.
Muscle biopsies. Muscle biopsy samples were obtained before and
after 10 wk of training from the vastus lateralis muscle of both legs.
The volunteers were told to abstain from any strenuous exercise 48 h
before these biopsies. In addition, muscle biopsies were obtained in
relation to training sessions (before, immediately after the first bout of
exercise, after2hofrest, and immediately after the second bout of
exercise). Muscle biopsies were analyzed for glycogen by using
enzymatic analyses with fluorometric detection (19). In addition,
biopsies were analyzed for CS and HAD activity (20).
Hormones. Glucose and lactate were measured by use of an
automated analyzer (Cobas Fara, Roche, Basel, Switzerland). Plasma
insulin (Insulin RIA 100, Amersham Pharmacia Biotech, Uppsala,
Sweden), glucagon (Linco Research, St. Charles, MO), and cortisol
(Diagnostic Products, Los Angeles, CA) were determined by RIA, and
plasma epinephrine and norepinephrine were determined by HPLC
(9, 47).
Fiber types and capillaries. Serial sections (10 m) of the muscle
biopsy samples were cut in a cryostat at 20°C, and routine ATPase
histochemistry analysis performed after preincubation at pH 4.37,
4.60, and 10.30 (10). Five different fiber types were defined: types I,
I/IIA, IIA, IIAX, and IIX. The terms “IIAX” and “IIX” have been
used instead of “IIAB” and “IIB,” to match the predominant
nomenclature used for the human myosin heavy chain (MHC)
isoforms (1). Fibers determined to be type II fibers, but showing an
intermediate staining with pH 4.60 preincubation, were categorized
as type IIAX fibers. These fibers covered a wide range from fibers
with only a light staining (i.e., fibers with predominately MHC IIA
expression) to fibers with a much darker staining (i.e., fibers with
predominantly MHC IIX expression). In some individuals, the
number of the minor fiber types (I/IIA, IIAX, and IIX) were so
small that a reliable statistical comparison of changes in fiber-type
size was impossible. Therefore, calculations of fiber-type size were
performed for three major categories of fiber types (type I, type
IIA, and type IIAX). Staining of capillaries was performed by
using the double-staining method (45).
The serial sections of the various ATPase and capillary stainings
were visualized and analyzed for fiber-type percent, fiber-type area
percent, fiber size, and capillary density expressed as capillaries per
fiber and as capillaries per millimeter squared by using a TEMA
image analyzing system (Scanbeam, Hadsund, Denmark) as used
Fig. 1. Schematic overview showing the design of the study. Before onset of the training period, the maximal power output (P
) and the time to exhaustion
) at 90% of P
were determined for each leg on separate occasions. At least 48 h after the last performance test, a blood sample as well as a muscle biopsy
from the vastus laterialis (gray arrows) were obtained during rest after an overnight fast. After the first set of performance tests, the participants trained both legs
for 10 wk, followed by a second posttraining set of performance tests similar to those performed before training. The training consisted of a 14-day cycle repeated
5 times. During one 14-day period (box at top), one leg (Low) was trained for 5 days by the subjects performing 2 bouts of dynamic knee extensor exercise,
each bout lasting 1 h and separated by a 2-h break. Meanwhile, the other leg (High) was trained every day for 5 days/wk by the subjects performing 1 bout of
dynamic knee extensor exercise for 1 h. Numbers in the box at top denote the number of the day during the 14-day training cycle. The workload was initially
set to 75% of the pretraining P
, and increased by 5–10% every 14-days, depending on the progress of each participant. Of note, the workload for each leg
was equal during the training sessions; thus the total work for each leg during the training period was equal.
F, One 1-hour training bout; E, contralateral resting leg.
J Appl Physiol VOL 98 JANUARY 2005
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previously by our laboratory (45). We examined an average of 105
16 fibers in each biopsy.
and time until exhaustion. In response to 10 wk of
training, P
increased significantly, being the same in the two
legs (Table 1). The endurance at 90% of this new P
markedly increased for both legs, but time until exhaustion was
twice as long for Low compared with High. In accordance, the
actual work performed by Low was also markedly larger
compared with High.
Hormones and lactate in relation to a training session.
Plasma insulin, glucagon, norepinephrine, epinephrine, corti-
sol, and lactate were measured before and after1hofknee
extensor exercise with both legs, which corresponded to the
first exercise at that particular day; before and after knee
extensor exercise for 1 h with the Low leg, which was per-
formed 2 h after the exercise with both legs; as well as before
and after1hofexercise with the High leg, which corresponded
to the first bout of exercise on the following day. During both
exercises with two legs as well as one leg, plasma insulin
decreased, whereas plasma glucaogon, norepinephrine, and
epinephrine increased (Table 2). These changes occurred to the
same extent when exercise was performed with two legs and
when exercise was performed with the Low leg. The hormonal
responses to exercise with the Low leg were in general more
pronounced compared with exercise performed with the High
leg. The difference in responses between the Low and High
legs was significant for norepinephrine and epinephrine.
Plasma cortisol did not change in response to exercise.
Muscle glycogen. Muscle glycogen content was measured at
rest before, after 5 wk, and after 10 wk of training (Fig. 2A).
Training induced a marked increase in muscle glycogen. This
effect was, however, only significant for Low. Muscle glyco-
gen was also measured in relation to two training sessions.
Muscle glycogen declined during the first bout of exercise.
Because the subjects were not allowed to eat in the recovery
period of the first bout of exercise, the second bout of exercise
undertaken by Low was initiated at a low muscle glycogen
level. Therefore, every second time the Low leg trained, it was
with a markedly low muscle glycogen level, whereas the High
leg initiated each training session with a high muscle glycogen
content (Fig. 2B).
Mitochondrial enzymes The activities of the mitochondrial
enzymes HAD and CS were measured in muscle biopsies
obtained at rest before and after 5 and 10 wk of training (Fig.
3). HAD activity increased with training, but only significantly
so in Low, whereas CS activity increased in both Low and
High. When the relative change from pretraining to after 10 wk
of training was estimated, there was a significantly more
pronounced increase in CS activity when Low was compared
with High.
Muscle fibers and capillaries. Percent number and percent
area of type IIX fibers decreased significantly in High, but
there was no difference between the two legs postexercise
(Table 3). There were no significant effects of training and no
difference between Low and High with regard to distribution of
fiber types or size or with regard to capillaries.
The main findings of the present study were that 1) that time
until exhaustion, 2) resting muscle glycogen concentration, and
3) CS activity were enhanced by training twice every second
day when compared with training once daily. The protocol
allowed us to compare the work performed in the prolonged
time trial with each leg at the same absolute as well as exercise
intensity. Using a study design where the two legs were trained
at different protocols further allowed us to distinguish possible
systemic and local effects. Thus systemic concentrations of, for
example, hormones and glucose were equal for the two legs,
and the study design therefore only measured possible local
differences as a consequence of different training schedules.
The present study was based on an overall hypothesis, which
can be expressed as follows: “Muscle glycogen: train low,
compete high.” This hypothesis refers to the fact that, whereas
numerous studies have demonstrated that low muscle glycogen
Table 1. Maximal power output and time until exhaustion at
90% of maximal power output before and after 10 wk of
training and total work before and after 10 wk of training
Pretraining Posttraining
Low High Low High
747776 1077* 1066
, min
5.00.7 5.61.2 19.72.4*
Total work, kJ 225257 11414*
Values are means SE. Low, leg trained with low muscle glycogen
protocol; High, leg trained with high muscle glycogen protocol; P
, maximal
power output; T
, time until exhaustion; total work, P
. *Significant
difference (P 0.05) from pretraining in Low. Significant difference (P
0.05) from pretraining, in High. Significant difference (P 0.05) between
Low and High..
Table 2. Hormone and lactate levels
Both Legs Low High
Pretraining Posttraining Pretraining Posttraining Pretraining Posttraining
Insulin 47.212.76 19.563.37* 28.298.60 17.867.81* 35.547.98 21.173.36*
Glucagon 90.115.61 137.4824.23* 74.338.37 129.5217.99* 75.688.69 109.5517.09*
Norepinephrine 2.10.25 5.790.82* 2.210.19 4.650.35* 2.110.26 3.370.36
Epinephrine 0.30.07 0.740.16* 0.280.05 0.890.18* 0.300.07 0.660.14
Cortisol 16.32.46 14.304.17 15.484.07 11.091.60 16.203.51 12.532.00
Lactate 1.10.37 3.280.66 1.130.13 3.110.70 1.380.11 2.080.34
Values are means SE. No significant differences were observed between pretraining values for Low and High legs. *Difference between pretraining and
posttraining; P 0.05.
Difference between Low and High legs posttraining value, P 0.05.
J Appl Physiol VOL 98 JANUARY 2005
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content is a limiting factor with regard to performance (6, 15,
28, 31, 36), this may not be valid when it comes to training
adaptation. In fact, data have accumulated showing that low
muscle glycogen content enhances the transcription and the
transcription rate of a number of genes involved in training
adaptation (22, 32, 42).
In the present study, the two legs were trained according to
different protocols: one leg performed one training session
Fig. 2. A: resting muscle glycogen concentration before (pre), halfway through
the training period (mid), and at the end (post) of the training period. Values are
geometric means SE. †Difference from pretraining level, P 0.05. B: muscle
glycogen content at rest, after one bout of two-legged training (Post 1st bout), and
after the subsequent bout of one-legged training (Post 2nd bout; with the Low leg).
The biopsies obtained after the 1st and 2nd bouts are from the Low leg only.
Values are geometric means SE. †Difference from pretraining level, P 0.05.
Fig. 3. A: resting muscle citrate synthase (CS) activity pretraining, midtrain-
ing, and posttraining. Values are means SE. †Difference from pretraining
level in Low, P 0.05. ‡Difference from pretraining level in High P 0.05.
B: resting muscle 3-hydroxyacyl-CoA dehydrogenase (HAD) activity pretrain-
ing, midtraining, and posttraining. Values are means SE. †Difference from
pretraining level in Low, P 0.05. ‡Difference from pretraining level in High,
P 0.05. C: change in resting muscle CS and HAD activity from pretraining
to posttraining. Values are means SE. $Difference between Low and High,
P 0.05.
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daily, whereas the other leg performed two training sessions
separated by only 2 h every second day. The latter training
schedule resulted in a marked decrease in muscle glycogen
content after the first bout of exercise. Therefore, when the
second bout of exercise was performed within the same day, it
was undertaken with very low muscle glycogen content. Thus
we succeeded in developing a protocol that allowed us to
compare training at a low muscle glycogen with training at a
high muscle glycogen content. The finding that the catechol-
amine response to exercise performed at low muscle glycogen
was higher than at exercise performed at high muscle glycogen
concentration demonstrates that a higher stress response was
elicited when the muscle glycogen was low.
In the present study, resting muscle glycogen content in-
creased with training in accordance to numerous previous
studies (25). However, the increase in muscle glycogen was
only significant for Low. This indicates that training at the Low
protocol may be a more efficient training mode with respect to
enhancing muscle glycogen stores. It has long been known that
glycogen synthase (GS) activity is closely coupled to the
muscle glycogen content in both rodent (16, 17) and human
skeletal muscle (7), both in the resting state and after muscle
contraction (16, 38, 51). The rate-limiting conversion of UDP-
glucose to glycogen is catalyzed by GS, which in skeletal
muscle is known to be bound to glycogen particles (5, 35) and
myofibrils (33, 50). Rat studies have demonstrated that con-
traction-induced increase in GS activity is strongly dependent
on muscle glycogen (38). Exercise regulation of GS is charac-
terized by great complexity (39). GS is a substrate of kinases
and phosphatases acting on several phosphorylation sites of
GS, and exercise seems to activate both stimulatory and inhib-
itory regulators of GS, including activation of 5-AMP-acti-
vated protein kinase (11, 13, 40). The mechanisms responsible
for inhibition and especially activation are poorly understood.
It may be proposed that the GS activity during exercise may
depend on the relative strength of opposing signals. Glycogen
breakdown may be considered the major stimulatory signal.
The finding that training on the Low and High protocols
influence glycogen metabolism differently talks in favor of the
idea that glycogen breakdown and low muscle glycogen are
important stimulatory GS signals, which result in a total
increase in muscle glycogen concentration.
The effect on resting muscle glycogen does, however, not
explain the difference in “time until exhaustion” because this
test was carried out on a relatively high intensity, which did not
allow the volunteers to exercise for more than a maximum of
25 min. Therefore, muscle glycogen content was not a limiting
The study did not aim to measure peak muscle oxygen
consumption, and therefore we did not consider measuring the
rate-limiting enzyme -keto acid glutamate dehydrogenase (8).
Rather, we focused on citrate synthase as a more general
marker of the tricarboxylic acid cycle flux and HAD as the
most-used marker enzyme for the -oxidation.
The activity of the mitochondrial enzymes HAD and CS
increased with training in both Low and High. However,
regarding CS activity, this increase was more pronounced in
the leg that was trained in the low muscle glycogen protocol.
Transcriptional activities of HAD and CS are only markedly
influenced by acute muscle contractions (43).
However, the possibility exists that the mRNA for these
genes peak late in the recovery phase. The effect of low muscle
glycogen on HAD and CS gene activation has not been studied.
The finding that the low muscle glycogen protocol induced a
more pronounced enhancement of CS activity may represent
one mechanism explaining the enhanced endurance time in the
low muscle glycogen-trained leg.
We were unable to identify any major effects of training on
muscle fiber types, fiber size, or capillaries, although there was
the expected decrease in the amount of type 2X fibers in the
High leg, with a corresponding tendency in the Low leg.
Similarly, there was a clear, but not significant, tendency of an
increased capillary density in both legs. This lack of significant
adaptations in fiber types and capillary density is most likely
due to the major limitation of the present study: the training
protocol was demanding to such an extent that the cost limited
us to carry through only seven subjects. An n value of seven is
sufficient to study parameters with little variation, but can be a
major limitation in relation to adaptations in fiber types and
The present study should be viewed as one among hopefully
many studies to be conducted in the coming decade, investi-
gating the effect of muscle glycogen content on training adap-
tation using molecular biological methods as well as exercise
physiological parameters. Coaches and athletes should be care-
ful not to draw practical consequences of the present study with
regard to training regimens. In the real world, training on a
high muscle glycogen content may allow the athlete to train for
longer periods and thereby obtain better results. In addition,
training schedules that allow muscle glycogen to decrease to
low values may increase the risk for the so-called overtraining
syndrome (41).
In summary, in a human experimental laboratory setting,
training twice every second day was superior to training once
daily. The present study therefore suggests that perhaps some
adaptations to physical activity may require a cycling of
Table 3. Muscle fiber and capillary characteristics
pretraining and posttraining
Pretraining Posttraining
Low High Low High
Percent number
Type I 67.05.1 62.76.7 64.75.7 61.85.1
Type I/IIA 0.20.1 0.10.1 0.80.4 0.20.1
Type IIA 25.03.4 27.24.2 26.34.9 35.25.9
Type IIAX 5.02.1 6.52.0 7.53.8 2.31.0
Type IIX 2.41.3 3.21.1 0.40.3 0.30.3*
Percent area
Type I 65.25.0 58.86.3 63.76.3 61.86.6
Type I/IIA 0.20.1 0.00.0 0.80.4 0.20.1
Type IIA 28.84.3 31.84.9 27.95.3 35.27.2
Type IIAX 3.91.5 6.31.8 6.83.3 2.31.1
Type IIX 1.70.9 2.80.9 0.50.3 0.20.2*
Fiber size
Type I 4,963843 5,061893 5,216659 5,564781
Type II 5,394926 5,867676 5,319550 5,464558
Capillaries/type I
fiber 5.60.6 5.50.6 6.00.3 6.50.4
Capillaries/type II
fiber 5.30.7 5.70.5 5.70.4 6.10.5
55516 55237 59827 61033
Values are means SE. *Difference from pretraining, P 0.05.
J Appl Physiol VOL 98 JANUARY 2005
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muscle glycogen stores as recently suggested by Chakravarthy
and Booth (12).
We thank the subjects for participation. Ruth Rousing and Hanne Villumsen
are acknowledged for excellent technical assistance.
The study was also supported by grants from The Danish National Research
Foundation (no. 504-14), the Novo Nordisk Foundation, Lundbeckfonden,
Rigshospitalet, Member of H:S-Copenhagen Hospital. Civil Engineer Frode V.
Nyegaard og Hustrus Fond, Danfoss, Augustinus Fonden, Team Danmark, and
Kulturministeriets Udvalg for Idrætsforskning.
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... The intensity and duration of a 20-min effort means the predominant energy substrates are endogenous CHO stores, specifically, skeletal muscle glycogen [65,66]. Whilst increased resting muscle glycogen content is frequently observed following chronic low CHO training [3,5,20,67,68], the duration of the FTP test disallows muscle glycogen depletion as a limiting factor to performance [69]. Alternatively, augmented muscle oxidative capacity is a potential mechanism for increased 20-min PPO via improved mitochondrial function and/or biogenesis [70,71]. ...
... An augmented molecular response to exercise under conditions of low muscle glycogen leads to elevated PGC-1⍺ mRNA expression [3-5, 17, 74], and nuclear translocation [75]. Furthermore, the chronic application of "train-low" has shown an amplified adaptive response with increased markers of mitochondrial adaptation such as citrate synthase, OXPHOS subunit COX IV [20], 3-hydroxyacyl-CoA dehydrogenase (β HAD) [22, 67,71], and succinate dehydrogenase (SDH) [27] activities suggestive of improved mitochondrial efficiency [71]. Utilising an alternative CHO periodisation strategy (twice daily), Cochran et al. [76] showed improved performance following two weeks of training with low CHO availability, despite no changes in mitochondrial protein content, speculating that improved performance may be due to changes in efficiency, which can occur independent of changes in content [77]. ...
Full-text available
Background"Sleep Low-Train Low" is a training-nutrition strategy intended to purposefully reduce muscle glycogen availability around specific exercise sessions, potentially amplifying the training stimulus via augmented cell signalling. The aim of this study was to assess the feasibility of a 3-week home-based "sleep low-train low" programme and its effects on cycling performance in trained athletes.Methods Fifty-five trained athletes (Functional Threshold Power [FTP]: 258 ± 52W) completed a home-based cycling training program consisting of evening high-intensity training (6 × 5 min at 105% FTP), followed by low-intensity training (1 hr at 75% FTP) the next morning, three times weekly for three consecutive weeks. Participant's daily carbohydrate (CHO) intake (6 g·kg-1·d-1) was matched but timed differently to manipulate CHO availability around exercise: no CHO consumption post- HIT until post-LIT sessions [Sleep Low (SL), n = 28] or CHO consumption evenly distributed throughout the day [Control (CON), n = 27]. Sessions were monitored remotely via power data uploaded to an online training platform, with performance tests conducted pre-, post-intervention.ResultsLIT exercise intensity reduced by 3% across week 1, 3 and 2% in week 2 (P < 0.01) with elevated RPE in SL vs. CON (P < 0.01). SL enhanced FTP by +5.5% vs. +1.2% in CON (P < 0.01). Comparable increases in 5-min peak power output (PPO) were observed between groups (P < 0.01) with +2.3% and +2.7% in SL and CON, respectively (P = 0.77). SL 1-min PPO was unchanged (+0.8%) whilst CON improved by +3.9% (P = 0.0144).Conclusion Despite reduced relative training intensity, our data demonstrate short-term "sleep low-train low" intervention improves FTP compared with typically "normal" CHO availability during exercise. Importantly, training was completed unsupervised at home (during the COVID-19 pandemic), thus demonstrating the feasibility of completing a "sleep low-train low" protocol under non-laboratory conditions.
... Furthermore, repeated bouts of train-low exercise can subsequently augment many hallmark muscle adaptations inherent to the endurance phenotype (as reviewed in Impey et al. 2018). For example, the strategic periodization of dietary CHO in order to commence exercise with low muscle glycogen (during 3-10 weeks of training) enhances mitochondrial enzyme activity and protein content (Hansen et al. 2005;Morton et al. 2009;Yeo et al. 2008) and whole body and intra-muscular lipid metabolism (Hulston et al. 2010) and in some instances improves exercise capacity (Hansen et al. 2005) and performance (Marquet et al. 2016a, b), though performance enhancing effects are not always evident (Yeo et al. 2008;Hulston et al. 2010;Burke et al. 2017;Gejl et al. 2017a, b;. As such, the train-low paradigm and wider CHO periodization strategies have subsequently gained increased recognition among athletic populations (Stellingwerff 2012;Burke et al. 2018;Impey et al. 2018). ...
... Furthermore, repeated bouts of train-low exercise can subsequently augment many hallmark muscle adaptations inherent to the endurance phenotype (as reviewed in Impey et al. 2018). For example, the strategic periodization of dietary CHO in order to commence exercise with low muscle glycogen (during 3-10 weeks of training) enhances mitochondrial enzyme activity and protein content (Hansen et al. 2005;Morton et al. 2009;Yeo et al. 2008) and whole body and intra-muscular lipid metabolism (Hulston et al. 2010) and in some instances improves exercise capacity (Hansen et al. 2005) and performance (Marquet et al. 2016a, b), though performance enhancing effects are not always evident (Yeo et al. 2008;Hulston et al. 2010;Burke et al. 2017;Gejl et al. 2017a, b;. As such, the train-low paradigm and wider CHO periodization strategies have subsequently gained increased recognition among athletic populations (Stellingwerff 2012;Burke et al. 2018;Impey et al. 2018). ...
... The training protocols utilized in these studies [11,12] that reported to improve FatOx were very demanding and poorly tolerated by certain individuals; hence, it is necessary to elucidate whether a more practical and attainable model of low-volume HIIT could be as effective in improving substrate metabolism as the allout protocols. Furthermore, the exercise twice-a-day approach is considered to be an effective strategy to induce adaptations related to mitochondrial biogenesis and FatOx [13,14]. However, it remains to be determined whether a practical model of low volume HIIT administered twice a day could improve resting substrate oxidation in less than 2 weeks. ...
It remains unclear whether a practical model of low-volume high-intensity interval exercise improves resting fat oxidation (FatOx) which is associated with metabolic health. We aimed to determine the effects of a short-term practical model of high-intensity interval training (HIIT) on resting FatOx in young, healthy males. Thirty healthy males were randomly assigned to either single (HIITsingle; n=13) or double HIIT (HIITdouble; n=17) group. The HIITsingle group trained once a day, 3 days/ week for 2 weeks, whilst the HIITdouble group performed 6 sessions of high-intensity exercise over 5 days by exercising twice a day every second day. Both groups completed 6 high-intensity exercise sessions consisting of 10×60 s of cycling at peak power output, interspersed by 75 s cycling at 60 W. With 1% false discovery rate (FDR) significance threshold, resting respiratory exchange ratio similarly decreased in HIITsingle (pre=0.83±0.03 vs post=0.80±0.03) and HIITdouble group (pre=0.82±0.04 vs post=0.80±0.02) [(p=0.001; partial eta squared (ηp2) =0.310, FDR-adjusted p value=0.005)]. Resting FatOx increased similarly in HIITsingle (pre=1.07±0.39 mg·kg-1 fat free mass (FFM)·min-1 vs post=1.44±0.36 mg·kg-1 FFM·min-1) and HIITdouble group (pre=1.35±0.45 mg·kg-1 FFM·min-1 vs post=1.52±0.29 mg·kg-1 FFM·min-1) [(p<0.001; ηp2=0.411, FDR-adjusted p value=0.005)]. Our results demonstrate that only six sessions of a practical model of low-volume high-intensity exercise improves resting FatOx in young, healthy males.
... To our knowledge, there has never been a controlled trial of the potential benefit of low monotony training on the adaptive response to training. However, studies showing the benefit of distinct hard day versus easy day training are available (21,22). Within this context, it is probably necessary to recognize that a >2-h run or 4-h ride in z1 may be as stressful as an interval (z2 or z3) session. ...
... Finalement, des entraînements avec de faibles réserves de glycogène sembleraient favoriser l'augmentation du volume de travail total et l'augmentation du temps jusqu'à l'épuisement après une resynthèse des réserves de glycogène (24). ...
... One explanation for the benefits of polarised training (Seiler, 2010;Seiler & Tønnessen, 2009) is the lower overall stress (both perceptual and physiological) load induced by long-duration, low-intensity exercise compared with highly intensive sessions at/ above lactate threshold. This approach facilitates more rapid recovery, which consequently allows more frequent training (twice daily), giving an important long-term adaptive advantage over those completing the similar training volumes but less frequently (Hansen et al., 2005). It would therefore seem an optimal recovery-stress balance is an important factor relating to the effectiveness of polarised training. ...
... Strategies of nutritional periodisation include manipulating carbohydrate and fat intake to upregulate key signalling pathways in the skeletal muscle and promote mitochondrial biogenesis, angiogenesis and increased lipid oxidation (Hansen et al., 2005, Hulston et al., 2010, Morton et al., 2009 or optimising protein intake to support hypertrophic responses in skeletal muscle . However, numerous metabolic processes and reactions involved in energy extraction from macronutrients, oxygen delivery and transfer, tissue repair, and growth and development are dependent on essential vitamins and minerals manuscripts published in English were included (abstracts, theses and conference proceedings were not included). ...
Optimising nutrition intake is a key component for supporting athletic performance and supporting adaption to training. Athletes often use micronutrient supplements in order to correct vitamin and mineral deficiencies, improve immune function, enhance recovery and or to optimise their performance. The aim of this review was to investigate the recent literature regarding micronutrients (specifically iron, vitamin C, vitamin E, vitamin D, calcium) and their effects on physical performance. Over the past ten years, several studies have investigated the impacts of these micronutrients on aspects of athletic performance, and several reviews have aimed to provide an overview of current use and effectiveness. Currently the balance of the literature suggests that micronutrient supplementation in well-nourished athletes does not enhance physical performance. Excessive intake of dietary supplements may impair the body's physiological responses to exercise that supports adaptation to training stress. In some cases, micronutrient supplementation is warranted, for example, with a diagnosed deficiency, when energy intake is compromised, or when training and competing at altitude, however these micronutrients should be prescribed by a medical professional. Athletes are encouraged to obtain adequate micronutrients from a wellbalanced and varied dietary intake.
... Instead, HIIT with low glycogen stores may elicit higher perturbation in steady-state and higher increase in mitochondrial volume [161], when compared to HIIT with normal glycogen stores, resulting in higher training adaptation and endurance performance. Further, Hansen et al. [166] reported a higher catecholamine response to HIIT performed at low muscle-glycogen stores than at exercise performed at high muscle-glycogen stores, indicating higher stress response when the muscle glycogen is low, whilst Hulston et al. [163] reported that exercising with low muscle glycogen was not more effective for training adaptation than with high muscle glycogen in already well-trained athletes. Taken together, two workouts in close proximity, with the second bout of exercise performed at low muscle-glycogen content, seems to be a time-efficient method of maintaining training adaptations and performance, especially for untrained individuals. ...
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Engaging in regular exercise results in a range of physiological adaptations offering benefits for exercise capacity and health, independent of age, gender or the presence of chronic diseases. Accumulating evidence shows that lack of time is a major impediment to exercise, causing physical inactivity worldwide. This issue has resulted in momentum for interval training models known to elicit higher enjoyment and induce adaptations similar to or greater than moderate-intensity continuous training, despite a lower total exercise volume. Although there is no universal definition, high-intensity interval exercise is characterized by repeated short bursts of intense activity, performed with a "near maximal" or "all-out" effort corresponding to ≥90% of maximal oxygen uptake or >75% of maximal power, with periods of rest or low-intensity exercise. Research has indicated that high-intensity interval training induces numerous physiological adaptations that improve exercise capacity (maximal oxygen uptake, aerobic endurance, anaerobic capacity etc.) and metabolic health in both clinical and healthy (athletes, active and inactive individuals without any apparent disease or disorder) populations. In this paper, a brief history of high-intensity interval training is presented, based on the novel findings of some selected studies on exercise capacity and health, starting from the early 1920s to date. Further, an overview of the mechanisms underlying the physiological adaptations in response to high-intensity interval training is provided.
Large intramuscular triglyceride (IMTG) stores in sedentary, obese individuals have been linked to insulin resistance, yet well-trained athletes exhibit high IMTG levels whilst maintaining insulin sensitivity. Contrary to previous assumptions, it is now known that IMTG content per se does not result in insulin resistance. Rather, insulin resistance is caused, at least in part, by the presence of high concentrations of harmful lipid metabolites, such as diacylglycerols and ceramides in muscle. Several mechanistic differences between obese sedentary individuals and their highly-trained counterparts have been identified, that determine the differential capacity for IMTG synthesis and breakdown in these populations. In this review, we first describe the most up-to-date mechanisms by which a low IMTG turnover rate (both breakdown and synthesis) leads to the accumulation of lipid metabolites and results in skeletal muscle insulin resistance. We then explore current and potential exercise and nutritional strategies which target IMTG turnover in sedentary obese individuals, to improve insulin sensitivity. Overall, improving IMTG turnover should be an important component of successful interventions which aim to prevent the development of insulin resistance in the ever-expanding sedentary, overweight and obese populations. Novelty Bullet points • A description of the most up-to-date mechanisms regulating turnover of the IMTG pool. • An exploration of current and potential exercise/nutritional strategies to target and enhance IMTG turnover in obese individuals • Overall, highlights the importance of improving IMTG turnover to prevent the development of insulin resistance
The aim of this study was to investigate whether periodising carbohydrate intake around specific training sessions will enhance endurance training adaptations. Seventeen healthy recreationally endurance-trained males (n = 5) and females (n = 12) (27.5 ± 5.4 years) participated in a four-week training intervention. Participants were divided into two groups: FASTED (stayed fasted between evening high-intensity interval training session and low-intensity training session in the following morning) and FED (no restriction in food intake). Pre- and post-testing included peak oxygen uptake (VO2peak), anaerobic capacity, and 60 min submaximal running tests. Fasted venous blood samples were drawn for the determination of triglyceride and glucose concentrations. VO2peak increased in both FASTED (4.4 ± 3.0%, p=0.001) and FED (4.6 ± 4.2%, p=0.017), whereas maximal running velocity increased only in the FASTED (3.5 ± 2.7%, p=0.002). Lactate concentrations in the anaerobic test after intervention were greater in FASTED than FED (p=0.025-0.041). Running time in the anaerobic test was improved in FASTED (from 64.1 ± 15.6 to 86.3 ± 23.2 s, p<0.001) but not in FED (from 56.4 ± 15.2 to 66.9 ± 21.3 s, p=0.099). Substrate oxidation did not change after intervention in either of the groups (p=0.052-0.597). Heart rate was lower in the submaximal running test in FASTED (p<0.001) but not in FED (p=0.097). Training with periodised carbohydrate availability does not have any effect on substrate oxidation. However, it seems to enhance the capacity to perform high-intensity exercise.
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A fraction containing a protein-glycogen complex was obtained from rabbit muscle by different procedures involving acid precipitation followed by differential centrifugation, direct differential centrifugation, and acetone fractionation. All three preparations were essentially identical in terms of their physical, chemical, and enzymatic characteristics strongly suggesting that the protein-glycogen complex represents a structural and functional unit of the cell rather than artifacts resulting from a given isolation procedure. Electron micrographs of the isolated fractions showed the presence of glycogen granules together with vesicles arising from fragments of the sarcoplasmic reticulum. Sedimentation velocity patterns obtained in the analytical ultracentrifuge, sucrose gradient centrifugation, and Sepharose 2B gel filtration indicated that the material can be separated into a light (approximately 120 S) and a heavy (approximately 600 S) fraction. The light fraction consists mainly of glycogen particles to which are associated phosphorylase, phosphorylase kinase, and phosphatase among other enzymes. The heavy fraction contains mainly the elements of the sarcoplasmic reticulum characterized by a strong ATPase activity and some lysosomes as indicated by the presence of traces of acid phosphatase and amylase activity. Contamination of the glycogen particles by this latter enzyme resulted in their slow degradation that prevented further purification.
Protein dephosphorylation by phosphatase PP1 plays a central role in mediating the effects of insulin on glucose and lipid metabolism. A PP1C-targeting protein expressed in 3T3-L1 adipocytes (called PTG, for protein targeting to glycogen) was cloned and characterized. PTG was expressed predominantly in insulin-sensitive tissues. In addition to binding and localizing PP1C to glycogen, PTG formed complexes with phosphorylase kinase, phosphorylase a, and glycogen synthase, the primary enzymes involved in the hormonal regulation of glycogen metabolism. Overexpression of PTG markedly increased basal and insulin-stimulated glycogen synthesis in Chinese hamster ovary cells overexpressing the insulin receptor, which do not express endogenous PTG. These results suggest that PTG is critical for glycogen metabolism, possibly functioning as a molecular scaffold.
• The influence of muscle glycogen content on glycogen synthase (GS) localization and GS activity was investigated in skeletal muscle from male Wistar rats. • Two groups of rats were obtained, preconditioned with a combination of exercise and diet to obtain either high (HG) or low (LG) muscle glycogen content. The cellular distribution of GS was studied using subcellular fractionation and confocal microscopy of immunostained single muscle fibres. Stimulation of GS activity in HG and LG muscle was obtained with insulin or contractions in the perfused rat hindlimb model. • We demonstrate that GS translocates from a glycogen-enriched membrane fraction to a cytoskeleton fraction when glycogen levels are decreased. Confocal microscopy supports the biochemical observations that the subcellular localization of GS is influenced by muscle glycogen content. GS was not found in the nucleus. • Investigation of the effect of glycogen content on GS activity in basal and insulin- and contraction-stimulated muscle shows that glycogen has a strong inhibitory effect on GS activity. Our data demonstrate that glycogen is a more potent regulator of glycogen synthase activity than insulin. Furthermore we show that the contraction-induced increase in GS activity is merely a result of a decrease in muscle glycogen content. • In conclusion, the present study shows that GS localization is influenced by muscle glycogen content and that not only basal but also insulin- and contraction-stimulated GS activity is strongly regulated by glycogen content in skeletal muscle.
The muscle glycogen content of the quadriceps femoris muscle was determined in 9 healthy subjects with the aid of the needle biopsy technique. The glycogen content could be varied in the individual subjects by instituting different diets after exhaustion of the glycogen store by hard exercise. Thus, the glycogen content after a fat ± protein (P) and a carbohydrate-rich (C) diet varied maximally from 0.6 g/100g muscle to 4.7 g. In all subjects, the glycogen content after the C diet was higher than the normal range for muscle glycogen, determined after the mixed (M) diet. After each diet period, the subjects worked on a bicycle ergometer at a work load corresponding to 75 per cent of their maximal O2 uptake, to complete exhaustion. The average work time was 59, 126 and 189 min after diets P, M and C, and a good correlation was noted between work time and the initial muscle glycogen content. The total carbohydrate utilization during the work periods (54–798 g) was well correlated to the decrease in glycogen content. It is therefore concluded that the glycogen content of the working muscle is a determinant for the capacity to perform long-term heavy exercise. Moreover, it has been shown that the glycogen content and, consequently, the long-term work capacity can be appreciably varied by instituting different diets after glycogen depletion.
The results indicate a gradual conversion of a part of the type IIB fiber population into type IIA fibers in response to an endurance training program. The pretraining percentage distribution of type IIA and IIB fibers was in the same range as that reported by Hedberg and Jansson (1976) for 68 sixteen year old boys (32% IIA and 13% IIB fibers). It is worth emphasizing that the classification of the type II fibers into the subgroups IIA and IIB in this study is based on differences in the pH sensitivity of the myosin ATPase. According to Brooke and Kaiser (1970) this difference is related to the reactivity of sulfhydryl groups of the myosin molecule. Thus it is conceivable that the observed changes indeed indicate a change in the structure of the myosin molecule.
• Ten subjects performed incremental exercise up to their maximum work rate with the knee extensors of one leg. Measurements of leg blood flow and femoral arteriovenous differences of oxygen were made in order to be able to calculate oxygen uptake of the leg. • The volume of the quadriceps muscle was determined from twenty-one to twenty-five computer tomography section images taken from the patella to the anterior inferior iliac spine of each subject. • The maximal activities of three enzymes in the Krebs cycle, citrate synthase, oxoglutarate dehydrogenase and succinate dehydrogenase, were measured in biopsy samples taken from the vastus lateralis muscle. • The average rate of oxygen uptake over the quadriceps muscle at maximal work, 353 ml min−1kg−1, corresponded to a Krebs cycle rate of 4.6 mol min−1 g−1. This was similar to the maximal activity of oxoglutarate dehydrogenase (5.1 mol min−1 g−1), whereas the activities of succinate dehydrogenase and citrate synthase averaged 7.2 and 48.0 mol min−1 g−1, respectively. • It is suggested that of these enzymes, only the maximum activity of oxoglutarate dehydrogenase can provide a quantitative measure of the capacity of oxidative metabolism, and it appears that the enzyme is fully activated during one-legged knee extension exercise at the maximal work rate.
This study compared the effects of supplementing the normal diets of six trained cyclists [maximal oxygen uptake O2max) 4.5 (0.36)l · min−1; values are mean (SD)] with additional carbohydrate (CHO) on muscle glycogen utilisation during a 1-h cycle time-trial (TT). Using a randomised crossover design, subjects consumed either their normal diet (NORM) for 3 days, which consisted of 426 (137) g · day−1 CHO [5.9 (1.4) g · kg−1 body mass (BM)], or additional CHO (SUPP) to increase their intake to 661 (76) g · day−1 [9.3 (0.7) g · kg−1 BM]. The SUPP diet elevated muscle glycogen content from 459 (83) to 565 (62) mmol · kg−1 dry weight (d.w.) (P < 0.05). However, despite the increased pre-exercise muscle glycogen stores, there was no difference in the distance cycled during the TT [40.41 (1.44) vs 40.18 (1.76) km for NORM and SUPP, respectively]. With NORM, muscle glycogen declined from 459 (83) to 175 (64) mmol · kg−1 d.w., whereas with SUPP the corresponding values were 565 (62) and 292 (113) mmol · kg−1 d.w. Accordingly, both muscle glycogen utilisation [277 (64) vs 273 (114) mmol · kg−1 d.w.] and total CHO oxidation [169 (20) vs 165 (30) g · h−1 for NORM and SUPP, respectively] were similar. Neither were there any differences in plasma glucose or lactate concentrations during the two experimental trials. Plasma glucose concentration averaged 5.5 (0.5) and 5.6 (0.6) mmol · l−1, while plasma lactate concentration averaged 4.4 (1.9) and 4.4 (2.3) mmol · l−1 for NORM and SUPP, respectively. The results of this study show that when well-trained subjects increase the CHO content of their diet for 3 days from 6 to 9 g · kg−1 BM there is only a modest increase in muscle glycogen content. Since supplementary CHO did not improve TT performance, we conclude that additional CHO provides no benefit to performance for athletes who compete in intense, continuous events lasting 1 h. Furthermore, the substantial muscle CHO reserves observed at the termination of exercise indicate that whole-muscle glycogen depletion does not determine fatigue at this exercise intensity and duration.