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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-
thase
THE ROLE OF SUBSTRATE AVAILABILITY has been a key research
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
˙
O
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
(E-mail: bkp@rh.dk).
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
©
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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.
MATERIALS AND METHODS
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
max
),
followed by2hofrecovery. Thereafter, the Low leg trained for 1 h
at 75% of P
max
.On day 2, the High leg trained alone for1hat75%
of P
max
. 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
max
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
max
test was obtained for each leg
separately using the same cycle ergometer-knee extensor exercise
apparatus (Monark, Varberg, Sweden). Thereafter, a 90% P
max
en
-
durance test was performed for each leg.
In the first trial, the subjects performed a V
˙
O
2 max
test on each leg
to determine the individual knee P
max
. 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
max
) and the time to exhaustion
(T
exh
) at 90% of P
max
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
max
, 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.
94 MUSCLE GLYCOGEN: TRAIN LOW, COMPETE HIGH
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previously by our laboratory (45). We examined an average of 105 ⫾
16 fibers in each biopsy.
RESULTS
P
max
and time until exhaustion. In response to 10 wk of
training, P
max
increased significantly, being the same in the two
legs (Table 1). The endurance at 90% of this new P
max
was
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.
DISCUSSION
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
Parameter
Pretraining Posttraining
Low High Low High
P
max
,W
74⫾777⫾6 107⫾7* 106⫾6
†
T
exh
, min
5.0⫾0.7 5.6⫾1.2 19.7⫾2.4*
‡
11.9⫾1.3
†
Total work, kJ 22⫾525⫾7 114⫾14*
‡
69⫾8
†
Values are means ⫾ SE. Low, leg trained with low muscle glycogen
protocol; High, leg trained with high muscle glycogen protocol; P
max
, maximal
power output; T
exh
, time until exhaustion; total work, P
max
⫻ T
exh
. *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 47.2⫾12.76 19.56⫾3.37* 28.29⫾8.60 17.86⫾7.81* 35.54⫾7.98 21.17⫾3.36*
Glucagon 90.1⫾15.61 137.48⫾24.23* 74.33⫾8.37 129.52⫾17.99* 75.68⫾8.69 109.55⫾17.09*
Norepinephrine 2.1⫾0.25 5.79⫾0.82* 2.21⫾0.19 4.65⫾0.35* 2.11⫾0.26 3.37⫾0.36
†
Epinephrine 0.3⫾0.07 0.74⫾0.16* 0.28⫾0.05 0.89⫾0.18* 0.30⫾0.07 0.66⫾0.14
†
Cortisol 16.3⫾2.46 14.30⫾4.17 15.48⫾4.07 11.09⫾1.60 16.20⫾3.51 12.53⫾2.00
Lactate 1.1⫾0.37 3.28⫾0.66 1.13⫾0.13 3.11⫾0.70 1.38⫾0.11 2.08⫾0.34
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.
95MUSCLE GLYCOGEN: TRAIN LOW, COMPETE HIGH
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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.
96 MUSCLE GLYCOGEN: TRAIN LOW, COMPETE HIGH
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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
factor.
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
capillarization.
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 67.0⫾5.1 62.7⫾6.7 64.7⫾5.7 61.8⫾5.1
Type I/IIA 0.2⫾0.1 0.1⫾0.1 0.8⫾0.4 0.2⫾0.1
Type IIA 25.0⫾3.4 27.2⫾4.2 26.3⫾4.9 35.2⫾5.9
Type IIAX 5.0⫾2.1 6.5⫾2.0 7.5⫾3.8 2.3⫾1.0
Type IIX 2.4⫾1.3 3.2⫾1.1 0.4⫾0.3 0.3⫾0.3*
Percent area
Type I 65.2⫾5.0 58.8⫾6.3 63.7⫾6.3 61.8⫾6.6
Type I/IIA 0.2⫾0.1 0.0⫾0.0 0.8⫾0.4 0.2⫾0.1
Type IIA 28.8⫾4.3 31.8⫾4.9 27.9⫾5.3 35.2⫾7.2
Type IIAX 3.9⫾1.5 6.3⫾1.8 6.8⫾3.3 2.3⫾1.1
Type IIX 1.7⫾0.9 2.8⫾0.9 0.5⫾0.3 0.2⫾0.2*
Fiber size
Type I 4,963⫾843 5,061⫾893 5,216⫾659 5,564⫾781
Type II 5,394⫾926 5,867⫾676 5,319⫾550 5,464⫾558
Capillaries
Capillaries/type I
fiber 5.6⫾0.6 5.5⫾0.6 6.0⫾0.3 6.5⫾0.4
Capillaries/type II
fiber 5.3⫾0.7 5.7⫾0.5 5.7⫾0.4 6.1⫾0.5
Capillaries/mm
2
555⫾16 552⫾37 598⫾27 610⫾33
Values are means ⫾ SE. *Difference from pretraining, P ⬍ 0.05.
97MUSCLE GLYCOGEN: TRAIN LOW, COMPETE HIGH
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muscle glycogen stores as recently suggested by Chakravarthy
and Booth (12).
ACKNOWLEDGMENTS
We thank the subjects for participation. Ruth Rousing and Hanne Villumsen
are acknowledged for excellent technical assistance.
GRANTS
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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