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Prévia do material em texto

Eur J Appl Physiol (2006) 97: 591–597 
DOI 10.1007/s00421-006-0218-5
ORIGINAL ARTICLE
François Hug · Tanguy Marqueste · Yann Le Fur · 
Patrick J. Cozzone · Laurent Grélot · David Bendahan 
Selective training-induced thigh muscles hypertrophy 
in professional road cyclists
Accepted: 14 April 2006 / Published online: 10 June 2006
© Springer-Verlag 2006
Abstract Muscular adaptations linked to a high vol-
ume and intensity of training have been scarcely
reported. We aimed at documenting, using MRI, the
cross-sectional area changes associated with a high vol-
ume and intensity of training in 11 thigh muscles of a
population of professional road cyclists as compared
with sport science students. We were also interested in
determining, whether selective muscle hypertrophy in
professional road cyclists, if any, was correlated to selec-
tive exercise-induced T2 changes during a pedaling exer-
cise on a cycloergometer. Cross-sectional area of 11 thigh
muscles was quantiWed in sixteen subjects (i.e. eight pro-
fessional road cyclists and eight sport science students)
using MRI. In addition, transverse relaxation times (T2)
were measured before and just after a maximal standard-
ized constant-load exercise in order to investigate exer-
cise-related T2 changes in these muscles. Professional
road cyclists had a signiWcantly higher relative amount
of muscle (including the whole set of thigh muscles,
90.5§3.3%) as compared to controls (81.6§7.3%).
Regarding relative values expressed with respect to the
total thigh muscles CSA, Vastus lateralis and Biceps
femoris CSA were signiWcantly larger in cyclists whereas
CSA of the Vastus intermedius was smaller. However,
this selective hypertrophy was not correlated to the exer-
cise-induced T2-increase. We have reported, for the Wrst
time, a selective hypertrophy of Vastus lateralis and
Biceps femoris in professional road cyclists conWrming
their involvement in pedaling task and suggesting a pos-
sible cause–eVect relationship between muscle activation
and hypertrophy, associated with a speciWc pedaling
skill.
Keywords T2 · Cross sectional area (CSA) · Muscle · 
Pedaling · Training · MRI
Introduction
Professional cyclists probably represent the pinnacle of
natural selection and physiological adaptations to
endurance exercise. A professional road cyclist covers
approximately 30,000–35,000 km/year including train-
ing and competition corresponding to about 25 h/week
(Faria et al. 2005; Lucia et al. 1999). Although road
cycling, especially professional cycling, is considered as
an extreme endurance sport, subjects involved in com-
petitive cycling had also to possess the ability to perform
repetitive short duration (i.e. few minutes) high power
output exercise bouts. During the competition period (i.e.
spring and summer) professional road cyclists perform
about 77% of their training/competition time at low
intensity (<65% VO2 max), 15% at moderate intensity
(65–90% VO2 max) and 8% at high intensity (>90% VO2
max) (Lucia et al. 1996).
This high volume and intensity of training are linked
to neuromuscular adaptations including changes in
motor unit recruitment and changes occurring at the
level of muscle tissue. Indeed, skeletal muscle Wbers have
a remarkable ability to alter their phenotype in response
to environmental stimuli (i.e. training for example).
There is a general consensus that resistance training
induces muscle hypertrophy in humans (Green et al.
1999; Kraemer et al. 1995; Sipila and Suominen 1995)
F. Hug (&)
Laboratory of Biomechanics and Physiology , INSEP, 
National Institute for Sports and Physical Education, 
11, avenue du Tremblay, 75012 Paris, France
E-mail: francois_hug@hotmail.com
Tel.: +33-141-744165
Fax: +33-141-744535
F. Hug
Faculty of Medicine, University “Pierre et Marie Curie”, 
Paris 6, Paris, France
F. Hug · L. Grélot
Faculty of Sport Sciences, University of the Mediterranean, 
IFR Marey - Marseille, France
T. Marqueste · Y. Le Fur · P. J. Cozzone · D. Bendahan
Faculty of Medicine, University of the Mediterranean, 
Marseille, France
592
and animals (Adams et al. 2004). In addition, most of study and the possible risks and discomfort associated
these results come from needle biopsy studies, an inva-
sive procedure allowing the investigation of a limited
amount of tissue. For obvious reasons, well-trained
sportsmen are very reluctant to take part in invasive
studies for research purposes and few data are conse-
quently available regarding their muscles characteristics.
Magnetic resonance imaging (MRI) is widely
accepted as the most accurate and detailed imaging tech-
nique currently in used. MR images of muscles provide a
clear distinction between fat, muscles, bone and connec-
tive tissues. Muscle MRI has been previously used in
order to investigate training-induced muscular changes
in sedentary subjects (McCall et al. 1996) and alterations
in patients (Kongsgaard et al. 2004) and in elderly sub-
jects (Esmarck et al. 2001). However, to the best of our
knowledge, it is still unknown whether a high volume of
cycling training results in an overall or selective thigh
muscles hypertrophy. We could hypothesize that a selec-
tive muscle hypertrophy would occur in the muscles
most implicated in the pedaling task.
Magnetic resonance imaging is also a non-invasive
technique allowing functional investigations of muscle
activation during exercise. This functional application of
MRI is based on proton transverse relaxation time (T2)
changes measured immediately after exercise which
appear to be graded with exercise intensity (Fisher et al.
1990) and correlated to integrated EMG (Adams et al.
1992). This has been used in order to investigate muscle
recruitment pattern during exercise (Akima et al. 2000)
and more speciWcally in a pedaling task (Akima et al.
2005; Hug et al. 2004; Reid et al. 2001). Because of the
limitations inherent to surface EMG measurements such
as cross-talk from adjacent muscles and, impossibility of
studying deep muscles, the use of exercise-induced T2
changes is considered as a good alternative to identify
muscles recruited during a particular task.
In the present study, we aimed at determining, using
MRI, whether a high volume and intensity of training in
a population of professional road cyclists would account
for an overall or localized muscle hypertrophy. In addi-
tion we aimed at documenting, whether a selective mus-
cle hypertrophy in professional road cyclists, if any,
would be correlated to a higher exercise-induced T2
changes during a pedaling exercise on a cyclo-ergometer.
Materials and methods
Subjects
Sixteen men volunteered for the study. Eight were pro-
fessional cyclists (P) (Wve in the top-200 UCI ranking
and three in the top-400) and eight were age-matched
students (S) from the Department of Sport Sciences
(University of the Mediterranean, France). None of them
had recent or ancient pathology of limb muscles or
joints. All subjects were informed of the nature of the
with the experimental procedures before they gave their
written consent to participate. The study was approved
by the Aix-Marseille II ethics committee and was done in
accordance with the Declaration of Helsinki.
Professional road cyclists were members of diVerent
division 1 trade teams (i.e. CoWdis, Bonjour,
FDJeux.com, AG2R, Crédit Agricole). They had a
7§3 years of international competitive experience. Dur-
ing the last season before the experimentation, they had
covered an average of 30,000 kms (range: 28,000–
34,000 km corresponding to 22§3 h of training and com-
petition per week). Three of the subjects have partici-
pated to the Tour de France and to the World
Championships for professional road cyclists in 2002.
Two others have participated to the Vuelta in 2002.
Some of them had won major international races (stages
in the tour de France and inVuelta, 4 days of Dunker-
que...). Sport sciences students performed 6§2 h of phys-
ical activity per week. Each of them practiced several
recreational activities including football, climbing, bas-
ketball, swimming, and/or rugby but none of them was
involved in cycling. All subjects were instructed to
refrain from intense physical activities during the 2 days
before testing. Professional cyclists did not participate to
any competition during these 2 days and the students did
not perform any physical activity.
Physical and physiological characteristics
The physical and physiological characteristics of the sub-
jects involved in the present study have been previously
reported in a diVerent work devoted to the investigation
of metabolic recovery in professional road cyclists using
31P-MR spectroscopy (Hug et al. 2005). These character-
istics were recorded in the mid morning prior to the
experimentation throughout an incremental bicycle exer-
cise (starting at 100 W; workload increments of 25 W/
min until exhaustion) and are summarized in Table 1.
Table 1 Morphological and physiological characteristics of the
professional road cyclists as compared to the sport science students
The Wrst ventilatory threshold (VT1) refers to the power output val-
ue at which VE/VO2 exhibits a systematic increase without a con-
comitant increase in VE/VCO2. The second ventilatory threshold
(VT2) has been determined on the basis of an increase in both ratios.
VT1 and VT2 have been determined by two independent observers
BMI body mass index, MPT maximal power tolerated
a SigniWcant diVerence between the two populations
Sport science 
students
Professional 
road cyclists
Age (year) 24.0§2.8 24.3§3.2
Height (m) 1.77§0.07 1.83§0.03a
Body mass (kg) 72.1§7.7 73.4§3.9
BMI (kg m¡2) 22.8§2.2 22.0§1.3
VO2 max 
(ml min¡1 kg¡1)
55.9§4.7 74.6§5.1a
MPT (W) 334§24 477§28a
VT1 (% MPT) 54§9 60§7a
VT2 (% MPT) 80§5 89§5a
593
MRI measurements issue of a relationship between exercise-induced T2
After a 4-h recovery period from the incremental exer-
cise, including a freely chosen meal, MRI investigations
were performed at 1.5 T on a Siemens-Vision Imaging
system (Siemens, Germany). The dominant thigh was
placed in the middle of an “extremity coil” (central
diameter = 25 cm). Subjects were scanned in a supine
position with the knee joint fully extended and relaxed.
For each subject, mid-thigh was ink-marked and the cor-
responding mark was aligned with the crosshairs of the
MRI system so that identical positioning was ensured in
the magnet bore over repeated MRI scans. Transverse
T1-weighted images (four slices) were recorded with the
following parameters (TR=441 ms, TE=12 ms, 200 mm
Weld of view, 270£512 acquisition matrix, slice thickness
5 mm, 2.5 mm gap) and a total duration of 122 s. For
each professional road cyclist, axial multiecho MR
images (TR=2,000 ms, TE incremented by 22.5 ms from
22.5 to 360 ms, 25 cm Weld of view, 3 slices, 1 cm slice
thickness, 5 mm gap, 256£256 acquisition matrix, total
acquisition time 257 s) were acquired before and just
after an exercise bout. Post-exercise MRI acquisitions
started 46§8 s after the end of exercise.
Exercise protocol
Professional road cyclists performed a maximal con-
stant-load exercise in the hallway of the MRI center
adjacent to the superconducting magnet room so that
they were always scanned less than a minute after com-
pletion of the exercise. After 10 min of pedaling at
100 W, the load was automatically increased (rate of
change = 50 W s¡1) to the maximum power tolerated
(MPT) which was determined during an incremental
pedaling exercise performed in the morning (Hug et al.
2005). Subjects were asked to maintain this power until
exhaustion (i.e. time to exhaustion at MPT: TlimMPT).
T2-weighted MR images were recorded on the dominant
thigh before and immediately after the exercise. Control
subjects did not perform the exercise test because the
changes and muscle cross-sectional area was addressed
in professional cyclists only.
Images processing
CSA measurements
T1-weighted MR Images were processed using an IDL
(Interactive Data Language, RSI) home-written routine.
BrieXy, on the basis of a signal intensity threshold, fat
and muscle signals were clearly separated and quantiWed
either in the whole thigh or in each of 11 selected muscles
(Vastus lateralis, Rectus femoris, Vastus medialis, Sarto-
rius, Vastus intermedius, Adductor longus, Adductor mag-
nus, Hip adductor, Biceps femoris, Semitendinosus and
Semimembranosus) (Fig. 1). For each subject, we calcu-
lated the ratio of power to muscle cross sectional area
(i.e. MPT/sum of thigh muscles CSA) as previously
described (Reid et al. 2001).
T2 measurements
For each T2-weighted image, a T2 map was generated
from a pixel by pixel analysis from the multiecho images.
T2 values were measured on the 11 thigh muscles. Care
was taken to exclude inter-muscular fat and vascular
structures. T2 values were computed for each muscle and
each slice. Given that these values were not signiWcantly
diVerent among slices; results were averaged over the
three slices. In addition, T2 values recorded at end of the
exercise period were expressed in percentage of the corre-
sponding T2 value recorded at rest and referred as �T2%.
�T2%=100£((T2ex/T2rest)–1).
Statistical analyzes
A Kolmogorov–Smirnov test was used in order to verify
that the values were normally distributed. Then, Mann–
Whitney tests were performed in order to compare
Fig. 1 Localization of the 11 
thigh muscles. VL Vastus latera-
lis, RF Rectus femoris, VM Vas-
tus medialis, Sar Sartorius, VI 
Vastus intermedius, ADL Adduc-
tor longus, ADM Adductor mag-
nus, HA Hip adductor, BF Biceps 
femoris, ST Semitendinosus and 
SM Semimembranosus
FatBoneMuscle
594
variables between the two groups. Exercise-induced T2
changes and diVerences between muscles were analyzed
using a one way analysis of variance (ANOVA). In order
to evaluate the relationship between variables, Pearson
correlation coeYcient was calculated. Statistical signiW-
cance was established at the P<0.05 level. Results are
expressed as mean § SD.
Results
Physiological and physical characteristics
Table 1 depicts morphological and physiological charac-
teristics of both groups. As expected, professional road
cyclists have a higher maximal VO2 and MPT as com-
pared to sport sciences students. For each population, a
typical MR Image at rest is shown in Fig. 2.
CSA measurements
The relative amount of fat in the thigh was signiWcant
higher in sport science students (17.8§7.4%) than in
cyclists (8.8§3.2%). Conversely, professional road
cyclists had a signiWcantly higher relative amount of
muscle (including the whole set of thigh muscles,
90.5§3.3%) as compared to controls (81.6§7.3%). It is
noteworthy that the total thigh CSA including fat, mus-
cles and bone marrow was similar in both groups
(Table 2).
A detailed analysis of each muscle indicated that
absolute CSA values for VL, SAR, AM and BF were
higher in cyclists (Table 2). The total absolute Quadri-
ceps femoris CSA (i.e. VL + VI + RF + VM) was also
signiWcantly higher in professional road cyclists as com-
pared to sport sciences students (8,999§620 and
7,669§891 mm2, respectively). Regarding relative values
expressed with respect to the total thigh muscles CSA,
VL and BF CSA were signiWcantly larger in cyclists
whereas CSA of the VI was smaller (Fig. 3).
Table 2 Cross sectional area value for each thigh muscle
Thigh CSA corresponds to the sum of muscles and fat CSA, and all muscles CSA represents only the muscles CSA
a SigniWcant diVerence between the two populations
CSA (mm2) Sport science students Professional road cyclists
Mean § SD Range Mean § SD Range
Thigh 19,295§3,701 15,158–24,478 20,176§1,869 17,440–23,308
All muscles 14,183§1,856 11,425–16,60817,114§1,335a 15,330–18038
Vastus lateralis 2,829§546 2,216–3,303 3,797§275a 3,505–4,312
Rectus femoris 1,017§286 610–1,345 1,257§168 1,138–1,514
Vastus medialis 921§169 562–1,212 968§187 730–1,257
Vastus intermedius 2,901§255 2,682–3,302 2,976§282 2,630–3,512
Sartorius 406 § 63 290–501 507§88a 401–656
Adductor longus 936 § 397 449–1,472 1,019§188 863–1,446
Adductor magnus 2652 § 684 1,869–4,003 3,413§589a 2,626–4,352
Hip adductor 520 § 111 362–696 649§198 461–1,083
Biceps femoris 951 § 102 787–1390 1,372§179a 1,128–1,641
Semitendinosus 1036 § 275 457–1370 1,117§300 689–1,528
Semimembranosus 530 § 166 299–824 685§149 494–955
Fig. 2 Individual example of a thigh MR image obtained in a pro-
fessional road cyclist and in a Sport science student
VL
RF
VM
VI
Sar
ADL
HA
BF
ST
SM
BF
ADM
ADM
50 mm
50
 m
m
VL
RF
VM
VI
Sar
ADL
HA
BF
ST
SM
BF
ADM
ADM
50 mm50 mm
50
 m
m
50
 m
m
VL
RF
VM
VI
Sar
ADL
HA
BF
ST
SM
BF
ADM
ADM
VL
RF
VM
VI
Sar
ADL
HA
BF
ST
SM
BF
ADM
ADM
595
cyclists, a population restricted to approximately 40025
Exercise-induced T2 changes
TlimMPT measured during the maximal constant-load
exercise was 174§29 s (range: 75–300 s, variation
coeYcient = 16.6%). T2 maps were generated on a pixel
by pixel analysis and recorded before and immediately
after the exercise period. The corresponding �T2% values
are summarized in Table 3. T2 values signiWcantly
increased after exercise, the magnitude of changes rang-
ing from 0.5 to 33.3%. The statistical analysis indicated a
similar exercise induced T2 changes for the whole set of
muscles (except between Sartorius and Adductor longus).
We found no signiWcant correlation between exercise T2
changes and muscle CSA.
Discussion
In the present study, we reported for the Wrst time a
selective muscle hypertrophy of two thigh muscles i.e.
vastus lateralis and biceps femoris in professional road
members all over the world.
CSA measurements
Considering that muscle hypertrophy has been largely
reported as a result of resistance training (Green et al.
1999; Kraemer et al. 1995; Sipila and Suominen 1995),
this muscle hypertrophy measured in professional
cyclists could be considered as unexpected given that
they generate high power output exercises during only
few minutes during both training and competition peri-
ods. However, endurance (McCarthy et al. 2002) or com-
bined heavy resistance-endurance (Izquierdo et al. 2005)
training have also been shown to induce muscle hyper-
trophy. At this stage, one can wonder whether the selec-
tive muscle hypertrophy which is reported in the present
study is linked to an involvement of vastus lateralis and
biceps femoris in either resistance and/or endurance
training. In other words, one could wonder whether these
two muscles are more particularly involved in cycling
activity compared to the others thigh muscles.
During pedaling exercise, muscle groups and individ-
ual muscles surrounding the hip, knee, and ankle joints
work as primary contributors of power output. Based on
a dynamic mechanical model, it has been previously
reported that hip extensor, knee extensor and ankle plan-
tar Xexor muscles contribute respectively to 27, 39 and
20% of the total energy production during pedaling exer-
cise (Ericson et al. 1986). On the contrary, the relative
contribution of hip Xexor and knee Xexor muscles is,
according to the same model, much more reduced and
amounts to 4 and 10% respectively (Ericson et al. 1986).
These results suggest that knee extensor and knee Xexor
muscles contribute approximately to half of the work
output performed during cycling, and that thigh muscles
play the major role in the pedaling task. For this reason,
we chose to preferentially study thigh muscles. These
thigh muscles are actually involved in various actions.
The vastus lateralis and medialis muscles constitute half
of the powerful quadriceps group and extend the knee.
As a result of its localization (it crosses both hip and
knee joints), the Rectus femoris both Xexes the hip and
extends the knee. The Biceps femoris long head also
crosses two joints (i.e. hip and knee) and extends the hip
and Xexes the knee. Semimembranosus has the same role
as Biceps femoris. All these muscles can be recruited dur-
ing pedaling exercise at diVerent levels (Akima et al.
2005; Ericson et al. 1986; Hug et al. 2004). Previous
EMG (Ericson et al. 1986; Hug et al. 2006), and biopsy
studies (Essen et al. 1977) have demonstrated that the
Vastus lateralis was greatly activated during a pedaling
task. However, superWcial and deeper muscles cannot be
investigated simultaneously using these techniques and
the issue of a reliable quantiWcation is still controversial.
The relative contribution of Vastus lateralis is then
impossible to accurately determine on the basis of such
measurements. On the contrary, comparative analyzes
are possible using MRI. Recently, it has been reported
Fig. 3 Cross sectional area of each thigh muscle expressed in per-
centage of total thigh muscles CSA. Same legends as for Fig. 2.
Asterisks indicates signiWcant diVerence between the two popula-
tions
*
*
*
0
5
10
15
20
VL RF VM Sart VI ADL ADM HA BF ST SM
Muscles
R
el
at
iv
e 
CS
A,
%
Professional Road Cyclists
Sport Science Students*
*
*
Professional Road Cyclists
Sport Science Students
Professional Road Cyclists
Sport Science Students*
*
*
Table 3 Exercise-induced T2 changes in professional road cyclists
(T2%=100£((T2ex/T2rest)–1)
a SigniWcant diVerence between adductor longus and sartorius
Muscle �T2 (%) Range
Vastus lateralis 13.5§2.8 11.7–20.1
Rectus femoris 11.5§5.6 6.0–20.8
Vastus medialis 9.4§4.18 4.7–16.3
Vastus intermedius 15.3§9.8 4.1–33.3
Sartorius 17.1§5.01 11.0–23.8
Adductor longus 6.6§5.6a 0.5–14.0
Adductor magnus 13.2§4.5 2.3–6.2
Hip adductor 15.1§6.5 6.9–23.0
Biceps femoris 13.1§4.8 2.5–18.5
Semitendinosus 12.9§5.7 3.9–20.9
Semimembranosus 9.9§4.0 4.2–16.7
596
that VL was the most activated thigh muscle during a regarding the inXuence of hyperactivity on muscle Wbers
sub-maximal constant load exercise (Reid et al. 2001) or
sprints (Akima et al. 2005). Our results showing a selec-
tive hypertrophy of Vastus lateralis in professional road
cyclists further conWrm its involvement in pedaling tasks
and suggest a possible cause–eVect relationship between
muscle activation and hypertrophy.
Takaishi et al. (1998) showed that the Biceps femoris
normalized integrated EMG measured during a progres-
sive exercise increased in trained cyclists whereas it
remained unchanged in sedentary subjects. They sug-
gested that Biceps femoris acted on the rising phase of
the pedaling action in order to alleviate the involvement
of knee extensor muscles. This pedaling skill developed
in highly trained cyclists could account for the absolute
and relative hypertrophy we reported in the present
cyclists’ population.
Several studies performed in well-trained cyclists
(Coyle et al. 1992; Horowitz et al. 1994) suggest that the
high training status of this population accounts for a
homogeneous change in Wbres type composition with a
high percentage of type I muscle Wbers and 20 times
lower content of type IIB (Baumann et al. 1987). Stone
et al. (1996) showed that this muscle Wbers conversion is
accompanied by both slow and fast twitch muscle Wbers
hypertrophy which could explain the increased muscle
CSA observed in our study.
It could be argued that muscle area determined from
the single-slice method may not be representative of
changes that occur at other points along the length of the
muscle (Narici et al. 1996). However, it has been shown
that training-induced muscle hypertrophy is the greatest
in the region of largestCSA (mid-thigh), and that CSA
increase becomes progressively smaller toward the proxi-
mal and distal regions of the quadriceps (Narici et al.
1996; Tracy et al. 1999). For this reason and according to
the methodology employed by previous MRI studies
(Kongsgaard et al. 2004; Moser et al. 2000; Ploutz et al.
1994) we chose to determine thigh muscles CSA at mid-
thigh level. It is noteworthy that quadriceps femoris or
total thigh CSA measurements in our sport science stu-
dents’ population are similar to those previously
reported in sedentary healthy men (Ploutz et al. 1994;
Tracy et al. 1999). Also, one has to keep in mind that
many human muscles are characterized by a pennate
arrangement of muscle Wbers relative to the points of ori-
gin and insertion. In terms of muscle CSA, the phenome-
non of muscle Wber pennation allows to diVerentiate
physiological and anatomical muscle CSA. Physiological
muscle CSA takes account of muscle Wber area perpen-
dicular to the longitudinal axis of a given muscle and the
pennation angle (Powell et al. 1984). It usually exceeds
the anatomical muscle CSA measured in the axial plane.
Then, changes in anatomical CSA or total muscle vol-
ume caused by training may not be representative of the
changes in physiological CSA, and therefore in force
generating capacity, since muscle Wber pennation angle
could also change in response to training (Aagaard et al.
2001). However, only few and conXicting data exist
pennation angle.
Although Vastus intermedius absolute CSA was not
diVerent between the two populations, the relative value
was signiWcantly smaller in professional road cyclists
suggesting an underutilization of this muscle during ped-
aling with respect to the other thigh muscles (Fig. 3).
This result is in agreement with the smaller exercise-
induced T2 changes reported after a cycling sprint exer-
cise when compared to other knee extensor muscles (i.e.
vastus lateralis, rectus femoris) (Akima et al. 2005).
Exercise-induced T2 changes in professional road cyclists
Considering, as previously reported (Adams et al. 1992;
Akima et al. 2000; Fisher et al. 1990) that the exercise-
induced T2 increase indicates muscle recruitment, our
results show a similar recruitment of the whole thigh
muscles during the constant load pedaling exercise. We
identiWed a single exception linked to the adductor longus
which was signiWcantly less recruited than the sartorius
muscle. Our results do not conWrm those obtained during
a sprint cycling exercise (Akima et al. 2005). Akima et al.
(2005) reported that Vastus lateralis, Vastus intermedius
and Vastus medialis were diVerently activated during
such an exercise. However, this diVerence is likely to be
due to the experimental protocol given that a similar
activation among thigh muscles has been previously
reported during a constant load exercise performed at
90% of MPT (Richardson et al. 1998).
Based on this result, the selective thigh muscles hyper-
trophy in professional road cyclists (i.e. Vastus lateralis
and Biceps femoris) would not be in line with a higher
muscle activation, at least during a laboratory test. One
could argue that the laboratory exercise intensity is not
representative of what occurs throughout training and/
or races. Furthermore, Reid et al. (2001) have reported
that the relative contribution of thigh muscles to exercise
can vary with respect to the exercise intensity (i.e. 90 vs.
50% of MPT). However, MRI investigations of muscle
recruitment are only possible during laboratory tests. It
could also be speciWed that T2 changes could be not sen-
sitive enough to detect subtle diVerence regarding muscle
activation. It should be kept in mind that exercise-
induced T2 changes are related to the metabolic capacity
of the working muscle. In that respect, the comparison
among diVerent muscles with diVerent aerobic capacities
on the basis of T2 changes could be less reliable even
more when the diVerence of muscle activation is small
(Reid et al. 2001).
Overall, even if the selective hypertrophy is not clearly
linked to diVerent muscle activation, we cannot rule out
that such a relationship exists in real situation of training
and/or competition.
Acknowledgments This study was supported by a grant from Ama-
ury Sport Organisation (ASO-Société du Tour de France). We
would like to greatly acknowledge the professional road cyclists and
the sport sciences students for their active participation to the exer-
cises protocol. We also acknowledge the commitment of the team
597
managers who strongly supported this research protocol (CoWdis, Hug F, Laplaud D, Lucia A, Grélot L (2006) EMG threshold deter-
Bonjour, FDJeux.com, AG2R Prévoyance & Crédit Agricole).
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	Selective training-induced thigh muscles hypertrophy in professional road cyclists
	Abstract
	Introduction
	Materials and methods
	Subjects
	Physical and physiological characteristics
	MRI measurements
	Exercise protocol
	Images processing
	CSA measurements
	T2 measurements
	Statistical analyzes
	Results
	Physiological and physical characteristics
	CSA measurements
	Exercise-induced T2 changes
	Discussion
	CSA measurements
	Exercise-induced T2 changes in professional road cyclists
	Acknowledgments
	References

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