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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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J Appl Physiol 86(1):195–201 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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