Serge LE BOZEC - Academia.edu (original) (raw)

Papers by Serge LE BOZEC

Neurophysiologie Clinique-clinical Neurophysiology, Nov 1, 2015

Le but de ce travail a ete d'evaluer le role de la mobilite rachidienne dans le maintien de l... more Le but de ce travail a ete d'evaluer le role de la mobilite rachidienne dans le maintien de l'equilibre postural chez le sujet sain et chez le lombalgique, a partir de trois etudes distinctes. La premiere etude a evalue les deplacements du centre des pressions (CP) et les mouvements respiratoires au cours d'efforts de poussee manuels sub-maximum, en posture assisse. La mobilite lombo-pelvienne a ete modulee par l'utilisation de deux niveaux de surface d'assise. Les resultats ont montre que la diminution de mobilite du rachis lombo-pelvien augmentait la composante respiratoire des deplacements du CP, suggerant que cette region avait un role cle dans la compensation de la perturbation respiratoire a la posture. La deuxieme etude a analyse les deplacements du CP et les mouvements respiratoires en posture debout chez dix sujets lombalgiques et chez dix sujets sains, en condition de respiration normale lente et rapide. Chez les sujets lombalgiques, la stabilite posturale s'est revelee davantage perturbee par une augmentation de la frequence respiratoire. Il en a ete deduit que la respiration perturbe davantage la posture dans la lombalgie chronique. La troisieme etude a evalue les deplacements du CP en posture debout, et les amplitudes articulaires dorso-lombaires, chez dix sujets lombalgiques et chez dix sujets sains. Chez les sujets lombalgiques, l'augmentation significative des deplacements du CP n'a presente aucune correlation avec la faible diminution de la mobilite dorso-lombaire. Il en a ete deduit que l'augmentation des oscillations posturales dans la lombalgie chronique n'est pas due a une diminution des amplitudes articulaires rachidiennes.

The relative contribution of synergistic muscles has been studied during pedalling on a bicycle. ... more The relative contribution of synergistic muscles has been studied during pedalling on a bicycle. The electromyographic (EMG) activity of the different components of triceps surae (namely soleus or SOL and medial gastrocnemius or MG) has been recorded and analyzed for increasing pedalling speed performed against increasing resistance. The results indicate that SOL IEMG (integrated EMG) increases linearly (y = 2x-12.1; r = 0.98) with increasing load (10-70 N) at constant speed (60 rpm), whereas no change is noted in MG IEMG below 40 N. In contrast, when the pedalling speed is increased (from 30 to 170 rpm) at constant load, MG IEMG shows the largest increase. Furthermore, although in both muscles EMG activity appears earlier in the movement with increases in load and/or speed, the delay between the onset of both EMGs remains unchanged at constant speed and synchronization of MG with SOL is only observed when speed is increased above 140 rpm. These results suggest that the different mu...

L'objectif general de ce travail de these etait d'examiner, chez le sujet jeune et bien p... more L'objectif general de ce travail de these etait d'examiner, chez le sujet jeune et bien portant, l'adaptabilite des commandes motrices posturale et focale associees a une tâche de poussee bilaterale dynamique lorsque la capacite posturo-cinetique est specifiquement contrainte par trois types de facteurs : i) le changement d'appui de bipodal a unipodal (1ere experimentation), ii) la dominance posturale (appui unipodal sur la jambe dominante ou sur la jambe non dominante ; 2eme experimentation), et iii) la fatigue posturale (3eme et 4eme experimentation). Les resultats de la 1ere experimentation ont montre que le systeme nerveux central augmentait la duree des ajustements posturaux anticipateurs (APA) en condition unipodale de facon a maintenir un niveau de forces inertielles equivalent a celui obtenu en condition bipodale, et donc a maintenir un niveau de contreperturbation anticipatrice equivalent. Il en resultait une performance focale (vitesse maximale) optimale. L...

SCOPUS: NotDefined.jinfo:eu-repo/semantics/publishe

Experimental Brain Research, 2016

This paper deals with the influence of velocity on the postural adjustments that occur during the... more This paper deals with the influence of velocity on the postural adjustments that occur during the course of a voluntary movement, that is to say, simultaneous postural adjustments (SPA). To this aim, a pointing task performed at different velocities (V) was considered. Upper limb kinematics and body kinetics were recorded. Using a 2-DOF model, the body was divided into two parts: the right upper limb (termed the “focal” chain) and the rest of the body (termed the “postural” chain). This model allowed us to calculate the kinetics of both subsystems (−Fx and RtextxprimeR_{\text{x}}^{{\prime }}RtextxprimeRx′), with one corresponding to the resultant action on the shoulder (AoSh: −Fx) and the other to the resultant reaction of the shoulder (RoSh: RtextxprimeR_{\text{x}}^{{\prime }}RtextxprimeRx′). The influence of pointing velocity on peak amplitudes and durations was evaluated, as was their instantaneous relationship (“Lissajous ellipse”). The results showed that RoSh and AoSh display similar diphasic profiles, whose amplitude and duration vary with movement velocity. In addition, RoSh is in phase advance of AoSh, the advance being all the shorter as the focal movement velocity becomes faster. Finally, SPA appears to play a dual role, which includes a propulsive action during upper limb acceleration and body stabilization during deceleration. These new findings strengthen the hypothesis that the postural chain is programmed according to task velocity in the same way as the focal chain and that both are coping in order to make the task more efficient.

Determination of joint efforts in the human body during maximum ramp pushing efforts

Neurophysiologie Clinique

Neuroscience Letters, Apr 27, 2001

The purpose of this study was to explore how the muscles which control postural body segments are... more The purpose of this study was to explore how the muscles which control postural body segments are activated during bilateral isometric ramp pushes exerted with the upper limbs by seated subjects. The paradigm under study presents the advantage that the subject is in a quasi-static posture, and since upper limbs are stretched out, the dynamic phenomena, which might occur, can only originate from the rest of the body, which means from the postural chain. A dynamometer was used to measure the horizontal force, Fx, exerted on the bar, and a custom-designed force-plate was used to measure global reaction forces (Rx) and displacement of the centre of pressure (Xp) along the antero-posterior axis. Electromyograms (EMGs) were picked up by bipolar surface electrodes from 14 muscles crossing the lower limb, pelvis, trunk and upper limb joints. It was shown that transient push efforts require monotonous EMG increase in postural as well as in focal muscles. The EMG sequence starts with the postural muscles and ends with the focal ones. The postural EMG sequence is anticipatory. It is concluded that the EMG sequence is programmed according to the task parameters, and that its role is to counteract in advance the perturbing effect of the effort, in order to allow the effort to be performed ef®ciently. It is suggested that excitation between the postural muscles is distributed according to their biomechanical role in relation to the supports.

Experimental Brain Research, 2004

The Journal of Sports Medicine and Physical Fitness, 2015

Quantification of physical activity as energy expenditure is important since youth for the preven... more Quantification of physical activity as energy expenditure is important since youth for the prevention of chronic non communicable diseases in adulthood. It is necessary to quantify physical activity expressed in daily energy expenditure (DEE) in school children and adolescents between 8-16 years, by age, gender and socioeconomic level (SEL) in Bogotá. This is a Two Stage Cluster Survey Sample. From a universe of 4700 schools and 760000 students from three existing socioeconomic levels in Bogotá (low, medium and high). The random sample was 20 schools and 1840 students (904 boys and 936 girls). Foreshadowing desertion of participants and inconsistency in the questionnaire responses, the sample size was increased. Thus, six individuals of each gender for each of the nine age groups were selected, resulting in a total sample of 2160 individuals. Selected students filled the QAPACE questionnaire under supervision. The data was analyzed comparing means with multivariate general linear model. Fixed factors used were: gender (boys and girls), age (8 to 16 years old) and tri-strata SEL (low, medium and high); as independent variables were assessed: height, weight, leisure time, expressed in hours/day and dependent variable: daily energy expenditure DEE (kJ.kg-1.day-1): during leisure time (DEE-LT), during school time (DEE-ST), during vacation time (DEE-VT), and total mean DEE per year (DEEm-TY) RESULTS: Differences in DEE by gender, in boys, LT and all DEE, with the SEL all variables were significant; but age-SEL was only significant in DEE-VT. In girls, with the SEL all variables were significant. The Post-hoc multiple comparisons tests were significant with age using Fisher's Least Significant Difference (LSD) test in all variables. For both genders and for all SELs the values in girls had the higher value except SEL high (5-6) The boys have higher values in DEE-LT, DEE-ST, DEE-VT; except in DEEm-TY in SEL (5-6) In SEL (5-6) all DEEs for both genders are highest. For SEL (3-4) all DEEs are lowest. Children and adolescents in Bogotá have less DEE than at other latitudes. Girls have more free time but lower energy expenditure in their different activities. The socioeconomic level has influence in DEE.

Motor Control and Learning, 2006

Neuroscience Letters, 2010

The purpose of this study was to determine whether respiratory disturbance to posture varies as a... more The purpose of this study was to determine whether respiratory disturbance to posture varies as a function of the respiratory mode, i.e. thoracic or abdominal. To this aim, 10 healthy male subjects underwent a posturographic examination associated with a measurement of respiratory kinematics. Experimental conditions varied posture (sitting, standing) respiratory amplitude (quiet breathing, deep breathing) and respiratory mode (thoracic, abdominal). In addition to classical posturographic parameters, original peak detection algorithm and emergence parameter calculated from the Fast Fourier Transform were used to assess the respiratory component in CP displacements. Results showed that along the antero-posterior axis, time domain and frequency domain parameters were both significantly greater in thoracic breathing mode than in abdominal mode. It was concluded that respiratory kinematics have a more prominent disturbing effect on posture when they involve the rib cage rather than the abdomen.

Neuroscience Letters, 2007

The current study was designed to test the effect of changing the base of support (BoS) size in t... more The current study was designed to test the effect of changing the base of support (BoS) size in the initial posture on the performance of a pointing task and the associated "anticipatory postural adjustments" (APAs). Subjects performed series of arm pointing tasks at maximal velocity, from five postures that differed by the antero-posterior (AP) distance between the heels. This distance was increased stepwise from 0 cm (P0 condition) to 40 cm (P40 condition). Kinetics data were collected with a large force-plate, and kinematics data of the pointing were collected with a bi-axial accelerometer (AP and vertical direction) fixed at the wrist. ANOVA showed that the amplitude and the efficiency of the APAs, as well as the performance of the pointing, all statistically increased from P0 to P40 (with 0.0001 < P < 0.01). Altogether, these results provide support to the "Posturo-Kinetic Capacity" theory according to which the performance of the focal component of a motor task tightly depends on the capacity of the postural component to develop efficient anticipatory dynamics.

Journal of Biomechanics, 1994

Gait & Posture, 2014

The aim of this study was to determine whether increased muscular tension disturbs postural equil... more The aim of this study was to determine whether increased muscular tension disturbs postural equilibrium more when it is asymmetrical. Ten healthy male subjects underwent a posturographic examination associated with an original uni and bilateral compressive load paradigm designed to set the active muscular tension at different controlled levels along each side of the torso. Respiratory kinematics were recorded by means of two sensing belts. Two electromyographic pre-tests were used to map out the main motor muscles of the task and to quantify the level of asymmetry induced by unilateral loads. The posturographic examination revealed that the mean deviation of the CP along the medial-lateral axis was significantly greater in unilateral than in bilateral compressive loads. It was suggested that increased muscular tension along the torso induces a more disturbing effect on posture when it is asymmetrical.

Gait & Posture, 2011

Eleven healthy male subjects, recruited from the university population, took part in this study. ... more Eleven healthy male subjects, recruited from the university population, took part in this study. None of them had any recent history of neurological, musculo-skeletal or respiratory disease. The mean (AESD) age, height, weight and body mass index were 21 (AE3) years, 175 (AE5) cm, 68 (AE5) kg, 22 (AE2), respectively. Experiments were approved by the local ethics committee, and complied with the Helsinki declaration. Written informed consent was obtained from all subjects.

Gait & Posture, 2007

This study investigated the effect of postural chain muscular stiffening on postural steadiness w... more This study investigated the effect of postural chain muscular stiffening on postural steadiness when it is rhythmically perturbed by respiration. It consisted of an analysis of centre of pressure (CP) displacements when constant sub-maximum pushing efforts were performed in a sitting posture. Muscular stiffness, assessed by surface electromyography (iEMG), was imposed at two controlled levels, using two intensities of pushing effort (20% and 40% of the maximum voluntary contraction: 20MVC and 40MVC). Lumbo-pelvic mobility was varied using two different support areas at the seat contact (100% and 30% of the ischio-femoral length: 100BP and 30BP). Respiratory disturbance to posture was varied using two respiratory rate conditions (quiet breathing (QB), which is the spontaneous rate, and fast breathing (FB) at a rate imposed by a metronome). The results demonstrated that an increased push effort was associated to a higher iEMG level, and induced greater mean deviation ðX p Þ and sway path (SP) of antero-posterior CP displacements. It was concluded that postural muscle stiffness reduces postural steadiness. It was suggested that it could be related to a weaker compensation of respiratory disturbance to body posture.