Publications by authors named "Georges Poumarat"

7 Publications

  • Page 1 of 1

Posture and muscular behaviour in emergency braking: an experimental approach.

Accid Anal Prev 2010 May;42(3):797-801

Laboratoire de Biomécanique Appliquée, UMRT24 INRETS/University of Mediterranée, Boulevard Pierre Dramard, Marseille, France.

In the field of numerical crash simulations in road safety research, there is a need to accurately define the initial conditions of a frontal impact for the car occupant. In particular, human models used to simulate such impacts barely take into account muscular contracting effects. This study aims to quantify drivers' behaviour in terms of posture and muscular activity just before a frontal impact. Experiments on volunteers were performed in order to define these conditions, both on a driving simulator and on a real moving car. Brake pedal loads, lower limbs kinematics and muscle activation were recorded. Coupling instantaneous data from both experimental protocols (simulator versus Real car), a standard emergency braking configuration could be defined as (1) joint flexion angles of 96 degrees, 56 degrees and 13 degrees for the right hip, knee and ankle respectively; (2) a maximum brake pedal load of 780N; (3) a muscular activation of 55% for the anterior thigh, 26% for the posterior thigh, 18% for the anterior leg and 43% for the posterior leg. The first application of this research is the implementation of muscle tone in human models designed to evaluate new safety systems.
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May 2010

Tibiofemoral joint kinetics during squatting with increasing external load.

J Sport Rehabil 2008 Aug;17(3):300-15

Department of Physical Medicine and Functional Rehabilitation, Habib Bourguiba Hospital, University of Sfax, Tunisia.

Context: There is limited information about the effects of increasing load while squatting.

Objective: To quantify tibiofemoral joint kinetics during squatting with variable loads.

Setting: Research laboratory.

Participants: 20 male students.

Intervention: Tibiofemoral joint kinetics and electromyographic (EMG) activity of four involved muscles were determined by recording the half squat with variable external loads.

Main Outcome Measures: Tibiofemoral joint force and external moment components and EMG activity of four involved muscles.

Results: Throughout the exercise, a posterior direction for the antero-posterior shear force and a net extension for the external moment were observed. They increased with knee flexion reaching peak force of 29% of the subject body weight (BW) and moment of 88Nm (without external load). All force and moment components and muscle activities increased as the external load increased.

Conclusion: These findings suggest that half squat may be safe to use for quadriceps strengthening with very low potential loading on the anterior cruciate ligament (ACL). Our data can help clinicians choose the appropriate external load.
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August 2008

New insights into the function of the vastus medialis with clinical implications.

Med Sci Sports Exerc 2007 Jul;39(7):1153-9

Cardiff School of Biosciences, University of Cardiff, Museum Avenue, Cardiff, United Kingdom.

Purpose: To investigate the gross anatomy of the distal portion of the quadriceps, and to compare the relative contributions of the vastus medialis oblique (VMO) and vastus lateralis (VL) during dynamic weight-bearing conditions.

Methods: Dissection was carried out on 10 cadavers by a longitudinal incision from the anterior superior iliac spine to the patella and completed with upper and lower transverse cuts to reinvestigate the gross anatomy and innervation patterns of the quadriceps femoris. A biomechanical test of knee kinematics was conducted on 10 healthy male volunteers. Maximal isometric force, squat jump, and drop movement jump exercises were performed on a force plate and filmed using a Saga-3 3D system, and surface EMG activity was recorded for the VMO and the VL.

Results: The oblique fibers of the vastus medialis (VM) are not only attached to the medial border of the patella, but they also have a small region of direct continuity with the patellar tendon. Furthermore, VMO fibers in the middle and proximal thirds of the thigh attached to vastus intermedius, whereas distally, the fibers were independent. Both parts of the VM (proximal and distal) had independent motor points. During jumping exercises, the VMO and VL were activated in a coordinated manner in a squat jump using both legs. However, in a single-leg squat jump (which challenged the stability of the knee joint more acutely), VMO activation was higher during landing.

Conclusion: VMO activity was pronounced during the weight-bearing conditions, with increased medial and lateral knee movements. This suggests that the VM should not be considered simply as a knee extensor or as a muscle whose main role is to maintain normal patellar tracking.
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July 2007

Fatigue and muscle-tendon stiffness after stretch-shortening cycle and isometric exercise.

Appl Physiol Nutr Metab 2006 Oct;31(5):565-72

ERIM EA 3295, University of Auvergne Medical School, 63000 Clermont-Ferrand, France.

The purpose of the present study was to compare vertical jump performance after 2 different fatigue protocols. In the first protocol, subjects performed consecutive sets of 10 repetitions of stretch-shortening cycle (SSC) contractions. In the second protocol, successive sets of 10 repetitions of isometric contractions were performed for 10 s with the knee at 90 degrees of flexion. The exercises were stopped when the subjects failed to reach 50% of their maximum voluntary isometric contractions. Maximal isometric force and maximal concentric power were assessed by performing supine leg presses, squat jumps, and drop jumps. Surface EMG was used to determine changes in muscle activation before and after fatigue. In both groups, the fatigue exercises reduced voluntary isometric force, maximal concentric power, and drop jump performance. Kinematic data showed a decrease in knee muscle-tendon stiffness accompanied by a lengthened ground contact time. EMG analysis showed that the squat and drop jumps were performed similarly before and after the fatigue exercise for both groups. Although it was expected that the stiffness would decrease more after SSC than after isometric fatigue (as a result of a greater alteration of the reflex sensitivity SSC), our results showed that both protocols had a similar effect on knee muscle stiffness during jumping exercises. Both fatigue protocols induced muscle fatigue, and the decrease in jump performance was linked to a decrease in the strength and stiffness of the knee extensor muscles.
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October 2006

Vastus medialis: anatomical and functional considerations and implications based upon human and cadaveric studies.

J Manipulative Physiol Ther 2006 Feb;29(2):139-44

Département de Kinanthropologie, Université du Québec à Montréal, Montreal, Quebec, Canada.

Objective: To provide an electrophysiological and functional description of the vastus medialis (VM) and contrast it to an anatomical description.

Methods: Motor points of all superficial portions of the quadriceps were identified on the dominant side of 8 human subjects and electrically stimulated to achieve a light contraction to trace and measure the orientation of the fibers. Electromyography of the VM was then recorded over 2 motor points during isometric and isokinetic maximum knee extensions. An independent laboratory dissected 39 cadaveric specimens focusing on fiber orientations and distal insertions of the VM.

Results: Results revealed 5 motor points for the quadriceps: 1 point for the vastus lateralis, 1 point for the rectus femoris (RF), and 3 points for the VM. The 3 VM motor points suggest 3 separate groups of fibers: proximal (pf), median (mf), distal (df). Fiber orientations ranged from 45 degrees for VMpfs to 55 degrees for VMdfs. Motor point stimulation and anatomical dissection clearly showed that the VMpfs and VMmfs were inserted on a tendon common to the RF, whereas VMdfs were attached directly to the medial aspect of the patella. Furthermore, the VMpfs were more active (P < .05) than VMdfs during maximum knee extensions.

Conclusion: The anatomy, motor points, and electromyography clearly support an important distinction between the VMpfs and VMdfs. The role of the VMpfs would be one of assisting the RF in knee extension, whereas the VMdfs would track the patella medially without participating in knee extension. Because of these anatomical and functional differences, the VMpfs and VMdfs should be addressed very differently during quadriceps rehabilitation in patellofemoral dysfunctions.
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February 2006

[Design of a prototype operating seat with SESAM (Ergonomic System of Mobile Forearm Rests) mobile armrests designed to optimize the surgeon's ergonomy during pelvic laparoscopy].

Prog Urol 2004 Dec;14(6):1181-7

Service d'Urologie, CHU de Saint-Etienne, France.

Introduction: Pelvic laparoscopic surgery offers multiple advantages for patients, but requires uncomfortable, non-ergonomic positions for the surgeon. Only a remote operator (Robot "slave" reproducing the surgeon's movements performed on a "master" console situated away from the patient), like Da-Vinci or Zeus (Intuitive Surgical) can improve the laparoscopic surgeon's working conditions. The objective of this study, based on an ergonomic analysis and recording of a laparoscopic surgeon's movements, was to define the specifications for the manufacture of an operating seat with armrests, based on the surgeon's position using a remote operator.

Material And Methods: Movements of the centre of pressure and upper limbs of 12 urologists and gynaecologists with various levels of experience, were recorded using a force platform and a SAGA 3 RT movement analysis system (Biogesta), during 4 exercises performed on a pelvi-trainer, with the surgeon positioned to the left (introduction of a needle, unravelling of a cord, dissection, suture). Ergonomic analysis of the laparoscopic surgeon's movements was based on video recordings of a surgeon under real operating conditions. The specifications were defined from all of these data.

Results And Discussion: The small amplitude of movements of the surgeon 's centre of pressure (< 45 cm2) confirmed that surgeons can be seated during laparoscopy. Recordings of the upper defined the elbow working zones and the need for 3D mobile armrests. Ergonomic analysis of posture defined the characteristics of the prototype. On the basis of these specifications, a prototype operating seat was developed. This prototype now needs to be validated or invalidated clinically.
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December 2004

[Effect of antenatal gymnastics on childbirth: a study on 50 sedentary women in the Republic of Benin during the second and third quarters of pregnancy].

Sante 2003 Oct-Dec;13(4):235-41

Institut national de la jeunesse, de l'éducation physique et du sport, Porto-Novo, 01 BP 169, Benin.

Antenatal gymnastics is a form of non-pharmacological childbirth preparation methods. It helps maintain rachidian statics and to relieve painful syndromes (joints, lumbar pains) during pregnancy. It also helps correct gravidic problems (leg cramps, back ache, weight increase, etc.). It is both a physical and psychological training method in accordance with the natural mechanisms of childbirth, implying personal involvement on the part of the parturient. Fifty (50) pregnant women of Benin (apart from pathological pregnancies) divided into two groups of 25 subjects (experimental group) and 25 subjects (control group) voluntarily took part in the study after having given their written assent. Each involved subject is paired with a counterpart of control following the same criteria: age of the gestante, parity, characteristic of the pelvis. Subjects aged from 17 to 42 trained twice a week with a minimum of 24 hours rest between two sessions; the training period intensity of exercise is limited to 60% of the maximum heart frequency and each training session lasts 45 min. The results show a lower number of caesareans and a significant lower number of untorn perineas in the experimental group. Apgar scores are also statistically higher in the children of trained women. This study confirms that sedentary pregnant women without any medical counter-indications (repetitive miscarriages, premature births, placenta praevia, cervical gaping, cardiac diseases, hypertension, narrow pelvis) can participate in antenatal gymnastics at a moderated rhythm, for their own benefit and that of their babies. Muscular force improvement (quality of the abdominal pushing), psychological control (absence of stress and panic), and good body form, can be noticed in trained mothers. However, abnormal presentation of baby, fetal suffering and the inherent characteristics of the pelvis (narrow) are factors requiring a caesarean. On the whole, antenatal gymnastics is an effective non-pharmacological means to avoid complications in childbirth. This method might be one of the solutions which could benefit pregnant women in Africa, considering its low cost compared to the exorbitant cost of medicines and hospitalisation.
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April 2004