DETERMINATION OF INERTIA ELEMENTS FOR THE LOWER LIMBS

INTRODUCTION: For kinematic and dynamic studies of the lower limbs, using a three dimensional model is useful. Such models allow one to determine segment movements and forces acting on joints. Inverse Dynamic Analysis can be used to calculate the biomechanical loads applied (Elftman,1939). The reliability of the results depends on the degree of accuracy of the kinematic and anthropometric data (Kingma et al.,1996).The purpose of this paper is to explain a simple way to determine inertia elements of the lower limbs using anthropometric data available in the literature. METHODS: Body mass and stature are the only anthropometric parameters known for a subject. Body segment inertia parameters are obtained from cadavers and we use here de Leva (1996) segmental data for males to perform our calculations. We consider each segment of the lower limb (foot, shank and thigh) as rigid and independent. The model supposes a knowledge of the relative mass and the spatial coordinates of at least three points for each segment. A mathematical method is developed in order to obtain data which take into account the individual characteristics of the subjects. For each segment we have to determine three successive elements:- the localization of the center of mass,- a coordinate system assigned, - an inertia matrix assigned. RESULTS: The main difficulty is to place the markers properly on subjects. A simple test, allowing distance determination between markers, was proposed previously to further calculations. The mathematical model is developed in such a way as to be easily used. Conclusions: These simple-to-use methods presuppose a reducing hypothesis. We assume that for each joint a geometrical center exists. This point lies on the longitudinal axis of the segments and has a fixed three dimensional position relative to the segments forming the joint. The localization of the ‘joint center’ is not referenced to the sagittal and transversal axis. We use data reported by de Leva (1996). This supposes that the lower limb is a standard limb, reducing accuracy for subjects with some pathological segment orientation or for young, old and female subjects. As the error introduced by using inappropriate segment parameters could be substantial, the choice of the biomechanical model, as well as the optimal measurement method, is absolutely necessary to obtain for example a good evaluation of the forces acting on the different joints

INFLUENCE OF REST PERIOD ON ELECTRICAL STIMULATION EFFICIENCY

INTRODUCTION: Electrical stimulation (ES) is now widely used as a modality of strengthening in healthy subjects and highly trained athletes. Most of the previous studies have reported that training by ES induces strength gains (Portmann, 1991; Fredon & Poumarat, 1995). Pulse parameters and stimulus regimens are well documented, especially for frequency of stimulation and electrode localization (Ferry & Poumarat, 1994; Ferry et al., 1994). There is a lack of information on training protocols. These should include periodic rest periods to minimize muscle fatigue and maintain an adequate level of contraction during the training session. The aim of this paper is to clarify the effect of rest periods on muscular performance

The Estimation of the Time Constant of the Human Inner Ear Pressure Change by Noninvasive Technique

We propose a noninvasive method to estimate the time constant. The calculation of this factor permits us to understand the pressure variations of the inner ear and also predict the behavior of the flow resistance of the cochlear aqueduct. A set of mathematical relationships incorporating the intralabyrinthine pressure, the intracranial pressure, and the time constant was applied. The modeling process describes the hydrodynamic effects of the cerebrospinal fluid in the intralabyrinthine fluid space, where the input and output of the created model are, respectively, the sinusoidal variation of the respiration signal and the distortion product of otoacoustic emissions. The obtained results were compared with those obtained by different invasive techniques. A long time constant was detected each time when the intracranial pressure increased; this phenomenon is related to the role of the cochlear aqueduct described elsewhere. The interpretation of this model has revealed the ability of these predictions to provide a greater precision for hydrodynamic variation of the inner ear, consequently the variation of the dynamic process of the cerebrospinal fluid

L'entrainement a l'aide de charges additionnelles

SIGLECNRS T Bordereau / INIST-CNRS - Institut de l'Information Scientifique et TechniqueFRFranc

Determination des centres de rotation de l'articulation du coude chez l'Homme

SIGLECNRS T 55705 / INIST-CNRS - Institut de l'Information Scientifique et TechniqueFRFranc

Détermination des efforts articulaires induits par le mouvement de 1/2 squat avec charge additionnelle (approche cinématique et cinétique)

CLERMONT FD-BCIU Sci.et Tech. (630142101) / SudocCLERMONT FD-UBP-UFR STAPS (630142215) / SudocSudocFranceF

Adaptations nerveuses et périphériques du muscle squelettique à l'entraînement de force

CLERMONT FD-BCIU Sci.et Tech. (630142101) / SudocCLERMONT FD-UBP-UFR STAPS (630142215) / SudocSudocFranceF

Muscle plasticity after weight and combined (weight + jump) training

The purpose of this study was to compare the effects of jump training as a complement to weight training on jump performance and muscle strategy during the squat and countermovement jump. Twenty-two male handball players, between the ages of 17 and 24, and in good health, were randomly divided into three groups. Two were trained groups, weight training (WTG) and jump training combined with weight training (CTG), and one was a control group (CG). Maximal isometric force and maximal concentric power were assessed by a supine leg press, squat jump (SJ), counter movement jump (CMJ), and surface EMG was used to determine changes in muscle adaptation before and after the training period. After 6-wk training programs, the two training groups increased maximal isometric force, maximal concentric power, and squat jump performance. However, only combined training presented a significant increase in height jump performance during the countermovement jump (P < 0.05). EMG analysis (as interpreted through the root mean square values) showed that the SJ was performed similarly before and after the training period for the two training groups. However, during the CMJ, only the CTG group adopted a new technique manifested by a short transition phase together with an increase in knee joint stiffness and knee extensor muscle activation and rectus femoris ratio. It was suggested that the central activities in knee joint during the transition phase, in conjunction with intrinsic muscle contractile properties, play a major role in the regulation of performance during a CMJ. Furthermore, our study suggests that a change in maximal strength and/or explosive strength does not necessarily cause changes in combined movement such as the stretch shortening cycle

Analyse du comportement mécanique d'un os à partir d'images scanner

Ce travail propose une méthode pour l'analyse du comportement mécanique d'un os ostéoporotique basée sur l'imagerie scanner. Dans un premier temps, les propriétés mécaniques de l'os cortical et de l'os trabéculaire d'une tête de radius sont identifiées pour des échantillons numériques tridimensionnels construits à partir d'images scanner. Pour chaque pixel, la valeur locale du module d'Young est reliée à l'indice de gris. La simulation d'essais de compression et de cisaillement permet d'identifier un comportement isotrope pour l'os cortical et un comportement orthotrope pour l'os trabéculaire. Dans un second temps, les différentes images scanner sont utilisées pour construire un modèle numérique 3D de la tête du radius. Une analyse par éléments finis du modèle élaboré, basée sur les propriétés mécaniques identifiées précédemment, permet d'examiner le comportement global et local de la tête du radius sous différentes hypothèses de sollicitation