ELECTROSTIMULATION AND FORCE PRODUCTION

INTRODUCTION For muscular and sport exercise, the force production is one of the first important parameter to control. It is always possible to regulate force production via the intensity, but in order to minimize fatigue phenomenon it may be interesting to have a better control of parameters of stimulation. The aim of this work is to determine the interest of multi-electrodes with a new current type. METHOD The experiment was conducted on 8 healthy male volunteer subjects (P.E. students, 1.72111, 75kg, 29 years). The subjects were seated with the knee flexed at 60degr. Trunk and thigh angle was fixed at 1 lode. A force transducer linked to a computer is fixed on the ankle. Electrostimulation was provided by mean of a SG4 apparatus. A reference electrode was secured over the femoral nerve and the active electrodes were put in regards of the motor point of VL,VM, and Vl muscle. Left and right legs are stimulated alternately. A symmetrical square wave signal with a 2 ms rest between positive and negative phase (150 s) was applied at 80 Hz frequency. RESULTS After an initial ramp a nearly flat curve corresponding to tetanos was reached. The stimulation procedure allows to reach 90% and 100% of MVC on the left and right leg respectively. After training session (18 periods) we got a similar result and force induced on the right leg about 110% of the force considered as MVC. DISCUSSION For beginners as well as after electrical training sessions inducing performance increase, the new muscular stimulation procedures proposed allow to get maximal contraction with a relative comfort. Most of the studies report that ES can induce nearly 70 to 80% of MVC. With the proposed technique we can reached quite easily 100% of MVC. This will be a powerful tool to improve maximal force

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

SPINE MOVEMENT DURING HALF SQUAT EXERCISE

INTRODUCTION .Postural variations of the spine can be studied using radiological technique, but in order to minimize the ionizing radiation we suggested previously to use a non-invasive method. The aim of this study is to describe the movement of the different vertebral segments during half squat exercise. MATEFUAL AND METHOD As described previously external markers are glued to the projecting contours of the spinous processes on 20 voluntary subjects (10 males, 10 females). Markers were implanted on T7, T12, L1, L3, L5 and S1 vertebra levels. This technique was designed to locate angular displacement. Three positions were studied: neutral (vertical trunk, without additional charge), in charge (vertical trunk + 50 kg) and half squat with 50 kg on the shoulders. From the photos were measured, in the sagittal plane, the angular variations at each vertebral segment. RESULTS In standing position the barbell weight induces a general flexion on the cervical and thoracic levels. A verticalization of S1 with an extension of L5 is noticed. In squat position, the main displacement occurs in S1 according to the important movement of the coxo-femoral joint. L5 remains in a constant position. An important flexion is noticed in L3 and L1. T12 seems well fixed. T7 angulation is dependent of head position and of general trunk flexion. DISCUSSION In physical training session emphasis should be laid on the voluntary development of muscles surrounding pelvis, but also of muscles allowing the fixation of thoraco-lumbar joint

FORCES APPLIED BY A BACKPACK ON THE SHOULDERS

INTRODUCTION While the physiological responses of individuals to load carrying have been studied (Bloom et al. 1987; Evans et al. 1983), there is still a lack of information in biomecanics research focused on the forces applied to the trunk and the shoulders. The aim of this work is to present a way of measuring forces applied by a backpack to the shoulders when the subject walks for 30 min on a treadmill. MATERIALS AND METHODS Twelve subjects volunteered to participate in the experiment, four were hikers (>20 trekking/year: expert), four were occasional hikers

MECHANICAL STRESS ON KNEES DURING HALF-SQUAT EXERCISES

INTRODUCTION Articular forces and moments have been found to be affected by the lifting technique in ergonomics (Trafirnow et al., 1993) and in weight-training (Poumarat et al.,1989).While these researchers have improved our understanding of biomechanical aspects of lifting as related to the spine and the lower extremities, most of them remain related to either static orquasi-static conditions. The purpose of this study was to determine the mechanical stress on the knee joint using a 3-D dynamic model. MATERIALS AND METHODS Three male volunteer students participated in the study. They were asked to perform three different sets of 10 half-squat exercises: no load, 100% and 120% of total body mass of the subject additional weight. To determine kinematic data, the movement of the half-squat exercises was recorded using the Mac Reflex optoelectronic system (4 cameras) with markers on the left lower extremity at the fust metatarsal, the external rnalleolus, the external lateral femoral condyle and the greater trochanter. A six components force-plate (AMTI) provided kinetic data. Compressive and the shear forces acting on the thigh at the knee joint were calculated where; Fx represents the compressive force; Mx, the external rotatory moment of the thigh; Fy, the medio-lateral shear force; My, the extension moment of the thigh; Fz, the antero-posterior shear force; and Mz, the abductor moment of the thigh. The resultant knee force, in all subjects, increases when lifted load increases. A similar increase in the resultant moment at the knee joint was found. These pic values were calculated for a knee angle of 108. The medio-lateral shear force (Fy) was not affected by the load. However, during the middle phase of the exercise, the mtero-posterior shear force increased from 0.72 to 0. 88 times body weight when lifted mass increased from 1 to 1.20 times body weight. For the compressive component (Fx), no clear variation as a function of load was found in this study in all subjects. Even for the heaviest load (120% body weight), no increase in forces and moments was recorded from the first to the last repetition of one set. CONCLUSION The results of this study demonstrated that mechanical stress acting on knee joint in half-squat exercise increased with lifted barbell. For knee force components, load was found to affect only the antero-posterior shear force. The medio-lateral shear force was independent of this variable. Force and moment values were affected by REFERENCES Poumarat, G., Dabonneville, M., Chandezon, R., & Roddier, P. (1989). Les squats: Forces induites sur I'articulation du genou et sur L5 S 1 en fonction des postures adoptCes. CinCsiologie, 69-74. Trafimow, J.H., Schipplein, O.D., Novak, G.H.,& Andersson, G.B.J. (1993). The effects ofquadriceps fatigue on the technique of lifting. Spine, 18,364-367

Contamination by metallic elements released from joint prostheses

When a metallic implant is in contact with human tissues, the organism reacts and a corrosion process starts. Consequently, we might observe liberation of metallic debris and wear. Our purpose is to measure the contamination and the migration of these metallic elements in the surrounding tissues of the implant. Two types of samples have been studied. First type is sample taken on post-mortem tissues around prostheses to study contamination gradients. Second type is sample taken on pathologic joints on periprosthetic capsular tissues in surgical conditions. These allow estimating contamination degree. The experiments were made on a Van de Graaff accelerator located at CERI (Centre d'Etude et de Recherche par Irradiation, Orl\'{e}ans, France). We measure elemental concentrations resulting from the contamination of the surface of each sample. Results are analysed in function of the pathology and the type of implants. According to the pathology and the location of the sampling, these measurements show a very heterogeneous contamination by metallic elements under particles and/or ionic species which can migrate through soft tissues by various mechanism

A GIS tool for flood risk analysis in Flanders (Belgium)

In the past decades, the low-lying region Flanders (Belgium) has fall victim to numerous flood events, causing substantial damage to buildings and infrastructure. In response to this, the Flemish government proposed a new approach which considers the level of risk as a way for safety measurement. Using geographical information systems, this evolution has lead to a comprehensive risk methodology, and more recently to the development of a flood risk assessment tool called LATIS. By estimating the potential damage and the number of casualties during a flood event, LATIS offers the possibility to perform risk analysis in a fast and effective way. This paper presents a brief overview of the currently used methodology for flood risk management in Flanders and its implementation in the LATIS tool. The usefulness of this new tool is demonstrated by a sequence of risk calculations, performed in the framework of climate change impacts on flood risk in Flanders

Vital capacity evolution in patients treated with the CMCR brace: statistical analysis of 90 scoliotic patients treated with the CMCR brace

<p>Summary</p> <p>Objective</p> <p>To study the evolution of pulmonary capacity during orthopaedic treatment of scoliosis with the CMCR brace.</p> <p>Background</p> <p>Investigating the impact of moderate scoliosis on respiratory capacity and its evolution during CMCR brace treatment with mobile pads.</p> <p>Context</p> <p>Several studies demonstrate the impact of scoliosis on respiratory capacity but few of them focus on the impact of bracing treatment. We studied the evolution of the pulmonary capacity of a cohort of 90 scoliotic patients.</p> <p>Methods</p> <p>This retrospective study included 90 scoliotic patients treated since 1999 with a brace with mobile pads called CMCR (n = 90; mean age: 13 years; 10-16). These patients were diagnosed with an idiopathic scoliosis (mean angulation 20.6°). All patients underwent a radiographic and respiratory evaluation at the beginning, the middle and the end of treatment.</p> <p>Results</p> <p><it>Mean age at treatment start was </it>13. Before treatment, our patients did not have a normal pulmonary capacity: Forced Vital Capacity (FVC) was only 75% of the theoretical value. All curvature types (thoracic, thoraco-lumbar and combined scoliosis) involved this reduced pulmonary capacity, with moderate-angulated scoliosis having a negative impact. At the beginning of brace treatment, the loss of real vital capacity with brace (0.3 litres) was 10% lower than without brace.</p> <p>At CMCR removal, the FVC had increased by 0.4 litre (21% +/- 4.2% compared to the initial value). The theoretical value had increased by 3%. This positive evolution was most important in girls at a low Risser stage (0,1,2), and before 11 years of age.</p> <p>Conclusion</p> <p>These results supported our approach of orthesis conception for adolescent idiopathic scoliosis which uses braces with mobile pads to preserve thorax and spine mobility.</p