Papers by Gilles Dietrich
Dictionnaire culturel du sport
Gait & Posture, 2018
Due to the intensity and repetition of movement, roboticassisted gait training therapy could have... more Due to the intensity and repetition of movement, roboticassisted gait training therapy could have a beneficial effect on the recovery and improvement of postural and locomotor functions of the patient. This study sought to highlight the effects of robotic-assisted gait rehabilitation in gait of children with Cerebral Palsy (CP). We analyzed the different strategies before and after this rehabilitation which was used in order to generate forward motion while maintaining balance. Data were collected by a motion analysis system (Vicon®-Oxford Metrics, Oxford, UK). The children were divided into two groups in such a way as to obtain a randomized controlled population: i) a group of fourteen children (Treated Group) underwent 20 sessions of roboticassisted gait training therapy using the driven gait orthosis Lokomat®Pediatric (Hocoma AG, Volketswil, Switzerland) compared to ii) a group of sixteen children without sessions of Lokomat®Pediatric (Control Group). Significant differences are observed for the TG between the preand post-test values of the locomotor parameters and of the kinetic data of the propulsive forces of the Center of Mass (COM) and of the Center of Pressure (COP) dynamic trajectory. This first study, although performed on a limited number of patients, shows the usefulness of this robotic gait rehabilitation mainly in the balance control in gait. Indeed after this rehabilitation, these children improve their gait that is especially characterized by a more appropriate time lag between the time instant of COM-COP trajectory divergence and the time instant when the forward propulsive forces became apparent.
Journal of Applied Biomechanics, 2002
This paper presents a conceptual model for studying the contribution of each leg to sideways stab... more This paper presents a conceptual model for studying the contribution of each leg to sideways stability of a four-link biped. It was assumed that a linear feedback controller maintained balance with torque related to the deviation from a reference value of the angle made by the trunk with the vertical. Predictions for ground reaction forces produced in resisting sideways push at the pelvis, based on simulation using a simple linear controller, are presented for two special cases (using one or both legs). This simple model was then compared to experimental data in which participants were asked to resist a sideways push. It was observed that all participants employed a strategy in which one leg was used to develop the force response. With this simple model, it was possible to simulate different kinds of responses to the balance perturbation. This model could be considered the first step of a more complex model in order to include specific components related to physiological parameters.
Journal of Applied Biomechanics, 2010
The purpose of the present work was to study swimmers’ efficiency during the underwater phase of ... more The purpose of the present work was to study swimmers’ efficiency during the underwater phase of the grab start. Eight high-level swimmers participated in this study. They performed two types of start: a regular grab start (with underwater leg propulsion after the glide) and a grab start with no underwater movement (swimmers had to remain in a streamlined position). Four cameras filmed the entire underwater phase of all starts. Nine anatomic landmarks were identified on the swimmers’ bodies and their positions were calculated using a modified double plan DLT technique. From these positions and Dempster’s anthropometric data, the center of mass position and velocity were also determined. Kinetic energies were also calculated. This velocity and kinetic energies for the two types of start were compared. Swimmers began underwater leg propulsion 1.69 m too soon. The global and internal energies were significantly higher for the start with underwater leg propulsion. Nevertheless, swimmers...
Neurophysiologie Clinique/Clinical Neurophysiology, 2015
Learning to walk is viewed here from a functional point of view. To move forward it is necessary ... more Learning to walk is viewed here from a functional point of view. To move forward it is necessary to produce propulsive forces that necessitate creating and tuning a distance between the center of mass (CoM) and the center of pressure (CoP) along the anteroposterior axis .We hypothesize that learning to walk consists in learning to produce these propulsive forces. We present here a longitudinal study showing that the distance between the centre of mass and the centre of pressure along the antero-posterior axis increases during the first months of learning to walk, and that this increase is correlated with velocity CoP CoM Ground CoM
Human Movement Science, 1996
Abstract This study deals with the learning of a complex motor task. The example used is rock cli... more Abstract This study deals with the learning of a complex motor task. The example used is rock climbing, where the subject's motricity is highly constrained by the natural environment. The working hypothesis is that the sensorimotor system searches for behavioral solutions characterized by minimal energy expenditure in the dissipation of forces. Harmonic systems — which satisfy this requirement — are used as models for testing the source signal defined by the acceleration curve at the learner's center of gravity. It is shown that only the dynamics of an expert's motor behavior are harmonic, while those of a beginner are stochastic (or chaotic). It is also shown that for experts, the process of adaptation to environmental constraints involves the relaxation of the dynamics and the ensuing emergence of a stable state which corresponds to a quasi-periodic attractor. A harmonic analysis is used to distinguish the environmental and intrinsic components of the behavioral dynamics, shown to result from the coupling of these two components via resonance.
Human Movement Science, 1994
The study deals with the segmental organization of single-and multi-step walking. Local (segmenta... more The study deals with the segmental organization of single-and multi-step walking. Local (segmental) and global (center of gravity) anticipatory movements associated with the initiation of the stepping movement were investigated in 5 normal subjects. Each subject performed a single-step walking task under three conditions of step velocity. Global anticipatory phenomena were indicated by the acceleration of the center of gravity and displacement of the center of foot pressure. Local anticipatory movements, i.e. the accelerations of trunk, shoulders, hips and shanks were recorded simultaneously. The biomechanical data suggest that there are two distinct parts in the anticipatory phase. The earlier correspond to the static postural changes, which are correlated to the velocity of the forthcoming movements. As in multi-step walking, global and local accelerations are specific to the forthcoming movement. The latter part aims to counterbalance the disruption induced by heel-off and is related to postural necessities. These results suggest that the same parameters are programmed in the execution of the single-or multi-step walking process.
Archives of Physiology and Biochemistry, 1995
Isbs Conference Proceedings Archive, Mar 25, 2008
Journal of Motor Behavior, Apr 1, 2010
Experimental Brain Research, 2015
This study examines the process of learning to walk from a functional perspective. To move forwar... more This study examines the process of learning to walk from a functional perspective. To move forward, one must generate and control propulsive forces. To achieve this, it is necessary to create and tune a distance between the centre of mass (CoM) and the centre of pressure (CoP) along the antero-posterior axis. We hypothesize that learning to walk consists of learning how to calibrate these self-generated propulsive forces to control such distance. We investigated this question with six infants (three girls and three boys) who we followed up weekly for the first 8 weeks after the onset of walking and then biweekly until they reached 14-16 weeks of walking experience. The infants' walking patterns (kinematics and propelling forces) were captured via synched motion analysis and force plate. The results show that the distance between the CoM and the CoP along the antero-posterior axis increased rapidly during the first months of learning to walk and that this increase was correlated with an increase in velocity. The initial small values of (CoM-CoP) observed at walking onset, coupled with small velocity are interpreted as the solution infants adopted to satisfy a compromise between the need to generate propulsive forces to move forward while simultaneously controlling the disequilibrium resulting from creating a with distance between the CoM and CoP.
Journal of Strength and Conditioning Research, 2010
The aim of this study was to determine a predictive equation of 1 repetition maximum (1RM) from l... more The aim of this study was to determine a predictive equation of 1 repetition maximum (1RM) from local muscular endurance. Different athletic male populations were assessed: racket/ball games players (n = 31), power lifters (n = 22), swimmers (n = 28), and rowers (n = 29). After the 1RM assessment for the bench press, the maximum number of repetitions (MNR) relative to the 1RM (85%, 75%, 60%, 40%, and 20%) was tested. No significant differences in strength evolution from 20% to 100% of the 1RM was found between power lifters and racket/ball games players and between swimmers and rowers. However, differences in the strength evolution appeared between these 2 mixed groups (p < 0.01), with differences appearing from 75% of 1RM to lesser relative strength (p < 0.05). Nonlinear equations fitted best with the actual data for the capacity to repeat lifts. The evolution of strength from 100% to 20% of 1RM was better described when the groups' specific equations were used as demonstrated by r, and residuals range between the predicted minus the measured 1RM. The strength endurance competences for high loads (100%-75%) were adequately modelled by the equation based on the total population. The accuracy of the 1RM prediction was better when a reduced number of lifts was performed. For untrained or novice subjects, the use of group-specific equations for the all evolutionary profile of strength allows a good estimate of 1RM and provides adequate numbers of lifts for all levels of strength, thus optimizing the training programs.
Journal of Biomechanics, 1994
Journal of motor behavior, 2002
Maintaining an unstable equilibrium requires that multiple joints be coordinated so that the cent... more Maintaining an unstable equilibrium requires that multiple joints be coordinated so that the center of mass is kept above the base of support. The authors' aim in the present study was to discover the underlying dynamics of local (foot, hip, or head) and global (center of mass) components involved in balance control and how those dynamics are affected by changes in the available information. Participants (N = 6) had to maintain their balance on an unstable platform. Using dimensional analyses (largest Lyapunov exponent and correlation dimension), the authors examined the active degrees of freedom involved in balance control. Results indicated a similarity in dimension between local (joints) and global (center of mass) components, between a fixed point and a limit cycle. The behavior of the center of mass was found to be more predictable than the behavior of its local constituents. In addition, the available visual information affected the predictability of the postural behavior...
Philosophical transactions of the Royal Society of London. Series B, Biological sciences, Jan 19, 2015
Various authors have suggested similarities between tool use in early hominins and chimpanzees. T... more Various authors have suggested similarities between tool use in early hominins and chimpanzees. This has been particularly evident in studies of nut-cracking which is considered to be the most complex skill exhibited by wild apes, and has also been interpreted as a precursor of more complex stone-flaking abilities. It has been argued that there is no major qualitative difference between what the chimpanzee does when he cracks a nut and what early hominins did when they detached a flake from a core. In this paper, similarities and differences between skills involved in stone-flaking and nut-cracking are explored through an experimental protocol with human subjects performing both tasks. We suggest that a 'functional' approach to percussive action, based on the distinction between functional parameters that characterize each task and parameters that characterize the agent's actions and movements, is a fruitful method for understanding those constraints which need to be mas...
Proceedings of the 1st Augmented Human International Conference on - AH '10, 2010
Background. Based on personal experience of ski teaching, ski training and ski competing, we have... more Background. Based on personal experience of ski teaching, ski training and ski competing, we have noticed that some gaps exist between classical models describing bodytechniques and actual motor acts made by performing athletes. The evolution of new parabolic shaped skis with new mechanical and geometric characteristics increase these differences even more. Generally, scientific research focuses on situations where skiers are separated from their skis. Also, many specialized magazines, handbooks and papers print articles with similar epistemology. In this paper, we describe the development of a three-dimensional analysis to model the skier-skis' system. We subsequently used the model to propose an evaluation template to coaches that includes eight techniques and three observable consequences in order to make objective evaluations of their athletes' body-techniques. Once the system is modeled, we can develop a computer simulation in the form of a jumping jack, respecting degrees of freedom of the model. We can manipulate movement of each body segment or skis' gears' characteristics to detect performance variations. The purpose of this project is to elaborate assumptions to improve performance and propose experimental protocols to coaches to enable them to evaluate performance. This computer simulation also involves board and wheeled sports.
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Papers by Gilles Dietrich