INTERACTION EFFECTS OF POSTURE AND UNEVEN GROUND ON ABLE-BODIED WALKING KINETICS

Interactions between trunk orientation and gait kinetics are proposed to be inevitable for maintaining dynamic balance, and these interactions are unknown for walking on uneven ground. The purpose of this study was to investigate the interaction effects of posture (regular erect, 30°, 50° and 70° trunk flexion) and step category (unperturbed, perturbation, pre- and post-perturbation) on able-bodied walking kinetics. Statistical analysis revealed interactions posture×step: with increased trunk flexion, walking on uneven ground exhibited less changes in GRF kinetic parameters relative to upright walking. Pre-adaptations were more pronounced in the approach step to the drop in regular erect gait. It seems that in trunk-flexed gaits trunk is used in a compensatory way during the step-down to accommodate changes in ground level. In conclusion, exploitation of this mechanism resembles the ability of small birds in adjusting their zigzag- like configured legs to cope with changes in ground level

REARFOOT ANGLE VELOCITIES DURING RUNNING - A COMPARISON BETWEEN OPTOELECTRONIC AND GYROSCOPIC MOTION ANALYSIS

The aim of this study was a verification of a gyroscopic measurement device mounted on the heel counter of a running shoe. For this purpose 15 subjects performed 10 running trials in a laboratory environment. Rearfoot angular velocities from the gyroscope were compared qualitatively and quantitatively to rearfoot angular velocities observed with a 3D motion analysis system (VICON). Based on the qualitative and quantitative analysis the results are very good in the sagittal plane, good in the frontal plane and poor in the transverse plane

From the Spider Leg to a Hydraulic Device

Workspace and control of multibody systems in nature and engineering are to a large extent determined by the properties of the connecting joints. In contrast to technical joints the natural systems are less stiff incorporating viscoelastic properties and even a simple hinge joint allows for movement and limited control in directions perpendicular to its main plane. Joints of spiders are of special interest as they are driven by hydraulic pressure which mayfacilitate the construction of micro-devices. In a first step structure and function of a spider‘s leg has been investigated simulating movements observed in nature. Following the example from nature a multibody system was developed. Important properties are a) continuity of the material, b) local change of material properties, c) active control of local material properties, and d) hydraulic or pneumatic actuation. The joints can be cascaded thus allowing for the construction of branched multijointed systems driven by a single pressure source. Each joint can be controlled independently. The nonactivated joints remain as stiff as the connected bodies. Thus implementation of such joints do not increase the compliance of the total structure.In order to facilitate the design we develop a suitable mathematical model including structure, material properties, and control. The model is based on the theory of curved beams with large displacements

Das Fourierspektrum von Gesichtsbildern in Photographie und Kunst und dessen Einfluss auf die Gesichtswahrnehmung

Ästhetische gemalte Bilder haben einen Anstieg von -2 im radiär gemittelten Fourierspektrum (1/f2-Eigenschaften), ähnlich wie natürliche Szenen. Wir untersuchten, wie Künstler Gesichter, die einen anderen Anstieg besitzen, abbilden. Dafür wurden 300 gemalte ästhetische Porträts von namhaften Künstlern digitalisiert. Der Anstieg von Porträts und Gesichtsfotografien wurde ermittelt und verglichen. Unsere erste Studie zeigte, dass ästhetische gemalte Porträts 1/f2-Eigenschaften haben, die denen natürlicher Szenen ähnlich sind und sich in dieser Hinsicht deutlich von Gesichtsfotografien unterscheiden. Wir fanden Hinweise, dass Künstler ihre Abbildungen an Kodierungsmechanismen des visuellen Systems anpassen und nicht die Eigenschaften der Objekte abbilden, welche diese natürlicherweise besitzen. Ich konnte durch Manipulation des Anstiegs von Gesichtsfotos den relativen Anteil von groben und feinen Strukturen im Bild verändern. Wir untersuchten, wie das Erlernen und Erkennen unbekannter Gesichter durch Manipulation von 1/fp-Eigenschaften des Fourierspektrums beeinflusst wurde. Wir erstellten zwei Gruppen von Gesichtsfotografien mit veränderten 1/fp-Eigenschaften: Zum einen Gesichter mit steilerem Anstieg, zum anderen Gesichter mit flacherem Anstieg und 1/f2-Eigenschaften. In einem Gesichter-Lernexperiment wurden Verhaltensdaten und EEG-Korrelate der Gesichterwahrnehmung untersucht. Fotos mit steilem Anstieg konnten schlechter gelernt werden. Es zeigten sich langsamere Reaktionszeiten und verminderte neuro-physiologische Korrelate der Gesichterwahrnehmung. Im Gegensatz dazu konnten Gesichtsfotos mit flacherem Anstieg, der gemalten Porträts und natürlichen Szenen ähnlich ist, leichter gelernt werden und es fanden sich größere neurophysiologische Korrelate der Gesichterwahrnehmung

Force direction patterns promote whole body stability even in hip-flexed walking, but not upper body stability in human upright walking

Directing the ground reaction forces to a focal point above the centre of mass of the whole body promotes whole body stability in human and animal gaits similar to a physical pendulum. Here we show that this is the case in human hip-flexed walking as well. For all upper body orientations (upright, 25°, 50°, maximum), the focal point was well above the centre of mass of the whole body, suggesting its general relevance for walking. Deviations of the forces' lines of action from the focal point increased with upper body inclination from 25 to 43 mm root mean square deviation (RMSD). With respect to the upper body in upright gait, the resulting force also passed near a focal point (17 mm RMSD between the net forces' lines of action and focal point), but this point was 18 cm below its centre of mass. While this behaviour mimics an unstable inverted pendulum, it leads to resulting torques of alternating sign in accordance with periodic upper body motion and probably provides for low metabolic cost of upright gait by keeping hip torques small. Stabilization of the upper body is a consequence of other mechanisms, e.g. hip reflexes or muscle preflexes

NEURAL NETWORK MODELING IN SPORT BIOMECHANICS BASED ON THE EXAMPLE OF SHOT-PUT FLIGHT

In this study, a modeling method based on Multi-Layer-Perceptron neural networks (MLP) is presented, using the example of shot-put flight. This method can be used for rapid construction of models. For performance of shot-put, a physical model based on the shots’ equations of motion is easily designed. In this way, an analysis of the shot-put projectory can be used to illustrate the effectiveness of the neural network modeling method. Using the physical model, release data has been determined and altered with random errors such as those introduced by video analysis. A technique for optimal learning with the neural networks has been developed. The resulting MLP models the shot-put flight successfully. The difference between the model’s predicted distance and the distance reached by the physical model are within 2.5%. In conclusion, this method allows rapid creation of models to solve biomechanical problems and can serve as a useful tool for coaches and athletes

Increasing trunk flexion transforms human leg function into that of birds despite different leg morphology

© 2017. Published by The Company of Biologists Ltd. Pronograde trunk orientation in small birds causes prominent intra-limb asymmetries in the leg function. As yet, it is not clear whether these asymmetries induced by the trunk reflect general constraints on the leg function regardless of the specific leg architecture or size of the species. To address this, we instructed 12 human volunteerstowalk at a self-selected velocity with four postures: regular erect, or with 30 deg, 50 deg and maximal trunk flexion. In addition, we simulated the axial leg force (along the line connecting hip and centre of pressure) using two simple models: spring and damper in series, and parallel spring and damper. Astrunk flexion increases, lower limb joints become more flexed during stance. Similar to birds, the associated posterior shift of the hip relative to the centre of mass leads to a shorter leg at toe-off than at touchdown, and to a filatter angle of attack and a steeper leg angle at toe-off. Furthermore, walking with maximal trunk flexion induces right-skewed vertical and horizontal ground reaction force profiles comparable to those in birds. Interestingly, the spring and damper in series model provides a superior prediction of the axial leg force across trunk-flexed gaits compared with the parallel spring and damper model; in regular erect gait, the damper does not substantially improve the reproduction of the human axial leg force. In conclusion, mimicking the pronograde locomotion of birds by bending the trunk forward in humans causes a leg function similar to that of birds despite the different morphology of the segmented legs

Posture alteration as a measure to accommodate uneven ground in able-bodied gait

Though the effects of imposed trunk posture on human walking have been studied, less is known about such locomotion while accommodating changes in ground level. For twelve able participants, we analyzed kinematic parameters mainly at touchdown and toe-off in walking across a 10-cm visible drop in ground level (level step, pre-perturbation step, step-down, step-up) with three postures (regular erect, ~30° and ~50° of trunk flexion from the vertical). Two-way repeated measures ANOVAs revealed step-specific effects of posture on the kinematic behavior of gait mostly at toe-off of the pre-perturbation step and the step-down as well as at touchdown of the step-up. In preparation to step-down, with increasing trunk flexion the discrepancy in hip−center of pressure distance, i.e. effective leg length, (shorter at toe-off versus touchdown), compared with level steps increased largely due to a greater knee flexion at toe-off. Participants rotated their trunk backwards during step-down (2- to 3-fold backwards rotation compared with level steps regardless of trunk posture) likely to control the angular momentum of their whole body. The more pronounced trunk backwards rotation in trunk-flexed walking contributed to the observed elevated center of mass (CoM) trajectories during the step-down which may have facilitated drop negotiation. Able-bodied individuals were found to recover almost all assessed kinematic parameters comprising the vertical position of the CoM, effective leg length and angle as well as hip, knee and ankle joint angles at the end of the step-up, suggesting an adaptive capacity and hence a robustness of human walking with respect to imposed trunk orientations. Our findings may provide clinicians with insight into a kinematic interaction between posture and locomotion in uneven ground. Moreover, a backward rotation of the trunk for negotiating step-down may be incorporated into exercise-based interventions to enhance gait stability in individuals who exhibit trunk-flexed postures during walking