The effects of the antagonist muscle force on intersegmental loading during isokinetic efforts of the knee extensors

Hamstrings activation when acting as antagonists is considered very important for knee joint stability. However, the effect of hamstring antagonist activity on knee joint loading in vivo is not clear. Therefore, the purpose of this study was to examine the differences in antagonistic muscle force and their effect on agonist muscle and intersegmental forces during isokinetic eccentric and concentric efforts of the knee extensors. Ten males performed maximum isokinetic eccentric and concentric efforts of the knee extensors at 30 degrees s(-1). The muscular and tibiofemoral joint forces were then estimated using a two-dimensional model with and without including the antagonist muscle forces. The antagonist moment was predicted using an IEMG-moment model. The predicted antagonist force reached a maximum of 2.55 times body weight (BW) and 1.16 BW under concentric and eccentric conditions respectively. Paired t-tests indicated that these were significantly different (p<0.05). A one-way analysis of variance indicated that when antagonist forces are included in the calculations the patella tendon, compressive and posterior shear joint forces are significantly higher compared to those calculated without including the antagonist forces. The anterior shear force was not affected by antagonist activity. The antagonists produce considerable force throughout the range of motion and affect the joint forces exerted at the knee joint. Further, it appears that the antagonist effect depends on the type of muscle action examined as it is higher during concentric compared to eccentric efforts of the knee extensors.     

Postural dynamics in maximal isometric ramp efforts

 A global biomechanical model of transient push efforts is proposed where transient efforts are taken into consideration, with the aim to examine in greater depth the postural adjustments associated with voluntary efforts. In this context, the push effort is considered as a perturbation of balance, and the other reaction forces as a counter-perturbation which is necessary for the task to be performed efficiently. The subjects were asked to exert maximal horizontal two-handed isometric pushes on a dynamometric bar, as rapidly as possible. They were seated on a custom-designed device which measured global and partitive dynamic quantities. The results showed that the horizontal reaction forces and the horizontal displacement of the centre of pressure increased quasi-proportionally with the perturbation. In addition, it was established that vertical reaction forces increased at seat level whereas they decreased at foot level, resulting in minor vertical acceleration and displacement of the centre of gravity. On the contrary, the anteroposterior reaction forces increased both at foot and at seat levels. Based on a detailed examination of the various terms of the model, it is concluded that transient muscular effort induces dynamics of the postural chain. These observations support the view that there is a postural counter-perturbation which is associated with motor activity. More generally, the model helped to specify the effect of postural dynamic phenomena. It makes it possible to stress the importance of adherence at the contact level between the subject and the seat in the course of transient efforts. Received: 1 February 2001 / Accepted in revised form: 20 February 2002     

Managing alterity from within: the ontological turn in anthropology and indigenous efforts to shape shamanism

The ontological turn is gaining momentum among many anthropologists today, evidenced by multiple debates and symposia in recent years addressing the role of ontological approaches within the discipline. Equal to the force of the ontological turn are the growing number of passionate critiques that question everything from the ethnographic and historical integrity of this body of work to its intellectual motivations and political effects. This article commends ontologists for bringing greater attention to the crucial role of spirits in many people's lives and for their efforts to gain deeper understandings of different realities. Yet we also agree with critics in their identification of various troubling tendencies in prominent ontologists’ analyses. We highlight how many of these disturbing inclinations emerge through ontologists’ attempts to connect their ethnographic analyses to Eduardo Viveiros de Castro's theory of multinaturalist perspectivism. Finally, we analyse one of the favourite research topics of those associated with the ontological turn – shamanism – in one of the regions most often heralded as an oasis of radical alterity – the Amazon – in a way that specifically aims to avoid the problematic orientations we identify. Specifically, we describe a series of historical changes in the relationships between shamans and indigenous leaders to draw attention to how relationships to shamanic power/knowledge are unevenly distributed, actively debated, and co‐constructed through changing historical and political contexts.     

A computational model for dynamic analysis of the human gait

Biomechanical models are important tools in the study of human motion. This work proposes a computational model to analyse the dynamics of lower limb motion using a kinematic chain to represent the body segments and rotational joints linked by viscoelastic elements. The model uses anthropometric parameters, ground reaction forces and joint Cardan angles from subjects to analyse lower limb motion during the gait. The model allows evaluating these data in each body plane. Six healthy subjects walked on a treadmill to record the kinematic and kinetic data. In addition, anthropometric parameters were recorded to construct the model. The viscoelastic parameter values were fitted for the model joints (hip, knee and ankle). The proposed model demonstrated that manipulating the viscoelastic parameters between the body segments could fit the amplitudes and frequencies of motion. The data collected in this work have viscoelastic parameter values that follow a normal distribution, indicating that these values are directly related to the gait pattern. To validate the model, we used the values of the joint angles to perform a comparison between the model results and previously published data. The model results show a same pattern and range of values found in the literature for the human gait motion.     

Standing sway: iterative estimation of the kinematics and dynamics of the lower extremities from force-plate measurements

In this study, a model for the estimation of the dynamics of the lower extremities in standing sway from force plate data only is presented. A three-dimensional, five-segment, four-joint model of the human body was used to describe postural standing sway dynamics. Force-plate data of the reactive forces and centers of pressure were measured bilaterally. By applying the equations of motion to these data, the transversal trajectory of the center of gravity (CG) of the body was resolved in the sagittal and coronal planes. An inverse kinematics algorithm was used to evaluate the kinematics of the body segments. The dynamics of the segments was then resolved by using the Newton-Euler equations, and the model's estimated dynamic quantities of the distal segments were compared with those actually measured. Differences between model and measured dynamics were calculated and minimized, using an iterative algorithm to re-estimate joint positioning and anthropometric properties. The above method was tested with a group of 11 able-bodied subjects, and the results indicated that the relative errors obtained in the final iteration were of the same order of magnitude as those reported for closed loop problems involved in direct kinematics measurements of human gait. Received: 22 July 1997 / Accepted in revised form: 29 January 1998     

Computational techniques for using insole pressure sensors to analyse three-dimensional joint kinetics

This study evaluated the feasibility of using insole pressure sensors together with whole body dynamics to analyse joint kinetics while running. Local affine transformations of shoe kinematics were first used to track the position of insole sensors during locomotion. Centre of pressure estimates derived from the insoles were within 10 mm of forceplate measures through much of stance, while vertical force estimates were within 15% of peak forceplate recordings. Insole data were then coupled with a least squares whole body dynamic model to obtain shear force estimates that were comparable to forceplate records during running. We demonstrated that these techniques provide a viable approach for analysing joint kinetics when running on uninstrumented surfaces.     

Human genome efforts in Japan

Some project-oriented biosciences have been promoted cooperatively by three governmental agencies in Japan: the Ministry of Education, Science and Culture, the Ministry of Health and Welfare, and the Science and Technology Agency. All three agencies have increased their budgetary requests for human genome analyses for FY 1991. The Panel on Life Sciences (chaired by Dr. W. Mori, former president of the University of Tokyo) of the Science and Technology Council of Japan which is chaired by the Prime Minister has decided to organize a working group to suggest how best to coordinate efforts in human genome analyses in Japan. The genome project was initially promoted by the Science and Technology Agency through a program for the design and construction of automated machines for DNA sequencing. Work is ongoing at the Institute of Physical and Chemical Research to integrate, by system engineering, instruments that can separate DNA fragments, perform plaque selection, carry out dideoxy reaction, and read the resulting DNA sequence. However, scientists now realize the enormity of the tasks of compiling DNA sequence data and of mapping the genes and fragments obtained, and efforts are being made to solve these problems. Academic societies have organized symposia to promote general interest in this subject. The most important way for Japan to contribute to research on human genome analyses, however, may be in the evaluation of supporting mechanisms (technical assistance and research resources) and in the recognition and preparation of the transition of biology to a big science approach.     

A Neuro-Muscular Elasto-Dynamic Model of the Human Arm Part 1: Model Development

In this paper we develop an elasto-dynamic model of the human arm for use in neuro-muscular control and dynamic interactionstudies.The motivation for this work is to present a case for developing and using non-quasistatic models of humanmusculo-skeletal biomechanics.The model is based on hybrid parameter multiple body system(HPMBS)variational projectionprinciples.In this paper,we present an overview of the HPMBS variational principle applied to the full elasto-dynamic model ofthe arm.The generality of the model allows one to incorporate muscle effects as either loads transmitted through the tendon atpoints of origin and insertion or as an effective torque at a joint.Though the technique is suitable for detailed bone and jointmodeling,we present in this initial effort only simple geometry with the bones discretized as Rayleigh beams with elongation,while allowing for large deflections.Simulations demonstrate the viability of the mcthod for use in the companion paper and infuture studies.     

Sensitivity analysis of an energetic muscle model applied at whole body level in recumbent pedalling

Musculoskeletal models are used in order to describe and analyse the mechanics of human movement. In order to get a complete evaluation of the human movement, energetic muscle models were developed and were shown to be promising. The aim of this work is to determine the sensitivity of muscle mechanical and energetic model estimates to changes in parameters during recumbent pedalling. Inputs of the model were electromyography and joint angles, collected experimentally on one participant. The sensitivity analysis was performed on muscle-specific tension, physiological cross-sectional area, muscle maximal force, tendon rest length and percentage of fast-twitch fibres using an integrated sensitivity ratio. Soleus, gastrocnemius, vasti, gluteus and medial hamstrings were selected for the analyses. The energetic model was found to be always less sensitive to parameter changes than the mechanical model. Tendon slack length was found to be the most critical parameter for both energetic and mechanical models even if the effect on the energetic output was smaller than on muscle force and joint moments.     

Muscle energy transfer during a given wave-like movement of human body segments

The paper deals with a movement of two voluntary segments fixed in a joint and connected by a muscle in a multi-segment biomechanical system of human body. The muscle model is a four-element mechanical system. The mechanical movement energy brought into the "segments-muscle" system from the segments preceding the next ones is studied. The movement in which the total multi-segment system of the human body participates is described by the wave equation. Conditions concerning applying active muscle efforts and correlating velocities of muscle ends movement which provide the maximal value of transferred energy have been found. It is shown that the use of "artificial muscles" type devices promotes activization of energy transfer processes between segments.     

Sensitivity analysis of an energetic muscle model applied at whole body level in recumbent pedalling

Musculoskeletal models are used in order to describe and analyse the mechanics of human movement. In order to get a complete evaluation of the human movement, energetic muscle models were developed and were shown to be promising.

The aim of this work is to determine the sensitivity of muscle mechanical and energetic model estimates to changes in parameters during recumbent pedalling.

Inputs of the model were electromyography and joint angles, collected experimentally on one participant. The sensitivity analysis was performed on muscle-specific tension, physiological cross-sectional area, muscle maximal force, tendon rest length and percentage of fast-twitch fibres using an integrated sensitivity ratio. Soleus, gastrocnemius, vasti, gluteus and medial hamstrings were selected for the analyses.

The energetic model was found to be always less sensitive to parameter changes than the mechanical model. Tendon slack length was found to be the most critical parameter for both energetic and mechanical models even if the effect on the energetic output was smaller than on muscle force and joint moments.     

Reshaping Conflict through School Ceremonial Events in Israeli Palestinian–Jewish Coeducation

This article on the joint Hanukkah/Id'l Fitter/Christmas celebration examines Arab-Jewish coeducation aimed at encouraging each group to take pride in their cultural heritage while experiencing and respecting the heritage of the other. The study is an attempt to better understand the ways in which bilingual/multicultural efforts can shape individual and group perspectives and help overcome intergroup tensions and conflict, inquiring into the potential of ritual events to support this endeavor. The article aims to assist teacher educators in (redesigning new or existing multicultural education programs for conflict-ridden areas, and to illuminate the dynamic interaction between the declared expectations of those programs and the conflictual contexts that constrain them.     

Effect of body weight support variation on muscle activities during robot assisted gait: a dynamic simulation study

Background and Objectives: While body weight support (BWS) intonation is vital during conventional gait training of neurologically challenged subjects, it is important to evaluate its effect during robot assisted gait training. In the present research we have studied the effect of BWS intonation on muscle activities during robotic gait training using dynamic simulations. Methods: Two dimensional (2-D) musculoskeletal model of human gait was developed conjointly with another 2-D model of a robotic orthosis capable of actuating hip, knee and ankle joints simultaneously. The musculoskeletal model consists of eight major muscle groups namely; soleus (SOL), gastrocnemius (GAS), tibialis anterior (TA), hamstrings (HAM), vasti (VAS), gluteus maximus (GLU), uniarticular hip flexors (iliopsoas, IP), and Rectus Femoris (RF). BWS was provided at levels of 0, 20, 40 and 60% during the simulations. In order to obtain a feasible set of muscle activities during subsequent gait cycles, an inverse dynamics algorithm along with a quadratic minimization algorithm was implemented. Results: The dynamic parameters of the robot assisted human gait such as joint angle trajectories, ground contact force (GCF), human limb joint torques and robot induced torques at different levels of BWS were derived. The patterns of muscle activities at variable BWS were derived and analysed. For most part of the gait cycle (GC) the muscle activation patterns are quite similar for all levels of BWS as is apparent from the mean of muscle activities for the complete GC. Conclusions: Effect of BWS variation during robot assisted gait on muscle activities was studied by developing dynamic simulation. It is expected that the proposed dynamic simulation approach will provide important inferences and information about the muscle function variations consequent upon a change in BWS during robot assisted gait. This information shall be quite important while investigating the influence of BWS intonation on neuromuscular parameters of interest during robotic gait training.     

Getting in shape: Reconstructing three-dimensional long-track speed skating kinematics by comparing several body pose reconstruction techniques

In gait studies body pose reconstruction (BPR) techniques have been widely explored, but no previous protocols have been developed for speed skating, while the peculiarities of the skating posture and technique do not automatically allow for the transfer of the results of those explorations to kinematic skating data. The aim of this paper is to determine the best procedure for body pose reconstruction and inverse dynamics of speed skating, and to what extend this choice influences the estimation of joint power. The results show that an eight body segment model together with a global optimization method with revolute joint in the knee and in the lumbosacral joint, while keeping the other joints spherical, would be the most realistic model to use for the inverse kinematics in speed skating. To determine joint power, this method should be combined with a least-square error method for the inverse dynamics. Reporting on the BPR technique and the inverse dynamic method is crucial to enable comparison between studies. Our data showed an underestimation of up to 74% in mean joint power when no optimization procedure was applied for BPR and an underestimation of up to 31% in mean joint power when a bottom-up inverse dynamics method was chosen instead of a least square error approach. Although these results are aimed at speed skating, reporting on the BPR procedure and the inverse dynamics method, together with setting a golden standard should be common practice in all human movement research to allow comparison between studies.     

Models of Postural Control: Shared Variance in Joint and COM Motions

This paper investigated the organization of the postural control system in human upright stance. To this aim the shared variance between joint and 3D total body center of mass (COM) motions was analyzed using multivariate canonical correlation analysis (CCA). The CCA was performed as a function of established models of postural control that varied in their joint degrees of freedom (DOF), namely, an inverted pendulum ankle model (2DOF), ankle-hip model (4DOF), ankle-knee-hip model (5DOF), and ankle-knee-hip-neck model (7DOF). Healthy young adults performed various postural tasks (two-leg and one-leg quiet stances, voluntary AP and ML sway) on a foam and rigid surface of support. Based on CCA model selection procedures, the amount of shared variance between joint and 3D COM motions and the cross-loading patterns we provide direct evidence of the contribution of multi-DOF postural control mechanisms to human balance. The direct model fitting of CCA showed that incrementing the DOFs in the model through to 7DOF was associated with progressively enhanced shared variance with COM motion. In the 7DOF model, the first canonical function revealed more active involvement of all joints during more challenging one leg stances and dynamic posture tasks. Furthermore, the shared variance was enhanced during the dynamic posture conditions, consistent with a reduction of dimension. This set of outcomes shows directly the degeneracy of multivariate joint regulation in postural control that is influenced by stance and surface of support conditions.     

Co-existence between the traditional societies and wildlife in western Serengeti, Tanzania: its relevancy in contemporary wildlife conservation efforts

This paper seeks to show how the traditional societies in western Serengeti have coexisted and continue to coexist with wildlife. It also recognizes the relevancy of this coexistence in furthering contemporary conservation efforts although there are practical constraints to putting this into practice. The following questions are examined: (1) How did/do traditional societies in Serengeti interact with their nature? (2) Which traditional management institutions governed/govern interaction between people and wildlife species, resources and ecosystems and, how do they operate? (3) Which factors were (or are) responsible for erosion of traditional management institutions? (4) What can the traditional practices offer to contemporary conservation efforts and what are the limitations? The paper identifies four ways in which traditional institutions and practices can contribute to current conservation efforts: regulating the overexploitation of resources; complementing the current incentives aiming at diffusing prevailing conflicts between conservation authorities and communities; minimising the costs of law enforcement and; complementing the modern scientific knowledge in monitoring and responding to ecosystem processes and functions. The practical constraints likely to limit adoption of these practices are presented as: methodological complications of acquiring indigenous knowledge; prevailing historical conflicts; human population growth; poverty and lack of appreciation among the conservation planners and managers. In conclusion the need to address the current constraints in order to achieve effective taping of the existing potentials is emphasized.     

Elastic properties of an intact and ACL-ruptured knee joint: measurement, mathematical modelling, and haptic rendering

An analytical, dynamic model of the human knee joint has been developed to simulate the unloaded knee joint behaviour in 6 degrees of freedom. It is based on extensive robot-based measurements of the elastic properties of a human cadaver knee joint. The measured data are compared with data from the literature to ensure that a proper database for modelling is used. The analytical modelling of the passive elastic joint properties is done with Local Linear Model Trees. The deduced knee joint model incorporates passive elastic properties of the internal knee joint structures, passive elastic muscle forces, damping forces, gravitational forces, and external forces. There are two sets of parameters, one simulating the movement of the intact knee joint, and a second simulating the knee joint with ruptured anterior cruciate ligament. The dynamic model can be easily processed in real-time. It is implemented in the haptic display of the Munich Knee Joint Simulator (MKS), which enables a person to move a plastic leg driven by a robot manipulator and feel the simulated knee joint force. Orthopaedic physicians judged the performance of the dynamic knee joint model by executing physical knee joint tests at the MKS.     

A 3-D dynamic model of human finger for studying free movements.

The purpose of this work is to develop a 3D inverse dynamic model of the human finger for estimating the muscular forces involved during free finger movements. A review of the existing 3D models of the fingers is presented, and an alternative one is proposed. The validity of the model has been proved by means of two simulations: free flexion-extension motion of all joints, and free metacarpophalangeal (MCP) adduction motion. The simulation shows the need for a dynamic model including inertial effects when studying fast movements and the relevance of modelling passive forces generated by the structures studying free movements, such as the force exerted by the muscles when they are stretched and the passive action of the ligaments over the MCP joint in order to reproduce the muscular force pattern during the simulation of the free MCP abduction-adduction movements.     

Evaluation of an intact,an ACL-deficient,and a reconstructed human knee joint finite element model

The human knee joint has a three-dimensional geometry with multiple body articulations that produce complex mechanical responses under loads that occur in everyday life and sports activities. Understanding the complex mechanical interactions of these load-bearing structures is of use when the treatment of relevant diseases is evaluated and assisting devices are designed. The anterior cruciate ligament (ACL) in the knee is one of four main ligaments that connects the femur to the tibia and is often torn during sudden twisting motions, resulting in knee instability. The objective of this work is to study the mechanical behavior of the human knee joint and evaluate the differences in its response for three different states, i.e., intact, ACL-deficient, and surgically treated (reconstructed) knee. The finite element models corresponding to these states were developed. For the reconstructed model, a novel repair device was developed and patented by the author in previous work. Static load cases were applied, as have already been presented in a previous work, in order to compare the calculated results produced by the two models the ACL-deficient and the surgically reconstructed knee joint, under the exact same loading conditions. Displacements were calculated in different directions for the load cases studied and were found to be very close to those from previous modeling work and were in good agreement with experimental data presented in literature. The developed finite element model for both the intact and the ACL-deficient human knee joint is a reliable tool to study the kinematics of the human knee, as results of this study show. In addition, the reconstructed human knee joint model had kinematic behavior similar to the intact knee joint, showing that such reconstruction devices can restore human knee stability to an adequate extent.     

Exploring disparities between global HIV/AIDS funding and recent tsunami relief efforts: an ethical analysis

Objective: To contrast relief efforts for the 26 December 2004 tsunami with current global HIV/AIDS relief efforts and analyse possible reasons for the disparity. Methods: Literature review and ethical analysis. Results: Just over 273,000 people died in the tsunami, resulting in relief efforts of more than US$10 bn, which is sufficient to achieve the United Nation’s long‐term recovery plan for South East Asia. In contrast, 14 times more people died from HIV/AIDS in 2004, with UNAIDS predicting a US$8 bn funding gap for HIV/AIDS in developing nations between now and 2007. This disparity raises two important ethical questions. First, what is it that motivates a more empathic response to the victims of the tsunami than to those affected by HIV/AIDS? Second, is there a morally relevant difference between the two tragedies that justifies the difference in the international response? The principle of justice requires that two cases similarly situated be treated similarly. For the difference in the international response to the tsunami and HIV/AIDS to be justified, the tragedies have to be shown to be dissimilar in some relevant respect. Are the tragedies of the tsunami disaster and the HIV/AIDS pandemic sufficiently different, in relevant respects, to justify the difference in scope of the response by the international community? Conclusion: We detected no morally relevant distinction between the tsunami and the HIV/AIDS pandemic that justifies the disparity. Therefore, we must conclude that the international response to HIV/AIDS violates the fundamental principles of justice and fairness.