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Body Center (body + center)
Selected AbstractsKinematic study of whole body center of mass position during gait in Parkinson's disease patients with and without festination,MOVEMENT DISORDERS, Issue 6 2010Marcelo Merello MD Abstract Gait festination (FE) can cause serious disability in Parkinson's disease (PD) patients. It is argued that the center of pressure position (COP) and body center of mass (COM) are possibly implicated in FE pathogenesis. The relationship between them remains unclear. The goal of this study was to determine spatiotemporal relationships between COM and COP in PD and to explore whether FE arises as a consequence of lack of physiological link between COP and COM during step stride. Twenty patients with idiopathic PD, in OFF state and 17-age-matched control subjects completed a 10-m walking protocol. PD patients were divided in two groups: those with FE and those without (NF). COM position, excursion, and its relationship with COP, as well as other kinematic parameters were analyzed. COM displacement along the horizontal and vertical plane was significantly lower in FE patients as was the maximum position on the movement direction axis compared with controls or NF patients. Significant difference in minimal COM position in FE patients was also observed. The percentage of stride time during which COM was situated ahead of COP along the movement axis in FE patients was significantly greater than for controls or NF patients. This would seem to indicate that FE patients are constantly attempting to align COP to COM, causing FE. The explanation might be that FE arises as a postural strategy to align COP within the area of COM displacement. Findings illustrate a putative role for postural strategies in the treatment of FE. © 2010 Movement Disorder Society [source] Wearable Data Collection System for Online Gait Stability AnalysisNEUROMODULATION, Issue 3 2004Tomaz Karcnik DSc Abstract We had shown in our previous research that the stability assessment and control are essential for generation of faster and more energy efficient functional electrical stimulation (FES) and/or crutch-assisted gait. The objective of our recent research work has been to design a wearable and portable system for gait stability analysis with online capabilities that is also applicable to crutch-assisted gait modes. The developed wearable stability assessment system for as yet only biped gait consists of foot switches and goniometers attached to the leg joints. The instantaneous static and dynamic stability is, within the wearable system, assessed from the trajectory of the estimated body center of gravity (COGHAT) and the supporting area shape/size as derived from step length and foot-floor contact state. We used motion analysis system data as reference for testing the wearable system accuracy. The wearable system was tested on five healthy subjects and one above-knee amputee. It proved to be reasonably accurate if compared to the classical, motion analysis system based method. However, additional work is required to port the system to the FES assisted and/or crutch assisted gait. [source] Understanding hind limb weight support in chimpanzees with implications for the evolution of primate locomotionAMERICAN JOURNAL OF PHYSICAL ANTHROPOLOGY, Issue 4 2009David A. Raichlen Abstract Most quadrupedal mammals support a larger amount of body weight on their forelimbs compared with their hind limbs during locomotion, whereas most primates support more of their body weight on their hind limbs. Increased hind limb weight support is generally interpreted as an adaptation that reduces stress on primates' highly mobile forelimb joints. Thus, increased hind limb weight support was likely vital for the evolution of primate arboreality. Despite its evolutionary importance, the mechanism used by primates to achieve this important kinetic pattern remains unclear. Here, we examine weight support patterns in a sample of chimpanzees (Pan troglodytes) to test the hypothesis that limb position, combined with whole body center of mass position (COM), explains increased hind limb weight support in this taxon. Chimpanzees have a COM midway between their shoulders and hips and walk with a relatively protracted hind limb and a relatively vertical forelimb, averaged over a step. Thus, the limb kinematics of chimpanzees brings their feet closer to the COM than their hands, generating greater hind limb weight support. Comparative data suggest that these same factors likely explain weight support patterns for a broader sample of primates. It remains unclear whether primates use these limb kinematics to increase hind limb weight support, or whether they are byproducts of other gait characteristics. The latter hypothesis raises the intriguing possibility that primate weight support patterns actually evolved as byproducts of other traits, or spandrels, rather than as adaptations to increase forelimb mobility. Am J Phys Anthropol, 2009. © 2008 Wiley-Liss, Inc. [source] Hip extensor EMG and forelimb/hind limb weight support asymmetry in primate quadrupedsAMERICAN JOURNAL OF PHYSICAL ANTHROPOLOGY, Issue 3 2009Susan G. Larson Abstract Higher weight support on the hind limb than forelimb is among the distinctive characteristics of primate quadrupeds. Although often assumed to be due to a more posteriorly positioned whole body center of mass, there are little data to support such a difference. Reynolds (1985. Am J Phys Anthropol 67:335,349) notes that the distribution of forces on the limbs can also be influenced by average limb posture, but suggests that this effect is too small to account for the asymmetry in weight support observed in primates. Instead, he proposes that high hind limb forces are brought about by an active process of shifting weight off the forelimbs and onto the hind limbs through use of hind limb retractors. In this study, we use video records of walking animals to explore the degree to which average limb posture in primates and other quadrupedal mammals deviates from vertical, and use electromyography to test Reynolds' model of hind limb retractor activity and posterior weight shift. The limb posture results indicate that primate forelimbs oscillate about a vertical or slightly retracted axis, and though the hind limbs are slightly protracted, the magnitude of deviation from vertical is too small to have a major effect on weight support distribution. The electromyographic results reveal higher levels of hip extensor activity in antipronograde primates that bear a higher proportion of weight on their hind limbs. This lends support to Reynolds' suggestion that some primates use muscles to actively shift weight onto hind limbs to relieve stresses on forelimbs less well structured for weight support. Am J Phys Anthropol, 2009. © 2008 Wiley-Liss, Inc. [source] Mal de Debarquement and Posture: Reduced Reliance on Vestibular and Visual CuesTHE LARYNGOSCOPE, Issue 3 2004Zohar Nachum MD Abstract Objective The neural mismatch theory assumes that the intersensory conflicts leading to motion sickness are resolved by changes in the relative weighting of the various senses that contribute to orientation. If this sensory rearrangement persists after disembarkment, it might result in mal de debarquement (MD): ataxia and a rocking sensation sometimes felt after landing. The objective of the present study was to examine possible changes in sensory organization in naval crew members with differing susceptibility to MD with computerized dynamic posturography (CDP). Study Design Cross-sectional parallel-group design. Methods Seventeen subjects susceptible to MD (SMD) and 17 subjects nonsusceptible to MD (NSMD) (healthy male volunteers aged 18,22) participated in the study. CDP was performed twice with each subject, before and immediately after sailing, using the EquiTest system (NeuroCom, Inc., Clackamas, OR). Results The SMD group showed a significant reduction in their scores on sensory organization tests 3, 4, and 5 after sailing. Sensory pattern analysis revealed reduced use of inputs from the vestibular and visual systems to maintain balance. Prolonged latencies of the motor responses to unexpected pitch perturbations were also recorded in the postsailing CDP of the SMD group. Reduced performance on the presailing CDP task, which presents the greatest challenge to the vestibular system, was found to control for the presence of MD postsailing. Conclusions The results show that MD is associated with postural instability, slower motor reflexes, and larger sways in response to abrupt changes in the body's center of gravity. These findings may be explained by under reliance on vestibular and visual inputs and increased dependence on the somatosensory system for the maintenance of balance. [source] Aerodynamic Characteristics of the Crest with Membrane Attachment on Cretaceous Pterodactyloid NyctosaurusACTA GEOLOGICA SINICA (ENGLISH EDITION), Issue 1 2009Lida XING Abstract: The Nyctosaurus specimen KJ1 was reconstructed under the hypothesis that there is a membrane attached to the crest; the so-called headsail crest. The aerodynamic forces and moment acting on the headsail crest were analyzed. It was shown that KJ1 might adjust the angle of the headsail crest relative to the air current as one way to generate thrust (one of the aerodynamic forces, used to overcome body drag in forward flight) and that the magnitude of the thrust and moment could vary with the gesture angle and the relative location between the aerodynamic center of the headsail crest and body's center of gravity. Three scenarios were tested for comparison: the crest with membrane attachment, the crest without membrane attachment and the absence of a cranial crest. It was shown that the aerodynamic characteristics (increasing, maintaining and decreasing thrusts and moment) would have almost disappear in flight for the crest without membrane attachment and was non-existent without the cranial crest. It is suggested from aerodynamics evidence alone that Nyctosaurus specimen KJ1 had a membrane attached to the crest and used this reconstructed form for auxiliary flight control. [source] | ||||||||||