2,569 research outputs found
The magnitude of the effect of calf muscles fatigue on postural control during bipedal quiet standing with vision depends on the eye-visual target distance
The purpose of the present experiment was to investigate whether, with
vision, the magnitude of the effect of calf muscles fatigue on postural control
during bipedal quiet standing depends on the eye-visual target distance. Twelve
young university students were asked to stand upright as immobile as possible
in three visual conditions (No vision, Vision 1m and Vision 4m) executed in two
conditions of No fatigue and Fatigue of the calf muscles. Centre of foot
pressure displacements were recorded using a force platform. Similar increased
variances of the centre of foot pressure displacements were observed in the
fatigue relative to the No fatigue condition for both the No vision and Vision
4m conditions. Interestingly, in the vision 1m condition, fatigue yielded: (1)
a similar increased variance of the centre of foot pressure displacements to
those observed in the No vision and Vision 4m conditions along the
medio-lateral axis and (2) a weaker destabilising effect relative to the No
vision and Vision 4m conditions along the antero-posterior axis. These results
evidence that the ability to use visual information for postural control during
bipedal quiet standing following calf muscles fatigue is dependent on the
eye-visual target distance. More largely, in the context of the multisensory
control of balance, the present findings suggest that the efficiency of the
sensory reweighting of visual sensory cues as the neuro-muscular constraints
acting on the subject change is critically linked with the quality of the
information the visual system obtains
Feedback Control of an Exoskeleton for Paraplegics: Toward Robustly Stable Hands-free Dynamic Walking
This manuscript presents control of a high-DOF fully actuated lower-limb
exoskeleton for paraplegic individuals. The key novelty is the ability for the
user to walk without the use of crutches or other external means of
stabilization. We harness the power of modern optimization techniques and
supervised machine learning to develop a smooth feedback control policy that
provides robust velocity regulation and perturbation rejection. Preliminary
evaluation of the stability and robustness of the proposed approach is
demonstrated through the Gazebo simulation environment. In addition,
preliminary experimental results with (complete) paraplegic individuals are
included for the previous version of the controller.Comment: Submitted to IEEE Control System Magazine. This version addresses
reviewers' concerns about the robustness of the algorithm and the motivation
for using such exoskeleton
Development of bipedal and quadrupedal locomotion in humans from a dynamical systems perspective
The first phase in the development 0f locomotion, pr,öary variability would occur in normal fetuses and infants, and those with Uner Tan syndrome. The neural networks for quadrupedal locomotion have apparently been transmitted epigenetically through many species since about 400 MYA.\ud
The second phase is the neuronal selection process. During infancy, the most effective motor pattern(s) and their associated neuronal group(s) are selected through experience.\ud
The third phase, secondary or adaptive variability, starts to bloom at two to three years of age and matures in adolescence. This third phase may last much longer in some patients with Uner Tan syndrome, with a considerably delay in selection of the well-balanced quadrupedal locomotion, which may emerge very late in adolescence in these cases
Uner Tan Syndrome: History, Clinical Evaluations, Genetics, and the\ud Dynamics of Human Quadrupedalism
Abstract: This review includes for the first time a dynamical systems analysis of human quadrupedalism in Uner Tan syndrome, which is characterized by habitual quadrupedalism, impaired intelligence, and rudimentary speech. The first family was discovered in a small village near Iskenderun, and families were later found in Adana and two other small villages near Gaziantep and Canakkale. In all the affected individuals dynamic balance was impaired during upright walking,and they habitually preferred walking on all four extremities. MRI scans showed inferior cerebellovermian hypoplasia with slightly simplified cerebral gyri in three of the families, but appeared normal in the fourth. PET scans showed a decreased glucose metabolic activity in the cerebellum, vermis and, to a lesser extent the cerebral cortex, except for one patient,\ud
whose MRI scan also appeared to be normal. All four families had consanguineous marriages in their pedigrees,\ud
suggesting autosomal recessive transmission. The syndrome was genetically heterogeneous. Since the initial discoveries\ud
more cases have been found, and these exhibit facultative quadrupedal locomotion, and in one case, late childhood onset. It has been suggested that the human quadrupedalism may, at least, be a phenotypic example of reverse evolution. From the viewpoint of dynamic systems theory, it was concluded there may not be a single factor that predetermines human quadrupedalism in Uner Tan syndrome, but that it may involve self-organization, brain plasticity, and rewiring, from the many decentralized and local interactions among neuronal, genetic, and environmental subsystems
Tongue-placed tactile biofeedback suppresses the deleterious effects of muscle fatigue on joint position sense at the ankle
Whereas the acuity of the position sense at the ankle can be disturbed by
muscle fatigue, it recently also has been shown to be improved, under normal
ankle neuromuscular state, through the use of an artificial tongue-placed
tactile biofeedback. The underlying principle of this biofeedback consisted of
supplying individuals with supplementary information about the position of
their matching ankle position relative to their reference ankle position
through electrotactile stimulation of the tongue. Within this context, the
purpose of the present experiment was to investigate whether this biofeedback
could mitigate the deleterious effect of muscle fatigue on joint position sense
at the ankle. To address this objective, sixteen young healthy university
students were asked to perform an active ankle-matching task in two conditions
of No-fatigue and Fatigue of the ankle muscles and two conditions of
No-biofeedback and Biofeedback. Measures of the overall accuracy and the
variability of the positioning were determined using the absolute error and the
variable error, respectively. Results showed that the availability of the
biofeedback allowed the subjects to suppress the deleterious effects of muscle
fatigue on joint position sense at the ankle. In the context of sensory
re-weighting process, these findings suggested that the central nervous system
was able to integrate and increase the relative contribution of the artificial
tongue-placed tactile biofeedback to compensate for a proprioceptive
degradation at the ankle
Respiratory, postural and spatio-kinetic motor stabilization, internal models, top-down timed motor coordination and expanded cerebello-cerebral circuitry: a review
Human dexterity, bipedality, and song/speech vocalization in Homo are reviewed within a motor evolution perspective in regard to 

(i) brain expansion in cerebello-cerebral circuitry, 
(ii) enhanced predictive internal modeling of body kinematics, body kinetics and action organization, 
(iii) motor mastery due to prolonged practice, 
(iv) task-determined top-down, and accurately timed feedforward motor adjustment of multiple-body/artifact elements, and 
(v) reduction in automatic preflex/spinal reflex mechanisms that would otherwise restrict such top-down processes. 

Dual-task interference and developmental neuroimaging research argues that such internal modeling based motor capabilities are concomitant with the evolution of 
(vi) enhanced attentional, executive function and other high-level cognitive processes, and that 
(vii) these provide dexterity, bipedality and vocalization with effector nonspecific neural resources. 

The possibility is also raised that such neural resources could 
(viii) underlie human internal model based nonmotor cognitions. 

Effects of training on postural control and agility when wearing socks of different compression levels
Study aim: The aim of this study was to evaluate the effects of training while wearing socks differing in compression level (clinical, sub-clinical, regular) on performance of static and dynamic balancing and agility tasks in healthy, physically active people. We sought to understand whether socks with different compression properties supported postural regulation and agility task performance by enhancing somatosensory perception, unskewed by specific age range effects. Material and methods: Participants comprised 61 adults aged 18-75 years, divided into three groups (two experimental groups wearing clinical or sub-clinical level compression socks, and one control group wearing regular non-compression socks during training). An 8-week (2 Ă— 1h per week) intervention programme was administered to train static and dynamic balance and postural control, leg strength and agility. Results: A mixed model ANOVA revealed no differences in static and dynamic balance and postural control and agility performance between clinical, sub-clinical, and control groups before and after training. All groups significantly improved their test performance, suggesting that training had some benefit on motor performance. Conclusions: These results raised interesting questions requiring further investigation to examine the effects of wearing socks (with and without different levels of compression) on motor behaviours in specific groups of elderly vs. young participants, in physically active vs. less physically active people, and in performance settings outside standardized laboratory tests to study applications in natural performance environments
The test-retest reliability of centre of pressure measures in bipedal static task conditions - A systematic review of the literature
Summary of background data: The analysis of centre of pressure (COP) excursions is used as an index of postural stability in standing. Conflicting data have been reported over the past 20 years regarding the reliability of COP measures and no standard procedure for COP measure use in study design has been established. Search methods: Six online databases (January 1980 to February 2009) were systematically searched followed by a manual search of retrieved papers. Results: Thirty-two papers met the inclusion criteria. The majority of the papers (26/32, 81.3%) demonstrated acceptable reliability. While COP mean velocity (mVel) demonstrated variable but generally good reliability throughout the different studies (r= 0.32-0.94), no single measurement of COP appeared significantly more reliable than the others. Regarding data acquisition duration, a minimum of 90 s is required to reach acceptable reliability for most COP parameters. This review further suggests that while eyes closed readings may show slightly higher reliability coefficients, both eyes open and closed setups allow acceptable readings under the described conditions (r≥0.75). Also averaging the results of three to five repetitions on firm surface is necessary to obtain acceptable reliability. A sampling frequency of 100. Hz with a cut-off frequency of 10. Hz is also recommended. No final conclusion regarding the feet position could be reached. Conclusions: The studies reviewed show that bipedal static COP measures may be used as a reliable tool for investigating general postural stability and balance performance under specific conditions. Recommendations for maximizing the reliability of COP data are provided
Using step width to compare locomotor biomechanics between extinct, non-avian theropod dinosaurs and modern obligate bipeds
How extinct, non-avian theropod dinosaurs locomoted is a subject of considerable interest, as is the manner in which it evolved on the line leading to birds. Fossil footprints provide the most direct evidence for answering these questions. In this study, step width—the mediolateral (transverse) distance between successive footfalls—was investigated with respect to speed (stride length) in non-avian theropod trackways of Late Triassic age. Comparable kinematic data were also collected for humans and 11 species of ground-dwelling birds. Permutation tests of the slope on a plot of step width against stride length showed that step width decreased continuously with increasing speed in the extinct theropods (p < 0.001), as well as the five tallest bird species studied (p < 0.01). Humans, by contrast, showed an abrupt decrease in step width at the walk–run transition. In the modern bipeds, these patterns reflect the use of either a discontinuous locomotor repertoire, characterized by distinct gaits (humans), or a continuous locomotor repertoire, where walking smoothly transitions into running (birds). The non-avian theropods are consequently inferred to have had a continuous locomotor repertoire, possibly including grounded running. Thus, features that characterize avian terrestrial locomotion had begun to evolve early in theropod history
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