1,721,011 research outputs found
Perceptual-motor planning and performance in dynamical postural control
No full textLo scopo principale di questa dissertazione è di comprendere in maniera più approfondita il controllo dinamico della postura nel movimento umano. In particolare, qui ci approcciamo al problema prendendo in considerazione differenti compiti motori e analizzando differenti popolazioni in tre studi diversi. Nel primo viene presa in considerazione l’azione motoria della salita delle scale. In questo esperimento le popolazioni testate erano giovani ed anziani e lo scopo principale era di comprendere se ci sono differenti strategie posturali e percettive sia durante la pianificazione che durante l’esecuzione del movimento a causa della diminuzione del livello di capacità motorie. Gli altri due studi invece focalizzano più l’attenzione sullo sviluppo degli aggiustamenti posturali, prima e durante l’azione motoria, quando le capacità motorie raggiungono livelli ottimali di prestazione. In questi ultimi due casi le popolazioni prese in considerazione erano atleti di alto livello in cui essi primeggiano nell’azione da loro eseguita nell’esperimento, per cui di conseguenza lo scopo di questi studi era di spiegare come l’alta prestazione emerge in specifiche sinergie muscolari causate dall’esperienze motoria degli atleti. Anche se i tre esperimenti hanno in comune il controllo dinamico della postura, differenti modelli teorici del controllo motorio ispirano ciascuno di essi. Da una parte ci riferiamo al concetto di “equifinalità” formulata da Nicolay Bernstein (1967) e al concetto di “affordance” formulata da J.J. Gibson (1979). Queste due idee prese insieme ispirano il primo studio presentato. Dall’altra parte, la legge formulata da Paul Fitts (1954) ispira gli ultimi due esperimenti. Nel’introduzione presenteremo in sequenza queste idee e i loro relativi modelli: per prima l’equifinalità, seguendo l’affordance e poi la legge di Fitts. Per cui questi tre concetti teorici verranno applicati al controllo dinamico della postura, e un capitolo finale affronterà i modo dettagliato l’argomento riguardante il controllo posturale. Successivamente verranno presentati i tre esperimenti.The main aim of this dissertation is to obtain a deeper understanding about the dynamics of postural control in human movement. In particular here we approach the problem by including several motor tasks and by testing different populations in three separate studies. The first one deals with the action of climbing stairs. In this experiment the populations tested were old and young adults and the main aim was to reveal whether there are different perceptive/motor postural strategies either for planning as well as for executing the action due to the decrease of the level of motor skill. The other two studies instead focalize more the attention on the development of postural adjustments, before and during the action performance, when the level of motor skill reaches its optimality. In these latter two cases the populations tested were elite athletes performing actions in which they excel, and as a consequence the aim of these studies was to reveal how excellence merges from the developments of specific muscular synergies due to practice. Even though the three experiments share issues related to the dynamics of postural control, different models and theoretical frameworks inspire each one. On the one hand, we refer to the concept of movement “equifinality” formulated by Nicolay Bernstein (1967) and to the concept of “affordance” formulated by J.J. Gibson (1979). These two ideas taken together inspired the first study presented. On the other hand, the law formulated by Paul Fitts (1954) inspired the latter two experiments. In the introduction we will present in sequence these ideas and their relative models: first equifinality, followed by affordance, and then Fitts’ law. Since these three theoretical concepts are applied to the dynamics of postural control, a final chapter will discuss more in depth issues related to the control of posture. Then the three experiments will be presented
Coupling between punch efficacy and body stability for elite karate
No full textCoupling between punch efficacy and body stability for elite
karate
Dimensional analysis and ground reaction forces for stair climbing: effects of age and task difficulty
No full textAltered perception–action capability is often associated with falls and diminished self-efficacy in olderpeople. This study evaluated and compared perception–action capability in stair-climbing performanceof 18 healthy volunteers assigned to two age groups (mean age, 26.3 ! 4.3 years and 66.4 ! 4.7 years,respectively). The experimental set-up included 14 stairs (50 cm wide, 60 cm deep, riser height 35–90 cm)positioned at the edge of a force platform. The task was to climb the stair with the greatest riser heightsubjects thought they could climb without outside support or use of hands. Dimensional and dynamic datawere collected and analyzed to reveal the invariant relationships that sustain action preparation andexecution. All subjects chose the same proportion between stair height and distance covered before mountingthe stair, as expressed by the invariant angle (a). While the geometric invariant relationship was picked up asa visual guide prior to action, there was a dynamic invariance in the forces applied during actual execution. Toestablish whether the invariance still held in extreme cases, two perturbed conditions were introduced inwhich stair distances were changed, forcing subjects to execute a foot-strike, either very far from or near tothe stair, before climbing it, so as to reveal any significant adaptations the climber would undertake to avoidslips or falls. Older and younger subjects applied appropriate visual and motor guidance by scaling their motorcapabilities to the environmental dimensions
The fitts’ law and the anticipatory postural adjustment
No full textThe fitts’ law and the anticipatory postural adjustmen
The speed-accuracy trade-off effects on the gait initiation planning
No full textThe speed-accuracy trade-off effects on the gait initiation plannin
Can the period of postnatal codevelopment of the rubrospinal and corticospinal systems provide new insights into refinement of limb movement?
No full textThe corticospinal and the rubrospinal tracts are thought to synergistically contribute to the limb control during motor development. Williams et al. (J Neurosci 34: 4432-4441, 2014) demonstrate that the postnatal maturation of red nucleus motor map and the rubrospinal tract develops earlier than the corticospinal tract, to support early forelimb control. They have two distinct phases of maturation; a "precorticospinal" phase characterized by development of the rubrospinal system, and a "cocorticospinal" phase where they overlap with corticospinal development
Current and emerging strategies for treatment of childhood dystonia
No full textChildhood dystonia is a movement disorder characterized by involuntary sustained or intermittent muscle contractions causing twisting and repetitive movements, abnormal postures, or both (Sanger et al, 2003). Dystonia is a devastating neurological condition that prevents the acquisition of normal motor skills during critical periods of development in children. Moreover, it is particularly debilitating in children when dystonia affects the upper extremities such that learning and consolidation of common daily motor actions are impeded. Thus, the treatment and rehabilitation of dystonia is a challenge that continuously requires exploration of novel interventions. This review will initially describe the underlying neurophysiological mechanisms of the motor impairments found in childhood dystonia followed by the clinical measurement tools that are available to document the presence and severity of symptoms. Finally, we will discuss the state-of-the-art of therapeutic options for childhood dystonia, with particular emphasis on emergent and innovative strategies
Speed-accuracy testing on the Apple iPad provides a quantitative test of upper extremity motor performance in children with dystonia
No full textThe currently available scales for quantitative measurement of the severity of childhood dystonia require human observer ratings and provide poor granularity in the scores for individual limbs. We evaluated the use of new-generation high-quality touchscreens (an iPad) according with the Fitts law, which is a mathematical model that takes into account the relation between movement time and the task accuracy. We compared the abilities of healthy subjects and children with dystonia. The linear relation described by Fitts law held for all the groups. The movement time and the information transmitted were age and severity related. Our results provide evidence for the usability and validity of using Fitts law as a quantitative diagnostic tool in children with dystonia. Furthermore, testing on touchscreen tablets may help to guide the design of user interfaces to maximize the communication rate for children who depend upon assistive communication devices
Fitts' Law in early postural adjustments.
No full textWe tested a hypothesis that the classical relation between movement time and index of difficulty (ID) in quick pointing action (Fitts’ Law) reflects processes at the level of motor planning. Healthy subjects stood on a force platform and performed quick and accurate hand movements into targets of different size located at two distances. The movements were associated with early postural adjustments that are assumed to reflect motor planning processes. The short distance did not require trunk rotation, while the long distance did. As a result, movements over the long distance were associated with substantial Coriolis forces. Movement kinematics and contact forces and moments recorded by the platform were studied. Movement time scaled with ID for both movements. However, the data could not be fitted with a single regression: Movements over the long distance had a larger intercept corresponding to movement times about 140 ms longer than movements over the shorter distance. The magnitude of postural adjustments prior to movement initiation scaled with ID for both short and long distances. Our results provide strong support for the hypothesis that Fitts’ Law emerges at the level of motor planning, not at the level of corrections of ongoing movements. They show that, during natural movements, changes in movement distance may lead to changes in the relation between movement time and ID, for example when the contribution of different body segments to the movement varies and when the action of Coriolis force may require an additional correction of the movement trajectory
Tuning of standing postural responses to instability and cost function
No full textWhole-body movements are performed daily, and humans must constantly take into account the inherent instability of a standing posture. At times these movements may be performed in risky environments and when facing different costs of failure. The aim of the study was to test the hypothesis that in upright stance participants continuously estimate both probability of failure and cost of failure such that their postural responses will be based on these estimates. We designed a snowboard riding simulation experiment where participants were asked to control the position of a moving snowboard within a snow track in a risky environment. Cost functions were provided by modifying the penalty of riding in the area adjacent to the snow track. Uncertainty was modified by changing the gain of postural responses while participants were standing on a rocker board. We demonstrated that participants continually evaluated the environmental cost function and compensated for additional risk with feedback-based postural changes, even when probability of failure was negligible. Results showed also that the participants' estimates of the probability of failure accounted for their own inherent instability. Moreover, participants showed a tendency to overweight large probabilities of failure with more biomechanically constrained standing postures that results in suboptimal estimates of risky environments. Overall, our results suggest that participants tune their standing postural responses by empirically estimating the cost of failure and the uncertainty level in order to minimize the risk of falling when cost is high
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