The role of unstable shoe constructions for the improvement of postural control (original) (raw)
Age and Ageing, 2006
Postural control is no longer considered simply a summation of static reflexes but, rather, a complex skill based on the interaction of dynamic sensorimotor processes. The two main functional goals of postural behaviour are postural orientation and postural equilibrium. Postural orientation involves the active alignment of the trunk and head with respect to gravity, support surfaces, the visual surround and internal references. Sensory information from somatosensory, vestibular and visual systems is integrated, and the relative weights placed on each of these inputs are dependent on the goals of the movement task and the environmental context. Postural equilibrium involves the coordination of movement strategies to stabilise the centre of body mass during both self-initiated and externally triggered disturbances of stability. The specific response strategy selected depends not only on the characteristics of the external postural displacement but also on the individual's expectations, goals and prior experience. Anticipatory postural adjustments, prior to voluntary limb movement, serve to maintain postural stability by compensating for destabilising forces associated with moving a limb. The amount of cognitive processing required for postural control depends both on the complexity of the postural task and on the capability of the subject's postural control system. The control of posture involves many different underlying physiological systems that can be affected by pathology or sub-clinical constraints. Damage to any of the underlying systems will result in different, context-specific instabilities. The effective rehabilitation of balance to improve mobility and to prevent falls requires a better understanding of the multiple mechanisms underlying postural control.
Voluntary control of postural equilibrium patterns
Behavioural Brain Research, 2003
The ability to voluntarily transit from one whole-body movement to another is based on the multisensory integration of visual, vestibular, and somatosensory information. The role of functional sensory ranges and mechanical constraints on the ability to voluntarily transit between whole-body movements was studied by requiring subjects to switch from a head-fixed-to-surface to head-fixed-in-space postural pattern (and vice versa). The head-fixed-to-surface pattern required an erect stance characterized by an in-phase relationship between center of pressure (CoP) and platform motion. The head-fixed-in-space pattern required subjects to fix trunk-head position in-space while producing an anti-phase relationship between CoP and platform motion. The voluntary transition was performed with and without vision while standing on a surface oscillating in the anterior-posterior (A/P) direction. The support surface oscillated at five frequencies (0.2-1 Hz) with amplitude fixed at 15 cm. The voluntary transition was initiated with an auditory cue. The appropriate CoP-platform phase relationship for the two postural patterns was produced for all frequencies with and without vision. Upper-trunk kinematics revealed that subjects often failed to produce the head-fixed-to-surface pattern for frequencies ≥0.6 Hz, while producing the head-fixed-in-space pattern at all frequencies with vision. Without vision, neither pattern was produced consistently based on upper-trunk kinematics. These findings demonstrate separate control processes for upper-and lower-body motion and that functional sensory ranges and mechanical constraints can facilitate or inhibit voluntary production of whole-body movements based on these control processes. The results are discussed in reference to neurological substrates that may be involved in the planning and execution of motor set-switching. The experimental protocol we employ may also have application as a diagnostic tool for the evaluation of postural deficits.
Journal of Electromyography and Kinesiology, 2010
The central nervous system (CNS) utilizes anticipatory (APAs) and compensatory (CPAs) postural adjustments to maintain equilibrium while standing. It is known that these postural adjustments involve displacements of the center of mass (COM) and center of pressure (COP). The purpose of the study was to investigate the relationship between APAs and CPAs from a kinetic and kinematic perspective. Eight subjects were exposed to external predictable and unpredictable perturbations induced at the shoulder level while standing. Kinematic and kinetic data were recorded and analyzed during the time duration typical for anticipatory and compensatory postural adjustments. When the perturbations were unpredictable, the COM and COP displacements were larger compared to predictable conditions with APAs. Thus, the peak of COM displacement, after the pendulum impact, in the posterior direction reached 28 ± 9.6 mm in the unpredictable conditions with no APAs whereas it was 1.6 times smaller, reaching 17 ± 5.5 mm during predictable perturbations. Similarly, after the impact, the peak of COP displacement in the posterior direction was 60 ± 14 mm for unpredictable conditions and 28 ± 3.6 mm for predictable conditions. Finally, the times of the peak COM and COP displacements were similar in the predictable and unpredictable conditions. This outcome provides additional knowledge about how body balance is controlled in presence and in absence of information about the forthcoming perturbation. Moreover, it suggests that control of posture could be enhanced by better utilization of APAs and such an approach could be considered as a valuable modality in the rehabilitation of individuals with balance impairment.
Somatosensory & motor research, 2012
Understanding postural control requires considering various mechanisms underlying a person´s ability to stand, to walk and to interact with the environment safely and efficiently. The purpose of this paper is to summarise the functional relation between biomechanical and neurophysiological perspectives related to postural control in both standing and walking based on movement efficiency. Evidence related to the biomechanical and neurophysiological mechanisms is explored as well as the role of proprioceptive input on postural and movement control.
Proprioceptive control of posture: a review of new concepts
Gait & Posture, 1998
The assumption that proprioceptive inputs from the lower legs are used to trigger balance and gait movements is questioned in this review (an outgrowth of discussions initiated during the Neural Control of Movement Satellite meeting held in Cozumel, Mexico, April 1997). Recent findings presented here suggest that trunk or hip inputs may be more important in triggering human balance corrections and that proprioceptive input from the lower legs mainly helps with the final shaping and intermuscular coordination of postural and gait movements. Three major questions were considered. First, what role, if any, do lower-leg proprioceptive inputs play in the triggering of normal balance corrections? If this role is negligible, which alternative proprioceptive inputs then trigger balance corrections? Second, what is the effect of proprioceptive loss on the triggering of postural and gait movements? Third, how does proprioceptive loss affect the output of central pattern generators in providing the final shaping of postural movements? The authors conclude that postural and gait movements are centrally organized at two levels. The first level involves the generation of the basic directionally-specific response pattern based primarily on hip or trunk proprioceptive input and secondarily on vestibular inputs. This pattern specifies the spatial characteristics of muscle activation, that is which muscles are primarily activated, as well as intermuscular timing, or the sequence in which muscles are activated. The second level is involved in the shaping of centrally set activation patterns on the basis of multi-sensorial afferent input (including proprioceptive input from all body segments and vestibular sensors) in order that movements can adapt to different task conditions.
Journal of Electromyography and Kinesiology, 2010
The central nervous system (CNS) utilizes anticipatory (APAs) and compensatory (CPAs) postural adjustments to maintain equilibrium while standing. It is known that these postural adjustments involve displacements of the center of mass (COM) and center of pressure (COP). The purpose of the study was to investigate the relationship between APAs and CPAs from a kinetic and kinematic perspective. Eight subjects were exposed to external predictable and unpredictable perturbations induced at the shoulder level while standing. Kinematic and kinetic data were recorded and analyzed during the time duration typical for anticipatory and compensatory postural adjustments. When the perturbations were unpredictable, the COM and COP displacements were larger compared to predictable conditions with APAs. Thus, the peak of COM displacement, after the pendulum impact, in the posterior direction reached 28 ± 9.6 mm in the unpredictable conditions with no APAs whereas it was 1.6 times smaller, reaching 17 ± 5.5 mm during predictable perturbations. Similarly, after the impact, the peak of COP displacement in the posterior direction was 60 ± 14 mm for unpredictable conditions and 28 ± 3.6 mm for predictable conditions. Finally, the times of the peak COM and COP displacements were similar in the predictable and unpredictable conditions. This outcome provides additional knowledge about how body balance is controlled in presence and in absence of information about the forthcoming perturbation. Moreover, it suggests that control of posture could be enhanced by better utilization of APAs and such an approach could be considered as a valuable modality in the rehabilitation of individuals with balance impairment.
Physiotherapy Theory and Practice, 1992
The reorganization of standing balance after a lower limb amputation is considered with emphasis on persons with an acquired un¡lateral amputation above the ankle and below the hip joint. ln the first section, three major peripheral motor and sensory impairments are discussed: (a) a lack of ankle torque generation to restore equilibrium in the sagittal plane, (b) a lack of weight-shifting capacity to control posture in the frontal plane, (c) a distorted somatosensory input from the síde of amputation. ln the second part of the paper, it is argued that a lower limb amputation, as any other seríous peripheral lesion, also affects the highest levels of the sensorimotor system, because the functional recovery after amputation requires a central adaptation to the alterations of peripheral motor and sensory conditions. A reduction in the cognitive regulation of posture as well as a decrease in visual dependency are proposed as two of the most critical parameters of the long-term central adaptation process and as relevant indicators of the restoration of (the safe performance of) gross-motor skills.
Adaptability of anticipatory postural adjustments associated with voluntary movement
World Journal of Orthopedics, 2012
The control of balance is crucial for efficiently performing most of our daily motor tasks, such as those involving goal-directed arm movements or whole body displacement. The purpose of this article is twofold. Firstly, it is to recall how balance can be maintained despite the different sources of postural perturbation arising during voluntary movement. The importance of the so-called "anticipatory postural adjustments" (APA), taken as a "line of defence" against the destabilizing effect induced by a predicted perturbation, is emphasized. Secondly, it is to report the results of recent studies that questioned the adaptability of APA to various constraints imposed on the postural system. The postural constraints envisaged here are classified into biomechanical (postural stability, superimposition of motor tasks), (neuro) physiological (fatigue), temporal (time pressure) and psychological (fear of falling, emotion). Overall, the results of these studies point out the capacity of the central nervous system (CNS) to adapt the spatio-temporal features of APA to each of these constraints. However, it seems that, depending on the constraint, the "priority" of the CNS was focused on postural stability maintenance, on body protection and/ or on maintenance of focal movement performance.
Identification of the Unstable Human Postural Control System
Maintaining upright bipedal posture requires a control system that continually adapts to changing environmental conditions, such as different support surfaces. Behavioral changes associated with different support surfaces, such as the predominance of an ankle or hip strategy, is considered to reflect a change in the control strategy. However, tracing such behavioral changes to a specific component in a closed loop control system is challenging. Here we used the joint input–output (JIO) method of closed-loop system identification to identify the musculoskeletal and neural feedback components of the human postural control loop. The goal was to establish changes in the control loop corresponding to behavioral changes observed on different support surfaces. Subjects were simultaneously perturbed by two independent mechanical and two independent sensory perturbations while standing on a normal or short support surface. The results show a dramatic phase reversal between visual input and body kinematics due to the change in surface condition from trunk leads legs to legs lead trunk with increasing frequency of the visual perturbation. Through decomposition of the control loop, we found that behavioral change is not necessarily due to a change in control strategy, but in the case of different support surfaces, is linked to changes in properties of the plant. The JIO method is an important tool to identify the contribution of specific components within a closed loop control system to overall postural behavior and may be useful to devise better treatment of balance disorders.
Coordination of posture and movement
Physical therapy, 1990
Movement is performed against a background of subtle postural adjustments that counteract destabilizing forces imposed by the movement. Despite the importance of these postural adjustments to the safe and efficient performance of movement, little is known about the properties of these postural accompaniments. The purpose of this article is twofold. First, it provides a review of properties of postural adjustments that accompany a variety of limb and trunk movements. Second, a schema for the coordination of posture and movement is proposed. This schema suggests that a central nervous system model of body dynamics is essential to anticipatory control of posture during movement.
Stability in human postural control
2000
In this paper the method of human posture identification is suggested. It is based on Pedotti's diagram, well known in human gait evaluation. During the experiment, undertaken by 12 healthy volunteers, ground reaction forces in sagittal plane were measured. Force vectors, with the origin in the center of pressure, oscillated in the shape of fan. By observing the characteristics of
Cortical control of postural responses
Journal of Neural Transmission, 2007
This article reviews the evidence for cortical involvement in shaping postural responses evoked by external postural perturbations. Although responses to postural perturbations occur more quickly than the fastest voluntary movements, they have longer latencies than spinal stretch reflexes, suggesting greater potential for modification by the cortex. Postural responses include short, medium and long latency components of muscle activation with increasing involvement of the cerebral cortex as latencies increase. Evidence suggests that the cortex is also involved in changing postural responses with alterations in cognitive state, initial sensory-motor conditions, prior experience, and prior warning of a perturbation, all representing changes in "central set." Studies suggest that the cerebellar-cortical loop is responsible for adapting postural responses based on prior experience and the basal ganglia-cortical loop is responsible for pre-selecting and optimizing postural responses based on current context. Thus, the cerebral cortex likely influences longer latency postural responses both directly via corticospinal loops and shorter latency postural responses indirectly via communication with the brainstem centers that harbor the synergies for postural responses, thereby providing both speed and flexibility for preselecting and modifying environmentally appropriate responses to a loss of balance.
Influence of wearing an unstable shoe construction on compensatory control of posture
Human movement science, 2013
This study investigated the influence of wearing unstable shoe construction (WUS) on compensatory postural adjustments (CPA) associated with external perturbations. Thirty two subjects stood on a force platform resisting an anteriorposterior horizontal force applied to a pelvic belt via a cable, which was suddenly released, under two conditions: barefoot and WUS. The electromyographic (EMG) activity of gastrocnemius medialis, tibialis anterior, rectus femoris, biceps femoris, rectus abdominis, and erector spinae muscles and the centre of pressure (CoP) displacement were acquired to study CPA.
Identification of Human Postural Control
IFAC Proceedings Volumes, 1990
Black box modelling and identification was applied to the motor-sensory feedback of a posture control system without external disturbances.The standing upright subject was modelled using an inverted-pendulum model. Analysis was extended to 28 healthy subjects engaged in cognitive verbal and visuo-spatial tasks. Further, 3 pathological subjects were examined, who were suffering from multiple scleros is. The transfer function of the who le closed loop system was then considered, and the relative poles were computed. The di stribution of the above poles on the z-plane showed an overall stabiliz ing effec t of the cogn iti ve tasks, both for healthy and pathological subjects, if compared to stance with open and closed eyes. Between the two tasks, the visuo-spatial one was found to be more stabili zi ng th an the verbal one. On the other hand, differences on the model order of the controller were found among the tested pathological and healthy people. In fact the order remained unchanged both interindividually for healthy subjects perfornling the same task, both among different tasks performed by the same subject. Instead , pathological subj ects were found to be characterized by a different model order, with respect to the healthy population, for the controller block of the posture control system.
Sensory and motor interdependence in postural adjustments
Journal of Vestibular Research, 1999
The sensory reafference from a movement depends upon the movement, and the movement chosen depends upon the available senses, as demonstrated by vestibular patients who abandon certain movements. Often, one variable is assumed to be dependent whereas the other is independent; however, sensory and motor dynamics in posture are interdependent as conditions upon each other. This paper applies conditional dynamics to characterize the global structure of interdependence between sensory states and motor strategies in fast postural adjustments. The mathematical formalism incorporates rich but disparate experimental, clinical, and theoretical results about sensory and motor control of posture. The control structures presented include relatively stable anatomical, physiological, and functional structures, both continuous and discrete, leading to a composite functional logic for the coordination of these structures in sensorimotor control. Results include sensorimotor control structures for p...
Physiological and circuit mechanisms of postural control
Current Opinion in Neurobiology, 2012
The postural system maintains a specific body orientation and equilibrium during standing and during locomotion in the presence of many destabilizing factors (external and internal). Numerous studies in humans have revealed essential features of the functional organization of this system. Recent studies on different animal models have significantly supplemented human studies. They have greatly expanded our knowledge of how the control system operates, how the postural functions are distributed within different parts of CNS, and how these parts interact with each other to produce postural corrections and adjustments. This review outlines recent advances in the studies of postural control in quadrupeds, with special attention given the neuronal postural mechanisms.
Balance and Gait Rehabilitation in Patients with Parkinson’s Disease
2011
In order to maintain balance, humans bring into play two types of postural responses, feedback and feedforward. The type of response activated depends on the postural task. Feedback postural responses have been well depicted in studies where subjects were submitted to unexpected disturbances of balance by means of controlled destabilizations. When the surface on which humans are standing unexpectedly moves, the body is destabilized in the direction opposite to that of the surface displacement (Leonard et al., 2009). To regain balance, humans produce medium-latency automatic postural responses in the supporting limbs that oppose the perturbation and drive the centre of mass (CoM) back toward its initial position relative to the support surface (Horak & Nashner, 1986). The latency from the initiation of the support surface movement to the onset of the evoked electromyographic (EMG) response is in the order of 80-120 ms in humans (Ting & Macpherson, 2004). These compensatory automatic postural responses are triggered by somatosensory feedback from the feet and legs (Bloem et al., 2000a, 2002), and unless prior warning of the upcoming perturbation is given (Jacobs & Horak, 2007) they are produced entirely using a feedback mode of neural control. Studies in animals and humans have examined feedback-based automatic postural responses to unexpected translations of the support surface in multiple directions with the aim of identifying strategies that the CNS may adopt to simplify the control of perturbed stance (Fung et al., 1995). These feedback responses may involve various levels of the CNS, depending on the complexity of the required response (Kuo, 2005). The route for all movement signals is the spinal cord, which also produces the lowest level of neural feedback. This feedback is in the form of local reflexes, in which stretch signals from a muscle are relayed to the spinal cord, passed across one or a few intermediate neural connections, and then fed directly back to the muscle, commanding a compensatory contraction. This short feedback loop has fast latency, in the range of 30-60 ms. However, the speed of such a loop comes with a disadvantage: local reflexes are the least integrative of postural responses, and are limited to relatively simple behaviours (Nashner, 1977). The second and most important level of feedback for balance control involves signals travelling up to the mid-brain. The brainstem serves as a relay and integration centre, receiving and sending great numbers of sensory and motor command signals. The mid-level feedback loop involves longer conduction paths and greater numbers of neural synapses, and consequently has a longer latency than spinal reflexes (often 90 ms and greater). However, the convergence of many signals and complexity of the connections allows the brain stem to generate much more complex movements, mostly of an automatic nature. The brainstem modulates the behaviour of lower level reflexes, and is itself modulated by the higher levels. The cerebral cortex and related structures generate highly complex movements, mostly of a voluntary nature, with longer latencies than the two lower feedback loops. The longer latencies suggest that the cerebral cortex has a modulatory, rather than a direct role in posture control. Unlike the condition of unexpected perturbation of balance, during daily life, most postural perturbations are caused by an individual's own movement (i.e. reaching forward). In this case, postural adjustments occur prior to movement onset, to prevent the CoM from shifting outside the base of support (Bouisset & Zattara, 1987; Commissaris et al., 2001). To ensure a controlled transition from one postural configuration to another, these adjustments of posture must be planned by the CNS in advance, and a feedforward mode of neural control sends commands to both focal and postural muscles to initiate and stabilize posture.