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Full-Text Articles in Medicine and Health Sciences
Muscle Synergies Of Feed-Forward Postural Adjustments During Reaching To Multi-Directional Targets In Standing, J Leonard, S Chvatal, L Ting, P Stapley
Muscle Synergies Of Feed-Forward Postural Adjustments During Reaching To Multi-Directional Targets In Standing, J Leonard, S Chvatal, L Ting, P Stapley
Dr Paul J Stapley
Standing balance can be controlled using feedback (FB) or feedforward (FF) mechanisms, depending on the nature of a postural disturbance. Unexpected disturbances of balance elicit automatic postural responses (APR) to restore body position (Horak and Macpherson 1996). Studies of APR have shown that the CNS recruits a small number of muscle synergies to simplify complex task-level goals (e.g. CoM stabilization) to produce the appropriate muscle activation patterns (Ting & McKay, 2007). Successful execution of goal-directed voluntary movements while standing requires FF programming of postural adjustments that serve to initiate movement of the body towards the target (preparatory postural adjustment, pPA) …
Decoupling Of Stretch Reflex And Background Muscle Activity During Anticipatory Postural Adjustments In Humans, Siddharth Vedula, Robert Kearney, Ross Wagner, Paul Stapley
Decoupling Of Stretch Reflex And Background Muscle Activity During Anticipatory Postural Adjustments In Humans, Siddharth Vedula, Robert Kearney, Ross Wagner, Paul Stapley
Dr Paul J Stapley
We studied the evolution of stretch reXexes in relation to background electromyographic (EMG) activity in the soleus muscle preceding the onset of voluntary arm raise movements. Our objective was to investigate if changes in reXex EMG and muscle activity occur simultaneously and are similarly scaled in amplitude. Ten human subjects stood with each foot on pedals able to exert short dorsiXexor pulses during stance. Subjects were asked to product consistent voluntary arm raise movements to a target upon a visual cue. In ¼ of trials, no pulse perturbations were given, but in the remaining ¾’s of all trials pulses were …
Postural Responses To Multidirectional Perturbations To The Hand During Stance, Ali Forghani, Sheida Rabipour, Theodore E. Milner, Paul J. Stapley
Postural Responses To Multidirectional Perturbations To The Hand During Stance, Ali Forghani, Sheida Rabipour, Theodore E. Milner, Paul J. Stapley
Dr Paul J Stapley
Humans are easily able to maintain their balance while applying force with their hands to move or stabilize objects. Based on Newton's laws, the applied force must be counteracted by ground reaction force (GRF) to maintain balance. However, because the GRF is partitioned between the two legs there is no unique solution. Furthermore, central nervous system (CNS) can employ an infinite number of muscle activation patterns to achieve ground reaction force (GRF) vectors needed to satisfy both the task-level goal and balance. This study examines the postural response when hand position must remain stable as an external force is applied …
Postural Responses To Unexpected Perturbations Of Balance During Reaching, Hari Trivedi, Julia Leonard, Lena Ting, Paul Stapley
Postural Responses To Unexpected Perturbations Of Balance During Reaching, Hari Trivedi, Julia Leonard, Lena Ting, Paul Stapley
Dr Paul J Stapley
To study the interaction between feedforward and feedback modes of postural control, we investigated postural responses during unexpected perturbations of the support surface that occurred during forward reaching in a standing position. We examined postural responses in lower limb muscles of nine human subjects. Baseline measures were obtained when subjects executed reaching movements to a target placed in front of them (R condition) and during postural responses to forward and backward support-surface perturbations (no reaching, P condition) during quiet stance. Perturbations were also given at different delays after the onset of reaching movements (RP conditions) as well as with the …
Bilateral Vestibular Loss In Cats Leads To Active Destabilization Of Balance During Pitch And Roll Rotations Of The Support Surface, Jane Macpherson, Dirk Everaert, Paul Stapley, Lena Ting
Bilateral Vestibular Loss In Cats Leads To Active Destabilization Of Balance During Pitch And Roll Rotations Of The Support Surface, Jane Macpherson, Dirk Everaert, Paul Stapley, Lena Ting
Dr Paul J Stapley
Although the balance difficulties accompanying vestibular loss are well known, the underlying cause remains unclear. We examined the role of vestibular inputs in the automatic postural response (APR) to pitch and roll rotations of the support surface in freely standing cats before and in the first week after bilateral labyrinthectomy. Support surface rotations accelerate the body center of mass toward the downhill side. The normal APR consists of inhibition in the extensors of the uphill limbs and excitation in the downhill limbs to decelerate the body and maintain the alignment of the limbs with respect to earth-vertical. After vestibular lesion, …
Bilateral Vestibular Loss Leads To Active Destabilization Of Balance During Voluntary Head Turns In The Standing Cat, Paul Stapley, Lena Ting, Chen Kuifu, Dirk Everaert, Jane Macpherson
Bilateral Vestibular Loss Leads To Active Destabilization Of Balance During Voluntary Head Turns In The Standing Cat, Paul Stapley, Lena Ting, Chen Kuifu, Dirk Everaert, Jane Macpherson
Dr Paul J Stapley
The purpose of this study was to determine the source of postural instability in labyrinthectomized cats during lateral head turns. Cats were trained to maintain the head in a forward orientation and then perform a rapid, large-amplitude head turn to left or right in yaw, while standing freely on a force platform. Head turns were biomechanically complex with the primary movement in the yaw plane accompanied by an ipsilateral ear-down roll and nose-down pitch. Cats used a strategy of pushing off by activating extensors of the contralateral forelimb while using all four limbs to produce a rotational moment of force …
Posture Control During Online Corrections Of Arm Movements Is Predictive, Julia Leonard, Paul Stapley
Posture Control During Online Corrections Of Arm Movements Is Predictive, Julia Leonard, Paul Stapley
Dr Paul J Stapley
The control of reaching to a target in standing involves the feed-forward programming of associated postural adjustments (a PAs) that decelerate the body and arm toward the target (Leonard et ai, 2009). However, little is known about the control of aPAs in situations where the final position of the target goal shifts after the reach movement has been initiated. We hypothesized that a predictive reprogramming of the aPA would occur prior to the adjustment of the arm movement to ensure correct execution of the reaching movement. Using a double step paradigm, we investigated the postural adjustments in standing humans exposed …
Independent Control Of Limb Force Underlies Stability During Voluntary Head Movements In Standing Humans, Paul Stapley, Alicia Hilderley, Julia Leonard
Independent Control Of Limb Force Underlies Stability During Voluntary Head Movements In Standing Humans, Paul Stapley, Alicia Hilderley, Julia Leonard
Dr Paul J Stapley
Postural stability during voluntary head movements is maintained through the integration of vestibular and neck afferent inputs. These inputs combine to accurately estimate trunk position in space, relative to a turning head. In animals, a loss of vestibular information leads to an active destabilization of balance as neck afferent information is interpreted as a movement of the trunk under a stable head (Stapley et al. 2006).