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Articles 1 - 18 of 18
Full-Text Articles in Life Sciences
The Pontomedullary Reticular Formation Contributes To The Compensatory Postural Responses Observed Following Removal Of The Support Surface In The Standing Cat, Paul Stapley, Trevor Drew
The Pontomedullary Reticular Formation Contributes To The Compensatory Postural Responses Observed Following Removal Of The Support Surface In The Standing Cat, Paul Stapley, Trevor Drew
Dr Paul J Stapley
This study was designed to determine the contribution of reticular neurons in the pontomedullary reticular formation (PMRF) to the postural responses produced to compensate for an unexpected perturbation. We recorded the activity of 48 neurons in the PMRF, including 41 reticulospinal neurons, to removal of the support surface under each of the four limbs in four cats. The perturbations produced robust postural responses that were divided into three periods: an initial postural response (P1) that displaced the center of vertical pressure over the two diagonal supporting limbs; a secondary response (P2) during which the cat restored a tripedal support pattern; …
Feedback Regulation Of Temporal Muscle Activation Patterns For Postural Control Before And After Peripheral Neuropathy, L Ting, D Lockhart, P Stapley, J Macpherson
Feedback Regulation Of Temporal Muscle Activation Patterns For Postural Control Before And After Peripheral Neuropathy, L Ting, D Lockhart, P Stapley, J Macpherson
Dr Paul J Stapley
Introduction: Neural mechanislllS determining temporal pattcl1ls of muscle activity during poshlral responses are not understood. Fulluwing pyridoxine inuuced somatosensory loss in cats, unset latencies of automatic poshu-al responses are delayed, and balance is impaired. We introduce a new method for correlating temporal patterns of muscle activation with task-level variahles in the context of postural responses to perturbation. Methods: We measured postmal responses to support smface tronslations before and after loss of group I afferents indnced by pyridoxine intoxication. We reconstructed temporal EMG patterns llsing a feedback loop with delays, on CoM acceleration. velocity, and displacement. Resnlts: Prior to lesion, temporal …
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) …
Independent Activation In Adjacent Lumbar Extensor Muscle Compartments, Marilee Nugent, Paul Stapley, Theodore Milner
Independent Activation In Adjacent Lumbar Extensor Muscle Compartments, Marilee Nugent, Paul Stapley, Theodore Milner
Dr Paul J Stapley
The purpose of this study was to examine compartmentalization in human lumbar spine extensors. Structure and innervation of these muscles would suggest the possibility of more segmentally specific biomechanical functions than have been found in previous studies examining muscle activation patterns during simple spine bending and twisting tasks. We selected specialized tasks to more effectively investigate the degree of independent control possible within lumbar spine extensors. We recorded surface electromyograms (SEMG) from the right posterior lumbar region during performance of two segmentally specific bellydance skills by seven novice and five trained subjects. These movements were performed at two frequencies (0.5 …
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 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 …
Age-Related Changes In Conventional Road Versus Off-Road Triathlon Performance, Romuald Lepers, Paul Stapley
Age-Related Changes In Conventional Road Versus Off-Road Triathlon Performance, Romuald Lepers, Paul Stapley
Dr Paul J Stapley
The aims of this study were: (i) to analyze agerelated declines in swimming, cycling, and running performances for road-based and off-road triathlons, and (ii) to compare age-related changes in these three disciplines between road-based and off-road triathlons. Swimming, cycling, running and total time performances of the top five males between 20 and 70 years of age (in 5-year intervals) were analyzed for short distance road-based (1.5 km swim, 40 km cycle, and 10 km run) and off-road (1.5 km swim, 30 km mountain bike, and 11 km trail run) triathlons at the 2009 World Championships. Independently of age, there was …
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 …
A Common Neural Substrate For The Control Of Anticipatory And Compensatory Postural Responses, Paul Stapley, Benedicte Schepens, Trevor Drew
A Common Neural Substrate For The Control Of Anticipatory And Compensatory Postural Responses, Paul Stapley, Benedicte Schepens, Trevor Drew
Dr Paul J Stapley
We have shown previously that reticulospinal neurones (RSNs) in the brainstem pontomedullary reticular formation (PMRF) contribute to the production of the anticipatory postural adjustments (APAs) that precede reaching movements executed in a standing pOSition (Schepens and Drew, 2004, 2006; Schepens, Stapley and Drew, 2008). More recently (Stapley and Drew, 2009), we have also shown that cells in the PMRF contribute to the production of the compensatory responses that are produced by unexpected perturbations (drops) of the support surface from under one paw during quiet stance. In this poster we address the question of whether the same cells in the PMRF …
Reaching To Multiple Targets When Standing: The Spatial Organization Of Feedforward Postural Adjustments, Julia Leonard, Ryan Brown, Paul Stapley
Reaching To Multiple Targets When Standing: The Spatial Organization Of Feedforward Postural Adjustments, Julia Leonard, Ryan Brown, Paul Stapley
Dr Paul J Stapley
We examined the spatial organization of feedforward postural adjustments produced prior to and during voluntary arm reaching movements executed while standing. We sought to investigate whether the activity of postural muscles before and during reaching was directionally tuned and whether a strategy of horizontal force constraint could be observed. To this end, eight human subjects executed self-paced reach-to-point movements on the random illumination of one of 13 light targets placed within a 180° array centered along the midline of the body. Analysis was divided into two periods: a first corresponding to the 250 ms preceding the onset of the reaching …
Differences In Gender And Performance In Off-Road Triathlon, Romuald Lepers, Paul Stapley
Differences In Gender And Performance In Off-Road Triathlon, Romuald Lepers, Paul Stapley
Dr Paul J Stapley
The aims of this study were: (1) to examine performance trends and compare elite male and female athletes at the off-road triathlon (1.5-km swim, 30-km mountain biking, and 11-km trail running) world championships since its inception in 1996, and (2) to compare gender-related differences between off-road triathlon and conventional road-based triathlon. Linear regression analyses and ANOVA were used to examine performance trends and differences between the sexes. Elite male performance times stabilized over the 2005-2009 period, whereas elite female performance times continued to improve, especially for the run leg. Differences in performance times between the sexes were less marked in …
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).
Postural Adjustments For Online Corrections Of Arm Movements In Standing Humans, Julia Leonard, Valeriya Gritsenko, Ryan Ouckama, Paul Stapley
Postural Adjustments For Online Corrections Of Arm Movements In Standing Humans, Julia Leonard, Valeriya Gritsenko, Ryan Ouckama, Paul Stapley
Dr Paul J Stapley
The aim of this study was to investigate how humans correct ongoing arm movements while standing. Specifically, we sought to understand whether the postural adjustments in the legs required for online corrections of arm movements are predictive or rely on feedback from the moving limb. To answer this question we measured online corrections in arm and leg muscles during pointing movements while standing. Nine health right-handed subjects reached with their dominant arm to a visual target in front of them and aligned with their midline. In some trials, the position of the target would switch from the central target to …
Equilibrium Constraints But Not Joint Constraints Determine Hand Trajectory Planning, C Paizis, C Papaxanthis, P Stapley, T Pozzo
Equilibrium Constraints But Not Joint Constraints Determine Hand Trajectory Planning, C Paizis, C Papaxanthis, P Stapley, T Pozzo
Dr Paul J Stapley
Introduction: Equilibrium constraints play a major role in finger trajectory formation and curved hand paths seem to be the result of a strong coupling between postural and focal task components. However, such curvatures might also result from joint constraints. To test this hyputhesis we investigated the elrect of imposed joint strategies and support conditions on hand trajectory formation during a pointing task beyond arm's length.
Neuromuscular Control And Exercise-Related Leg Pain In Triathletes, Andrew Chapman, Paul Hodges, Andrew Briggs, Paul Stapley, Bill Vicenzino
Neuromuscular Control And Exercise-Related Leg Pain In Triathletes, Andrew Chapman, Paul Hodges, Andrew Briggs, Paul Stapley, Bill Vicenzino
Dr Paul J Stapley
Previous studies have shown that cycling can directly influence neuromuscular control during subsequent running in some highly trained triathletes. A relationship between this altered neuromuscular control of running and musculoskeletal pain and injury has been proposed; however, this link has not been investigated. PURPOSE: This study aimed to evaluate the influence of cycling on neuromuscular control during subsequent running in highly trained triathletes with and without exercise-related leg pain (ERLP). METHODS: Participants were 34 highly trained triathletes: 10 triathletes with a history of ERLP and 24 training-matched control triathletes with no history of ERLP. Knee and ankle kinematics and leg …
Neurons In The Pontomedullary Reticular Formation Signal Posture And Movement Both As An Integrated Behavior And Independently, Benedicte Schepens, Paul Stapley, Trevor Drew
Neurons In The Pontomedullary Reticular Formation Signal Posture And Movement Both As An Integrated Behavior And Independently, Benedicte Schepens, Paul Stapley, Trevor Drew
Dr Paul J Stapley
We have previously suggested that the discharge characteristics of some neurons in the pontomedullary reticular formation (PMRF) are contingent on the simultaneous requirement for activity in both ipsilateral flexor muscles and contralateral extensors. To test this hypothesis we trained cats to stand on four force platforms and to perform a task in which they were required to reach forward with one forelimb or the other and depress a lever. As such the task required the cat to make a flexion movement followed by an extension in the reaching limb while maintaining postural support by increasing extensor muscle tonus in the …