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7.15 Modulation of anticipatory postural adjustments incase of constant postural perturbation: Effect of components of a motor action
Chapter 7. Anticipatory postural control and representation of action [3] Kasai T, Yahagi S, Shimura K. Effect of vibration-induced postural illusion on anticipatory postural adjustment of voluntary arm movement in standing humans. Gait & Posture, 2002; 15:94 100.
[•5]
Modulation of anticipatory postural adjustments in case of constant postural perturbation: effect of components of a motor action
T. Shiratori, A. Aruin. Department of Physical Therapy, University
of illinois at Chicago, USA Introduction: The purpose of the study was to determine whether the
instruction of movement speed and amplitude of a motor action used to trigger the same perturbation to the body posture affect anticipatory postural adjustments (APAs). Methods: Seven standing subjects held a 2.2kg load between their hands with arms extended in front of their body. Then, subjects performed bilateral horizontal shoulder abduction movements (motor action) of three amplitudes at three instructed speeds. These actions lead to the release of the load, inducing an unloading perturbation in the sagittal plane. Electromyographic activities of the leg and trunk muscles were recorded and used to quantify APA activity. Results: A change in the background leg and/or trunk muscle activity was observed prior to unloading perturbation in all experimental series. Additionally, APAs depended on instructed speed of the motor action; larger APA activities were observed in the leg and trunk muscles with an increase in speed instruction. Meanwhile, modulation of APAs was not observed with changes in movement amplitude. Discussion: We conclude that the central nervous system uses information within a motor action (i.e., speed instruction) to approximate the magnitude of the forthcoming perturbation and modulate APAs, even when the perturbation is constant.
postural adjustments during stepping in [•.16] Anticipatory place S. Siwasakunrat, M.L. Latash. Department of Kinesiology, The
[•]
$47
Stepping on an unexpectedly lowered ground support surface: foot landing and ground reaction forces
M.H. van der Linden, M. Vermeulen, J.E.J. Duysens. Dep of Rehabilitation Medicine, Radboud University Nijmegen Medical Centre and SMK-Research Nijmegen, The Netherlands' Introduction: In order to study risk factors for ankle spraining, foot
landing and vertical ground reaction force (vGRF) were measured in healthy young adults, who stepped on an expectedly or unexpectedly lowered ground support surface. Methods: A 2.6 m long walkway was built, which embedded a platform that could unexpectedly be lowered 5.0 cm before foot contact. Plantar pressure and 3D-kinematic data were collected from ten subjects. Results: When subjects were unaware of the lowering of the ground surface, they showed a decreased vGRF and a more lateral and frontal foot placement after touchdown. They mostly landed on the heel (82%), but with more lateral and frontal foot placement compared to control trials. In contrast, when subjects were aware about the lowering, they often showed a forefoot landing (38%). Such landing resulted in higher ground reaction forces and more lateral foot placement compared to heel landing. When deprived of vision, subjects frequently exhibited a combination of the heel and forefoot landing (29%). In 4 of the subjects there was a clear difference between the vGRF of the first and the subsequent trials. Discussion and Conclusion: When aware about the lowered surface, many subjects choose a forefoot instead of a heel landing. Since the impact is higher and more laterally situated, it is questionable whether this is a safe strategy. Subjects exhibiting a forefoot landing may be at higher risk for ankle sprains.
[•8]
Reorganisation of postural adjustments associated with rapid voluntary stepping initiation during the synchronization with an upper limb pointing task
E. Yiou, D. Roussel. Centre for Research in Sport Sciences', UPRES EA 1609, UFR STAPS, University of Paris XI, France
Pennsylvania State University, University Park, PA 16802, USA Introduction: When a person releases the load from the extended
arms, anticipatory postural adjustments (APAs [1]) are seen in leg and trunk muscles. We analyzed APA modulation during stepping in place. Methods: Subjects stepped in place either with the feet side-byside or with one foot in front of the other timed by a metronome. They held a 2.2kg load acting upwards in the extended hands and released it in different step phases in a self-paced manner. EMG of postural muscles was analyzed within lOOms intervals prior to the load release. Results: Higher APAs were seen in the soleus during support phase and preceding double-support transition; these APAs were suppressed in the swing phase. Proximal muscles showed much smaller APA modulation with higher APAs in the biceps femoris during the doublesupport phases. Erector spinae showed minimal APA modulation within the step cycle. During one-foot-forward stepping, some subjects showed APA reversals in the trailing leg muscles during its support phase. Discussion and Conclusion: The results support a hypothesis on a general APA pattern provided by proximal muscles, while distal muscles produce its fine, task-specific modulation [2]. APA reversals suggest that they can act with the perturbation when safety concerns dictate so.
References [1] Massion, J. Movement, posture and equilibrium: interaction and coordination. Prog Neurobiol 1992; 38:35 56. [2] Shiratori T, Latash M. The roles of proximal and distal muscles in anticipatory postural adjustments under asymmetrical perturbations and during standing on rollerskates. Clin Neurophysiol 2000; 111:613 623.
Introduction: The goal of this study was to investigate the postural reorganisation of a rapid stepping initiation during the synchronization with a pointing. Methods: Subjects standing on a force-plate were instructed to perform the following conditions at maximal velocity: pointing the index towards a target from the erect posture, initiate an isolated stepping, and synchronize the stepping and the pointing. Surface electromyographical (EMG) activity of ankle muscles was analysed. Results: The duration of the anticipatory postural adjustments for stepping (APAs) was equivalent between the two stepping conditions, whatever the timing between the two actions in the synchronous task. In contrast, the duration of the swing phase and the total duration of the stepping were both shortened in the synchronous task. The maximal acceleration of the centre of gravity reached during the APAs was much higher in this latter task, and the step length was shorter. In contrast, neither of the analysed EMG parameters of the stepping was modulated by the superimposition of the pointing. Discussion: The discussion focuses on the biomechanical and central reorganisation of the stepping induced by the synchronous pointing. Conclusion: It is concluded (i) that the pointing has generated an enhanced postural instability at the foot-off and foot-contact times, which may be a factor of fall in disabled people with deficit in postural control and (ii) that the modulations of the biomechanical features of the stepping were due to an effect of the postural dynamics elicited by the pointing, not to a modulation of the APAs programming.
[•5]
Modulation of anticipatory postural adjustments in case of constant postural perturbation: effect of components of a motor action
T. Shiratori, A. Aruin. Department of Physical Therapy, University
of illinois at Chicago, USA Introduction: The purpose of the study was to determine whether the
instruction of movement speed and amplitude of a motor action used to trigger the same perturbation to the body posture affect anticipatory postural adjustments (APAs). Methods: Seven standing subjects held a 2.2kg load between their hands with arms extended in front of their body. Then, subjects performed bilateral horizontal shoulder abduction movements (motor action) of three amplitudes at three instructed speeds. These actions lead to the release of the load, inducing an unloading perturbation in the sagittal plane. Electromyographic activities of the leg and trunk muscles were recorded and used to quantify APA activity. Results: A change in the background leg and/or trunk muscle activity was observed prior to unloading perturbation in all experimental series. Additionally, APAs depended on instructed speed of the motor action; larger APA activities were observed in the leg and trunk muscles with an increase in speed instruction. Meanwhile, modulation of APAs was not observed with changes in movement amplitude. Discussion: We conclude that the central nervous system uses information within a motor action (i.e., speed instruction) to approximate the magnitude of the forthcoming perturbation and modulate APAs, even when the perturbation is constant.
postural adjustments during stepping in [•.16] Anticipatory place S. Siwasakunrat, M.L. Latash. Department of Kinesiology, The
[•]
$47
Stepping on an unexpectedly lowered ground support surface: foot landing and ground reaction forces
M.H. van der Linden, M. Vermeulen, J.E.J. Duysens. Dep of Rehabilitation Medicine, Radboud University Nijmegen Medical Centre and SMK-Research Nijmegen, The Netherlands' Introduction: In order to study risk factors for ankle spraining, foot
landing and vertical ground reaction force (vGRF) were measured in healthy young adults, who stepped on an expectedly or unexpectedly lowered ground support surface. Methods: A 2.6 m long walkway was built, which embedded a platform that could unexpectedly be lowered 5.0 cm before foot contact. Plantar pressure and 3D-kinematic data were collected from ten subjects. Results: When subjects were unaware of the lowering of the ground surface, they showed a decreased vGRF and a more lateral and frontal foot placement after touchdown. They mostly landed on the heel (82%), but with more lateral and frontal foot placement compared to control trials. In contrast, when subjects were aware about the lowering, they often showed a forefoot landing (38%). Such landing resulted in higher ground reaction forces and more lateral foot placement compared to heel landing. When deprived of vision, subjects frequently exhibited a combination of the heel and forefoot landing (29%). In 4 of the subjects there was a clear difference between the vGRF of the first and the subsequent trials. Discussion and Conclusion: When aware about the lowered surface, many subjects choose a forefoot instead of a heel landing. Since the impact is higher and more laterally situated, it is questionable whether this is a safe strategy. Subjects exhibiting a forefoot landing may be at higher risk for ankle sprains.
[•8]
Reorganisation of postural adjustments associated with rapid voluntary stepping initiation during the synchronization with an upper limb pointing task
E. Yiou, D. Roussel. Centre for Research in Sport Sciences', UPRES EA 1609, UFR STAPS, University of Paris XI, France
Pennsylvania State University, University Park, PA 16802, USA Introduction: When a person releases the load from the extended
arms, anticipatory postural adjustments (APAs [1]) are seen in leg and trunk muscles. We analyzed APA modulation during stepping in place. Methods: Subjects stepped in place either with the feet side-byside or with one foot in front of the other timed by a metronome. They held a 2.2kg load acting upwards in the extended hands and released it in different step phases in a self-paced manner. EMG of postural muscles was analyzed within lOOms intervals prior to the load release. Results: Higher APAs were seen in the soleus during support phase and preceding double-support transition; these APAs were suppressed in the swing phase. Proximal muscles showed much smaller APA modulation with higher APAs in the biceps femoris during the doublesupport phases. Erector spinae showed minimal APA modulation within the step cycle. During one-foot-forward stepping, some subjects showed APA reversals in the trailing leg muscles during its support phase. Discussion and Conclusion: The results support a hypothesis on a general APA pattern provided by proximal muscles, while distal muscles produce its fine, task-specific modulation [2]. APA reversals suggest that they can act with the perturbation when safety concerns dictate so.
References [1] Massion, J. Movement, posture and equilibrium: interaction and coordination. Prog Neurobiol 1992; 38:35 56. [2] Shiratori T, Latash M. The roles of proximal and distal muscles in anticipatory postural adjustments under asymmetrical perturbations and during standing on rollerskates. Clin Neurophysiol 2000; 111:613 623.
Introduction: The goal of this study was to investigate the postural reorganisation of a rapid stepping initiation during the synchronization with a pointing. Methods: Subjects standing on a force-plate were instructed to perform the following conditions at maximal velocity: pointing the index towards a target from the erect posture, initiate an isolated stepping, and synchronize the stepping and the pointing. Surface electromyographical (EMG) activity of ankle muscles was analysed. Results: The duration of the anticipatory postural adjustments for stepping (APAs) was equivalent between the two stepping conditions, whatever the timing between the two actions in the synchronous task. In contrast, the duration of the swing phase and the total duration of the stepping were both shortened in the synchronous task. The maximal acceleration of the centre of gravity reached during the APAs was much higher in this latter task, and the step length was shorter. In contrast, neither of the analysed EMG parameters of the stepping was modulated by the superimposition of the pointing. Discussion: The discussion focuses on the biomechanical and central reorganisation of the stepping induced by the synchronous pointing. Conclusion: It is concluded (i) that the pointing has generated an enhanced postural instability at the foot-off and foot-contact times, which may be a factor of fall in disabled people with deficit in postural control and (ii) that the modulations of the biomechanical features of the stepping were due to an effect of the postural dynamics elicited by the pointing, not to a modulation of the APAs programming.