Physiological Basis of Limb-Impedance Modulation During Free and Constrained Movements

Damm, Loïc; McIntyre, Joseph

doi:10.1152/jn.90471.2008

Cited by 23 publications

(26 citation statements)

References 41 publications

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“…However, reflex excitability changes during adaptation to environments (Akazawa et al 1983; Asai et al 2009; Damm and McIntyre 2008; Doemges and Rack 1992a,b; Krutky et al 2010; Perreault et al 2008). Moreover there is some evidence for reflex contributions to changes in end-point stiffness during movement (Franklin et al 2007a).…”

Section: Discussionmentioning

confidence: 99%

“…To develop these skills, he will need to tune his limb impedance (Burdet et al 2001; Gomi and Kawato 1996; Hogan 1984, 1985) to the instabilities that may vary across the workspace. To modulate the limb impedance, he can either change the limb posture (Hogan 1985; Rancourt and Hogan 2001; Trumbower et al 2009), modulate feedback control (Krutky et al 2010; Loram et al 2011, 2009; Morasso 2011), or coactivate muscles (Damm and McIntyre 2008; Hogan 1984; Milner 2002). In an unstable or unpredictable environment, the central nervous system (CNS) learns to co-contract suitable muscle pairs involved in the movement (Burdet et al 2001; Franklin et al 2007a, 2003b) stabilizing the limb end point and minimizing the production and effect of motor noise (Selen et al 2005, 2009).…”

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confidence: 99%

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Impedance control is selectively tuned to multiple directions of movement

Kadiallah

Liaw²,

Kawato

et al. 2011

Journal of Neurophysiology

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Humans are able to learn tool-handling tasks, such as carving, demonstrating their competency to make movements in unstable environments with varied directions. When faced with a single direction of instability, humans learn to selectively co-contract their arm muscles tuning the mechanical stiffness of the limb end point to stabilize movements. This study examines, for the first time, subjects simultaneously adapting to two distinct directions of instability, a situation that may typically occur when using tools. Subjects learned to perform reaching movements in two directions, each of which had lateral instability requiring control of impedance. The subjects were able to adapt to these unstable interactions and switch between movements in the two directions; they did so by learning to selectively control the end-point stiffness counteracting the environmental instability without superfluous stiffness in other directions. This finding demonstrates that the central nervous system can simultaneously tune the mechanical impedance of the limbs to multiple movements by learning movement-specific solutions. Furthermore, it suggests that the impedance controller learns as a function of the state of the arm rather than a general strategy.

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Section: Discussionmentioning

confidence: 99%

mentioning

confidence: 99%

Impedance control is selectively tuned to multiple directions of movement

Kadiallah

Liaw²,

Kawato

et al. 2011

Journal of Neurophysiology

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“…In designing this study, our aim was to emphasize the use of impedance control as a way of completing a task. These results, from the ballistic-release paradigm, expand upon studies of arm impedance that investigated the isolated effect of force (McIntyre et al 1996;Gomi and Osu 1998;Perreault et al 2002) or movement (Gomi and Kawato 1997;Burdet et al 2001;Darainy et al 2007;Franklin et al 2007;Piovesan et al 2013) and extend the concept that impedance can be specified predictively for object interaction (Lacquaniti et al 1993;Damm and McIntyre 2008).…”

Section: Discussionmentioning

confidence: 55%

Stiffness as a control factor for object manipulation

Kennedy

Schwartz

2018

Preprint

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We act on the world by producing forces that move objects. During manipulation, force is exerted with the expectation that an object will move in an intended manner. This prediction is a learned coordination between force and displacement. Mechanically, impedance is a way to describe this coordination. As an efficient control strategy, object interaction could be anticipated by setting impedance before the hand moves the object. We examined this possibility with a paradigm in which subjects moved a handle to a specific target position along a track. The handle was locked in place until the subject exerted enough force to cross a specific threshold; then the handle was abruptly released and could move along the track. We hypothesized that this ballistic-release task would encourage subjects to modify their arm impedance in anticipation of the upcoming movement. If we consider the handle as an object, this paradigm loosely approximates the uncertainty encountered at the end of a reach when contacting a fixed object. We found that one component of arm impedance, stiffness, varied in a way that matched the behavioral demands of the task and we were able to dissociate stiffness from changes in force and displacement. We also found separate components of muscle activity that corresponded to stiffness and to changes in force. Our results show that subjects used a robust and efficient strategy to coordinate force and displacement by modulating muscle activity in a way that was behaviorally relevant in the task. New & NoteworthyThe arm can behave like a spring, suggesting the concept of exerting force to move an object by selecting a spring of a certain length and stiffness that, respectively, depend on the movement and force requirements of the task. We show that these spring-like characteristics describe the strategy used to arrest a pre-loaded handle. These results extend our understanding of the arm's spring-like behavior to include force and movement constraints, important factors for object interaction.

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“…The limitation of using joint torques to study the CNS is that they do not capture the effects of muscle co-contraction, which is an important control strategy used to alter joint stiffness or whole arm impedance (Damm and McIntyre, 2008;Darainy et al, 2004). However, our approach may offer some insight into this control strategy by using decomposition methods.…”

Section: Discussionmentioning

confidence: 99%

Gravitational and dynamic components of muscle torque underlie tonic and phasic muscle activity during goal-directed reaching

Olesh

Pollard

Gritsenko

2017

Preprint

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Human reaching movements require complex muscle activations to produce the forces necessary to move the limb in a controlled manner. How gravity and the complex kinetic properties of the limb contribute to the generation of the muscle activation pattern by the central nervous system (CNS) is a longstanding question in neuroscience. To address this question, muscle activity is often subdivided into static and phasic components. The former is thought to be related to posture maintenance and transitions between postures. The latter represents the remainder of muscle activity and is thought to be related to active movement production and the compensation for the kinetic properties of the limb. In the present study, we directly addressed how this subdivision of muscle activity into static and phasic components is related to the corresponding components of active muscle torques. Eight healthy subjects pointed in virtual reality to visual targets arranged to create a standard center-out reaching task in three dimensions. Muscle activity and motion capture data were synchronously collected during the movements. The motion capture data were used to calculate gravitational and dynamic components of active muscle torques using a dynamic model of the arm with 5 degrees of freedom. Principal Component Analysis (PCA) was then applied to muscle activity and the torque components, separately, to reduce the dimensionality of the data. Muscle activity was also reconstructed from gravitational and dynamic torque components. Results show that the gravitational and dynamic components of muscle torque represent a significant amount of variance in muscle activity. This method could be used to identify static and phasic components of muscle activity using muscle torques. The contribution of both components to the overall muscle activity was largely equal, unlike their relative contribution to active muscle torques, which may reflect a neural control strategy.

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Physiological Basis of Limb-Impedance Modulation During Free and Constrained Movements

Cited by 23 publications

References 41 publications

Impedance control is selectively tuned to multiple directions of movement

Impedance control is selectively tuned to multiple directions of movement

Stiffness as a control factor for object manipulation

Gravitational and dynamic components of muscle torque underlie tonic and phasic muscle activity during goal-directed reaching

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