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Sandra K. Hnat, Musa L. Audu, Ronald J. Triolo, and Roger D. Quinn

applicable to walking exoskeletons. Various methods have been proposed to control the balance of bipedal robots, most notably the zero moment point, which is a projected point on the ground where the sum of the moments acting on the robot equal 0. 25 , 26 The zero moment point is equivalent to the center of

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Natalia V. Dounskaia, Caroline J. Ketcham, and George E. Stelmach

Influence of mechanical interactions between the shoulder and elbow on production of different coordination patterns during horizontal arm movements is investigated in the present study. Subjects performed cyclical movements along a circle and along lines of 4 different orientations. Cycling frequency was manipulated to highlight control features responsible for interactive torque regulation. When the shoulder was involved in motion, torque analysis revealed that this joint was controlled similarly during all movement types. At the elbow, however, each movement type required a specific pattern of regulation of interactive torque with muscle torque. When interactive torque acted in the direction of the required elbow rotation, the demands for active control were lower than when the interactive torque resisted elbow motion and had to be actively suppressed. Kinematic analysis demonstrated that increases in cycling frequency systematically deformed the fingertip path. The amount of these deformations differed across movement types, being more pronounced for movements where the interactive torque resisted joint motion. It appears that interactive torque can assist or resist movement at the joints, making control of some movement types more difficult than others.

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Robert Rein, Chris Button, Keith Davids, and Jeffery Summers

The present paper proposes a technical analysis method for extracting information about movement patterning in studies of motor control, based on a cluster analysis of movement kinematics. In a tutorial fashion, data from three different experiments are presented to exemplify and validate the technical method. When applied to three different basketball-shooting techniques, the method clearly distinguished between the different patterns. When applied to a cyclical wrist supination-pronation task, the cluster analysis provided the same results as an analysis using the conventional discrete relative phase measure. Finally, when analyzing throwing performance constrained by distance to target, the method grouped movement patterns together according to throwing distance. In conclusion, the proposed technical method provides a valuable tool to improve understanding of coordination and control in different movement models, including multiarticular actions.

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Gerald E. Loeb

The number of muscles in the body is actually fairly close to the number required to control completely all its degrees of freedom. The apparent need for a coordinating principle arises from the experimental practice of asking subjects to perform simple movements and assuming that they make no implicit assumptions about other constraints. Natural activities include implicit constraints that differ greatly for different tasks and circumstances and that would be met best by a nervous system free of a priori principles.

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Rahul Marwaha, Susan J. Hall, Christopher A. Knight, and Slobodan Jaric

The aim of the study was to reveal specific aspects of impaired hand function in mildly affected multiple sclerosis (MS) patients. Static manipulation tasks were tested in 13 mildly impaired (EDSS 1.5-4) MS patients and 13 age and gender matched controls. The tasks were based either on presumably visually (i.e., feedback) controlled tracing of depicted patterns of load force (LF; produced by symmetric bimanual tension and/or compression applied against an externally fixed device) or on predominantly feed-forward controlled amplitudes of sinusoidal patterns of LF. The task variables (based on accuracy of exerting the required LF pattern) suggested poor performance of MS subjects in feedback, but not in the feed-forward controlled tasks. The patients also revealed higher GF/LF ratio in all tasks. However, the coordination of GF and LF appeared to be comparable in the two groups. These results continue to support the chosen experimental paradigm and suggest that in mildly affected MS patients, sensorimotor deficits and overgripping precede the decoupling of grip and load forces observed in more severely affected patients.

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Nick Wadsworth and Adam Hargreaves

, and engaging in, the viva examination did allow me to reflect on how I articulated this approach to others. The “ ABC principle” is one way of understanding my philosophy of practice. The ABC principle ( Authenticity, Balance, and Control ) draws heavily from the existential literature ( Nesti

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Mark L. Latash

Over the past years, the notion of primitives has become prominent in studies on the neural control of movements (for reviews, see Flash & Hochner, 2005 ; Giszter, 2015 ; Giszter, Patil, & Hart, 2007 ; Hogan & Sternad, 2012 ; Ivanenko, Poppele, & Lacquaniti, 2006 ; Overduin, d’Avella, Roh

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Vennila Krishnan and Slobodan Jaric

Coordination of the hand grip (G; acting normally to the grasping surface) and load forces (L; acting in parallel) in bimanual static tasks was studied. L symmetry (either the magnitude or direction) and frequency were manipulated in healthy participants (N = 14). More complex tasks (i.e., the higher frequency and/or asymmetric ones) revealed expected deterioration in both the task performance (accuracy of the prescribed L force profiles) and force coordination (G/L ratio and G-L correlation) suggesting importance of L frequency and symmetry in prehension activities. However, the same tasks revealed a more prominent deterioration of interlimb than the within-limb force coordination. This could be interpreted by two partly different and noncompeting neural control mechanisms where the coordination of interlimb forces may be based on ad-hoc and task-specific muscle coordination (often referred to as muscle synergies) while the within-limb coordination of G and L could be based on more stable and partly reflex mechanisms.

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Mindy F. Levin and Daniele Piscitelli

There is growing interest in the prospect of improving rehabilitation by applying the principles underlying the control of motor actions to therapeutic interventions. Here, the word “control” implies the ability to direct, command, or rule the production of motor action. However, there is some

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David I. Anderson

perception is multimodal (i.e., that multiple sources of information are available and used to control actions) and amodal (i.e., that the same information can be picked up by multiple perceptual systems because it propagates across different energy arrays [optical, acoustical, inertial]; Gibson, 1979