scholarly journals The Central Nervous System Does Not Minimize Energy Cost in Arm Movements

2010 ◽  
Vol 104 (6) ◽  
pp. 2985-2994 ◽  
Author(s):  
Dinant A. Kistemaker ◽  
Jeremy D. Wong ◽  
Paul L. Gribble
Keyword(s):  
Force Field ◽  
Energy Cost ◽  
Degrees Of Freedom ◽  
Muscle Activation ◽  
Arm Movements ◽  
Dominant Factor ◽  
Minimal Energy ◽  
Null Field ◽  
Muscle Activation Patterns ◽  
Point To Point

It has been widely suggested that the many degrees of freedom of the musculoskeletal system may be exploited by the CNS to minimize energy cost. We tested this idea by having subjects making point-to-point movements while grasping a robotic manipulandum. The robot created a force field chosen such that the minimal energy hand path for reaching movements differed substantially from those observed in a null field. The results show that after extended exposure to the force field, subjects continued to move exactly as they did in the null field and thus used substantially more energy than needed. Even after practicing to move along the minimal energy path, subjects did not adapt their freely chosen hand paths to reduce energy expenditure. The results of this study indicate that for point-to-point arm movements minimization of energy cost is not a dominant factor that influences how the CNS arrives at kinematics and associated muscle activation patterns.

The Rat Lumbosacral Spinal Cord Adapts to Robotic Loading Applied During Stance

2002 ◽  
Vol 88 (6) ◽  
pp. 3108-3117 ◽  
Author(s):  
W. K. Timoszyk ◽  
R. D. de Leon ◽  
N. London ◽  
R. R. Roy ◽  
V. R. Edgerton ◽  
...  
Keyword(s):  
Spinal Cord ◽  
Force Field ◽  
Muscle Activation ◽  
Interlimb Coordination ◽  
Medial Gastrocnemius ◽  
Step Cycle ◽  
Adult Rats ◽  
Robotic Arms ◽  
Lumbosacral Spinal Cord ◽  
Muscle Activation Patterns

Load-related afferent information modifies the magnitude and timing of hindlimb muscle activity during stepping in decerebrate animals and spinal cord–injured humans and animals, suggesting that the spinal cord mediates load-related locomotor responses. In this study, we found that stepping on a treadmill by adult rats that received complete, midthoracic spinal cord transections as neonates could be altered by loading the hindlimbs using a pair of small robotic arms. The robotic arms applied a downward force to the lower shanks of the hindlimbs during the stance phase and measured the position of the lower shank during stepping. No external force was applied during the swing phase of the step. When applied bilaterally, this stance force field perturbed the hindlimb trajectories so that the ankle position was shifted downward during stance. In response to this perturbation, both the stance and step cycle durations decreased. During swing, the hindlimb initially accelerated toward the normal, unperturbed swing trajectory and then tracked the normal trajectory. Bilateral loading increased the magnitude of the medial gastrocnemius electromyographic (EMG) burst during stance and increased the amplitude of the semitendinosus and rectus femoris EMG bursts. When the force field was applied unilaterally, stance duration decreased in the loaded hindlimb, while swing duration was decreased in the contralateral hindlimb, thereby preserving interlimb coordination. These results demonstrate the feasibility of using robotic devices to mechanically modulate afferent input to the injured spinal cord during weight-supported locomotion. In addition, these results indicate that the lumbosacral spinal cord responds to load-related input applied to the lower shank during stance by modifying step timing and muscle activation patterns, while preserving normal swing kinematics and interlimb coordination.

scholarly journals Simultaneous control of natural and extra degrees of freedom by isometric force and electromyographic activity in the muscle-to-force null space

2022 ◽  
Author(s):  
Sergio Gurgone ◽  
Daniele Borzelli ◽  
Paolo De Pasquale ◽  
Denise J Berger ◽  
Tommaso Lisini Baldi ◽  
...  
Keyword(s):  
Degrees Of Freedom ◽  
Muscle Activation ◽  
Null Space ◽  
Isometric Force ◽  
Individual Variability ◽  
Electromyographic Activity ◽  
Simultaneous Generation ◽  
Muscle Activation Patterns ◽  
Simultaneous Control ◽  
End Effectors

Abstract Objective. Muscle activation patterns in the muscle-to-force null space, i.e., patterns that do not generate task-relevant forces, may provide an opportunity for motor augmentation by allowing to control additional end-effectors simultaneously to natural limbs. Here we tested the feasibility of muscular null space control for augmentation by assessing simultaneous control of natural and extra degrees of freedom. Approach. We instructed eight participants to control translation and rotation of a virtual 3D end-effector by simultaneous generation of isometric force at the hand and null space activity extracted in real-time from the electromyographic signals recorded from 15 shoulder and arm muscles. First, we identified the null space components that each participant could control more naturally by voluntary co-contraction. Then, participants performed several blocks of a reaching and holding task. They displaced an ellipsoidal cursor to reach one of nine targets by generating force, and simultaneously rotated the cursor to match the target orientation by activating null space components. We developed an information-theoretic metric, an index of difficulty defined as the sum of a spatial and a temporal term, to assess individual null space control ability for both reaching and holding. Main Results. On average, participants could reach the targets in most trials already in the first block (72%) and they improved with practice (maximum 93%) but holding performance remained lower (maximum 43%). As there was a high inter-individual variability in performance, we performed a simulation with different spatial and temporal task conditions to estimate those for which each individual participants would have performed best. Significance. Muscular null space control is feasible and may be used to control additional virtual or robotics end-effectors. However, decoding of motor commands must be optimized according to individual null space control ability.

A Limited Set of Muscle Synergies for Force Control During a Postural Task

2005 ◽  
Vol 93 (1) ◽  
pp. 609-613 ◽  
Author(s):  
Lena H. Ting ◽  
Jane M. Macpherson
Keyword(s):  
Degrees Of Freedom ◽  
Neural Control ◽  
Muscle Activation ◽  
Balance Control ◽  
Computational Techniques ◽  
Muscle Synergies ◽  
Support Surface ◽  
Muscle Activation Patterns ◽  
Automatic Postural Response ◽  
Postural Responses

Recently developed computational techniques have been used to reduce muscle activation patterns of high complexity to a simple synergy organization and to bring new insights to the long-standing degrees of freedom problem in motor control. We used a nonnegative factorization approach to identify muscle synergies during postural responses in the cat and to examine the functional significance of such synergies for natural behaviors. We hypothesized that the simplification of neural control afforded by muscle synergies must be matched by a similar reduction in degrees of freedom at the biomechanical level. Electromyographic data were recorded from 8–15 hindlimb muscles of cats exposed to 16 directions of support surface translation. Results showed that as few as four synergies could account for >95% of the automatic postural response across all muscles and all directions. Each synergy was activated for a specific set of perturbation directions, and moreover, each was correlated with a unique vector of endpoint force under the limb. We suggest that, within the context of active balance control, postural synergies reflect a neural command signal that specifies endpoint force of a limb.

Trajectory Planning of Spine Motion During Flexion Using a Stability-Based Optimization

2010 ◽  
Author(s):  
Majid Khorsand Vakilzadeh ◽  
Hassan Salarieh ◽  
Mohsen Asghari ◽  
Mohamad Parnianpour
Keyword(s):  
Degrees Of Freedom ◽  
Muscle Activation ◽  
Inverse Dynamics ◽  
Joint Stiffness ◽  
Static Stability ◽  
Computational Method ◽  
Muscle Activation Patterns ◽  
Spine Motion ◽  
The Stability ◽  
The Many

A central problem in motor control is to understand how the many biomechanical degrees of freedom are coordinated to achieve a goal. A common assumption is that Central Nervous System (CNS) would minimize a performance index to achieve this goal which is called objective function. In this paper, two popular objective functions are utilized to design the optimal trajectory of trunk movements. A 3D computational method incorporated with 18 anatomically oriented muscles is used to simulate human trunk system. Inverse dynamics allows us to compute torque which is generated around Lumbosacral joint. This torque is divided among muscles by static stability-based optimization. Trunk movement from the upright standing to 30 degrees of flexion is simulated based on this method. Incorporation of the stability condition with the static optimization resulted in an increase of antagonistic activities which would increase the joint stiffness around the Lumbosacral joint in response to gravity perturbation. Results would shed light on the interaction mechanisms in muscle activation patterns, seen in various performance indices.

A Model of the Learning of Arm Trajectories from Spatial Deviations

1994 ◽  
Vol 6 (4) ◽  
pp. 359-376 ◽  
Author(s):  
Michael I. Jordan ◽  
Tamar Flash ◽  
Yoram Arnon
Keyword(s):  
Network Architecture ◽  
Muscle Activation ◽  
Human Subjects ◽  
Neural Network Architecture ◽  
Activation Patterns ◽  
Reaching Task ◽  
Hand Path ◽  
Muscle Activation Patterns ◽  
Point To Point ◽  
Simple Paths

Unconstrained point-to-point reaching movements performed in the horizontal plane tend to follow roughly straight hand paths with smooth, bell-shaped velocity profiles. The objective of the research reported here was to explore the hypothesis that these data reflect an underlying learning process that prefers simple paths in space. Under this hypothesis, movements are learned based only on spatial errors between the actual hand path and a desired hand path; temporally varying targets are not allowed. We designed a neural network architecture that learned to produce neural commands to a set of muscle-like actuators based only on information about spatial errors. Following repetitive executions of the reaching task, the network was able to generate point-to-point horizontal arm movements and the resulting muscle activation patterns and hand trajectories were found to be similar to those observed experimentally for human subjects. The implications of our results with respect to current theories of multijoint limb movement generation are discussed.

Muscle activation patterns in point-to-point and reversal movements in healthy, older subjects and in subjects with Parkinson?s disease

2004 ◽  
Vol 157 (1) ◽  
pp. 67-78 ◽  
Author(s):  
C. L. Comella ◽  
M. Brandabur ◽  
D. M. Corcos ◽  
J. A. Robichaud ◽  
G. L. Gottlieb ◽  
...  
Keyword(s):  
Muscle Activation ◽  
Activation Patterns ◽  
Muscle Activation Patterns ◽  
Older Subjects ◽  
Point To Point

Modification of Muscle Activation Patterns During Fast Goal-directed Arm Movements

1984 ◽  
Vol 16 (1) ◽  
pp. 2-19 ◽  
Author(s):  
C. C. A. M. Gielen ◽  
P. J. M. van den Heuvel ◽  
J. J. Denier van der Gon
Keyword(s):  
Muscle Activation ◽  
Arm Movements ◽  
Activation Patterns ◽  
Muscle Activation Patterns

Driving Torsion Scans with Wavefront Propagation

2020 ◽  
Author(s):  
Yudong Qiu ◽  
Daniel Smith ◽  
Chaya Stern ◽  
mudong feng ◽  
Lee-Ping Wang
Keyword(s):  
Potential Energy ◽  
Force Field ◽  
Degrees Of Freedom ◽  
Computational Cost ◽  
Initial Guess ◽  
Field Development ◽  
Force Field Development ◽  
Wavefront Propagation ◽  
Open Source Software Package

<div>The parameterization of torsional / dihedral angle potential energy terms is a crucial part of developing molecular mechanics force fields.</div><div>Quantum mechanical (QM) methods are often used to provide samples of the potential energy surface (PES) for fitting the empirical parameters in these force field terms.</div><div>To ensure that the sampled molecular configurations are thermodynamically feasible, constrained QM geometry optimizations are typically carried out, which relax the orthogonal degrees of freedom while fixing the target torsion angle(s) on a grid of values.</div><div>However, the quality of results and computational cost are affected by various factors on a non-trivial PES, such as dependence on the chosen scan direction and the lack of efficient approaches to integrate results started from multiple initial guesses.</div><div>In this paper we propose a systematic and versatile workflow called \textit{TorsionDrive} to generate energy-minimized structures on a grid of torsion constraints by means of a recursive wavefront propagation algorithm, which resolves the deficiencies of conventional scanning approaches and generates higher quality QM data for force field development.</div><div>The capabilities of our method are presented for multi-dimensional scans and multiple initial guess structures, and an integration with the MolSSI QCArchive distributed computing ecosystem is described.</div><div>The method is implemented in an open-source software package that is compatible with many QM software packages and energy minimization codes.</div>

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