Joint angle variability in the time course of reaching movements
ABSTRACT Investigating motor control processes is of primary interest in a number of scientific and practical fields. Movement variability is of increasing interest in this context. However, until now little has been known about the time course of variability during movement execution. The objective of this study was to investigate the influence of visual information and task specification on the variability of joint angle motion in reaching movements.
Subjects repetitively reached for a handle. Movement variability was quantified by the within-subjects standard deviation of mean joint angle. The analysis focused on the time course of variability during movement execution.
The availability of visual information did not influence the time course of joint angle variability whereas task specification on reaching accuracy did. Under high accuracy demand variability was reduced more strongly after reaching its maximum.
Results suggest that the availability of visual information plays a minor role in the control of well-trained reaching movements. This suggests that proprioceptive information is the main feedback source to control these movements.
The analysis of the time course of movement variability might be a valuable method to investigate the central or peripheral causes of movement disorders for diagnostic and rehabilitation purposes.
SourceAvailable from: Melanie KrügerMotor control 01/2014; 18(1):102-102. DOI:10.1123/mc.2014-0005 · 1.45 Impact Factor
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ABSTRACT: Empirical evidence suggests that the ability to stabilize important task variables of everyday movements by synergistically coordinating redundant degrees of freedom decreases with aging. The aim of the current study was to investigate whether this decrease may be regarded as a characteristic that also applies for the control of multiple task variables. We asked younger and older subjects to repeatedly reach towards and grasp a handle, while joint angle movement of the arm was recorded. The handle constrained final hand position and final hand orientation. Movement variability was analyzed during movement execution by using the uncontrolled manifold method. Results showed that hand orientation was less stabilized in younger than in older subjects. We conclude that aging changes the stability of important task variables. These changes may lead to decreased stability in some task variables, as reported in the literature, but also to increased stability in other task variables.Motor control 07/2013; 17(3):313-9. · 1.45 Impact Factor
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ABSTRACT: It is unclear to what extent control strategies of 2D reaching movements of the upper limbs also apply to movements with the full seven degrees of freedom (DoFs) including rotation of the forearm. An increase in DoFs may result in increased movement complexity and instability. This study investigates the trajectories of unconstrained reaching movements and their stability against perturbations of the upper arm. Reaching movements were measured using an ultrasound marker system, and the method of inverse dynamics was applied to compute the time courses of joint torques. In full DoF reaching movements, the velocity of some joint angles showed multiple peaks, while the bell-shaped profile of the tangential hand velocity was preserved. This result supports previous evidence that tangential hand velocity is an essential part of the movement plan. Further, torque responses elicited by external perturbation started shortly after perturbation, almost simultaneously with the perturbation-induced displacement of the arm, and were mainly observed in the same joint angles as the perturbation torques, with similar shapes but opposite signs. These results indicate that these torque responses were compensatory and contributed to system stabilization.Experimental Brain Research 01/2014; 232(4). DOI:10.1007/s00221-014-3826-z · 2.17 Impact Factor