TY - JOUR
T1 - Directional effects of changes in muscle torques on initial path during simulated reaching movements
AU - Koshland, Gail F.
AU - Marasli, Barsam
AU - Arabyan, Ara
N1 - Funding Information:
Acknowledgements The authors would like to thank Drs. C. Galloway, A. Fuglevand, and D. Glendinning for critical reading of the manuscript, as well as anonymous reviewers who also provided careful and insightful improvements. This work was partially supported by NIH grant NS 07309.
PY - 1999
Y1 - 1999
N2 - Adults are able to reach for an object for the first time with appropriate direction, speed, and accuracy. The rules by which the nervous system is able to set muscle activities to accomplish these outcomes are still debated and, indeed, the sensitivity of kinematics to variations in muscle torques is unknown for complex arm movements. As a result, this study used computer simulations to characterize the effects of change in muscle torque on initial hand path. The same change was applied to movements towards 12 directions in the horizontal plane, and changes were systematically manipulated such that: (1) torque amplitude was changed at one joint, (2) timing of torque was changed at one joint, and (3) amplitude and/or timing was changed at two joints. Results showed that simultaneous changes in torque amplitude at shoulder and elbow joints affected initial speed uniformly across direction. These results add to conclusions from previous experimental and modeling work that the simplest rule to produce a desired change in speed for any direction is to scale torque amplitude at both joints. In contrast, all simulations showed nonuniform effects on initial path direction. For some regions of the workspace, initial path direction was little affected by either a ± 30% change in amplitude or a ± 100-ms change in timing, whereas for other regions the same changes produced large effects on initial path direction. These findings suggest that the range of possible torque solutions to achieve a particular initial path direction varies within the workspace and, consequently, the requirements for an accurate initial path will vary within the workspace.
AB - Adults are able to reach for an object for the first time with appropriate direction, speed, and accuracy. The rules by which the nervous system is able to set muscle activities to accomplish these outcomes are still debated and, indeed, the sensitivity of kinematics to variations in muscle torques is unknown for complex arm movements. As a result, this study used computer simulations to characterize the effects of change in muscle torque on initial hand path. The same change was applied to movements towards 12 directions in the horizontal plane, and changes were systematically manipulated such that: (1) torque amplitude was changed at one joint, (2) timing of torque was changed at one joint, and (3) amplitude and/or timing was changed at two joints. Results showed that simultaneous changes in torque amplitude at shoulder and elbow joints affected initial speed uniformly across direction. These results add to conclusions from previous experimental and modeling work that the simplest rule to produce a desired change in speed for any direction is to scale torque amplitude at both joints. In contrast, all simulations showed nonuniform effects on initial path direction. For some regions of the workspace, initial path direction was little affected by either a ± 30% change in amplitude or a ± 100-ms change in timing, whereas for other regions the same changes produced large effects on initial path direction. These findings suggest that the range of possible torque solutions to achieve a particular initial path direction varies within the workspace and, consequently, the requirements for an accurate initial path will vary within the workspace.
KW - Human
KW - Kinetics
KW - Multijoint arm
KW - Muscle torques
KW - Simulations
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U2 - 10.1007/s002210050855
DO - 10.1007/s002210050855
M3 - Article
C2 - 10501807
AN - SCOPUS:0032861827
SN - 0014-4819
VL - 128
SP - 353
EP - 368
JO - Experimental Brain Research
JF - Experimental Brain Research
IS - 3
ER -