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Author (up) Friedman, J; Latash, M.L.; Zatsiorsky, V.M. pdf  doi
  Title Directional variability of the isometric force vector produced by the hand in multi-joint planar tasks Type Journal Article
  Year 2011 Publication Journal of Motor Behavior Abbreviated Journal  
  Volume 43 Issue 6 Pages 451-463  
  Abstract Numerous studies have examined control of force magnitude, but relatively little research has considered force direction control. In this study, subjects applied isometric forces to a handle and we compared within-trial variability when producing force in different directions. The standard deviation (SD) of the force parallel to the prescribed direction of force production increased linearly with the targeted force level, as did the SD of the force perpendicular to the instructed direction. In contrast, the SD of the angle of force production decreased with increased force level. In the four (of eight) instructed force directions where the endpoint force was generated due to a joint torque in only one joint (either the shoulder or elbow) the principal component axes in force space were well aligned with the prescribed direction of force production. In the other directions, the variance was approximately equal along the two force axes. The variance explained by the first principal component was significantly larger in torque space compared to the force space, and mostly corresponded to positive correlation between the joint torques. Such coordinated changes suggest that the torque variability was mainly due to the variability of the common drive to the muscles serving two joints, although this statement needs to be supported by direct studies of muscle activation in the future.  
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  Notes Approved no  
  Call Number Penn State @ @ Serial 26  
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