Analysis of kinematically redundant reaching movements using the equilibrium-point hypothesis

 Six subjects performed a planar reaching arm movement to a target while unpredictable perturbations were applied to the endpoint; the perturbations consisted of pulling springs having different stiffness. Two conditions were applied; in the first, subjects had to reach for the target despite the perturbation, in the second condition, the subjects were asked to not correct the motion as a perturbation was applied. We analyzed the kinematics profiles of the three arm segments and, by means of inverse dynamics, calculated the joint torques. The framework of the equilibrium-point (EP) hypothesis, the λ model, allowed the reconstruction of the control variables, the “equilibrium trajectories”, in the “do not correct” condition for the wrist and the elbow joints as well as for the end point final position, while for the other condition, the reconstruction was less reliable. The findings support and extend to a multiple-joint planar movement, the paradigm of the EP hypothesis along with the “do not correct” instruction.

Authors and Affiliations

1.  Department of Kinesiology, The Pennsylvania State University, University Park, PA 16802, , , , ,

   Paola Cesari & Takako Shiratori

2.  I.S.E.F. – Istituto Superiore di Educazione Fisica, Verona, Italy, , , , , , IT

   Paolo Olivato

3.  Escola de Educação Fisica e Esporte, Universidade de São Paulo, Av. Mello Moraes 65, 05508-900, São Paulo/SP, Brazil, , , , , , BR

   Marcos Duarte

Received: 3 May 1999 / Accepted in revised form: 19 May 2000

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