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The viscoelastic properties of the human arm were measured by means of short force perturbations during fast reaching movements in two orthogonal directions. A linear spring model with time delay described the neuromuscular system of the human arm. The obtained viscoelastic parameters ensured movement stability in spite of the time delay of 50 ms. The(More)
It has been widely claimed that linear models of the neuromuscular apparatus give very inaccurate approximations of human arm reaching movements. The present paper examines this claim by quantifying the contributions of the various non-linear effects of muscle force generation on the accuracy of linear approximation. We performed computer simulations of a(More)
Human subjects sitting in a chair were asked to maintain their right forearm in a horizontal position in half supination. The forearm was loaded with a constant weight of one kilogram. Vertical force at the wrist level, angular position of the elbow and EMG activity of biceps, brachio-radialis and triceps muscles were recorded. Unloading was tested under(More)
The role of the sensorimotor cortex in the postural adjustments associated with conditioned paw lifting movements was investigated in the cat. Cats were trained to stand quietly on four strain gauge equipped platforms and to perform a lift-off movement with one forelimb when a conditioned tone was presented. The parameters recorded were the vertical forces(More)
The acquisition of co-ordination between posture and movement was investigated in human subjects performing a load lifting task. Sitting subjects held their left (postural) forearm in a horizontal position while supporting a 1 kg load via an electromagnet. Perturbation of the postural forearm position consisted of the load release triggered either by the(More)
In this study, the equilibrium-point hypothesis of muscle-torque generation is used to evaluate the changes in central control parameters in the process of postural-maintenance learning. Muscle torque is described by a linear spring equation with modifiable stiffness, viscosity, and equilibrium angle. The stiffness is considered to be the estimation of the(More)
The present experimental series was designed to test the possibility that an anticipatory postural adjustment learned during the performance of a bimanual load lifting task may be transferred between the upper extremities. Eight seated subjects were asked to maintain horizontally one forearm (postural arm) loaded with a 1-kg load, which was fixed to the arm(More)
A bimanual loading task was studied in eight right-handed normal subjects and nine hemiparetic patients in order to detect anticipatory adjustments and to analyse the reflex and voluntary, responses induced by the perturbation. The left forearm (or the impaired side in patients) was flexed at approximately 90 degrees and free to rotate in a vertical(More)