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When a person produces isometric force with one, two, or three fingers, the other fingers of the hand also produce a certain force. Enslaving is the involuntary force production by fingers not explicitly involved in a force-production task. This study explored the enslaving effects (EE) in multi-finger tasks in which the contributions of the flexor(More)
Movements by a standing person are commonly associated with adjustments in the activity of postural muscles to cause a desired shift of the center of pressure (COP) and keep balance. We hypothesize that such COP shifts are controlled (stabilized) using a small set of central variables (muscle modes, M-modes), while each M-mode induces changes in the(More)
We studied how the central nervous system (CNS) organizes outputs of effectors in a redundant motor task. During four-finger ramp force production, finger forces show positive covariations across trials at low forces, which turn into negative covariations at a critical force value (F(CR)). Subjects performed such tasks with different target amplitudes and(More)
The aim of this study was to test Bernstein's idea that motor synergies provide solutions to the motor redundancy problem. Forces produced by individual fingers of one hand were recorded in one-, two-, three-, and four-finger tasks. The subjects (n=10) were asked to produce maximal total force (maximal voluntary contraction, MVC) and to match a ramp total(More)
A method of decomposing stabilograms into two components, termed rambling, was developed. The rambling component reveals the motion of a moving reference point with respect to which the body's equilibrium is instantly maintained. The trembling component reflects body oscillation around the reference point trajectory. The concepts of instant equilibrium(More)
During maximal voluntary contraction (MVC) with several fingers, the following three phenomena are observed: (1) the total force produced by all the involved fingers is shared among the fingers in a specific manner (sharing); (2) the force produced by a given finger in a multi-finger task is smaller than the force generated by this finger in a single-finger(More)
We studied the coordinated action of fingers during static tasks involving exertion of force and torque on a handheld object. Subjects were asked to keep a handle with an attachment that allowed for independent change of the suspended load (0.5-2.0 kg) and external torque (0.375-1.5 N m) in a vertical position while applying minimal effort. Normal and shear(More)
The goal of the study was to investigate force-sharing patterns in multi-finger tasks. Maximal normal force (MNF) as well as the force-time curves produced by individual fingers were measured in 10 young male subjects in three tasks: (1) holding an instrumented handle in a pad opposition with the thumb at seven different locations, from opposing the index(More)
This article proposes a technique to calculate the coefficient of friction for the fingertip- object interface. Twelve subjects (6 males and 6 females) participated in two experiments. During the first experiment (the imposed displacement method), a 3-D force sensor was moved horizontally while the subjects applied a specified normal force (4 N, 8 N, 12 N)(More)
We consider the problem of what is being optimized in human actions with respect to various aspects of human movements and different motor tasks. From the mathematical point of view this problem consists of finding an unknown objective function given the values at which it reaches its minimum. This problem is called the inverse optimization problem. Until(More)