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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)
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)
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)
We studied the coordination of forces and moments exerted by individual digits in static tasks that required balancing an external load and torque. Subjects ( n=10) stabilized a handle with an attachment that allowed for change of external torque. Thumb position and handle width systematically varied among the trials. Each subject performed 63 tasks (7(More)
We tested a hypothesis that humans can change patterns of finger force covariation in a task-specific manner in preparation to a change in the total force. Subjects performed quick targeted force pulses by pressing with four fingers on force sensors from a certain background force level to a target level. In self-paced trials, finger force modes(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)
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)
We studied the coordination of muscle activity during voluntary body sway performed by human subjects at different frequencies. Subjects stood on the force platform and performed cyclic shifts of the center of pressure (COP) while being paced by the metronome. A major question was: does the makeup of muscle synergies and their ability to assure reproducible(More)