Force sharing among fingers as a model of the redundancy problem

  title={Force sharing among fingers as a model of the redundancy problem},
  author={Zong-Ming Li and Mark L. Latash and Vladimir M. Zatsiorsky},
  journal={Experimental Brain Research},
Abstract 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 force profile using different combinations of fingers. We found that individual finger forces were smaller in multifinger MVC tasks… 
Motor redundancy during maximal voluntary contraction in four-finger tasks
Maximal normal force as well as the force-time curves produced by individual fingers were measured in 10 young male subjects and are in agreement with the hypothesis that the total force is shared among individual fingers, minimizing the moment with respect to the functional hand axis.
Hierarchies of synergies: an example of two-hand, multi-finger tasks
The main result of the study is the significantly weaker or even lacking two-finger force stabilizing synergies within-a-hand during two- hand tasks while such synergies were present in one-hand tasks, indicating a potential limitation in the ability of the CNS to organize synergies at two levels of a control hierarchy simultaneously.
A principle of error compensation studied within a task of force production by a redundant set of fingers
The data are interpreted as results of the action of a feed-forward central mechanism leading to parallel changes in forces produced by fingers united into a structural unit.
Multi-finger synergies and the muscular apparatus of the hand
The findings suggest that multi-finger synergies are defined at the level of abundant transformation between the low-dimensional hand level and higher dimensional finger level while being relatively immune to transformations between the finger level and muscle level.
Control of finger force direction in the flexion-extension plane
It is concluded that a multi-finger synergy is involved in the control of the finger force direction in tasks that required the production of the total force by a subset of fingers in a particular direction in the flexion–extension plane.
Hand dominance and multi-finger synergies
Force-stabilizing synergies in motor tasks involving two actors
The observations show that sensory information on the task-specific performance variable is sufficient for the organization of performance-stabilizing synergies, but suggest, however, that two actors are less likely to follow a single optimization criterion as compared to a single performer.
Coordinated force production in multi-finger tasks: finger interaction and neural network modeling
A neural network model that accounts for all the three effects of involuntary force production by individual fingers during tasks when (an)other finger(s) of the hand generated maximal voluntary pressing force in isometric conditions suggests that no direct correspondence exists between neural command and finger force.
Effect of Kinetic Degrees of Freedom on Multi-Finger Synergies and Task Performance during Force Production and Release Tasks
It is concluded that the controller actively utilizes extra DOFs to increase the stability of the performance, which is associated with the improved accuracy and precision of the task.


Limited independent flexion of the thumb and fingers in human subjects.
It is not possible to direct a sufficiently focal motor command to flex selectively the distal joint of the fingers and thumb when forces exceeding 2.5% MVC are generated and movement of adjacent digits may also involve ‘in‐series’ mechanical links between adjacent components of FDP.
Contributions and co-ordination of individual fingers in multiple finger prehension.
The results indicate that nearly 40% force reduction can be obtained when a non-slippery surface is used, suggesting that all individual finger force adjustments for light loads less than 800 g are controlled comprehensively simply by using a single common scaling value.
Maximum bilateral contractions are modified by neurally mediated interlimb effects.
Results suggest that interlimb interactions during maximal bilateral contractions are mediated by neural mechanisms, similar to other bilateral deficits found to be due to neural mechanisms.
Maximal voluntary force of bilateral and unilateral leg extension.
Arguments against a reduced activation of the knee extensor muscles being the cause of the lower bilateral leg extension force are arguments against a general inability to activate fully a large number of muscles simultaneously.
Variation of finger forces in maximal isometric grasp tests on a range of cylinder diameters.
  • A. Amis
  • Biology
    Journal of biomedical engineering
  • 1987
Adaptability of innate motor patterns and motor control mechanisms
It is proposed that central regulation of stretch reflex thresholds governs voluntary control over muscle force and length and concluded that voluntary movements are effected by the central nervous system with the help of the mechanisms that underlie the variability and modifiability of innate motor patterns.
Coordination and inhomogeneous activation of human arm muscles during isometric torques.
The activity of motor units of the important muscles acting across the elbow joint during combinations of voluntary isometric torques in flexion/extension direction and supination/pronation direction at different angles of the elbow joints is recorded.
Two functionally different synergies during arm reaching movements involving the trunk.
The data imply that reaching movements result from two control synergies: one coordinates trunk and arm movements leaving the position of the endpoint unchanged, and the other produces interjoint coordination shifting the arm endpoint to the target.
Muscular synergism--II. A minimum-fatigue criterion for load sharing between synergistic muscles.