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Related Experiment Video

Updated: May 17, 2026

Force and Position Control in Humans - The Role of Augmented Feedback

Force and Position Control in Humans - The Role of Augmented Feedback

Published on: June 19, 2016

Forces and moments generated by the human arm: variability and control.

Y Xu¹, A V Terekhov, M L Latash

¹Department of Kinesiology, The Pennsylvania State University, University Park, PA 16802, USA. yangxu@psu.edu

Experimental Brain Research

|October 20, 2012

Summary

Human arm force production in isometric conditions is complex. This study found that grasp moment is always produced, and force variability trends are inversely related to directional precision, challenging simple optimization models.

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Area of Science:

Biomechanics
Human Motor Control
Robotics

Background:

Understanding human arm force production is crucial for fields like rehabilitation robotics and ergonomics.
Previous models often assume simplified force generation strategies.
The role of unintended torques, like grasp moment, is not fully understood.

Purpose of the Study:

To explore accurate endpoint force vector production by the human arm under isometric conditions.
To investigate the relationship between instructed force parameters and joint torques.
To test common-sense hypotheses regarding human force generation.

Main Methods:

Ten subjects exerted static forces in eight directions at four magnitude levels (10-40% of maximal voluntary contractions).
Recorded force components and grasp moment; computed shoulder, elbow, and wrist joint torques.
Analyzed force vector variability, grasp moment characteristics, and joint torque correlations.

Main Results:

Grasp moment was consistently produced and dependent on instructed force magnitude and direction.
Angular precision of the force vector was independent of target force magnitude.
Force magnitude variability and directional variability showed opposite trends.
Joint torques were positively correlated across trials, even with opposing flexion/extension.
Grasp moment and wrist torque correlations varied between tasks and within trials.
Joint torque distribution patterns did not align with simple additive optimization cost functions.

Conclusions:

Human arm force production is a complex, coordinated process involving unintended torques.
Simple optimization principles may not fully explain observed joint torque patterns.
Findings suggest a need for more sophisticated models of human motor control in biomechanics and robotics.