Paper Info
Title
Key Insights into Hand Biomechanics: Human Grip Stiffness Can Be Decoupled from Force by Cocontraction and Predicted from Electromyography.
Abstract
We investigate the relation between grip force and grip stiffness for the human hand with and without voluntary cocontraction. Apart from gaining biomechanical insight, this issue is particularly relevant for variable-stiffness robotic systems, which can independently control the two parameters, but for which no clear methods exist to design or efficiently exploit them. Subjects were asked in one task to produce different levels of force, and stiffness was measured. As expected, this task reveals a linear coupling between force and stiffness. In a second task, subjects were then asked to additionally decouple stiffness from force at these force levels by using cocontraction. We measured the electromyogram from relevant groups of muscles and analyzed the possibility to predict stiffness and force. Optical tracking was used for avoiding wrist movements. We found that subjects were able to decouple grip stiffness from force when using cocontraction on average by about 20% of the maximum measured stiffness over all force levels, while this ability increased with the applied force. This result contradicts the force stiffness behavior of most variable stiffness actuators. Moreover, we found the thumb to be on average twice as stiff as the index finger and discovered that intrinsic hand muscles predominate our prediction of stiffness, but not of force. EMG activity and grip force allowed to explain 72 +/- 12% of the measured variance in stiffness by simple linear regression, while only 33 +/- 18% variance in force. Conclusively the high signal-to-noise ratio and the high correlation to stiffness of these muscles allow for a robust and reliable regression of stiffness, which can be used to continuously teleoperate compliance of modern robotic hands.
Year
DOI
Venue
2017
10.3389/fnbot.2017.00017
FRONTIERS IN NEUROROBOTICS
Keywords
Field
DocType
grip stiffness,cocontraction,grip force,intrinsic hand muscles,interosseus muscles,electromyography,soft robotics,variable-stiffness actuators
Thumb,Computer science,Control theory,Artificial intelligence,Biomechanics,Grip force,Index finger,Wrist,Stiffness,Simulation,Electromyography,Optical tracking,Machine learning
Journal
Volume
ISSN
Citations 
11
1662-5218
3
PageRank 
References 
Authors
0.47
7
5
Name
Order
Citations
PageRank
Hannes Hoppner1123.83
Maximilian Große-Dunker230.47
Georg Stillfried3293.19
Justin Bayer415732.38
Patrick van der Smagt518824.23