Time-varying stiffness of human elbow joint during cyclic voluntary movement

The objective of this study was to determine the extent to which subjects modulate their elbow joint mechanical properties during ongoing arm movement. Small pseudo-random force disturbances were applied to the wrist with an airjet actuator while subjects executed large (1 rad) elbow joint movements...

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Bibliographic Details
Published in:Experimental brain research 1992-02, Vol.88 (2), p.433-442
Main Authors: BENNETT, D. J, HOLLERBACH, J. M, HUNTER, I. W
Format: Article
Language:English
Subjects:
Adult
Biological and medical sciences
Elbow - physiology
Feedback - physiology
Fundamental and applied biological sciences. Psychology
Gravitation
Humans
Movement - physiology
Posture
Proprioception - physiology
Skeleton and joints
Space life sciences
Vertebrates: osteoarticular system, musculoskeletal system
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Summary:The objective of this study was to determine the extent to which subjects modulate their elbow joint mechanical properties during ongoing arm movement. Small pseudo-random force disturbances were applied to the wrist with an airjet actuator while subjects executed large (1 rad) elbow joint movements. Using a lumped parameter model of the muscle, tendon and proprioceptive feedback dynamics, a time-varying system identification technique was developed to analyze the phasic changes in the elbow joint's mechanical response. The mechanical properties were found to be time-varying, and well approximated by a quasi-linear second-order model. The stiffness of the arm was found to drop during movement. The arm was always underdamped, with the damping ratio changing during movement. Inertia estimates were constant and consistent with previous measurements. Overall, the moving arm was found to be very compliant, with a peak stiffness value less than the lowest value measured during posture, and a natural frequency of less than 3 Hz. Changing the speed of movement, or the load from gravity, changed the stiffness measured, but not in strict proportion to the change in net muscle torque.
ISSN:0014-4819
1432-1106
DOI:10.1007/BF02259118