Virtual biomechanics: A new method for online reconstruction of force from EMG recordings

Aymar de Rugy, Gerald E. Loeb, Timothy J. Carroll
Journal of Neurophysiology. 2012-12-15; 108(12): 3333-3341
DOI: 10.1152/jn.00714.2012

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1. J Neurophysiol. 2012 Dec;108(12):3333-41. doi: 10.1152/jn.00714.2012. Epub 2012
Sep 26.

Virtual biomechanics: a new method for online reconstruction of force from EMG

de Rugy A(1), Loeb GE, Carroll TJ.

Author information:
(1)Centre for Sensorimotor Neuroscience, School of Human Movement Studies, The
University of Queensland, Brisbane, Australia.

Current methods to reconstruct muscle contributions to joint torque usually
combine electromyograms (EMGs) with cadaver-based estimates of biomechanics, but
both are imperfect representations of reality. Here, we describe a new method
that enables online force reconstruction in which we optimize a « virtual »
representation of muscle biomechanics. We first obtain tuning curves for the five
major wrist muscles from the mean rectified EMG during the hold phase of an
isometric aiming task when a cursor is driven by actual force recordings. We then
apply a custom, gradient-descent algorithm to determine the set of « virtual
pulling vectors » that best reach the target forces when combined with the
observed muscle activity. When these pulling vectors are multiplied by the
rectified and low-pass-filtered (1.3 Hz) EMG of the five muscles online, the
reconstructed force provides a close spatiotemporal match to the true force
exerted at the wrist. In three separate experiments, we demonstrate that the
technique works equally well for surface and fine-wire recordings and is
sensitive to biomechanical changes elicited by a modification of the forearm
posture. In all conditions tested, muscle tuning curves obtained when the task
was performed with feedback of reconstructed force were similar to those obtained
when the task was performed with real force feedback. This online force
reconstruction technique provides new avenues to study the relationship between
neural control and limb biomechanics since the « virtual biomechanics » can be
systematically altered at will.

DOI: 10.1152/jn.00714.2012
PMID: 23019006 [Indexed for MEDLINE]

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