Dynamic relationship between EMG and torque at the human ankle: Variation with contraction level and modulation |
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Authors: | W F Genadry R E Kearney I W Hunter |
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Institution: | (1) Biomedical Engineering Unit, Faculty of Medicine, McGill University, 3775 University Street, H3A 2B4 Montréal, Québec, Canada |
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Abstract: | Stochastic system identification techniques were used to determine the dynamic relationship between the electromyogram (EMG)
and torque in the ankle muscles of normal human subjects. EMG and torque were recorded while subjects modulated ankle torque
by tracking a computer-generated stochastic waveform. Nonparametric impulse response functions (IRFs) relating EMG to ankle
torque were computed and parameterised by determining the parameters of the second-order system which provided the best least-squares
fit. Two sets of experiments were carried out. In the first, the mean level of torque was varied from 5 per cent of the maximum
voluntary contraction (MVC) to 30 per cent MVC while the depth of modulation was held constant at ±5 per cent of MVC. In the
second series of experiments the mean torque was held constant at 25 per cent MVC while the depth of modulation was varied
from ±2.5 per cent to ±25 per cent. The major findings were: (1) A second-order, low-pass filter provided a good quasilinear
model of the EMG/force dynamics under all conditions; (2) The model parameters depended only weakly on the mean level of torque;
(3) In contrast, the model parameters depended strongly on the amplitude with which the contraction was modulated; the natural
frequency increased significantly with the depth of modulation. |
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Keywords: | Activation dynamics Dynamics Electromyogram EMG EMG-force dynamics Human ankle System identification Tibialis anterior Torque Triceps surae |
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