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TECHNICAL PAPERS

Predictions of Mechanical Output of the Human M. Triceps Surae on the Basis of Electromyographic Signals: The Role of Stimulation Dynamics

[+] Author and Article Information
J. P. van Zandwijk, M. F. Bobbert

Institute for Fundamental and Clinical Human Movement Sciences, Vrije Universiteit, Amsterdam, The Netherlands

J. Harlaar

Department of Rehabilitation Medicine, Free University Hospital, Amsterdam, The Netherlands

J Biomech Eng 122(4), 380-386 (Mar 09, 2000) (7 pages) doi:10.1115/1.1286562 History: Received December 09, 1998; Revised March 09, 2000
Copyright © 2000 by ASME
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References

Figures

Grahic Jump Location
Moment histories during isometric twitches elicited in m. triceps surae (TS) by means of electrical stimulation of the tibial nerve for subject 3. The thin line pertains to the experimentally recorded twitch, while the thick line pertains to the twitch generated by the model. The simulated twitch is obtained by optimization of parameters pertaining to the excitation dynamics, using the normalized M-wave of m. gastrocnemius medialis (GM) as input. This normalized GM M-wave is shown in the lower panel.
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Predictions of moment histories for electrically elicited and voluntary twitches of TS on the basis of normalized electromyographic signals (NEMG signals) recorded from m. gastrocnemius (left-hand side) and m. soleus (right-hand side). In both upper panels, the thin line is experimentally recorded muscle moment, the thick line muscle moment predicted by the model. Simulated moment histories are obtained using parameters for the excitation dynamics that have been obtained by optimization of model behavior for an electrically elicited isometric twitch (i.e., the data shown in Fig. 1 for m. gastrocnemius). The corresponding NEMG histories used as input for the model are shown in the lower panels. Electrically elicited twitches are indicated by “el,” voluntary twitches by “vol.” Same subject as in Fig. 1. For the lefthand side, the normalized rms error ε=0.28, for the right-hand side, ε=0.70.
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Top panel: Experimentally recorded isometric moment histories during maximal voluntary contractions of TS. Middle panel: Predictions of moment histories by the model of TS, using voluntary NEMG signals from GM as input. For both panels, the thin line pertains to a contraction in which the subject was instructed to contract TS as forcefully as possible, while the thick line pertains to a contraction in which the subject was asked to contract TS as quickly as possible. Moment is normalized with respect to the isometric value. Note the difference in moment rise time between the two contractions in both the experiment and the model calculations. Lower panel: NEMG histories of GM used as inputs for the simulations shown in the middle panel. Note the increased NEMG amplitude at the onset of the contraction in case of the fast contraction. The upper NEMG trace has been shifted upward 1.0 unit to facilitate comparison between traces. Same subject as in Figs. 1 and 2.
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Scatter plot of rise times (RTs) of isometric moment histories during MVCs of TS for all subjects versus RTs of moment in the model, using GM NEMG signals as input. For each subject, excitation dynamics is optimized for a GM M-wave and contraction dynamics is determined in a separate experiment.
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Example of time histories of variables obtained during execution of jumplike movements of the ankle joint. Top panel : Ankle joint moment. Thin line: joint moment derived from inverse dynamic analysis, thick line: moment predicted by the muscle model on the basis of GM NEMG signals and TS MTC length histories as inputs. For this trial, the normalized rms error ε=0.28.Middle panel : GM NEMG signals, expressed as fraction of peak M-wave amplitude. Bottom panel : length changes of TS MTC, expressed in angular coordinates.
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Arrangement of the contractile element (CE), the series elastic element (SEE) and the parallel elastic element (PEE) with respect to each other. The lengths of the elements in angular coordinates are indicated. Note that in all cases, PEE angle equals CE angle.

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