Relating agonist-antagonist electromyograms to joint torque during isometric, quasi-isotonic, nonfatiguing contractions

This paper describes an experimental study which relates simultaneous elbow flexor-extensor electromyogram (EMG) amplitude to joint torque. Investigation was limited to the case of isometric, quasi-isotonic (slowly force-varying), nonfatiguing contractions, For each of the flexor and extensor muscle groups, the model relationship between mascle group torque contribution and EMG amplitude was constrained to be a sum of basis functions which had a linear dependence on a set of fit parameters, With these constraints, the problem of identifying the EMG-to-torque relationship was reduced to a linear least squares problem, Surface EMG's from elbow flexors and extensors, and joint torque were simultaneously recorded for nonfatiguing, quasi-isotonic, isometric contractions spanning 0-50% maximum voluntary contraction, Single-/multiple-channel unwhitened/whitened/adaptively-whitened EMG amplitude processors were used to identify an EMG-to torque relation, and then estimate joint torque based on this relation. Each unwhitened multiple-channel EMG-to-torque estimator had a standard error (SE) approximately 70% of its respective single-channel estimator, The adaptively whitened multiple-channel joint torque estimator had an SE approximately 90% of the unwhitened multiple-channel estimator, providing an estimation Error approximate to 3% of the combined flexion/extension torque range, The experimental studies demonstrated that higher fidelity EMG amplitude processing led to improved joint torque estimation.