Partition Between Volitional and Induced Forces in Electrically Augmented Dynamic Isometric Muscle Contractions

Abstract

Augmentation of force in partially deficient muscles can be achieved by combining electrical stimulation (ES) with their volitional activation (hybrid activation). However, while the overall torque results from the combination of the volitional and the electrically-induced torque components, the exact share between these components is not known. In a previous work, we described a method to resolve the share between the torque components under isometric static contractions. In this work, we extend our analysis to the case of isometric dynamic contractions. Five healthy subjects were instructed to contract their Tibialis Anterior (TA) muscles according to a typical gait-like dynamic torque pattern, that was visually displayed to them, while monitoring their actual ankle torque and TA electromyography (EMG). These experiments were done with and without augmented activation by means of ES. A computational algorithm was developed to dissociate the volitional from the overall torque, based on EMG signal processing and on precalibration of the dynamic system of the volitional torque versus EMG. The results indicated the quantitative relations between decrease in the volitional torque and the required increase in ES enhancement. The developed method also demonstrated what ES intensity profile is necessary to produce a desired overall torque output. This provides the means for designing an adaptive rehabilitation device for the hybrid activation of deficient muscles.

Iterative Learning Control in Health Care: Electrical Stimulation and Robotic-Assisted Upper-Limb Stroke Rehabilitation

“…Although this can be captured by the recording of EMG during movement, the incorporation of EMG into model-based controllers is only beginning to receive attention in the literature, but is not well understood [60]. Within the ILC framework the trial-invariant component of voluntary effort can be treated as a repeating disturbance and completely canceled, however incorporation of EMG within the model is still an open problem.…”

The Role of Electromyograms in Resolving Musculoskeletal Interactions in Able-Bodied and Disabled Human Individuals

“…While in complete paralysis muscle activation is the result of ES only, in incomplete paralysis muscle activation may generally result from the combined volitional and ES-induced activations. In these latter cases ES is being used for the enhancement of muscle force and for improvement of function and motion of human populations with muscle disabilities [Katz et al 2003[Katz et al , 2008Langzam et al, 2006aLangzam et al, , 2006bLangzam et al, , 2007. This modality of muscle activation has been termed hybrid activation (Langzam et al, 2006b), whereby the muscle force results from the combined volitional and electricallyinduced components.…”

“…Additional studies focused on the facilitation of the volitional force due to the accumulated training effect with ES, but did not address the effect of facilitation during stimulation (Katz et al, 2003;Knash et al, 2003;Liron-Keshet et al, 2001;Thompson & Stein, 2004). The more recent studies dealing with the actual hybrid modality of activation [Langzam et al, 2006a[Langzam et al, , 2006b[Langzam et al, , 2007 go well beyond the previous ones, where the volitional EMG is used solely as a bio-trigger for the external stimulator in a hybrid contraction system (Peasgood et al, 2000;Rakos et al, 1999;Thorsen et al, 1999Thorsen et al, , 2002. In those recent studies the myoelectric signal assumes a key role.…”

“…In the recent studies dealing with hybrid activation [Langzam et al, 2006a[Langzam et al, , 2006b[Langzam et al, , 2007, the tested subjects were requested to track in real-time a visually displayed torque-time profile by activating the Tibialis Anterior muscle through the application of a dorsi-flexion torque at the ankle. Tracking was made in two modes of activation: 1) purely volitional activation, for calibration and system identification of the volitional component, and 2) hybrid activation, where volitional and ES-induced activations took place simultaneously.…”

“…If processed in the frequency domain, EMG may point to the development of muscle fatigue (De Luca, 1997;Mizrahi et al, 2001). The electromyographic signal may also be used as a bio-control signal in conjunction with bio-assistive motion (Langzam et al 2006a(Langzam et al , 2007Mizrahi et al 1994;Peasgood et al, 2000;Saxena et al 1995;Thorsen et al, 1999). This Chapter deals with the role of electromyography in facilitating the biomechanical solutions of musculo-skeletal systems characterized by neuro-muscular indeterminacies.…”