ReflexES

ReflexES: Shaping Ankle Mechanical Impedance in Neurological Disorders using Electrical Stimulation for muscle activation and inhibition

Project name: ReflexES: Shaping Ankle Mechanical Impedance in Neurological Disorders using Electrical Stimulation for muscle activation and inhibition

Project code: ReflexES

Project timeline: 2022 - 2024

Research group: Intelligent Systems

Objective

The goal of this proposal is to promote motor function and shape the mechanical impedance, i.e., the dynamic behavior, of the ankle joint in neurological patients, using Electrical Stimulation to simultaneously promote muscle activation and inhibit involuntary and unwanted muscle activity. The research on neuromotor control of movement and orthotic devices is in line with the United Nations Sustainable Development Goal #3 to ensure healthy lives and promote well-being for all ages. This view is in line with the Global Challenges and European Industrial Competitiveness set out by the new Horizon Europe Programme. In particular, this research actuates on the Health cluster, intervening in the areas of technology for Healthcare and Robotics, which overlap with the specialization domains of the national Smart Specialization Strategy. Locomotion can be affected by neurological disorders, such as stroke or cerebral palsy, which have high incidence globally (Miller 2018; George et al. 2017). These lesions will often result in a syndrome of spastic paresis, in which reduced voluntary activation of muscles is accompanied by involuntary and unwanted muscle activation, with deleterious effects on gait. When passive or active electromechanical ankle-foot orthoses (AFO) are employed to restrain or aid joint movement, they may apply external forces opposite to these involuntary contractions, which could bring harm to the user. Electrical stimulation (ES) can trigger action potentials in motor neurons to activate muscle fibers, which is the principal used in Functional ES (FES). However, FES is typically used only for muscle activation and not suppression of involuntary activity. Hence, applying FES on the agonist muscle alone may not be sufficient to counterbalance involuntary contraction of the antagonist, and thus proper function cannot be achieved. Electrical stimulation-based orthoses typically focus on muscle activation and neglect the involuntary activation of spastic muscles. To overcome these major drawbacks, we propose the use of ES to shape the mechanical impedance of the ankle joint in neurological patients, through the EScontrolled activation and inhibition of agonist-antagonist muscles. FES and transcutaneous electrical nerve stimulation (TENS) can elicit several inhibition mechanisms underlying neuromotor control of movement to inhibit involuntary and undesired muscle activity in spastic paresis. To achieve our goal of modulating ankle impedance using ES, we focus on three specific aims: Development of a computational model of neuromotor regulation of ankle mechanical impedance, contemplating normal functioning and alterations due to Neurologic disorders in volitional patterns and reflex arcs. It will describe neurologic disorders such as spasticity, spastic dystonia, spastic-co-contraction stretch-sensitive paresis and nociceptive spasms; Electrical Stimulation inhibition and activation of muscle activity at a joint, using Functional Electrical Stimulation (FES) and Transcutaneous Electrical Nerve Stimulation (TENS); Exploring both efferent and afferent pathways, ES will be able to inhibit and unwanted muscle activation in the agonist-antagonist pair; Experimental modulation of ankle mechanical impedance using FES/TENS, in healthy individuals and in neurological patients. Regulating mechanical impedance determines the dynamic behavior of the joint in response to external perturbations. It will be possible to inhibit and activate the agonistantagonist pair with precise co-contraction levels to achieve the desired joint behavior. While we will focus in this project on the ankle, the techniques may be adapted to other articulations. Significant contributions will be given to the current understanding of neurologic disorders and motor control, and towards the development of better ES orthotic devices.

Project team

R.M. Coelho (PI)