title: Identification of ankle plantar-flexors dynamics in response to electrical stimulation.
abstract: Modeling the muscle response to functional electrical stimulation (FES) is an essential step in the design of closed-loop controlled neuroprostheses. This study was aimed at identifying the dynamic response of ankle plantar-flexors to FES during quiet standing. Thirteen healthy subjects stood in a standing frame that locked the knee and hip joints. The ankle plantar-flexors were stimulated bilaterally through surface electrodes and the generated ankle torque was measured. The pulse amplitude was sinusoidally modulated at five different frequencies. The pulse amplitude and the measured ankle torque fitted by a sine function were considered as input and output, respectively. First-order and critically-damped second-order linear models were fitted to the experimental data. Both models fitted similarly well to the experimental data. The coefficient of variation of the time constant among subjects was smaller in the case of the second-order model compared to the first-order model (18.1%vs. 79.9%, p<0.001). We concluded that the critically-damped second-order model more consistently described the relationship between isometric ankle torque and surface FES pulse amplitude, which was applied to the ankle plantar-flexors during quiet standing.
authors.affiliation: Department of Mechanical Engineering, University of Alberta, 10-368 Donadeo Innovation Centre for Engineering, Edmonton, Alberta, T6G 1H9, Canada. Electronic address: hrouhani@ualberta.ca.
authors.forename: Hossein
authors.initials: H
authors.lastname: Rouhani
authors.affiliation: Rehabilitation Engineering Laboratory, Lyndhurst Centre, Toronto Rehabilitation Institute - University Health Network, 520 Sutherland Drive, Toronto, Ontario, M4G 3V9, Canada; Rehabilitation Engineering Laboratory, Institute of Biomaterials and Biomedical Engineering, University of Toronto, 164 College Street, Toronto, Ontario, M5S 3G9, Canada.
authors.forename: Milos R
authors.initials: MR
authors.lastname: Popovic
authors.affiliation: Rehabilitation Engineering Laboratory, Lyndhurst Centre, Toronto Rehabilitation Institute - University Health Network, 520 Sutherland Drive, Toronto, Ontario, M4G 3V9, Canada; Rehabilitation Engineering Laboratory, Institute of Biomaterials and Biomedical Engineering, University of Toronto, 164 College Street, Toronto, Ontario, M5S 3G9, Canada.
authors.forename: Michael
authors.initials: M
authors.lastname: Same
authors.affiliation: Rehabilitation Engineering Laboratory, Lyndhurst Centre, Toronto Rehabilitation Institute - University Health Network, 520 Sutherland Drive, Toronto, Ontario, M4G 3V9, Canada; Rehabilitation Engineering Laboratory, Institute of Biomaterials and Biomedical Engineering, University of Toronto, 164 College Street, Toronto, Ontario, M5S 3G9, Canada.
authors.forename: Ya Qi
authors.initials: YQ
authors.lastname: Li
authors.affiliation: Rehabilitation Engineering Laboratory, Lyndhurst Centre, Toronto Rehabilitation Institute - University Health Network, 520 Sutherland Drive, Toronto, Ontario, M4G 3V9, Canada; Rehabilitation Engineering Laboratory, Institute of Biomaterials and Biomedical Engineering, University of Toronto, 164 College Street, Toronto, Ontario, M5S 3G9, Canada.
authors.forename: Kei
authors.initials: K
authors.lastname: Masani
mesh_terms: D000842:Ankle / Q000502:physiology; D000843:Ankle Joint / Q000502:physiology; D004558:Electric Stimulation; D005260:Female; D005528:Foot; D006801:Humans; D008297:Male; D011187:Posture; D019415:Torque; D055815:Young Adult
keywords: Functional electrical stimulation; Muscle response; Neuroprosthesis; Time constant; Transfer function