title: Low-intensity functional electrical stimulation can increase multidirectional trunk stiffness in able-bodied individuals during sitting.
abstract: The inability to voluntarily control the trunk musculature is a major problem following spinal cord injury as it can compromise functional independence and produce unwanted secondary complications. Recent developments suggest that neuroprostheses utilizing functional electrical stimulation (FES) may be able to facilitate or restore trunk control during sitting, standing, and other tasks involving postural control. In spite of these efforts, no study to date has used low-intensity FES to increase multidirectional trunk stiffness and damping in an attempt to bolster stability while minimizing muscle fatigue. Therefore, we set out to investigate how multidirectional trunk stiffness changes in response to low-intensity FES of a few selected trunk muscles. Fifteen healthy participants sitting naturally were randomly perturbed in eight horizontal directions. Trunk stiffness and damping during natural and FES-supported sitting conditions were quantified using force and trunk kinematics in combination with two models of a mass-spring-damper system. Our results indicate that low-intensity FES can increase trunk stiffness in healthy individuals, and this specifically for directions associated with the stimulated muscles. In contrast, trunk damping was not found to be altered during FES. The presented results suggest that low-intensity FES is a simple and effective method for increasing trunk stiffness on demand.
authors.affiliation: Department of Mechanical Engineering, University of Alberta, 4-9 Mechanical Engineering Building, Edmonton, Alberta T6G 2G8, Canada; Glenrose Rehabilitation Hospital, Alberta Health Services, 10230 111 Avenue NW, Edmonton, Alberta T5G 0B7, Canada.
authors.forename: Albert H
authors.initials: AH
authors.lastname: Vette
authors.affiliation: Institute of Biomaterials and Biomedical Engineering, University of Toronto, 164 College Street, Toronto, Ontario M5S 3G9, Canada; Lyndhurst Centre, Toronto Rehabilitation Institute, 520 Sutherland Drive, Toronto, Ontario M4G 3V9, Canada.
authors.forename: Noel
authors.initials: N
authors.lastname: Wu
authors.affiliation: Institute of Biomaterials and Biomedical Engineering, University of Toronto, 164 College Street, Toronto, Ontario M5S 3G9, Canada; Lyndhurst Centre, Toronto Rehabilitation Institute, 520 Sutherland Drive, Toronto, Ontario M4G 3V9, Canada. Electronic address: k.masani@utoronto.ca.
authors.forename: Kei
authors.initials: K
authors.lastname: Masani
authors.affiliation: Institute of Biomaterials and Biomedical Engineering, University of Toronto, 164 College Street, Toronto, Ontario M5S 3G9, Canada; Lyndhurst Centre, Toronto Rehabilitation Institute, 520 Sutherland Drive, Toronto, Ontario M4G 3V9, Canada.
authors.forename: Milos R
authors.initials: MR
authors.lastname: Popovic
mesh_terms: D000328:Adult; D000704:Analysis of Variance; D004548:Elasticity; D004599:Electric Stimulation Therapy / Q000379:methods*; D006801:Humans; D008297:Male; D018482:Muscle, Skeletal / Q000502:physiology; D011187:Posture / Q000502:physiology; D060726:Torso / Q000502:physiology
keywords: Balance; Damping; Functional electrical stimulation; Mathematical model; Neuroprosthesis; Optimization; Sitting; Spinal cord injury; Stiffness; System identification; Trunk