Multidirectional quantification of trunk stiffness and damping during unloaded natural sitting.
Trunk instability during sitting is a major problem following neuromuscular injuries such as stroke and spinal cord injury. In order to develop new strategies for alleviating this problem, a better understanding of the intrinsic contributions of the healthy trunk to sitting control is needed. As such, this study set out to propose and validate a novel methodology for determining multidirectional trunk stiffness during sitting using randomized transient perturbations. Fifteen healthy individuals sitting naturally on a custom-made seat were randomly perturbed in eight horizontal directions. Trunk stiffness and damping were quantified using force and trunk kinematics in combination with translational and torsional models of a mass-spring-damper system. The results indicate that stiffness and damping of the healthy trunk are roughly symmetrical between the two body sides. Moreover, both quantities are smallest in the anterior and largest in the lateral directions. In conclusion, a novel protocol for identifying intrinsic trunk stiffness and damping has been developed, eliminating anticipation effects with respect to perturbation timing and direction. Subsequent studies will use these findings as a reference not only for quantifying trunk stiffness and damping in individuals with various neuromuscular disorders, but also for assessing whether neuroprostheses could increase upper body stiffness and, hence, stability.
Department of Mechanical Engineering, University of Alberta, 4-9 Mechanical Engineering Building, Edmonton, Alberta T6G 2G8, Canada; Glenrose Rehabilitation Hospital, 10230 111 Avenue NW, Edmonton, Alberta T5G 0B7, Canada.
Albert H
AH
Vette
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.
Kei
K
Masani
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.
Noel
N
Wu
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.
Milos R
MR
Popovic
D000328:Adult; D001696:Biomechanical Phenomena; D006801:Humans; D008297:Male; D055595:Mechanical Phenomena; D008954:Models, Biological; D011187:Posture / Q000502:physiology*; D015203:Reproducibility of Results; D013997:Time Factors; D060726:Torso / Q000502:physiology*
Balance; Damping; Human; Mathematical model; Motor control; Optimization; Sitting; Stiffness; System identification; Trunk