Journal
JOURNAL OF APPLIED BIOMECHANICS
Volume 26, Issue 3, Pages 332-340Publisher
HUMAN KINETICS PUBL INC
DOI: 10.1123/jab.26.3.332
Keywords
sitting stability; trunk stiffness; force perturbation; kinematic response
Categories
Funding
- Canadian Institute of Health Research [129179]
- Natural Sciences and Engineering Research Council of Canada [249669]
- Ministry of Health and Long Term Care in Ontario
- Canadian Paraplegic Association Canada
- Toronto Rehabilitation Institute
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Understanding how the human body responds to unexpected force perturbations during quiet sitting is important to the science of motor behavior and the design of neuroprostheses for sitting posture. In this study, the performance characteristics of the neck and trunk in healthy individuals were assessed by measuring the kinematic responses to sudden, unexpected force perturbations applied to the thorax. Perturbations were applied in eight horizontal directions. It was hypothesized that displacement of the trunk, settling time and steady-state error would increase when the perturbation direction was diagonal (i.e., anterior-lateral or posterior-lateral) due to the increased complexity of asymmetrical muscle responses. Perturbation forces were applied manually. The neck and trunk responded in a synchronized manner in which all joints achieved peak displacement simultaneously then returned directly to equilibrium. Displacement in the direction of perturbation and perpendicular to the direction of perturbation were both significantly greater in response to diagonal perturbations (p < .001). The center of mass returned to equilibrium in 3.64 +/- 1.42 s after the onset of perturbation. Our results suggest that the trunk sometimes behaves like an underdamped oscillator and is not controlled by simple stiffness when subjected to loads of approximately 200 N. The results of this study are intended to be used to develop a neuroprosthesis for artificial control of trunk stability in individuals with spinal cord injury.
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