Document Type : Full Research Paper
Authors
- Samane Moeini Sedeh 1
- Navid Arjmand 2
- Mohammad Ali Sanjari 3
- Hamid Reza Mokhtarinia 4
- Morteza Asgari 1
- Mohammad Parnianpour 5
1 M.Sc., Mechanical Engineering Department, Facualty of Biomechanics, Sharif university of Technology
2 Asistant Professor, Mechanical Engineering Department, Facualty of Biomechanics, Sharif university of Technology
3 Asistant Professor, Department of Rehabiliation Basic Sciences, Faculty of Rehabiliation, Iran University of Medical Sciences
4 Asistant Professor, Department of Ergonomics, University of Social Welfare and Rehabilitation Sciences
5 Adjunct Professer, Mechanical Engineering Department, Facualty of Biomechanics, Sharif university of Technology
Abstract
Stability is important to prevent falling during occupational and daily living activities. Control parameters such as direction of motion and external load can affect stability pattern. The purpose of this paper was to evaluate the effect of the mentioned control parameters on stability. Time series of lumbar rotation angle in 19 healthy subjects were investigated. Each subject performed spine flexionextension in two different directions of symmetric (sagittal plane) and asymmetric (between sagittal and transverse planes), with two loading cases of 8 Kg weight and load free. To evaluate dynamic stability of repetitive movement, a nonlinear method of largest Lyapunov exponent has been used. After calculating maximum Lyapunov exponent from each of the experimental cases, results of analysis of variance showed a significant difference between symmetric and asymmetric directions (p=0.016). To interpret this result we can suggest higher recruitment of the internal and external oblique muscle groups and higher mechanical constraints in spine during asymmetric tasks. Mean comparison showed that movement in symmetric direction has more instability than the asymmetric case. Moreover, presence of load and interaction between direction and load did not significantly affect local dynamic stability.
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