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Nonlinear dynamics analysis of the human balance control subjected to physical and sensory perturbations

100%

Ashtiani M. N., Azghani M.-R.

Acta Neurobiologiae Experimentalis

2017

tom 77

nr 2

Postural control after applying perturbation involves neural and muscular efforts to limit the center of mass (CoM) motion. Linear dynamical approaches may not unveil all complexities of body efforts. This study was aimed at determining two nonlinear dynamics parameters (fractal dimension (FD) and largest Lyapunov exponent (LLE)) in addition to the linear standing metrics of balance in perturbed stance. Sixteen healthy young males were subjected to sudden rotations of the standing platform. The vision and cognition during the standing were also interfered. Motion capturing was used to measure the lower limb joints and the CoM displacements. The CoM path length as a linear parameter was increased by elimination of vision (p<0.01) and adding a cognitive load (p<0.01). The CoM nonlinear metric FD was decreased due to the cognitive loads (p<0.001). The visual interference increased the FD of all joints when the task included the cognitive loads (p<0.01). The slightly positive LLE values showed weakly‑chaotic behavior of the whole body. The local joint rotations indicated higher LLEs. Results indicated weakly chaotic response of the whole body. Increase in the task difficulty by adding sensory interference had difference effects on parameters. Linear and nonlinear metrics of the perturbed stance showed that a combination of them may properly represent the body behavior.

Effects of postural and cognitive difficulty levels on the standing of healthy young males on an unstable platform

71%

Oliaei S., Ashtiani M. N., Azma K., Saidi S., Azghani M.-R.

Acta Neurobiologiae Experimentalis

2018

tom 78

nr 1

Standing on an unstable platform requires continuous effort of the neuro-musculoskeletal system. The aim of the present study is to evaluate the ability to remain standing on an unstable platform at different levels of postural and cognitive difficulty. Healthy young males stood in the sagittal plane on an unstable platform supported by a pair of springs with modifiable stiffness. The balance test also assessed different levels of vision and cognitive function. Linear and nonlinear metrics of standing, based on motion captured kinematic data, were assessed to analyze the stability of standing. Results showed that vision plays a significant role in maintaining balance in terms of linear metrics. Elimination of visual feedback changed the direction of body sway and increased standing instability. Placement of low stiffness springs led to unstable standing. The cognitive dual task, however, had no effect on the stability metrics and merely could be revealed in the simplest test condition. Standing on an unstable platform was closely related to visual feedback and decreasing the spring stiffness significantly reduced stability. The roles of cognitive involvement were subdued by increasing the postural difficulty in standing on an unstable platform.

Ograniczanie wyników

2 Acta Neurobiologiae Experimentalis

2 Ashtiani M. N.

2 Azghani M.-R.

1 Azma K.

1 Oliaei S.

1 Saidi S.

1 2018

1 2017

Wyniki wyszukiwania

Nonlinear dynamics analysis of the human balance control subjected to physical and sensory perturbations

Effects of postural and cognitive difficulty levels on the standing of healthy young males on an unstable platform