Analysis of body responses to an accelerating platform by the largest-Lyapunov-exponent method

Abstract

Various disciplines have benefited from the advent of high-performance computing in achieving practical solutions to their problems, and the area of health care is no exception to this. Non-linear signal-processing tools have been developed to understand the hidden complexity of the time series, and these will help clinicians in diagnosis and treatment. Postural study helps the elderly and people with a balancing problem due to various pathological conditions. In elderly subjects, falls are common and may result in injury. Correct postural balance is basic to well-being and it influences our daily life significantly. These postural signals are non-stationary; they may appear to be random in the time scale and it is difficult to observe the subtle changes for the human observer. Hence, more hidden information can be obtained from the signal using non-linear parameters. In this paper, ten young normal subjects are subjected to the balancing platform whose acceleration is gradually increased from 1 m/s2 to 5 m/s2 to study the postural response. The ankle front-back acceleration and ankle pitch angular velocity sensor data were studied using the largest Lyapunov exponent (LLE). The results show that for higher acceleration of the platform the ankle movement follows a particular rhythm, resulting in a lower Lyapunov exponent. During lower acceleration of the balancing platform, this value is higher because of the random movement of the ankle. In this work, the pattern of the body response was studied using LLE values for different accelerations using ankle data as the base signal for the normal subjects.

Analysis of Human Standing Balance by Largest Lyapunov Exponent

“…Schilling and Robinson [ 31 ] used an air bearing platform which was in sinusoidal AP motion in order to generate a periodic stimulus to postural control system, and then a mathematical model was established. Acharya et al, in [ 16 ], used platform perturbation whose acceleration was gradually increased from 1 m/s 2 to 5 m/s 2 to study the response of ten healthy subjects. The results showed that higher acceleration of the platform results in a lower LLE value, and lower acceleration of the platform results in a higher value.…”

“…Many researchers have tried an external force stimulus to improve the signal to noise ratio of human dynamic information. In [ 16 ], a random translational stimulus was applied to the feet by a movable support surface. However, the random sudden motion causes the body to remain in a stressed state for a long time.…”

Clinical Static Balance Assessment: A Narrative Review of Traditional and IMU-Based Posturography in Older Adults and Individuals with Incomplete Spinal Cord Injury

“…The most common posturographic measures used to characterize quiet standing include time-and frequency-domain measures, which quantify the dis-placement, velocity, area, and frequency properties of the COP or COM time-series in the anteroposterior and mediolateral directions [34]. Other measures are stabilogram diffusion function [33,50,51], detrended fluctuation analysis [54], approximate entropy and sample entropy [55][56][57], and Lyapunov exponent [58].…”

Non-linear analysis of body responses to functional electrical stimulation on hemiplegic subjects

“…A novel method based on the phase space technique was used to distinguish between normal and abnormal cases [19]. The effect of body responses to the accelerating platform was studied using the largest Lyapunov exponent (LLE) with the ankle front-back acceleration and ankle pitch angular velocity sensor data [20]. The results suggest that the LLE for the ankle front-back and ankle pitch rate decreases with increase in the balance platform acceleration.…”