Abstract
Reliable characterization of locomotor dynamics of human walking is vital to understanding the neuromuscular control of human locomotion and disease diagnosis. However, the inherent oscillation and ubiquity of noise in such non-strictly periodic signals pose great challenges to current methodologies. To this end, we exploit the state-of-the-art technology in pattern recognition and, specifically, dimensionality reduction techniques, and propose to reconstruct and characterize the dynamics accurately on the cycle scale of the signal. This is achieved by deriving a low-dimensional representation of the cycles through global optimization, which effectively preserves the topology of the cycles that are embedded in a high-dimensional Euclidian space. Our approach demonstrates a clear advantage in capturing the intrinsic dynamics and probing the subtle synchronization patterns from uni/bivariate oscillatory signals over traditional methods. Application to human gait data for healthy subjects and diabetics reveals a significant difference in the dynamics of ankle movements and ankle-knee coordination, but not in knee movements. These results indicate that the impaired sensory feedback from the feet due to diabetes does not influence the knee movement in general, and that normal human walking is not critically dependent on the feedback from the peripheral nervous system.
Highlights
Complex physiological rhythms and synchronization processes are ubiquitous in biological systems and are fundamental to life [1]
Despite the deterioration in peripheral nervous system, the knee movement of the NP group is still found to demonstrate a stable long range correlation indistinguishable from the CO group (bCO~0:63(mean)+0:21(std), bNP~0:62(mean)+0:19(std), which are statitcally identical with P~0:965), see Figure 8B. These results suggest that the impaired peripheral feedback caused by the dying nerves in the feet does not influence the upper-limb dynamics, which leds us to another fundamental problem in human walking, i.e., what is the role of sensory feedback in adjusting the global locomotor dynamics? To understand this, we examine further the degree of synchronization between the knee and ankle movement using dimension reduction
Central Nerve Control over Peripheral Nerve System A fundamental question concerning human walking is the origin of the long range correlation found in human gait data, the mechanism of which are not exactly clear [28]
Summary
Complex physiological rhythms and synchronization processes are ubiquitous in biological systems and are fundamental to life [1]. The human heartbeat [2,3], walking [4], vocal cords vibration [5], blood pressure and respiration [6], white blood-cell count and tremor in patients [7,8], epidemic dynamics [9] all demonstrate a stable, possibly nonlinear, oscillatory pattern along with highly irregular fluctuations from period to period. The fluctuation overlying the oscillatory pattern, or the cycle-to-cycle variability, arises from the combined effects from the changing environment, the nonlinear nature inherent to biological systems, and noise of various sources. It contains a wealth of information regarding the health or disease status of an individual subject. Accurately characterizing and quantifying such biological rhythms through data-driven approaches contributes significantly to our understanding of complex biological control systems [10] and have important applications in disease diagnosis
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