European Journal of Applied Physiology

, Volume 98, Issue 1, pp 30–40 | Cite as

Complexity analysis of stride interval time series by threshold dependent symbolic entropy

Original Article


The stride interval of human gait fluctuates in complex fashion. It reflects the rhythm of the locomotor system. The temporal fluctuations in the stride interval provide us a non-invasive technique to evaluate the effects of neurological impairments on gait and its changes with age and disease. In this paper, we have used threshold dependent symbolic entropy, which is based on symbolic nonlinear time series analysis to study complexity of gait of control and neurodegenerative disease subjects. Symbolic entropy characterizes quantitatively the complexity even in time series having relatively few data points. We have calculated normalized corrected Shannon entropy (NCSE) of symbolic sequences extracted from stride interval time series. This measure of complexity showed significant difference between control and neurodegenerative disease subjects for a certain range of thresholds. We have also investigated complexity of physiological signal and randomized noisy data. In the study, we have found that the complexity of physiological signal was higher than that of random signals at short threshold values.


Gait dynamics Neurodegenerative diseases Symbolic analysis Physiological complexity 


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Copyright information

© Springer-Verlag 2006

Authors and Affiliations

  1. 1.Department of Computer and Information SciencesPakistan Institute of Engineering and Applied Sciences (PIEAS)IslamabadPakistan
  2. 2.Department of Computer and Information technologyAzad Jammu and Kashmir University Muzaffarabad (AK)MuzaffarabadPakistan

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