Article

Evaluation of structural variability in biological time series
through measures such as sample entropy (SaEn) has provided important information
in neurology and cardiology. This has contributed to the development of the "loss
of complexity hypothesis" where high variability has been described as healthy
flexibility and low variability associated with pathology.
The purpose of this
study was to calculate sample entropy (SaEn) to establish normal values of
non-linear variability and to examine which factors are associated with SaEn in
midfoot kinematics. METHOD: Static foot posture was measured using Foot Posture
Index. A video sequence analysis system was used to quantify midfoot kinematics
during walking in the sagittal plane. SaEn was calculated for navicular drop
during stand phase as an expression of the dynamic complexity. RESULTS: A
significant difference was observed between the three major foot types and
between genders (p<0.001). Mean SaEn in women were 1.10+/-0.19 (supinated foot
posture), 0.96+/-0.17 (neutral foot posture) and 0.77+/-0.16 (pronated foot
posture) and 1.25+/-0.24 (supinated foot posture), 1.06+/-0.23 (neutral foot
posture) and 0.86+/-0.19 (pronated foot posture) in males. The regression model
showed that foot posture and dynamic navicular drop (dND) were both associated
with SaEn. CONCLUSION: This study confirmed that non-linear analysis is of
relevance in the interpretation of kinematic data. Pronated foot posture, large
navicular drop and women were characterized by low values of non-linear
variability. Future studies should investigate if measurements of SaEn are
capable of identifying subjects with an increased risk of injury.
CI - Copyright 2010 Elsevier B.V. All rights reserved.

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