Quantifying variability of young and older adults during gait with linear and nonlinear tools

Variability of the S₁ displacement in frontal plane during gait was quantified with nonlinear and traditional linear tools including Largest Lyapunov Exponent, Approximate entropy and standard deviation to discriminate between 2 healthy groups in mediolateral and vertical direction and to understand the relation between local stability and complexity. In both young and older adults, mediolateral direction was less stable and less complex than vertical direction which means that mediolateral direction is more sensitive to small perturbation and it´s more predictable in comparison to vertical direction. The result from linear tools shows greater variability in mediolateral direction. These results give information about the quality of gait in different age groups and may lead us in diagnosis and prognosis.