Sensitivity and Reliability of Local Dynamic Stability: Effects of Age and Altered Sensory Conditions

Abstract

Local dynamic stability was investigated during quiet upright stance with respect to age and altered sensory conditions. From center of pressure (COP) trajectories, the largest Lyapunov exponent (Λ_max) was extracted to directly parameterize local dynamic stability, and the reliability of Λ_max was assessed using the intra-class correlation coefficient (ICC). Thirty two participants volunteered for upright quiet stance trials. Vision and somatosenstaion were experimentally altered: vision was modified by eye closure, and somatosensation by using both a hard surface (HS) and a soft surface (SS). Age and vision had main effects on Λ_ma, and the age x vision and vision x surface interaction effects were also significant. In general, older participants were less stable (i.e., higher Λ_max) than younger, and altered sensory information resulted in a decrease in stability. Reliability was higher for older versus younger participants. Use of Λ_max enabled a direct assessment of age-related differences in local dynamic stability and effects of altered sensory conditions. Such non-linear measures can provide additional information to that available from traditional COP-based analyses.