ALTERED FRACTAL DYNAMICS OF GAIT - REDUCED STRIDE-INTERVAL CORRELATIONS WITH AGING AND HUNTINGTONS-DISEASE

Fluctuations in the duration of the gait cycle (the stride interval) d isplay fractal dynamics and long-range correlations in healthy young a dults. We hypothesized that these stride-interval correlations would b e altered by changes in neurological function associated with aging an d certain disease states. To test this hypothesis, we compared the str ide-interval time series of 1) healthy elderly subjects and young cont rols and of 2) subjects with Huntington's disease and healthy controls . Using detrended fluctuation analysis, we computed alpha, a measure o f the degree to which one stride interval is correlated with previous and subsequent intervals over different time scales. The scaling expon ent a was significantly lower in elderly subjects compared with young subjects (elderly: 0.68 +/- 0.14; young: 0.87 +/- 0.15; P < 0.003). Th e scaling exponent a was also smaller in the subjects with Huntington' s disease compared with disease-free controls (Huntington's disease: 0 .60 +/- 0.24; controls: 0.88 +/- 0.17; P < 0.005). Moreover, a was Lin early related to degree of functional impairment in subjects with Hunt ington's disease (r = 0.78, P < 0.0005). These findings demonstrate th at stride-interval fluctuations are more random (i.e., less correlated ) in elderly subjects and in subjects with Huntington's disease. Abnor mal alterations in tile fractal properties of gait dynamics are appare ntly associated with changes in central nervous system control.