Altered fractal dynamics of gait: reduced stride-interval correlations with aging and Huntington’s disease

Abstract

Fluctuations in the duration of the gait cycle (the stride interval) display fractal dynamics and long-range correlations in healthy young adults. We hypothesized that these stride-interval correlations would be altered by changes in neurological function associated with aging and certain disease states. To test this hypothesis, we compared the stride-interval time series of 1) healthy elderly subjects and young controls and of 2) subjects with Huntington's disease and healthy controls. Using detrended fluctuation analysis we computed alpha, a measure of the degree to which one stride interval is correlated with previous and subsequent intervals over different time scales. The scaling exponent alpha was significantly lower in elderly subjects compared with young subjects (elderly: 0.68 +/- 0.14; young: 0.87 +/- 0.15; P < 0.003). The scaling exponent alpha 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, alpha was linearly related to degree of functional impairment in subjects with Huntington's disease (r = 0.78, P < 0.0005). These findings demonstrate that strike-interval fluctuations are more random (i.e., less correlated) in elderly subjects and in subjects with Huntington's disease. Abnormal alterations in the fractal properties of gait dynamics are apparently associated with changes in central nervous system control.

Gait dynamics in Parkinson’s disease: Common and distinct behavior among stride length, gait variability, and fractal-like scaling

“…79,86 Thus, the fractal dynamics of the stride interval are normally quite robust, largely independent of speed, and intrinsic to the locomotor system. [77][78][79] Studies have also shown that the fractal-like behavior may not be completely mature even in healthy 7 yr old children whose gait appears perfectly adultlike, that different aspects of stride dynamics mature at different ages, 96 that the fractal scaling index is significantly lower in the healthy older adults compared to young adults, 97 and that among older adults with a "higher level gait disturbance," 98 the fractal scaling may distinguish fallers from nonfallers. Here, we describe how PD affects gait dynamics and the relationships between stride length, gait variability, and fractal-scaling.…”

Normal aging reduces motor synergies in manual pointing

“…In a similar vein and inspired by cybernetics, Thaler (2002) proposed that age-related changes in sensorimotor performance may be due to a reduction in the system's variety of perceptual states and available responses. Most of the empirical evidence for this general theoretical position stems from nonlinear time series analyses of "system output", such as physiological measures (Lipsitz and Goldberger, 1992), postural sway (Thurner et al, 2002), or step patterns (Hausdorff et al, 1997), addressing the temporal structure of variability ("dynamical degrees of freedom"). In contrast, potential age-related changes in the functional organization of variability across multiple biomechanical degrees of freedom have found only limited attention.…”

Statistical quantifiers of memory for an analysis of human brain and neuro-system diseases

“…The control and the HD subjects were predominantly female (9 of 10 control subjects and 8 of 10 HD subjects), while subjects with PD and ALS were predominantly male (7 of 10 and 8 of 10, respectively). The heights and the weights of the subjects in the four groups were not significantly different (and the heights and the weights were not significantly correlated with any of the measures of gait dynamics [13][14][15]). …”

“…Despite its welldeveloped experimental methods this field still lacks good and reliable theoretical quantitative indicators for human gait disorders. Interesting results in this field have been derived before by Hausdorff et al [13][14][15][16][17][18][19][20][21]. They studied the dynamical changes of human gait, connected with various diseases [13][14][15][16], the increasing instability of gait in elderly people [13,[16][17][18], presence of long-range correlations in stride interval fluctuations [19,20], stride-to-stride variability and its temporal organization in children [21].…”

“…Similar results have been obtained by Hausdorff et al (see for example Refs. [13,20]). In particular, our analysis which is based on statistical physics and non-linear dynamics, reveals that these stride time dynamics for healthy people possess a fractal (selfsimilar) organization: stride-to-stride variations over small time scales are statistically similar to those over extended time scales.…”