In human locomotion, the magnitude of gait variability is a strong predictor of fall risk and frailty due to aging and disease. Beyond variability magnitude, the past two decades have provided emerging alternative methodologies for studying biological variability. Specifically, coordination variability has been found to be critically important within a healthy, adaptive system. While many activities aim to minimize end-point variability, greater coordination variability indicates a more flexible system, and is greater in experts compared to novices, or healthy compared to diseased individuals. Finally, variability structure (i.e., fractal dynamics) may describe the overall adaptive capacity of the locomotor system. We provide empirical support that fractal dynamics are associated with step length symmetry during challenging split-belt treadmill walking. Individuals whose fractal scaling approached 1/f fractal scaling during constrained walking also exhibited the best gait adaptability performance. Importantly, this relation between fractality and gait adaptability was not observed in unperturbed preferred speed walking.
Scott W. Ducharme and Richard E.A. van Emmerik
Richard E.A. van Emmerik, Stephanie L. Jones, Michael A. Busa and Jennifer L. Baird
Postural instability, falls, and fear of falling that accompany frailty with aging and disease form major impediments to physical activity. In this article we present a theoretical framework that may help researchers and practitioners in the development and delivery of intervention programs aimed at reducing falls and improving postural stability and locomotion in older individuals and in those with disability due to disease. Based on a review of the dynamical and complex systems perspectives of movement coordination and control, we show that 1) central to developing a movement-based intervention program aimed at fall reduction and prevention is the notion that variability can play a functional role and facilitate movement adaptability, 2) intervention programs aimed at fall reduction should focus more on coordination and stability boundary measures instead of traditional gait and posture outcome variables, and 3) noise-based intervention techniques using stochastic resonance may offer external aids to improve dynamic balance control.
Jeffrey M. Haddad, Laura J. Claxton, Dawn K. Melzer, Joseph Hamill and Richard E. A. van Emmerik
Posture becomes integrated with other goal-directed behaviors early in infancy and continues to develop into the second decade of life. However, the developmental time course over which posture is stabilized relative to the base of support during a dynamic manual precision task has not been examined. Postural-manual integration was assessed in 7-year-olds, 10-year-olds, and adults using a postural-manual task in which task precision (target fitting size) and postural difficulty (reaching distance to a target) were manipulated. The main dependent variable was postural time-to-contact (TtC). Results indicated systematic age effects in which TtC was shortest in the 7-year-olds, increased in the 10-year-olds, and was longest in the adults. Across all age levels, TtC was longer when performing a precision ft compared with a nonprecision ft and when fitting at a near target compared with fitting at a far target. Finally, TtC increased over the course of the manual fitting task, suggesting that posture became increasingly stable as the hand approached the opening. The ability to modulate postural TtC during the course of the fitting trial was most pronounced in adults as compared with both groups of children. These results suggest that even by 10-years of age, children are not yet able to fully integrate postural movements with goal directed manual tasks at adult-like levels.