Whole-body Local Dynamic Stability during Walking and Running
نویسنده
چکیده
Highly-simplified models of walking and running can show passive dynamic (i.e. mechanical) stability[1-2]. Although these models capture many important aspects of locomotor dynamics, the extent to which they can describe the stability properties of human locomotion is still unclear. Human locomotion involves coordinating many degrees of freedom (DOFs), which are coupled (mechanically, kinematically, and neutrally) in the control of multijoint moments. Humans also commonly perform maneuvers (acceleration and deceleration, for example) in addition to constant-velocity locomotion. Several studies have focused on reducing multiple DOFs in a static behavior[3] or on the dynamic behavior of single DOF[4]. However, using individual DOFs to characterize locomotor stability could be incomplete because 1) some DOFs such as joint angles and vertical COM are constrained to limited ranges; 2) individual DOF may only reflect local dynamic behavior, and not the dynamics of the entire system[4]. Moreover, the effects of different maneuvers or gaits on dynamic stability have not been fully characterized. For example, walking might be expected to be more stable than running because there are more opportunities for continuous neural feedback to contribute to stability[5]. This study therefore sought to characterize whole body within-stride stability by analyzing many DOFs. We used Principal Component Analysis (PCA) and calculated Lyapunov exponents on the 1 principal component, which accounts for limb rotation with minor translation[3], to determine the stability among body DOFs within a stride[4]. Specifically, we hypothesized that 1) different joint DOFs do not show differences in stability properties during locomotion; 2) constant speed walking or running is more stable than acceleration or deceleration; 3) walking is more stable than running. METHODS
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