In this dissertation, the human posture and gait control adjustability were quantified using dynamic models, in order to understand why changes of control mechanism are required in challenging conditions such as larger perturbation and speed increase.
A quantitative postural control model, consisting of two-segment inverted pendulum with joint torque controller, was employed to explain abnormal postural responses of patients with Parkinson’s disease (PD). We hypothesized that postural control impairment of subjects with PD can be quantified as an abnormal scaling of postural feedback gain with increased postural challenges. The results showed that the model simulations can well reproduce postural responses in young, elderly and PD subject groups for a wide range of surface perturbations. Continuous feedback gain scaling was observed for all subject groups, implying that the nervous system automatically adjusts motor output to accommodate changes in biomechanical constraints. Abnormal postural responses of subjects with PD were consistent with smaller than normal ankle feedback gain, larger than normal hip feedback gains, and an inflexible selection of feedback gain as the perturbation conditions change.
As a part of postural control study, we also investigated whether postural responses to back push, as an impulse disturbance, can be described with continuous feedback manner as push size increased. The result showed that the model simulations reasonably well reproduced postural responses for a wide range of push perturbation and the feedback gain scaling was also observed with the increase of push size. In the view of gain scaling, subjects sensitively adjusted their ankle torque related gains to suppress ankle torque generation without violating constraints.
A compliant walking model having radial telescoping legs was proposed in order to understand the substantial dynamics of human walking within the framework of energetics. In this study we calculated t...