Interpreting lateral dynamic weight shifts using a simple inverted pendulum model.
Seventy-five young, healthy adults completed a lateral weight-shifting activity in which each shifted his/her center of pressure (CoP) to visually displayed target locations with the aid of visual CoP feedback. Each subject's CoP data were modeled using a single-link inverted pendulum system with a spring-damper at the joint. This extends the simple inverted pendulum model of static balance in the sagittal plane to lateral weight-shifting balance. The model controlled pendulum angle using PD control and a ramp setpoint trajectory, and weight-shifting was characterized by both shift speed and a non-minimum phase (NMP) behavior metric. This NMP behavior metric examines the force magnitude at shift initiation and provides weight-shifting balance performance information that parallels the examination of peak ground reaction forces in gait analysis. Control parameters were optimized on a subject-by-subject basis to match balance metrics for modeled results to metric values calculated from experimental data. Overall, the model matches experimental data well (average percent error of 0.35% for shifting speed and 0.05% for NMP behavior). These results suggest that the single-link inverted pendulum model can be used effectively to capture lateral weight-shifting balance, as it has been shown to model static balance.
Department of Aerospace and Mechanical Engineering, University of Notre Dame, Notre Dame, IN 46556, United States. Electronic address: mkenned7@nd.edu.
Michael W
MW
Kennedy
Department of Aerospace Engineering, University of Illinois at Urbana-Champaign, Urbana, IL 61801, United States.
Timothy
T
Bretl
Department of Aerospace and Mechanical Engineering, University of Notre Dame, Notre Dame, IN 46556, United States.
James P
JP
Schmiedeler
D000293:Adolescent; D000328:Adult; D056228:Feedback, Sensory / Q000502:physiology*; D005260:Female; D006801:Humans; D007596:Joints; D008954:Models, Biological; D004856:Postural Balance / Q000502:physiology*; D011312:Pressure; D011597:Psychomotor Performance / Q000502:physiology*; D012016:Reference Values; D016474:Weight-Bearing / Q000502:physiology*; D055815:Young Adult
Balance; Inverted pendulum model; Lateral shifting; Non-minimum phase behavior; Standing