Soft Tissue Oscillation Increases Gait Stability in Passive-dynamic Walkers

Open Access
Author:
Masters, Samuel Edward
Graduate Program:
Kinesiology
Degree:
Master of Science
Document Type:
Master Thesis
Date of Defense:
April 13, 2015
Committee Members:
  • John Henry Challis, Thesis Advisor
Keywords:
  • passive walker
  • soft tissue
  • stability
  • floquet multipliers
  • local divergence exponents
  • basin of attraction
  • variability
Abstract:
The majority of human body mass is comprised of soft tissue which can oscillate during human locomotion. Models of human locomotion that contain a soft-tissue component can be used to study the potential role of soft-tissue oscillations. Passive-dynamic walkers (PDWs) are models of human ambulation that can be used to study the underlying dynamics of walking gait. Passive-dynamic walkers can ambulate on an incline solely due to gravity. A PDW with a soft-tissue component was modeled to study the effects of soft-tissue oscillation on human gait dynamics. The control passive-dynamic walker (CPDW) contained point masses at the hip and at each foot. The legs were massless and rigid. The oscillating passive-dynamic walker (OPDW) was identical to the CPDW except for the addition of spring-mass-damper system attached to the hip mass to simulate soft-tissue oscillation. Floquet multipliers (FMs), local divergence exponents (LDEs), the basin of attraction (BOA), slope perturbation range (SPR), and step time variability (STV) were utilized to access stability. Floquet multipliers and LDEs measure short-term step-to-step and short-term inter-step stability, respectively. The BOA measures long-term step-to-step stability. Slope perturbation range and STV measure PDW robustness to uneven terrain in the short-term and long-term, respectively. The spring-damper parameters of the OPDW could be tuned such that the gait stability of the OPDW was greater than that of the CPDW by 38.1%, 6.2%, 135.1%, 131.9%, and 40.3% for the FMs, LDEs, the BOA, the SPR, and the STV, respectively. The walking gait of the PDW model with a soft-tissue component was more stable than the fully rigid model. This suggests damped soft-tissue oscillations may, in addition to their other roles, make human gait more stable.