Do horizontal propulsive forces influence the nonlinear structure of locomotion?
Max J Kurz1, Nicholas Stergiou
1Laboratory of Integrated Physiology, University of Houston, Department of Health and Human Performance, Houston, Texas, USA. mkurz@uh.edu
Journal of Neuroengineering and Rehabilitation
|August 19, 2007
Summary
Assisted walking on a treadmill altered nonlinear gait dynamics. Increased assistance to the center of mass movement led to greater complexity in hip, knee, and ankle joint movements, suggesting a link between locomotion control and gait patterns.
Area of Science:
- Biomechanics
- Human locomotion
- Dynamical systems theory
Background:
- Nonlinear gait dynamics are thought to reflect neural control of locomotion.
- Previous models suggested toe-off impulses influence gait dynamics, but direct human evidence was lacking.
Purpose of the Study:
- To investigate how neural control of locomotion, specifically forward center of mass progression, impacts nonlinear gait dynamics in humans.
- To test predictions from a passive dynamic walking model regarding assistive forces and gait complexity.
Main Methods:
- Nineteen participants walked on a treadmill with a mechanical actuator assisting forward center of mass translation during stance.
- Assistive forces varied (0-9% body weight) at self-selected medium-high walking speeds.
- The largest Lyapunov exponent was calculated for joint time series to quantify nonlinear dynamics.
Main Results:
- A systematic increase in the largest Lyapunov exponent was observed as the assistive force percentage increased.
- This indicates a direct relationship between the degree of assistance and the complexity of nonlinear gait dynamics.
Conclusions:
- The findings support the model's prediction that controlling center of mass progression directly influences nonlinear gait dynamics.
- Altered nonlinear gait dynamics in pathological populations may stem from an inability to control forward center of mass progression.
- Further research across various walking speeds is needed to fully understand these implications.
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