1st Joint ESMAC-GCMAS Meeting - Análise de Marcha

O-42
DYNAMIC SIMULATIONS OF SLOW, FREE, AND FAST WALKING:
HOW DO MUSCLES MODULATE FORWARD PROGRESSION?
Liu, May, M.S. 1 , Jonkers, Ilse, Ph.D. 2 , Arnold, Allison, Ph.D. 1 , Schwartz, Michael, Ph.D. 3 ,
Thelen, Darryl, Ph.D. 4 , Anderson, Frank, Ph.D. 1 , Delp, Scott, Ph.D. 1
1 Depts. of Mechanical Engineering & Bioengineering, Stanford University, Stanford, USA
2 Faculty of Kinesiology & Rehabilitation Sciences, KULeuven, Leuven, Belgium
3 Center for Gait & Motion Analysis, Gillette Children’s Specialty Healthcare, St. Paul, USA
4 Department of Mechanical Engineering, University of Wisconsin, Madison, USA
Summary/conclusions
Forward progression during walking is modulated by the same muscles, regardless of speed.
Propulsion from hip flexors and plantarflexors increases with speed, as does the braking
actions of knee extensors.
Introduction
Unimpaired children can increase or decrease walking speed with ease, a task that is often
difficult for children with musculoskeletal disorders. However, the mechanisms by which
unimpaired individuals modulate walking speed are unclear. Prior EMG studies have shown
that muscle activity increases with walking speed (e.g., [1]), but how this altered activity
influences walking dynamics is unknown. Muscle-actuated simulations have provided insight
into how muscles generate propulsion during walking at a typical free speed (e.g., [2-3]). Using
subject-specific dynamic simulations of walking, we tested the hypothesis that faster walking
speed is achieved by increasing the propulsive actions of the same muscles that modulate
progression at a normal walking speed.
Statement of clinical significance
A common therapeutic goal for patients with impairments is to improve walking speed.
Understanding how muscles generate forward progression at slow and fast speeds in
unimpaired children may aid the development of more effective treatments to improve walking
speed in patients with gait abnormalities.
Methods
Three-dimensional kinematics and ground reaction forces for an unimpaired child (11 y.o)
were collected at self-selected slow, free, and fast overground walking speeds. We scaled a
musculoskeletal model (21 degrees of freedom, 92 muscle-tendon actuators) to the subject’s
anthropometry and used computed muscle control [4] to generate forward dynamic walking
simulations at each speed. Computed kinematics and muscle excitations were consistent with
experimental kinematics and EMG. Each simulation consisted of a half-gait cycle, beginning at
the onset of double support (loading response of left limb, preswing of right limb). Muscleinduced
fore-aft accelerations of the body mass center were computed using a perturbation
analysis [3]. Accelerations from stance-limb muscles were averaged over four phases: loading
response (double support, negative fore-aft GRF), early single-limb support (negative fore-aft
GRF), late single-limb support (positive fore-aft GRF), and preswing (double support, positive
fore-aft GRF). In each phase, muscles that generated ≥ 80% of the total braking or propulsive
induced acceleration were identified.
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