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Jill S. Higginson,
PhD Biomedical Engineer |
650/736-0806
Education
- BS Mechanical Engineering - Cornell University - 1996
- MS Bioengineering - Penn State University - 1998
Dissertation Topic
Analysis of muscle coordination during slow and post-stroke
hemiparetic gait using simulation
Walking is a complex task with many muscles being coordinated. After
stroke, muscle coordination is impaired and may compromise walking performance.
This dissertation describes the development and application of simulation tools
to investigate the role of muscles during slow and post-stroke hemiparetic
gait.
A simulation of normal gait was perturbed to investigate a common gait
deviation associated with post-stroke hemiparetic gait. In the presence of
excess ankle plantarflexion at initial foot contact, the effect of individual
muscles on knee extension was isolated. We found that equinus foot placement
alone can induce knee extension, and may be mediated by the intrinsic response
of muscles.
To facilitate the development of muscle-actuated forward dynamic
simulations of pathological gait, a parallel optimization strategy based on
simulated annealing was designed. Using two test functions, we found that our
parallel algorithm scaled linearly with the number of processors recruited
while robustness was retained. The new algorithm has the capability to reduce
time to convergence for optimization of walking simulations by a factor of
about 20.
The parallel optimization algorithm was employed to minimize the
difference between simulated data and the experimental kinematics and kinetics
of healthy adults walking at a self-selected speed (1.5 m/s) and at an
extremely slow speed (0.3 m/s). Using these simulations, the contributions of
individual muscles to support and swing initiation in normal and slow speed
gait were compared. Our simulations suggest that the quadriceps assist the
plantarflexors to provide midstance support in slow gait, and that adequate
swing initiation can be achieved with less energy generation by muscles.
Finally, a simulation of post-stroke hemiparetic gait was produced to
emulate experimental kinematics and ground reaction forces from a single stroke
survivor. The contributions of paretic and non-paretic muscles to midstance
support and swing initiation were compared with the results from slow gait. The
role of non-paretic muscles resembles that of neurologically healthy
individuals, while paretic muscles exhibited increased co-contraction at the
knee and ankle, required recruitment of additional muscles to provide support,
and provided very little contribution to swing leg energy.
With the ability to generate muscle-actuated forward dynamic simulations
of subject-specific gait patterns, we hope to develop an improved understanding
of normal and pathological muscle function and to suggest rehabilitation
strategies for improvement of walking performance in stroke survivors.
Project
The contribution of ankle plantarflexors to forward progression in
hemiparetic gait
- A stroke inflicts damage to the neuronal pathways in the central nervous
system and impairs the function of the neuro-musculo-skeletal system. Walking
after stroke is complicated by asymmetrical loss of paretic and non-paretic
muscle strength and abnormal timing of muscle excitation. Forward dynamic
simulation has shown that ankle plantarflexors make significant contributions
to vertical support and forward progression of the trunk during walking.
Preliminary analyses indicate that reduced strength of soleus (an ankle
plantarflexor) results in a more flexed posture. Due to the new configuration,
soleus contributes less to forward progression and gait speed is reduced. Using
similar methods, future work will systematically analyze how changes in the
magnitude and timing of muscle excitation patterns cause inappropriate ankle
function which may impede forward progression after stroke.
2005
Affiliations
- Veterans Administration Palo Alto Health Care System, Rehabilitation
Research and Development Center
- Stanford University, Department of Mechanical Engineering, Biomechanical
Engineering Division
Research Interests
- Muscle Coordination
- Stroke Rehabilitation
Last updated 04/05/2006
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