How does increased medio-lateral trunk movement affect total system work and the work of ankle joints?

Master thesis (2020)

Authors

L.S. Boers Mechanical Engineering

Contributors

A. Seth Biomechatronics & Human-Machine Control - Mechanical, Maritime and Materials Engineering (mentor)
Jaap Harlaar Biomechatronics & Human-Machine Control - Mechanical, Maritime and Materials Engineering (graduation committee member)
R. Happee Intelligent Vehicles - Mechanical, Maritime and Materials Engineering (graduation committee member)
Faculty
Mechanical Engineering, Mechanical Engineering
Copyright: © 2020 Lars Boers
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Published Date

16-12-2020

Language

English

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Faculty

Mechanical Engineering

Abstract

Pathologiessuch as stroke
or cerebral palsy are often characterized by excessivemediolateral bending of
the trunk. However, it is unclear how mediolateral trunk-sway affects
mechanicalwork of more distal joints during gait. We therefore pose the
researchquestion: How does increased mediolateraltrunk-sway affect the total
system work and that of distal joints during gait? Instead of gait
experimentsthat ask subjects to walk with increased mediolateral trunk-sway,
optimalcontrol theory is used to find control sequences that impose
mediolateral-trunksway on normal gait patterns of 10 healthy subjects. In order
to findout how mediolateral trunk-sway affected mechanical output of gait,
resultingpower and work metrics are compared to those of normal gait. Optimal
controlproblems were solved by transforming the mediolateral trunk-sway
induction (TSI)problem into a nonlinear programming problem via direct
collocation. The TSIproblem was applied to a 31 DOF rigid body skeletal model
with in total 25ideal torque actuators for each subject. Foot ground
interaction was simulatedby 4 Hunt-Crossley spheres under each foot.              
Exaggeratedtrunk-sway resulted in a total increase of positive work of around
2% (p =0.871). Push-off work (~50-65% of gait cycle) decreased by 40% (p =
0,001)and rebound work (~15-35% of gait cycle) increased by 81% (p =
0,001).Analysis of positive work contribution about individual joints show a
massive660% increase in total positive lumbar work (p < 0,001), as well as
a35% decrease in positive ankle work (p = 0,01) during push-off.Additionally,
ground reaction force impulse during the push-off phase decreased by 37% (p
=0,004). Mediolateral trunk-sway gaitwas successfully imposed on normal
gait by using optimal control theory. It wasdemonstrated that mediolateral
trunk-sway is not an efficient gait pattern,since total work increased. Most of
this increase is due to increases in lumbarjoint work as a direct result of the
imposed movement pattern. Mediolateraltrunk-sway also resulted in a significant
decrease in required ankle work,combined with a small increase in hip work.
Additionally, ground-reactionanalysis showed a decrease in impulse measured
during the push-off phase as aresult of imposing trunk-sway. These combined
factors, could indicate that these joints might beused for forward propulsion
of the body within patients that use mediolateraltrunk-sway as an adaptation.