PROGRAM | Mechanical Engineering

By: Kaleb Burch Chair: Jill Higginson

ABSTRACT

Biomechanics research is at a crucial stage where researchers are seeking to translate
results in the lab into results in the real world. However, most technologies that have been
foundational to biomechanics research, such as optical motion capture systems, force plates,
instrumented treadmills, and robotic exoskeletons, are restricted to use in the lab. In order to
address this problem, biomechanists have sought to implement other approaches, one of the
foremost being wearable technologies. The purpose of this dissertation was to develop wearable
technology for measuring and assisting human motion outside of the lab.
In Aim 1, we validated a novel insole pressure sensor for quantifying ground reaction force
(GRF) during walking. We collected data from 7 participants walking on an instrumented treadmill
while wearing the insole pressure sensor. This sensor was validated by quantifying agreement with
gold-standard force plate measurements of peak GRF during walking at three different speeds. We
found that this sensor could achieve moderate agreement with the force plate with a basic
calibration procedure and a low-cost data acquisition system, which suggests potential to overcome
the economic barrier to more widespread adoption of this technology.
In Aim 2, we optimized cable-driven exosuit properties using musculoskeletal modeling
and simulation. We recruited 5 healthy adult subjects to perform reaching, drinking, and hairbrushing
motions, and used kinematics of these motions as inputs into a musculoskeletal model.
We ran computed muscle control (CMC) simulations to first estimate unassisted muscle activity
for these tasks, and then ran an optimization algorithm involving successive CMC simulations
with different cable actuator properties. We used this optimization algorithm to identify optimal
cable actuator attachment points and forces to minimize the combined activity of the middle and
anterior deltoids. This method successfully identified optimal actuator properties that substantially
reduced activity of the target muscles for all three motions.
In Aim 3, we developed and tested a physical prototype of a shoulder exosuit for reaching
and drinking assistance. In this study, we collected kinematic, EMG, and exosuit force data to
evaluate how individuals altered motion in response to exosuit assistance. Subjects performed a
series of 200 reaches while not wearing the exosuit, while wearing the exosuit without assistance,
and wearing the exosuit with assistance. Subjects performed 120 reaches with the powered exosuit
to learn how to use the device. Subjects also performed drinking motions with and without powered
assistance from the exosuit. We found that the exosuit successfully reduced muscle activity of the
middle and posterior deltoids during reaching and drinking. Furthermore, we found that
individuals altered kinematics in response to the exosuit by allowing their arms to follow exosuit
assistance. Finally, we found that subjects exhibited trial-to-trial changes in movement duration
and in the timing at which they used a switch to activate the exosuit. Future work should seek to
evaluate the learning mechanisms behind changes in muscle activity and movement duration when
using an exosuit and to integrate experimental results with musculoskeletal modeling and
simulation to improve exosuit design.

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