PROJECT SUMMARY/ABSTRACT
Muscular dystrophies (MD), such as Duchenne MD and Becker MD, are rare genetic diseases that cause
progressive muscle degeneration in approximately 14 in 100,000 males ages 5-24. Currently there is no known
treatment that can stop or reverse the damage caused by MD. Dystrophic muscle is especially susceptible to
damage during eccentric contraction. Soft exosuits are an emerging class of wearable device that may be able
to reduce eccentric contraction during functional movements such as downhill walking, which requires substantial
eccentric knee extensor contraction. Exosuits utilize compliant textile-based actuators to inherently provide
safety and comfort to the user, which is highly desirable for avoiding excessive muscle injury in boys with MD.
However, one potential barrier to development of exosuits for boys with MD is the risk of injury during human
subjects testing of new prototypes. Musculoskeletal simulations are an ideal tool for early-stage design of
exosuits for children with MD because simulations provide characterization of muscle eccentric contraction,
which is difficult to observe experimentally, and avoid risk of injury to human subjects when testing prototypes.
Thus, the overall objective of this project is to develop a musculoskeletal simulation framework for in silico design
and optimization of a soft exosuit for children with MD. First, existing simulations of healthy adults walking
downhill will be modified to include a simulated soft exosuit. The initial exosuit design will be based on existing
physical prototypes. A novel optimization framework will be used to optimize the exosuit to minimize eccentric
contraction in the rectus femoris (a knee extensor) during downhill walking. Statistical analysis will be performed
to test the hypotheses that (1) simulated eccentric contraction (i.e., net negative work) in the rectus femoris is
significantly reduced by the exosuit and (2) eccentric contraction is further reduced following optimization. In
addition, changes in joint reaction forces and eccentric contraction in other muscles will be quantified to
investigate potential adverse side effects. After establishing potential benefits of the exosuit using the adult
model, a musculoskeletal model of a child will be developed. A simulated isometric task will be used to calibrate
maximum isometric muscle force in a typically developing and MD child model to match published strength data.
Preliminary simulations of a child walking downhill with the exosuit will be generated by scaling the adult
movement data using a retargeting algorithm. The exosuit optimization framework will be applied to both the
typically developing child and child with MD models to determine whether the optimized exosuit provided a
sufficient reduction in rectus femoris eccentric contraction to be statistically significant in future human subjects
experiments. The proposed research aims to establish a foundation for design of an exosuit that can substantially
improve quality of life for children with MD in the near term. In addition, the musculoskeletal simulation-based
design optimization framework will facilitate rapid in silico design and testing of assistive devices, such as soft
exosuits, without risk to human subjects.
