  Generating stable walking gaits that yield natural locomotion when executed
on robotic-assistive devices is a challenging task that often requires
hand-tuning by domain experts. This paper presents an alternative methodology,
where we propose the addition of musculoskeletal models directly into the gait
generation process to intuitively shape the resulting behavior. In particular,
we construct a multi-domain hybrid system model that combines the system
dynamics with muscle models to represent natural multicontact walking. Provably
stable walking gaits can then be generated for this model via the hybrid zero
dynamics (HZD) method. We experimentally apply our integrated framework towards
achieving multicontact locomotion on a dual-actuated transfemoral prosthesis,
AMPRO3, for two subjects. The results demonstrate that enforcing muscle model
constraints produces gaits that yield natural locomotion (as analyzed via
comparison to motion capture data and electromyography). Moreover, gaits
generated with our framework were strongly preferred by the non-disabled
prosthetic users as compared to gaits generated with the nominal HZD method,
even with the use of systematic tuning methods. We conclude that the novel
approach of combining robotic walking methods (specifically HZD) with muscle
models successfully generates anthropomorphic robotic-assisted locomotion.
