Fig 1.
Simulation workflow (Fig 1A) and muscle dynamic simulation (Fig 1B) for each subject. Inverse kinematics and dynamics are computed using the OpenSim workflow. Moment arms and muscle-tendon lengths are computed from the inverse kinematic solution using the Muscle Analysis tool from OpenSim. We then tuned the muscle-tendon parameters–optimal fiber length, tendon slack length, and tendon stiffness–such that the simulated muscle fiber lengths and excursions matched reported findings from ultrasound imaging reported in the literature. Next, we tuned the muscle passive force-length relationships such that the simulated passive moments matched joint passive moment-angle relationships from an in vivo study reported in the literature. Finally, we simulated walking across various speeds with no actuators and with the various assistive actuators.
Fig 2.
Change in metabolic rates vs. reduction of muscle activations, shown as % of unassisted conditions, at slow, normal, and fast walking speeds with motor-based and spring-based assistance.
The values shown are average ± 1 standard deviation among all subjects and gait cycles.
Fig 3.
Assistive device moments [first column], net muscle moments [second column], muscle activations in ankle plantarflexors [third column] and ankle dorsiflexors [fourth column], and metabolic rates in ankle plantarflexors [fifth column] and ankle dorsiflexors [sixth column] in unassisted conditions and with motor-based and spring-based assistance during slow (upper row), normal (middle row), and fast (lower row) walking speed. Mean values ± 1 standard deviation among all subjects and gait cycles are illustrated. Positive moment refers to ankle plantarflexion, and negative to ankle dorsiflexion. Change in ankle plantarflexion (ΔτP) and ankle dorsiflexion (ΔτD) moments, ankle plantarflexor (ΔaP) and ankle dorsiflexor (ΔaD) muscle activations, and ankle plantarflexor () and ankle dorsiflexor (
) muscles’ metabolic rates, shown as % of unassisted conditions, are presented.
Fig 4.
Assistive device moments [first column], net muscle moments [second column], muscle activations in knee extensors [third column] and knee flexors [fourth column], and metabolic rates in knee extensors [fifth column] and knee flexors [sixth column] in unassisted conditions and with motor-based and spring-based assistance during slow (upper row), normal (middle row), and fast (lower row) walking speed. Mean values ± 1 standard deviation among all subjects and gait cycles are illustrated. Positive moment refers to knee extension, and negative to knee flexion. Change in knee extension (ΔτE) and knee flexion (ΔτF) moments, knee extensor (ΔaE) and knee flexor (ΔaF) muscle activations, and knee extensor () and knee flexor (
) muscles’ metabolic rates, shown as % of unassisted conditions, are presented.
Fig 5.
Assistive device moments [first column], net muscle moments [second column], muscle activations in hip extensors [third column] and hip flexors [fourth column], and metabolic rates in hip extensors [fifth column] and hip flexors [sixth column] in unassisted conditions and with motor-based and spring-based assistance during slow (upper row), normal (middle row), and fast (lower row) walking speed. Mean values ± 1 standard deviation among all subjects and gait cycles are illustrated. Positive moment refers to hip extension, and negative to hip flexion. Change in hip extension (ΔτE) and hip flexion (ΔτF) moments, hip extensor (ΔaE) and hip flexor (ΔaF) muscle activations, and hip extensor () and hip flexor (
) muscles’ metabolic rates, shown as % of unassisted conditions, are presented.
Fig 6.
Assistive device moments [first column], net muscle moments [second column], muscle activations in hip abductors [third column] and hip adductors [fourth column], and metabolic rates in hip abductors [fifth column] and hip adductors [sixth column] in unassisted conditions and with motor-based and spring-based assistance during slow (upper row), normal (middle row), and fast (lower row) walking speed. Mean values ± 1 standard deviation among all subjects and gait cycles are illustrated. Positive moment refers to hip abduction, and negative to hip adduction. Change in hip abduction (ΔτB) and hip adduction (ΔτD) moments, hip abductor (ΔaB) and hip adductor (ΔaD) muscle activations, and hip abductor () and hip adductor (
) muscles’ metabolic rates, shown as % of unassisted conditions, are presented.