Ultrasound Imaging of Plantarflexor Muscles During Robotic Ankle Assisted Walking: Effects on Muscle Tendon Dynamics and Application Towards Improved Exoskeleton and Exosuit Control
Ankle exosuits/exoskeletons can improve gait but the assistance needs to be tuned to the individual. We suspect that ankle assistance can affect underlying muscle-tendon dynamics and should be accounted for in the control design. We highlight two complementary studies that begin to address these issues. First, we use ultrasound imaging to directly measure the effect of ankle exoskeleton rotational stiffness on soleus contractile dynamics. With increasing stiffness, the soleus operating length and muscle economy increased in early stance, but this was offset by increased shortening velocity and reduced muscle economy in late stance. Second, we demonstrate an approach to rapidly estimate muscle contractile state and its application in prescribing assistance profiles. These results provide evidence for the importance of muscle dynamics and how it can be used to inform design of wearable devices.
