EMG-Constrained and Ultrasound-Informed Muscle-Tendon Parameter Estimation in Post-Stroke Hemiparesis

Abstract

Secondary morphological and mechanical property changes in the muscle-tendon unit at the ankle joint are often observed in post-stroke individuals. These changes may alter the force generation capacity and affect daily activities such as locomotion. This work aimed to estimate subject-specific muscle-tendon parameters in individuals after stroke by solving the muscle redundancy problem using direct collocation optimal control methods based on experimental electromyography (EMG) signals and measured muscle fiber length. Subject-specific muscle-tendon parameters of the gastrocnemius, soleus, and tibialis anterior were estimated in seven post-stroke individuals and seven healthy controls. We found that the maximum isometric force, tendon stiffness and optimal fiber length in the post-stroke group were considerably lower than in the control group. We also computed the root mean square error between estimated and experimental values of muscle excitation and fiber length. The musculoskeletal model with estimated subject-specific muscle tendon parameters (from the muscle redundancy solver), yielded better muscle excitation and fiber length estimations than did scaled generic parameters. Our findings also showed that the muscle redundancy solver can estimate muscle-tendon parameters that produce force behavior in better accordance with the experimentally-measured value. These muscle-tendon parameters in the post-stroke individuals were physiologically meaningful and may shed light on treatment and/or rehabilitation planning.

Experiment-guided tuning of muscle–tendon parameters to estimate muscle fiber lengths and passive forces

“…Our results support this assumption, as estimated fiber lengths were nearly unchanged with or without tuned muscle passive force-length relationships. Muscle parameters related to the active and passive force generation capacity can be optimized simultaneously if diverse sensor modalities, such as EMGs, dynamometer, and ultrasound imaging, are available [19][20][21] . Such comprehensive data collection, however, might be challenging to achieve due to the complexity of the experimental setups, which might confine it to describing single joint mechanics and a limited number of recorded muscle fibers.…”