Imaging and Simulation of Inter-muscular Differences in Triceps Surae Contributions to Forward Propulsion During Walking
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Annals of Biomedical Engineering ( 2020) https://doi.org/10.1007/s10439-020-02594-x
Original Article
Imaging and Simulation of Inter-muscular Differences in Triceps Surae Contributions to Forward Propulsion During Walking WILLIAM H. CLARK, RICHARD E. PIMENTEL, and JASON R. FRANZ Joint Department of Biomedical Engineering, University of North Carolina at Chapel Hill and North Carolina State University, 10010 Mary Ellen Jones, Chapel Hill, NC 27599, USA (Received 15 April 2020; accepted 11 August 2020) Associate Editor Daniel Elson oversaw the review of this article.
Abstract—Forward propulsion during the push-off phase of walking is largely governed at the ankle by differential neuromechanical contributions from the biarticular medial (MG) and lateral gastrocnemii (LG) and the uniarticular soleus (SOL). However, the relative contribution of these individual muscles to forward propulsion is equivocal, with important implications for the design and control of wearable assistive devices and for targeted therapeutics. The aim of this study was to evaluate the agreement between empirical and model-predicted triceps surae (i.e., MG, LG, and SOL) contributions to forward propulsion during walking using conditions that systematically manipulated both walking speed and the mechanical demand for forward propulsion at a fixed speed—through the use of aiding and impeding forces. Ten young adults (age: 24.1 ± 3.6 years, 6M/4F) participated. We found that muscle-specific responses derived from experimental measurements (i.e., activation and fascicle behavior) were consistent with those derived from musculoskeletal simulations (i.e., muscle force and positive mechanical work) within the same subjects. In vivo, compared to walking normally, only LG muscle activation was affected by both aiding and impeding forces. Similarly, increased propulsive demand elicited greater relative fascicle shortening in the MG but not the SOL. In silico, only MG and LG force and positive mechanical work increased significantly to meet the increased demands for forward propulsion. By combining electromyography, ultrasound imaging, and musculoskeletal modeling in the same subjects, our cumulative findings suggest that the biarticular gastrocnemius muscles play a more significant role than the uniarticular soleus in governing changes in forward propulsion during the mid to late stance phase of walking. Keywords—Triceps surae, Neuromechanics, Ultrasound, OpenSim, Forward propulsion.
Address correspondence to Jason R. Franz, Joint Department of Biomedical Engineering, University of North Carolina at Chapel Hill and North Carolina State University, 10010 Mary Ellen Jones, Chapel Hill, NC 27599, USA. Electronic mail: [email protected]. edu
INTRODUCTION Forward propulsion during the push-off phase of walking is largely governed by differential neuromechanical contributions from the biarticular medial (MG) and lateral gastrocnemius (LG) and the uniarticular soleus (SOL) spanning the ankle.30 Indeed, although they share a common Achilles tendon, some evidence su
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