Sep 19, 2017

Webinar: Understanding How Exoskeletons Affect Muscle-tendon Mechanics During Walking

Learn about using EMG-driven simulations and muscle-level energetic estimates to understand muscle-tendon function with application of an ankle-exoskeleton torque

DID YOU MISS THIS EVENT?

A recording of the event is available for viewing. Following is a publication for the study that was described in the presentation:

• Jackson, Rachel W., et al. "Muscle-tendon mechanics explain unexpected effects of exoskeleton assistance on metabolic rate during walking." Journal of Experimental Biology 220.11 (2017): 2082-2095.

Details

Title: Understanding How Exoskeletons Affect Muscle-tendon Mechanics During Walking
Speaker: Rachel W. Jackson, Carnegie Mellon University and Stanford University
Time: Tuesday, September 19, 2017 at 10:00 a.m. Pacific Daylight Time

Background

Ankle exoskeletons have the potential to improve mobility in able-bodied individuals and restore mobility to those with gait impairments. In order to achieve the desired improvements in locomotor performance, however, these exoskeletons must interact effectively with the highly complex human musculoskeletal system. Understanding the impact different exoskeleton behaviors have on muscle-tendon mechanics could help guide the development of more effective exoskeleton assistance strategies in the future, but directly measuring muscle-tendon mechanics during human walking is quite challenging. Musculoskeletal simulations provide a unique opportunity for studying how muscle-level mechanics and energetics change when operating in parallel with an assistive device.

Webinar Highlights

In this webinar, we will discuss how we used OpenSim to perform electromyography-driven simulations of a musculoskeletal model to obtain estimates of lower-limb muscle-tendon mechanics during walking with exoskeleton-applied torque. We will then discuss how we fed the results from these simulations into a model of individual muscle energy expenditure to obtain estimates of muscle-level energetics.

Throughout the webinar, we will highlight important strategies we used to improve confidence in our simulation results. By performing these simulations, we found that exoskeletons can affect the functioning of the muscles and tendons acting about the assisted joint. Specifically, when ankle exoskeleton torque was applied passively, without providing any net work input, the ankle plantarflexor muscles did more positive mechanical work, which is costly. These findings stress the importance of considering how muscle-tendon interactions might be affected by exoskeleton-applied torque when designing new devices.

Publications related to the webinar:

• This publication explains how the metabolic model was modified.
  Uchida, Thomas K., et al. "Stretching your energetic budget: how tendon compliance affects the metabolic cost of running." PloS one 11.3 (2016): e0150378.
• This paper by Farris and Sawicki motivated much of the work that was presented in the webinar and provided the foundation for the modified OpenSim workflow.
  Farris, Dominic James, et al. "Musculoskeletal modelling deconstructs the paradoxical effects of elastic ankle exoskeletons on plantar-flexor mechanics and energetics during hopping." Journal of Experimental Biology 217.22 (2014): 4018-4028.
• This publication describes the original lower-limb model that was adapted for the study that was presented in the webinar.
  Arnold, Edith M., et al. "A model of the lower limb for analysis of human movement." Annals of biomedical engineering 38.2 (2010): 269-279.
• This publication describes the muscle-tendon parameters of the model in the study that was presented in this webinar.
  Arnold, Edith M., et al. "How muscle fiber lengths and velocities affect muscle force generation as humans walk and run at different speeds." Journal of Experimental Biology 216.11 (2013): 2150-2160.