Oct 05, 2017

Webinar: Why Are Antagonists Co-activated in My Simulations? Simulating Cycling and Other

Learn practical tips for simulating and analyzing tasks with large hip and knee flexion


A recording of the event is available for viewing. You can read more about the study in the following publication:
Lai, A.K.M., Arnold, A.S. & Wakeling, J.M. Ann Biomed Eng (2017). https://doi.org/10.1007/s10439-017-1920-7


Title: Why Are Antagonists Co-activated in My Simulations? Simulating Cycling and Other "High Flexion" Tasks
Speakers: Adrian Lai from Simon Fraser University and Allison Arnold from Harvard University
Time: Thursday, October 5, 2017 at 10:00 a.m. Pacific Daylight Time


Pedaling is a popular task for exercise and rehabilitation, and pedaling on an instrumented ergometer provides a meaningful paradigm for lab-based studies of neuromuscular function. Like walking, pedaling involves reciprocal flexion/extension of the hips, knees and ankles; however, pedaling avoids the loading associated with repeated foot-ground contact, and it minimizes balance demands. For these reasons, the biomechanics of pedaling has been studied for decades.

We were surprised, therefore, when our initial attempts to generate subject-specific simulations of pedaling, in OpenSim, failed to reproduce subjects' measured EMG recordings. This webinar is motivated by our efforts to understand why, and our goal is to share practical tips for analyzing tasks, like pedaling, that involve substantial hip and knee flexion.

We found that existing musculoskeletal models have three major limitations. First, they overestimate the passive fiber forces developed by the hip and knee extensors and these large passive forces can lead to anomalous compensatory muscle activity in simulations. Another limitation is that the 3D paths of some muscles are poorly represented over the joint angles achieved by subjects during pedaling. Yet another limitation is that the gastrocnemii and other muscles become too short to generate active force during portions of the cycle that involve substantial hip and/or knee flexion.

Using illustrative examples from pedaling, walking and running, we will show that the anomalous co-activation of antagonist muscles, observed in our initial simulations, can be resolved if the passive fiber forces generated by the underlying model are diminished.

Our refined model is available from SimTK.org (https://simtk.org/projects/model-high-flex) and is suitable for generating simulations of movements involving up to 120 degrees of hip flexion and 140 degrees of knee flexion.