Simulation

KM Steele, MC Tresch, EJ Perreault, (2013) “The number and choice of muscles impact the results of muscle synergy analyses,” Frontiers in Computational Neuroscience

Dr. Steele JournalArticle, MotorControl ,
tVAF decreases with increasing number of muscles included in synergy analysis

Journal article accepted in Frontiers in Computational Neuroscience:

The number and choice of muscles impact the results of muscle synergy analyses

One theory for how humans control movement is that muscles are activated in weighted groups or synergies. Studies have shown that electromyography (EMG) from a variety of tasks can be described by a low-dimensional space thought to reflect synergies. These studies use algorithms, such as nonnegative matrix factorization, to identify synergies from EMG. Due to experimental constraints, EMG can rarely be taken from all muscles involved in a task. However, it is unclear if the choice of muscles included in the analysis impacts estimated synergies. The aim of our study was to evaluate the impact of the number and choice of muscles on synergy analyses. We used a musculoskeletal model to calculate muscle activations required to perform an isometric upper-extremity task. Synergies calculated from the activations from the musculoskeletal model were similar to a prior experimental study. To evaluate the impact of the number of muscles included in the analysis, we randomly selected subsets of between 5 and 29 muscles and compared the similarity of the synergies calculated from each subset to a master set of synergies calculated from all muscles. We determined that the structure of synergies is dependent upon the number and choice of muscles included in the analysis. When five muscles were included in the analysis, the similarity of the synergies to the master set was only 0.57 ± 0.54; however, the similarity improved to over 0.8 with more than ten muscles. We identified two methods, selecting dominant muscles from the master set or selecting muscles with the largest maximum isometric force, which significantly improved similarity to the master set and can help guide future experimental design. Analyses that included a small subset of muscles also over-estimated the variance accounted for (VAF) by the synergies compared to an analysis with all muscles. Thus, researchers should use caution using VAF to evaluate synergies when EMG is measured from a small subset of muscles. PDF

KM Steele, MC Tresch, EJ Perreault, “Using musculoskeletal modeling and simulation to investigate the accuracy and reliability of muscle synergies.” Neural Control of Movement (San Juan, Puerto Rico) April 17-20, 2013.

Keshia Abstract, Publications , ,
KM Steele, MC Tresch, EJ Perreault, “Using musculoskeletal modeling and simulation to investigate the accuracy and reliability of muscle synergies.” Neural Control of Movement (San Juan, Puerto Rico) April 17-20, 2013.

Kat Steele presents at Neural Control of Movement

Using musculoskeletal modeling and simulation to investigate the accuracy and reliability of muscle synergies

San Juan, Puerto Rico (April 17-20, 2013)

SR Hamner, A Seth, KM Steele, SL Delp, (2013) “A rolling constraint reduces ground reaction forces and moments in dynamic simulations of walking, running, and crouch gait.” Journal of Biomechanics

Dr. Steele JournalArticle, Orthoses
SR Hamner, A Seth, KM Steele, SL Delp, (2013) “A rolling constraint reduces ground reaction forces and moments in dynamic simulations of walking, running, and crouch gait.” Journal of Biomechanics

Journal article accepted in Journal of Biomechanics

A rolling constraint reduces ground reaction forces and moments in dynamic simulations of walking, running, and crouch gait

Recent advances in computational technology have dramatically increased the use of muscle-driven simulation to study accelerations produced by muscles during gait. Accelerations computed from muscle-driven simulations are sensitive to the model used to represent contact between the foot and ground. A foot-ground contact model must be able to calculate ground reaction forces and moments that are consistent with experimentally measured ground reaction forces and moments. We show here that a rolling constraint can model foot-ground contact and reproduce measured ground reaction forces and moments in an induced acceleration analysis of muscle-driven simulations of walking, running, and crouch gait. We also illustrate that a point constraint and a weld constraint used to model foot-ground contact in previous studies produce inaccurate reaction moments and lead to contradictory interpretations of muscle function. To enable others to use and test these different constraint types (i.e., rolling, point, and weld constraints) we have included them as part of an induced acceleration analysis in OpenSim, a freely-available biomechanics simulation package. PDF

KM Steele, A Seth, JL Hicks, MH Schwartz, SL Delp, (2013) “Muscle contributions to vertical and fore-aft accelerations are altered in subjects with crouch gait.” Gait & Posture

Dr. Steele JournalArticle, MotorControl ,
Musculoskeletal simulation used to evaluate crouch gait dynamics.

Journal article accepted in Gait & Posture:

Muscle contributions to vertical and fore-aft accelerations are altered in subjects with crouch gait.

The goals of this study were to determine if the muscle contributions to vertical and fore-aft acceleration of the mass center differ between crouch gait and unimpaired gait and if these muscle contributions change with crouch severity. Examining muscle contributions to mass center acceleration provides insight into the roles of individual muscles during gait and can provide guidance for treatment planning. We calculated vertical and fore-aft accelerations using musculoskeletal simulations of typically developing children and children with cerebral palsy and crouch gait. Analysis of these simulations revealed that during unimpaired gait the quadriceps produce large upward and backward accelerations during early stance, whereas the ankle plantarflexors produce large upward and forward accelerations later in stance. In contrast, during crouch gait, the quadriceps and ankle plantarflexors produce large, opposing fore-aft accelerations throughout stance. The quadriceps force required to accelerate the mass center upward was significantly larger in crouch gait than in unimpaired gait and increased with crouch severity. The gluteus medius accelerated the mass center upward during midstance in unimpaired gait; however, during crouch gait the upward acceleration produced by the gluteus medius was significantly reduced. During unimpaired gait the quadriceps and ankle plantarflexors accelerate the mass center at different times, efficiently modulating fore-aft accelerations. However, during crouch gait, the quadriceps and ankle plantarflexors produce fore-aft accelerations at the same time and the opposing fore-aft accelerations generated by these muscles contribute to the inefficiency of crouch gait. PDF