JournalArticle

KM Steele and S Lee (2014) “Using dynamic musculoskeletal simulation to evaluate altered muscle properties in cerebral palsy.” Proceedings of ASME Dynamics Systems and Control

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KM Steele and S Lee (2014) “Using dynamic musculoskeletal simulation to evaluate altered muscle properties in cerebral palsy.” Proceedings of ASME Dynamics Systems and Control

Paper accepted at ASME Dynamics Systems and Control Conference:

Using dynamic musculoskeletal simulation to evaluate altered muscle properties in cerebral palsy

Abstract: Cerebral palsy is caused by an injury to the brain, but also causes many secondary changes in the musculoskeletal system. Altered muscle properties such as contracture, an increased passive resistance to stretch, are common but vary widely between individuals and between muscles. Quantifying these changes is important to understand pathologic movement and create patient-specific treatment plans. Musculoskeletal modeling and simulation have increasingly been used to evaluate pathologic movement in CP; however, these models are based upon muscle properties of unimpaired individuals. In this study, we used a dynamic musculoskeletal simulation of a simple motion, passively moving the ankle, to determine (1) if a model based upon unimpaired muscle properties can accurately represent individuals with cerebral palsy, and (2) if an optimization can be used to adjust passive muscle properties and characterize magnitude of contracture in individual muscles. We created musculoskeletal simulations of ankle motion for nine children with cerebral palsy. Results indicate that the unimpaired musculoskeletal model cannot accurately characterize passive ankle motion for most subjects, but adjusting tendon slack lengths can reduce error and help identify the magnitude of contracture for different muscles.

R Klemetti, KM Steele, P Moilanen, J Avela, J Timonen, (2014) “Contributions of individual muscles to the sagittal- and frontal-plane angular accelerations of the trunk in walking.” Journal of Biomechanics

Dr. Steele JournalArticle, MotorControl
R Klemetti, KM Steele, P Moilanen, J Avela, J Timonen, (2014) “Contributions of individual muscles to the sagittal- and frontal-plane angular accelerations of the trunk in walking.” Journal of Biomechanics

Journal article accepted in Journal of Biomechanics:

Contributions of individual muscles to the sagittal- and frontal-plane angular accelerations of the trunk in walking.

This study was conducted to analyze the unimpaired control of the trunk during walking. Studying the unimpaired control of the trunk reveals characteristics of good control. These characteristics can be pursued in the rehabilitation of impaired control. Impaired control of the trunk during walking is associated with aging and many movement disorders. This is a concern as it is considered to increase fall risk. Muscles that contribute to the trunk control in normal walking may also contribute to it under perturbation circumstances, attempting to prevent an impending fall. Knowledge of such muscles can be used to rehabilitate impaired control of the trunk. Here, angular accelerations of the trunk induced by individual muscles, in the sagittal and frontal planes, were calculated using 3D muscle-driven simulations of seven young healthy subjects walking at free speed. Analysis of the simulations demonstrated that the abdominal and back muscles displayed large contributions throughout the gait cycle both in the sagittal and frontal planes. Proximal lower-limb muscles contributed more than distal muscles in the sagittal plane, while both proximal and distal muscles showed large contributions in the frontal plane. Along with the stance-limb muscles, the swing-limb muscles also exhibited considerable contribution. The gluteus medius was found to be an important individual frontal-plane control muscle; enhancing its function in pathologies could ameliorate gait by attenuating trunk sway. In addition, since gravity appreciably accelerated the trunk in the frontal plane, it may engender excessive trunk sway in pathologies. PDF

KM Steele, S Brunhaver, SD Sheppard (2014) “Feedback from in-class worksheets and discussion improves performance on the Statics Concept Inventory.” International Journal of Engineering Education

Dr. Steele JournalArticle
KM Steele, S Brunhaver, SD Sheppard (2014) “Feedback from in-class worksheets and discussion improves performance on the Statics Concept Inventory.” International Journal of Engineering Education

Journal article accepted in International Journal of Engineering Education:

Feedback from in-class worksheets and discussion improves performance on the Statics Concept Inventory.

The Statics Concept Inventory (SCI) is used to evaluate students’ conceptual understanding in introductory mechanics courses. Previous studies have shown that although performance on the SCI improves at the end of a course, performance is often still unsatisfactory with scores well below 100%. In this study, we sought to determine if providing feedback on conceptual topics through in-class worksheets and discussion would improve students’ performance on the SCI. To test this hypothesis, we designed eight multiple-choice worksheets, each inspired by a different topic on the SCI, for use during an introductory mechanics course. In order to evaluate the impact of the worksheets on SCI performance, we divided the eight worksheets into two groups and each group of worksheets was deployed in a different offering of the course. Each worksheet was completed at the end of a class period and, at the beginning of the next class period, the instructor led a discussion of the results and common misconceptions on each worksheet. Students took the SCI at the beginning and end of the course and the change in SCI scores for topics with and without worksheets were compared. Results from both course offerings indicated that the in-class worksheets were effective at improving performance on the SCI, as SCI scores improved significantly more for topics that had worksheets than the topics that did not have worksheets. Furthermore, overall SCI performance at the end of each course was greater than in previous courses. These results suggest that a quick and easy-to-implement addition to the curriculum using in-class worksheets and next-class discussion were effective at providing feedback on conceptual topics, exposing misconceptions, and improving performance on the SCI. The worksheets developed as part of this study are available on-line for other instructors to use (http://del.stanford.edu). The SCI is also free to use and can be found at cihub.org. PDF

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

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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

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