Engineering to enhance human mobility, play, and exploration
Congratulations to Gaurav Mukherjee for passing his qualifying exam!
At the University of Washington the qualifying exam is a combination of written and oral exams that test your knowledge in mechanical engineering. After passing, Gaurav is now officially a PhD Candidate in Mechanical Engineering.
Sasha Portnova – Northwest Biomechanics Symposium Best Poster Award!
Sasha Portnova, a junior in mechanical engineering who has been doing research in our lab for the past year was awarded the Best Poster Award – BS/MS Category at the 2015 Northwest Biomechanics Symposium. Her research focuses on using 3D-printing to improve the design of upper-extremity orthoses for individuals with spinal cord injury and other neurologic disorders.
Mike Schwartz presents at Gait & Clinical Movement Analysis Society Annual Conference:
Dynamic motor control predicts treatment outcome for individuals with cerebral palsy
Portland, OR (March 18-21, 2015)
Journal article in Journal of Neurophysiology:
Consequences of biomechanically constrained tasks in the design and interpretation of synergy analyses
Matrix factorization algorithms are commonly used to analyze muscle activity and provide insight into neuromuscular control. These algorithms identify low-dimensional subspaces, commonly referred to as synergies, which can describe variation in muscle activity during a task. Synergies are often interpreted as reflecting underlying neural control; however, it is unclear how these analyses are influenced by biomechanical and task constraints, which can also lead to low-dimensional patterns of muscle activation. The aim of this study was to evaluate whether commonly used algorithms and experimental methods can accurately identify synergy-based control strategies. This was accomplished by evaluating synergies from five common matrix factorization algorithms using muscle activations calculated from 1) a biomechanically constrained task using a musculoskeletal model and 2) without task constraints using random synergy activations. Algorithm performance was assessed by calculating the similarity between estimated synergies and those imposed during the simulations; similarities ranged from 0 (random chance) to 1 (perfect similarity). Although some of the algorithms could accurately estimate specified synergies without biomechanical or task constraints (similarity >0.7), with these constraints the similarity of estimated synergies decreased significantly (0.3-0.4). The ability of these algorithms to accurately identify synergies was negatively impacted by correlation of synergy activations, which are increased when substantial biomechanical or task constraints are present. Increased variability in synergy activations, which can be captured using robust experimental paradigms that include natural variability in motor activation patterns, improved identification accuracy but did not completely overcome effects of biomechanical and task constraints. These results demonstrate that a biomechanically constrained task can reduce the accuracy of estimated synergies and highlight the importance of using experimental protocols with physiological variability to improve synergy analyses. PDF
Journal article accepted in Disability and Rehabilitation:
Using musculoskeletal modeling to evaluate the effect of ankle foot orthosis tuning on musculotendon dynamics: a case study.
This case study examines the influence of an ankle foot orthosis footwear combination (AFO-FC) on musculotendon lengths and gait kinematics and kinetics after right thrombotic stroke resulting in left hemiplegia. Methods: Gait analysis was performed over three visits where the subject walked with an AFO-FC with two shank-to-vertical angle (SVA) alignments, a posterior leaf spring AFO (PLS AFO), and shoes alone. Biomechanical and musculoskeletal modeling was used to evaluate musculotendon lengths, kinematics, and kinetics for each condition. Results: The AFO-FC improved walking speed and non-paretic kinematics compared to the PLS AFO and shoes alone. The operating length of the paretic gastrocnemius decreased with the AFO-FC improving knee kinematics in swing, but not stance. As the SVA of the AFO-FC was reduced from 15° to 12°, internal ankle plantar flexor moment increased. Conclusions: Musculoskeletal modeling demonstrated that the AFO-FC altered gastrocnemius operating length during post-stroke hemiplegic gait. Using these tools to evaluate muscle operating lengths can provide insight into underlying mechanisms that may improve gait and guide future AFO-FC design. PDF