Muscle synergy constraints do not improve estimates of muscle activity from static optimization during gait for unimpaired children or children with cerebral palsy

Benjamin R. Shuman, Marije Goudriaan, Kaat Desloovere, Michael H. Schwartz, Katherine M. Steele*

*Corresponding author for this work

Research output: Contribution to JournalArticleAcademicpeer-review

Abstract

Neuromusculoskeletal simulation provides a promising platform to inform the design of assistive devices or inform rehabilitation. For these applications, a simulation must be able to accurately represent the person of interest, such as an individual with a neurologic injury. If a simulation fails to predict how an individual recruits and coordinates their muscles during movement, it will have limited utility for informing design or rehabilitation. While inverse dynamic simulations have previously been used to evaluate anticipated responses from interventions, like orthopedic surgery or orthoses, they frequently struggle to accurately estimate muscle activations, even for tasks like walking. The simulated muscle activity often fails to represent experimentally measured muscle activity from electromyographic (EMG) recordings. Research has theorized that the nervous system may simplify the range of possible activations used during dynamic tasks, by constraining activations to weighted groups of muscles, referred to as muscle synergies. Synergies are altered after neurological injury, such as stroke or cerebral palsy (CP), and may provide a method for improving subject-specific models of neuromuscular control. The aim of this study was to test whether constraining simulation to synergies could improve estimated muscle activations compared to EMG data. We evaluated modeled muscle activations during gait for six typically developing (TD) children and six children with CP. Muscle activations were estimated with: (1) static optimization (SO), minimizing muscle activations squared, and (2) synergy SO (SynSO), minimizing synergy activations squared using the weights identified from EMG data for two to five synergies. While SynSO caused changes in estimated activations compared to SO, the correlation to EMG data was not higher in SynSO than SO for either TD or CP groups. The correlations to EMG were higher in CP than TD for both SO (CP: 0.48, TD: 0.36) and SynSO (CP: 0.46, TD: 0.26 for five synergies). Constraining activations to SynSO caused the simulated muscle stress to increase compared to SO for all individuals, causing a 157% increase with two synergies. These results suggest that constraining simulated activations in inverse dynamic simulations to subject-specific synergies alone may not improve estimation of muscle activations during gait for generic musculoskeletal models.

Original languageEnglish
Article number102
Pages (from-to)1-11
Number of pages11
JournalFrontiers in Neurorobotics
Volume13
DOIs
Publication statusPublished - 17 Dec 2019

Funding

Research reported in this publication was supported by the National Institute of Neurological Disorders and Stroke (NINDS) of the National Institutes of Health under Award Number R01NS091056, the Dutch Organization for Scientific Research (NWO) VIDI (Grant No. 016.156.346 FirSTeps), by the Flemish Research Foundation FWO (Grant No. T-GIAT T003116N), and by internal KU Leuven funding (Grant No. OT/12/100).

FundersFunder number
Dutch Organization for Scientific Research
Flemish Research Foundation FWOT-GIAT T003116N
National Institutes of HealthR01NS091056
National Institute of Neurological Disorders and Stroke
Fonds Wetenschappelijk Onderzoek
Nederlandse Organisatie voor Wetenschappelijk Onderzoek016.156.346 FirSTeps
KU LeuvenOT/12/100

    Keywords

    • Cerebral palsy
    • Electromyography
    • Muscle synergies
    • Musculoskeletal modeling
    • Static optimization

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