Journal Article in The Royal Society:
This work highlights the potential of data-driven models grounded in dynamical systems theory to predict complex individualized responses to ankle exoskeletons., without requiring explicit knowledge of the individual’s physiology or motor control
Aim: Evaluate the ability of three classes of subject-specific phase-varying (PV) models to predict kinematic and myoelectric responses to ankle exoskeletons during walking, without requiring prior knowledge of specific user characteristics.
Method: Data from 12 unimpaired adults walking with bilateral passive ankle exoskeletons were captured. PV, linear PV (LPV), and nonlinear PV (NPV) models leveraged Floquet theory to kinematics and muscle activity in response to three exoskeleton torque conditions.
Results: The LPV model’s predictions were more accurate than the PV model when predicting less than 12.5% of a stride in the future and explained 49–70% of the variance in hip, knee and ankle kinematic responses to torque. The LPV model also predicted kinematic responses with similar accuracy to the more-complex NPV model. Myoelectric responses were challenging to predict with all models, explaining at most 10% of the variance in responses.
Interpretation: This work highlights the potential of data-driven PV models to predict complex subject-specific responses to ankle exoskeletons and inform device design and control.
Congratulations to Nicole Zaino for being awarded the ESMAC (European Society of Movement Analysis for Adults and Children) Best Paper Award. Nicole received this award at the 2019 ESMAC conference in Amsterdam, September 23-28, 2019 where she gave her talk: “Spasticity reduction in children with cerebral palsy is not associated with reduced energy during walking.” For more information, visit ESMAC.
Congratulations to Nicole Zaino and our colleague Mike Schwartz at Gillette Children’s Specialty Healthcare for both being nominated as finalists for the Best Presentation Award at the upcoming ESMAC Conference in Amsterdam. Their abstracts are among the top 16 submissions to the conference and the final award will be determined based upon their presentations.
Nicole will be presenting her research:
Spasticity reduction in children with cerebral palsy is not associated with reduced energy during walking
Selective dorsal rhizotomy reduces spasticity, but does it also reduce energy consumption during walking? In an analysis of over 300 children with cerebral palsy, Nicole demonstrated that although rhiztomy does reduce spasticity, it does not reduce energy consumption. These results provide further evidence that spasticity is not a main contributor to elevated energy among people with cerebral palsy. You can also learn more about this study from our recent submitted manuscript, available on bioRxiv.
Mike will be presenting his research:
The effects of walking speed and age on energy consumption in children with cerebral palsy and their typically developing peers
We know that walking energy is high among people with cerebral palsy, and that energy varies with speed and age. Using retrospective data of over 300 kids with cerebral palsy and 150 typically-developing peers, Mike used a statistical model to evaluate these speed and age effects. He found that energy decreases until 8-10 years of age for kids with CP, while it remains stable beyond age 5 for typically-developing peers. Kids with CP also have a greater elevation in energy with greater walking speeds. These results are important to help quantify and understand impacts of interventions, like surgery or assistive devices, which are often done during this time period when kids are still growing and developing.
They will both be presenting in the Optimizing Energy Cost session from 11:40-12:30 on Thursday, September 26th.
Best of luck to Nicole & Mike!
Journal Article in Gait & Posture:
Repeatability of EMG is similar between typically developing children and children with cerebral palsy.
Background: Clinical gait analysis is commonly used in the evaluation and treatment of children with cerebral palsy (CP). While the repeatability of kinematic and kinetic measures of gait has previously been evaluated, the repeatability of electromyography (EMG) recordings or measures calculated from EMG data, such as muscle synergies, remains unclear for this population.
Research Question: Are EMG recordings and muscle synergies from clinical gait analysis repeatable between visits for children with CP?
Methods: We recruited 20 children with bilateral CP who had been referred for clinical gait analysis. The children completed two visits less than six weeks apart with EMG data collected bilaterally from five muscles (rectus femoris, medial hamstrings, vastus lateralis, anterior tibialis, and medial gastrocnemius). Variance ratio and cosine similarity were used to evaluate repeatability of EMG waveforms between visits. Nonnegative matrix factorization was used to calculate synergies from EMG data at each visit to compare synergy weights and activations.
Results & significance: The inter-visit variance ratios of EMG data for children with CP were similar to previously reported results for typically-developing children and unimpaired adults (range: 0.39 for vastus lateralis to 0.66 for rectus femoris). The average cosine similarity of the EMG waveforms between visits was greater than 0.9 for all muscles, while synergy weights and activations also had high similarity – greater than 0.8 and 0.9 between visits, respectively. These results demonstrate that EMG repeatability between visits during clinical gait analysis for children with CP is similar to unimpaired individuals. These results provide a baseline for evaluating whether observed changes in EMG recordings between visits reflect real changes in muscle activity or are within the range of inter-visit variability.