YC Pan, B Goodwin, E Sabelhaus, KM Peters, KF Bjornson, KLD Pham, WO Walker, KM Steele (2020) “Feasibility of using acceleration-derived jerk to quantify bimanual arm use” Journal of NeuroEngineering and Rehabilitation

Journal Article in Journal of NeuroEngineering & Rehabilitation

Two plots illustrating jerk ratio results. The plot on the left shows the probability distribution from one child with cerebral palsy before, during, and after constraint induced movement therapy. Before therapy, the probability distribution is shifted to the left of the center line, indicating that the individual relies much more on their non-paretic hand during daily life. During therapy, when their non-paretic hand is in a cast, the curve shifts to the right of the center line. This indicates they are using their paretic hand much more - which makes sense, since the other hand is in a cast. Unfortunately, after the cast is removed at the end of therapy, the curve is nearly identical to the curve before treatment, suggesting that after this intensive therapy the child did not use their paretic hand more during daily life. The figure on the right shows the summary metric from this plot, called jerk ratio 50 - which is just the 50% value of the probability density function - for all 5 children with cerebral palsy before, during, and after therapy. All the children have JR50 greater than 0.5 before therapy, which means they use their non-paretic hand more during daily life. During therapy, these values drop to 0.2 - 0.5, indicating that they use their paretic hand much more during CIMT. However, after therapy the JR50 values for all five participants return to close to their baseline value before therapy.
(Left) Example of jerk ratio distribution for one child with cerebral palsy before, during, and after constraint induced movement therapy. (Right) Summary metric of jerk ratio (jerk ratio-50) for all five children with cerebral palsy.


Accelerometers have become common for evaluating the efficacy of rehabilitation for patients with neurologic disorders. For example, metrics like use ratio (UR) and magnitude ratio (MR) have been shown to differentiate movement patterns of children with cerebral palsy (CP) compared to typically-developing (TD) peers. However, these metrics are calculated from “activity counts” – a measure based on proprietary algorithms that approximate movement duration and intensity from raw accelerometer data. Algorithms used to calculate activity counts vary between devices, limiting comparisons of clinical and research results. The goal of this research was to develop complementary metrics based on raw accelerometer data to analyze arm movement after neurologic injury.


We calculated jerk, the derivative of acceleration, to evaluate arm movement from accelerometer data. To complement current measures, we calculated jerk ratio (JR) as the relative jerk magnitude of the dominant (non-paretic) and non-dominant (paretic) arms.  We evaluated the JR distribution between arms and calculated the 50th percentile of the JR distribution (JR50). To evaluate these metrics, we analyzed bimanual accelerometry data for five children with hemiplegic CP who underwent Constraint-Induced Movement Therapy (CIMT) and five typically developing (TD) children. We compared JR between the CP and TD cohorts, and to activity count metrics.


The JR50 differentiated between the CP and TD cohorts (CP = 0.578±0.041 before CIMT, TD = 0.506±0.026), demonstrating increased reliance on the non-dominant arm for the CP cohort. Jerk metrics also quantified changes in arm use during and after therapy (e.g., JR50 = 0.378±0.125 during CIMT, 0.591 ± 0.057 after CIMT). The JR was strongly correlated with UR and MR (r = -0.92, 0.89) for the CP cohort. For the TD cohort, JR50 was repeatable across three data collection periods with an average similarity of 0.945±0.015.


Acceleration-derived jerk captured differences in motion between TD and CP cohorts and correlated with activity count metrics. The code for calculating and plotting JR is open-source and available for others to use and build upon. By identifying device-independent metrics that can quantify arm movement in daily life, we hope to facilitate collaboration for rehabilitation research using wearable technologies.


The algorithm for calculating jerk ratio, as well as user-friendly code to produce plots similar to the figure above are provided open-source as Python 3.6 code as a Python Jupyter Notebook within Google Colab. With this resource, research groups can use existing or newly created data from accelerometers to analyze jerk ratio as a complementary metric to existing measures, enabling comparison between research studies or centers that may rely on different sensors and activity count algorithms.

NBC Learn: Exoskeletons and Engineering

NBC Learn logo for the Discovering YOU series - engineer your world. Supported by NSF, Chevron, and ASEE.

We partnered with NBC Learn to share some of our work on exoskeletons to help encourage students to consider a career in engineering. What can be more exciting than musculoskeletal modeling, exoskeletons, horses, and stuffed animals?

Check out the video – a lesson plan will also be posted soon for classrooms to use.

Go team!

ESMAC 2019: Award Finalists

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.

Logo for the 2019 ESMAC meeting overlaid on a classic Amsterdam scene, bikes lined up on a bridge over a canal with historic buildings in the background.

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!

US Patent Office Visit

Patent examiners spend their days critically evaluating the latest innovations, to determine if they are useful, novel, and non-obvious. When one of our students asked them what daily life is like as a patent examiner they responded, we basically write a 10-15 page report every 2-3 days.

Thankfully the patent office lets them escape from behind their computers a few times a year to meet with companies, research labs, and other entities. These visits help them see what is new and exciting in their specialty area.

We were lucky enough to host one of these teams this past week in the AMP Lab. Tim Stanis, a primary examiner from Art Unit 3786 that specializes in exoskeletons, orthoses, passive motion rehabilitation devices, and biomechanical technology led the visit. He was joined by nine other examiners.

One of the patent examiners in a red checkered shirt answers students questions. He is seated at a table with hands clasped in front of him.

Our lab demoed our latest creations in orthoses, biofeedback systems, and smartphone sensing. Patrick Aubin from the VA Hospital, Murray Maitland from Rehab Medicine, Chet Moritz from Electrical Engineering, and Tapo Bhattacharjee also shared their latest work.

We ended the session with a Q&A Panel for summer students to learn about career opportunities as a patent examiner and advice for new innovators. Most of the examiners had an undergraduate or master’s degree in engineering. They emphasized that working for the patent office is a great, flexible career path. As a patent examiner they are able to work remotely, have flexible hours, and enjoy other benefits such as having law school paid for.

Students listen attentively to the Q&A Panel. Some look bored, some look amused, and one is even taking notes, or maybe doodling!

For new innovators, they emphasized the importance of understanding the patent landscape. They recommended using Google Patents! Patents can seem intimidating. They recommended starting with the pictures and focusing on the claims. They also emphasized the importance of having a team. Translating technology requires team members with technical, business, and clinical backgrounds.

For our part, we were excited to meet real, live patent examiners. We appreciated seeing their faces and enjoyed sharing our work with them.

RehabWeek 2019 Recap

Modern meets colonial architecture at the huge Toronto Art Museum. An old colonial building sits in front of the modern, glass-fronted art museum.

Five members of our lab – Brandon, Christina, Nick, Michael, & Kat – attended RehabWeek 2019 in Toronto, Canada. This is a unique mega-conference where multiple conferences (ICORR, ACRM, ISPO, RESNA, etc) are hosted at the same time in the same location. Everyone attended common keynotes, poster sessions, and meals. In the morning and afternoon, each conference had their own scientific sessions.

While it was a bit overwhelming to figure out which sessions to attend, it was a great way to get a more diverse audience to provide feedback on your work. For future conferences, I would recommend that students just pick one conference (e.g., ICORR or RESNA) to attend and not bounce between sessions. This lets you more fully engage with a community, have long discussions, and identify common threads across presentations.

Our work at the conference included:

  • Michael Rosenberg: ISPO presented on how muscle coordination differs when you start to walk compared to steady-state walking. Synergies differ during the first step, but quickly converge to steady-state patterns and there was minimal effect of different AFO stiffnesses.
  • Christina Papazian: INERS poster demonstrating correlations between FIM scores and muscle activity in acute stroke care.
  • Brandon Nguyen: ISPO poster on the accuracy and repeatability of using a smartphone to monitor gait for AFO tuning – ISPO Best Student Poster Award
  • Nick Baicoianu: Developer’s Showcase for HuskySTEPS
  • Kat Steele: ISPO poster on synergy-based control of predictive simulations of walking.
Nick demonstrates HuskySTEPS at the Developer's Showcase.

I also served on the IEEE Women in Engineering panel at lunch on Thursday, which focused on new frontiers in technology that could increase accessibility and inclusion. A lot of the discussion focused on the potential of machine learning, wearable technology, and autonomous vehicles.

Flyer from the IEEE Women in Engineering panel with the moderator and four speaker pictures.

You can view our notes and take-aways from the conference in these slides.

We also got to visit with Naser Mehrabi, a former post-doc in the lab, who now works for General Motors. We took the train just north of downtown to visit with him, his wife, and their 9-week-old son. Not only did we get to enjoy some delicious Iranian food, but we also got to get lots of simulation questions answered.

The crew visits with Naser and his wife at their new home in Toronto.

The next RehabWeek will be 2021 in Rotterdam, Netherlands.