ECR Spotlight is a series of interviews with early-career authors from a selection of papers published in Journal of Experimental Biology and aims to promote not only the diversity of early-career researchers (ECRs) working in experimental biology during our centenary year but also the huge variety of animals and physiological systems that are essential for the ‘comparative’ approach. Jennifer Leestma is an author on ‘ Linking whole-body angular momentum and step placement during perturbed walking’, published in JEB. Jennifer is a PhD candidate in the lab of Gregory Sawicki and Aaron Young at Georgia Institute of Technology, USA, investigating how humans navigate complex and dynamic environments and how wearable robots can augment locomotion in these contexts.

Jennifer Leestma

Describe your scientific journey and your current research focus

During undergrad, I was eager to learn about rehabilitation engineering and biomechanics. While I was pursuing my BSc in Biomedical Engineering at the University of Wisconsin-Madison, I had phenomenal opportunities to explore these interests through on-campus research and internships. After my first summer of research, I was hooked and knew that this was the path that I wanted to follow.

After a few years focused on prosthetic research in undergrad, I moved to Georgia Tech to pursue my PhD in Robotics and to work with Dr Gregory Sawicki and Dr Aaron Young on lower limb robotic exoskeletons.

My doctoral work focuses on the biomechanics and augmentation of locomotion balance. This has been a very challenging and rewarding research area, as the projects have components that focus on biomechanics, mechanical and mechatronic design, controls and machine learning. I'm fascinated by wearable robotics because, in comparison to conventional robotics, the human that is working in parallel with the device is a challenging problem. For wearable robots to be truly effective, we need a thorough understanding of human mechanics, sensing and decision making, which can all change with the addition of a wearable robot. Both the robot and human make understanding the other more challenging, but also present a unique opportunity to learn more than we may otherwise learn without both components in the loop.

How would you explain the main finding of your paper to a member of the public?

We investigated human balance and recovery strategies during walking in response to perturbations, which are events that disrupt your balance. Examples of real-world perturbations are when you unexpectedly step off a curb or walk down the aisle of a moving bus. We investigated how things like the size of the perturbation, the direction that you fall in, and the start time of the perturbation affect your balance and ability to recover. We were able to narrow in on some perturbation characteristics that are particularly challenging for people to recover from. We also found that humans are fairly precise in determining where they place their feet following a perturbation, but certain perturbation start times may limit the effectiveness of their step, likely because humans are limited in how quickly they can respond and move their limbs.

Which part of this research project was the most rewarding/challenging?

The shear amount of data that we collected was very challenging. We were determined to test many conditions so that we could investigate a diverse set of perturbation conditions that can disrupt walking balance. But with so many conditions came long data collections, months of processing and cleaning the data, and a need for a detailed eye to be sure that we caught any errors across the 600+ minutes of recorded data. With so much data also came challenges in visualizing several independent and dependent variables and narrowing in on what we thought was the clearest way to convey our findings. Completing this data collection has been very rewarding, not just by enabling us to investigate questions that we were interested in but also because we are releasing this as an open-source dataset with our JEB paper. We are hoping that this leads to others being able to build off our work and dive into different research questions that we did not investigate. The ultimate reward in the long run is that this work and our future studies can positively impact the lives of individuals with balance impairments.

The experimental setup to collect perturbed walking data. We developed a closed-loop controller (shown partially on screen) that precisely times and applies perturbations by rapidly translating the platform that the participant is walking on.

The experimental setup to collect perturbed walking data. We developed a closed-loop controller (shown partially on screen) that precisely times and applies perturbations by rapidly translating the platform that the participant is walking on.

Why did you choose JEB to publish your paper?

When I began my PhD and was first jumping into the world of biomechanical stability, several JEB papers were very influential in my learning and in informing the direction that we decided to take for my doctoral project. Because JEB was already disseminating similar work, we knew that the scientific audience for the journal would be a great community to share our findings with. On top of that, I think that there is a lot of useful knowledge exchange, especially on the topic of stability, between the human and non-human/animal biomechanics communities. So, publishing in a journal that disseminates knowledge to both of those audiences is something that we're really excited about.

Are there any important historical papers from your field that have been published in JEB? If so, which paper, and how did it pave the way for later research?

Though it is only 16 years old, ‘Angular momentum in human walking’ by Herr and Popovic (2008; doi:10.1242/jeb.008573) was a very influential paper that introduced one of the most frequently used measurements to quantify human biomechanical stability. After investigating different ways to evaluate balance in our work, we opted to use angular momentum because of its ability to continuously capture whole-body dynamics, so this paper is one that we reference often.

If you had unlimited funding, what question in your research field would you most like to address?

The question that keeps me up at night is how humans decide how to move, especially when they're put in challenging or dynamic environments. During steady-state movement, the way we move tends to minimize energy cost, but that's likely not the case when environments and task demands become more complex. I would love to investigate how individuals are weighing energy cost, stability, comfort and other factors, how different mobility conditions and impairments affect those weights, and how this may influence what we should do with assistive wearable robots.

What's next for you?

During the remainder of my PhD, I'm investigating how we can integrate intelligent wearable robots with humans to augment their balance during locomotion. After I wrap up my doctoral work, I'm hoping to move on to a postdoctoral position where I can jump to a new research area that allows me to explore human movement and augmentation from a new lens. Long term, I'm very interested in an academic career and establishing a research lab that takes a multidisciplinary approach to truly integrate wearable robots with human movement.

Jennifer Leestma's contact details: Georgia Institute of Technology, 813 Ferst Drive NW, Atlanta, GA 30332, USA. E-mail:

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Linking whole-body angular momentum and step placement during perturbed human walking
J. Exp. Biol.