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. Kristen Jakubowski is an author on ‘ Non-linear properties of the Achilles tendon determine ankle impedance over a broad range of activations in humans’, published in JEB. Kristen conducted the research described in this article while a PhD candidate in Eric J. Perreault and Sabrina S. M. Lee's lab at Northwestern University, USA. She is now a Postdoctoral Fellow in the lab of Lena H. Ting and Gregory S. Sawicki at Emory University and Georgia Institute of Technology, USA, investigating an individual's neuromuscular control and their interactions with robotic devices and evaluating how devices can be designed and controlled to restore and augment human mobility.
Kristen Jakubowski
Describe your scientific journey and your current research focus
My interest in understanding human movement biomechanics stems from my lifelong involvement in sports and as a collegiate athlete. This led me to pursue undergraduate and master's degrees in biomedical engineering with a concentration on biomechanics. Following an injury that ended my collegiate athletic career, I changed my research focus from sports-performance research to seeking to improve the quality of life for people with mobility impairments. This shift in research interests first led me to Northwestern University's Department of Biomedical Engineering and Department of Physical Therapy and Human Movement Sciences (PTHMS), where I completed a PhD in Biomedical Engineering, focusing on Rehabilitation Engineering, with Drs Eric Perreault and Sabrina Lee. My doctoral work focused on understanding the muscle and tendon contributions to ankle mechanics, and how those contributions are impacted by healthy aging. Currently, under the mentorship of Drs Lena Ting and Gregory Sawicki at Georgia Tech and Emory University, I am developing an exoskeleton that can augment human balance and prevent falls. Ultimately, by combining my background with my current work, I aim to create a framework to restore, maintain and augment human mobility using wearable robotic devices that work symbiotically with the underlying human physiological system.
How would you explain the main finding of your paper to a member of the public?
Humans are remarkably adept at moving through their environment, whether it is standing on a moving bus, stepping off a curb, or maintaining balance when bumped. The ability to seamlessly perform these actions is achieved, in part, by appropriately regulating joint stiffness; specifically, ankle stiffness. The stiffness of the ankle is largely dictated by the stiffness of the calf muscle and the Achilles tendon, yet their relative contributions are largely unknown. This study sought to determine how the calf muscle and tendon contribute to ankle stiffness during conditions relevant to standing balance. It is commonly assumed that changes in ankle stiffness are directly linked to changes in muscle stiffness. However, our results demonstrate that, instead, the tendon is the dominant contributor to ankle stiffness at nearly all loads. The ability to leverage the mechanical properties of the tendon, a passive structure, to regulate ankle stiffness may simplify the control by the nervous system compared with the alternative strategy of having to regulate the complex mechanical properties of muscle.
What are the potential implications of this finding for your field of research, and is there anything that you learned during this study that you wish you had known sooner?
This work provides fundamental insight into how ankle mechanics are regulated to enable our seamless interactions with the physical world. This work can also aid in developing targeted rehabilitation when the muscle and tendon mechanical properties are altered as a result of aging, injury or disease. For example, we can now quantify how changes in tendon stiffness that occur because of aging or injury impact the stiffness of the ankle. This information can then be used to track the efficacy of rehabilitation targeted at increasing tendon stiffness.
The experimental setup to determine how the triceps surae and Achilles tendon contribute to the mechanics of the joint. We used our novel measurement technique that combines joint level perturbations with ultrasound imaging to quantify the mechanical properties of the ankle, triceps surae and Achilles tendon stiffness simultaneously.
The experimental setup to determine how the triceps surae and Achilles tendon contribute to the mechanics of the joint. We used our novel measurement technique that combines joint level perturbations with ultrasound imaging to quantify the mechanical properties of the ankle, triceps surae and Achilles tendon stiffness simultaneously.
Why did you choose JEB to publish your paper?
We chose JEB for two main reasons. First, JEB has a history of disseminating excellent research on muscle and tendon mechanics, so we knew it would be a great community for us to share our work. Second, JEB has a strong history of publishing comparative biology work. Given the implications of our results for both human and animal movement, we thought it would be beneficial to share our work with that scientific audience.
Are there any important historical papers from your field that have been published in JEB?
While it's not a historical paper, Glen Lichtwark and Alan Wilson's 2006 paper ‘Interactions between the human gastrocnemius muscle and the Achilles tendon during incline, level and decline locomotion’ (doi:10.1242/jeb.02434) shaped how I approached my dissertation work. This paper highlights how the muscle and tendon are a coupled system, where the properties of one can directly impact the performance of the other. This paper also emphasized the importance of looking at the muscle and tendon at the same time. We used this premise to motivate the development of our measurement technique, where we quantify muscle and tendon stiffness simultaneously.
What do you think experimental biology will look like 50 years from now?
I am excited for work that focuses on the comparative biomechanics of movement to continue to grow. There is so much knowledge and information that is relevant to both human and animal biomechanists. There is a lot of potential for collaborations across these fields, where animal studies aid in developing human studies and vice versa. Moreover, integrating these communities will aid in answering some of the most complex questions that face our field.
What's next for you?
I recently started my postdoc examining how to use lower limb robotic exoskeletons to augment human balance. I am very interested in pursuing a career in academia and establishing a lab that combines human physiology, robotics and engineering to assess an individual's neuromuscular control, their interactions with robotic devices, and how devices can be designed and controlled to restore human mobility.
Kristen Jakubowski's contact details: Wallace H. Coulter Department of Biomedical Engineering, Emory University and Georgia Institute of Technology, Atlanta, GA 30322, USA.
E-mail: kjakubo@emory.edu
