Exploring the Functional Boundaries and Metabolic Consequences of Triceps Surae Force-Length Relations during Walking (2021 Journal of Biomechanics Award Winner, American Society of Biomechanics)

Abstract. The relationship between individual muscle dynamics and whole-body metabolic cost is not well established. Here we use biofeedback to modulate triceps surae (TS) activity during walking. We hypothesized: (1) increased TS activity would increase metabolic cost via shorter muscle fascicle lengths and thus reduced force capacity and (2) decreased TS activity would decrease metabolic cost via longer muscle fascicle lengths and thus increased force capacity. 23 young adults walked on an instrumented treadmill at 1.25 m/s using electromyographic (EMG) biofeedback to match targets corresponding to ±20 and ±40% TS activity during push-off (late stance). B-mode ultrasound imaged the medial gastrocnemius (MG). Participants increased net metabolic power up to 85% and 21% when targeting increased and decreased TS activity, respectively (p < 0.001). At the instant of peak gastrocnemius force, MG fascicle length was 7% shorter (p < 0.001) and gastrocnemius force was 6% larger (p < 0.001) when targeting +40% TS activity. Fascicle length was 3% shorter (p = 0.004) and force was 7% lower (p = 0.004) when targeting -40% TS activity. Participants were unable to achieve decreased activation targets. MG fascicle length and activity mediated 11.7% (p = 0.036) and 57.2% (p = 0.006) of the changes in net metabolic power, respectively. MG force did not mediate changes in net metabolic power (p = 0.948). These findings suggest that changes in the functional operating length of muscle, induced by volitional changes in TS activity, mediate the metabolic cost of walking, relatively independently of force. Thus, shifts to shorter fascicle lengths may mediate activity-induced increases in metabolic cost.

Congratulations to all our lab members that attended and presented at the 2023 Annual Meeting of the American Society of Biomechanics!

Emily Eichenlaub, a third-year BME Ph.D. student, has received a National Research Service Award (NIH F31) from the National Institute of Aging. The award will fund her project titled “The Proactive and Reactive Neuromechanics of Instability in Aging and Dementia with Lewy Bodies.” The research will establish the effects of age and dementia on proactive and reactive neuromechanics underlying vulnerability to balance challenges. Emily will be sponsored by Dr. Jason Franz, Associate Professor in BME, and a mentoring committee that spans Engineering, Physical Therapy, Neurology and Biostatistics. Her research in the BME Applied Biomechanics Lab will pave the way for clinical translation in prescription of personalized interventions, wearable sensor monitoring to mitigate falls, and development of assistive devices with onboard monitoring of muscle neuromechanics to deliver assistance in the face of a balance challenge. Congratulations, Emily!!

Cone SG, Kim H, Thelen DG, Franz JR. 3D characterization of the triple-bundle Achilles tendon from in vivo high-field MRI. Journal of Orthopaedic Research.

The Achilles tendon consists of three subtendons that transmit force from the triceps surae muscles to the calcaneus. Potentially meaningful individual differences have been identified in subtendon morphology, with potential implications in triceps surae mechanics and function. Recently, advances in high-field magnetic resonance imaging (MRI) have previously been used to delineate boundaries within multi-bundle tendons and ligaments, including those between bundles of the anterior cruciate ligament. The objective of this study was to use high-field MRI (7T) to image and reconstruct Achilles subtendons arising from the triceps surae muscles. We imaged the dominant lower leg of a cohort of healthy human subjects (n=10) using a tuned musculoskeletal sequence (double echo steady state sequence, 0.4mm isotropic voxels). We then characterized the cross-sectional area and orientation of each subtendon between the MTJ and calcaneal insertion. Image collection and segmentation was repeated to assess repeatability. Subtendon morphometry varied across subjects, with average subtendon areas of 23.5±8.9 mm2 for the medial gastrocnemius, 25.4±8.9 mm2 for the lateral gastrocnemius, and 13.7±5.9 mm2 for the soleus subtendons. Repeatable subject-specific variations in size and position of each subtendon were identified over two visits, expanding on prior knowledge that high variability exists in Achilles tendon morphology across subjects.

We are thrilled to congratulate Ricky Pimentel for successfully defending his PhD dissertation, titled “An Energy Audit of Human Gait: Experimental and computational assessment of how structure and function shape walking economy”. We also thank the wonderful support of his committee members, Helen Huang (UNC/NCSU BME), Mike Lewek (UNC PT), Kate Saul (NCSU MAE), and Nitin Sharma(UNC/NCSU BME). Fantastic job, Ricky! We will miss you!

We are very proud to congratulate Amanda Munsch for successfully defending her PhD dissertation, titled “Optimizing Knee Joint Loading: Association Between Quadriceps Contractile Behavior, Knee Joint Biomechanics, and Cartilage Contact Forces”. Outstanding job! We also thank the wonderful support of his committee members, Drs. Brian Pietrosimone (UNC EXSS), Mike Lewek (UNC PT), Brian Diekman (UNC/NSCU BME), and Josh Roth (UW-Madison ME). We will miss you, Mandy!!

Ricky Pimentel, Doctoral Candidate in the Joint Department of Biomedical Engineering at UNC-Chapel Hill and NC State University, was recognized with the graduate student Bryan Award for outstanding community engagement and contributions through his work at the ReCyclery, and his leadership in cofounding Latinx in Biomechanix.

ReCyclery aims to increase the use of bicycles for transportation and recreation. Pimentel instructs community members, especially those with limited budgets, on the repair and refurbishment of bicycles, and he has raised more than $20,000 since the height of the pandemic for ReCyclery to continue its mission.

Latinx in Biomechanix (LiB) increases the representation of Latinx individuals in the collective fields of biomechanics and movement science. Pimentel has organized numerous virtual and in-person social and networking events with international reach, written a successful grant to build capacity for LiB, organized a leadership retreat and established federal non-profit status for the organization.

Through both of these activities, Ricky has successfully established strong partnerships with community members, inspired others in their mission to serve, responded to urgent and significant needs and worked to ensure the sustainability of his significant service activities to our local, regional and global communities

Andy Shelton, a third-year BME Ph.D. candidate, has received a National Research Service Award (NIH F31) from the National Institute of Aging. The award will fund his project titled “The Effects of Muscle Fatigability on Gait Instability in Aging and Age-Related Falls Risk.” The research will evaluate how local muscle fatigability compromises the neuromuscular control of walking balance and precipitates gait instability in direction-dependent and context-specific ways in older adults. Andy will be sponsored on the project by Dr. Jason Franz, Associate Professor in BME, and a mentoring committee that spans Engineering, Physical Therapy, Neurology and Biostatistics. Anticipated outcomes from his research in the BME Applied Biomechanics Lab will have the potential to inform novel advances in diagnostics, rehabilitation, mobile monitoring and wearable assistive technologies to mitigate falls.

Third-year BME PhD student Aubrey Gray has received one of only four highly competitive 2023 Grant-in-Aid Research awards from the American Society of Biomechanics. The award will provide support for her research project titled “Foot stiffness as a potentially modifiable factor to improve resilience to walking balance challenges in older adults” which she will complete in the Applied Biomechanics Laboratory directed by BME Associate Professor Dr. Jason Franz. The American Society of Biomechanics (ASB) was founded in 1977 to encourage and foster the exchange of information and ideas among biomechanists working in different disciplines and to facilitate the development of biomechanics as a basic and applied science. The society has a membership of approximately 850 academic researchers, clinicians, scientists, students, and industry members working to solve basic and applied problems in the realm of biomechanics and to improve understanding of the workings of biological systems.

Congratulations, Aubrey!!

https://asbweb.org/award-winners-spotlight/

The Applied Biomechanics Lab is excited to announce our new industry-sponsored research collaboration with Orthofeet, Inc. to study the effects of footwear on walking biomechanics in older and orthopaedic consumers. Orthofeet’s orthotic shoes are biomechanically engineered with unique comfort features to offer the footwear solutions for sensitive feet and other physical ailments affected by foot problems or poor posture. We are thrilled to develop this collaboration with Orthofeet, a company whose mission aligns with our own – to relieve pain and increase independence in the lives of older adults.