The Applied Biomechanics had a fantastic time attending the 2024 American Society of Biomechanics in Madison, WI. Many thanks to the meeting and program chairs, the presenters, and attendees for facilitating and participating in great scientific discussions!

Congratulations to the members of the Applied Biomechanics Lab that presented their research.

Presenters:

Plantar Sensation Associates With Gait Instability In Older Adults, Andrew Shelton

Do Shoe Structural Features Matter For Agility And Stability During Walking?, Kayva Katugam-Dechene

The Effects Of Calf Muscle Length On Local Muscle Fatigability, Anh Nguyen

The Effects of Age and Anticipation on Proactive and Reactive Balance Responses to Treadmill Belt Perturbations During Walking, Emily Eichenlaub

The Role Of Tendon Stiffness In Governing Leg Muscle Responsiveness To Unanticipated Slips In Younger And Older Adults, Ross Smith

The Effects Of Anticipation On Distal Leg Muscle Excitations In Response To Surface Translations During Standing, Virginie Ruest

Foot Specific Determinants Of Habitual Walking Speed And Endurance In Young Adults, Ross Smith

Reduced Achilles Tendon Stiffness In Aging Associates With Higher Metabolic Cost Of Walking, Aubrey Gray

The Effects Of Gluteus Medius Fatigability On Gait Instability In Older Adults, Andrew Shelton

The effect of prolonged walking on leg muscle activity patterns and vulnerability to perturbations. Journal of Electromyography and Kinesiology.

Abstract:
Understanding the consequences and ecological relevance of muscle fatigue is important to guide the development of strategies to preserve independence. However, few studies have examined walking-related fatigue and the effects on walking instability. Our purpose was to investigate the effects of prolonged walking on leg muscle activity and vulnerability to balance perturbations. Eighteen healthy young adults completed a 30-min walking trial at their preferred walking speed while leg muscle activities were recorded. Before and after the 30-min walk, participants responded to five 5% body weight lateral force perturbations. Time-frequency analysis with wavelet transformation and principal component analyses assessed neuromuscular adaptations of muscles to prolonged walking. Following prolonged walking, we observed a time-dependent increase in EMG intensities at slower frequencies for the soleus and tibialis anterior and a decrease in mean amplitudes for the soleus, lateral gastrocnemius, and semitendinosus. Mean mediolateral CoM displacement following perturbations averaged 21% larger after the 30-min walk. Our results suggest that walking for 30 minutes at a comfortable speed elicits complex neuromuscular adaptations indicative of local muscle fatigue and an increased vulnerability to walking balance perturbations. These findings could inform fatigue monitoring systems or walking assistive devices aimed at reducing walking-related fatigue and maintaining independent mobility.

Does the effect of walking balance perturbations generalize across contexts? Human Movement Science.

Abstract: Balance perturbations are used to study locomotor instability. However, these perturbations are designed to provoke a specific context of instability that may or may not generalize to a broader understanding of falls risk. The purpose of this study was to determine if the effect of balance perturbations on instability generalizes across contexts. 29 healthy younger adults and 28 older adults completed four experimental trials, including unperturbed walking and walking while responding to three perturbation contexts: mediolateral optical flow, treadmill-induced slips, and lateral waist-pulls. We quantified the effect of perturbations as an absolute change in margin of stability from unperturbed walking. We found significant changes in mediolateral and anteroposterior margin of stability for all perturbations compared to unperturbed walking in both cohorts (p<0.042). However, in older adults only mediolateral effects of waist-pull perturbations and optical flow perturbations and waist-pull perturbations and treadmill-induced slips correlated significantly (r ≥0.398, p-values≤0.036). In younger adults but not in older adults, we found positive and significant correlations between the anteroposterior effect of waist-pull perturbations and optical flow perturbations, and the anteroposterior and mediolateral effect of treadmill-induced slips (r≥0.428, p-values≤0.021). We found no “goldilocks” perturbation paradigm to endorse that would support universal interpretations about locomotor instability. Building the most accurate patient profiles of instability likely requires a series of perturbation paradigms designed to emulate the variety of environmental contexts in which falls may occur.

Sustained limb-level loading: A ground reaction force phenotype common to individuals at high-risk for and those with knee osteoarthritis. Arthritis & Rheumatology.

OBJECTIVE: To compare the vertical (vGRF), anterior-posterior (apGRF) and mediolateral (mlGRF) ground reaction force (GRF) profiles throughout the stance phase of gait: 1) between individuals 6-12 months post anterior cruciate ligament reconstruction (ACLR) and uninjured matched controls; and 2) between ACLR and individuals with differing radiographic severities of knee osteoarthritis (KOA) defined as Kellgren and Lawrence (KL) grades KL2, KL3, and KL4.METHOD: A total of 196 participants were included in this retrospective cross-sectional analysis. Gait biomechanics were collected from individuals 6-12 months post-ACLR (n=36), uninjured controls matched to the ACLR group (n=36), and individuals with KL2 (n=31), KL3 (n=67), and KL4 OA (n=26). Between-group differences in vGRF, apGRF, and mlGRF were assessed in reference to the ACLR group throughout each % of stance phase using a functional linear model.RESULTS: The ACLR group demonstrated lesser vGRF and apGRF in early and late stance compared to the uninjured controls, with large effects (d range: 1.35-1.66).
Conversely, the ACLR group exhibited greater vGRF (87-90%; 4.88%BW; d=0.75) and apGRF (84-94%; 2.41%BW; d=0.79) than the KL2 group in a small portion of late stance. No differences in mlGRF profiles were observed between the ACLR and either the uninjured controls or the KL2 group. The magnitude of difference in GRF profiles between the ACLR and OA groups increased with OA disease severity.CONCLUSION: Individuals 6-12 months post-ACLR exhibit strikingly similar GRF profiles as individuals with KL2 KOA, suggesting both patient groups may benefit from targeted interventions to address aberrant GRF profiles.

Simulations suggest walking with reduced propulsive force would not mitigate the energetic consequences of lower tendon stiffness. Ricky Pimentel, Greg Sawicki, and Jason R. Franz

Abstract. Aging elicits numerous effects that impact both musculoskeletal structure and walking function. Tendon stiffness (kT) and push-off propulsive force (FP) both impact the metabolic cost of walking and are diminished by age, yet their interaction has not been studied. We combined experimental and computational approaches to investigate whether age-related changes in function (adopting smaller FP) may be adopted to mitigate the metabolic consequences arising from changes in structure (reduced kT). We recruited 12 young adults and asked them to walk on a force-sensing treadmill while prompting them to change FP (±20% & ±40% of typical) using targeted biofeedback. In models driven by experimental data from each of those conditions, we altered the kT of personalized musculoskeletal models across a physiological range (2-8% strain) and simulated individual-muscle metabolic costs for each kT and FP combination. We found that kT and FP independently affect walking metabolic cost, increasing with higher kT or as participants deviated from their typical FP. Our results show no evidence for an interaction between kT and FP in younger adults walking at fixed speeds. Individual lower body muscles showed unique effects across the kT and FP landscape. Our simulations suggest that reducing FP during walking would not mitigate the metabolic consequences of lower kT. Wearable devices and rehabilitative strategies can focus on either kT or FP to reduce age-related increases in walking metabolic cost.

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.