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ABL and Collaborators Receive 2 New NIH Grants!

September 10, 2018

The UNC/NCSU Applied Biomechanics Laboratory, in a great example of the inter-disciplinary nature of biomedical engineering and the impact of collaborative science, was recently awarded two new research grants from the National Institutes of Health.

First, in collaboration with the UNC Division of Geriatrics and Co-PI Dr. Gregory Sawicki in the Georgia W. Woodruff School of Mechanical Engineering at Georgia Tech, we will begin work on a new five-year NIH R01 to study (1) neuromechanical explanations for the greater metabolic energy cost of walking in older adults and (2) translation of that understanding to biologically-inspired wearable robotics for preserving independent mobility in our aging population. Ultimately, we hope to use ultrasound imaging to guide optimal prescription of assistive devices to improve locomotor function in aging – an outcome that will have significant positive impact on quality of life for millions.

Second, in collaboration with Co-PI Dr. Brian Pietrosimone in the UNC Department of Exercise and Sport Science, we will begin work on a new NIH R21 to study how altered lower extremity loading affects knee joint biomechanics, joint tissue biochemistry, cartilage deformation, and quadriceps muscle contractile behavior during walking in people following ACL reconstruction. By combining real-time biofeedback, ultrasound imaging, and biochemical markers, this study will be the first to determine the acute effects of joint loading on a collection of critical factors associated with the pathogenesis of post-traumatic osteoarthritis in a relevant patient population.

We are incredibly excited to continue our work with these exceptional groups of colleagues and collaborators.

Paper Accepted (September 2018)

September 10, 2018

Image result for clinical biomechanicsThompson JD, Plummer P, Franz JR. Age and falls history effects on antagonist leg muscle coactivation during walking with balance perturbations. Clinical Biomechanics.






Background: Inspired by a reliance on visual feedback for movement control in older age, optical flow perturbations provide a unique opportunity to study the neuromuscular mechanisms involved in walking balance control, including aging and falls history effects on the response to environmental balance challenges. Specifically, antagonist leg muscle coactivation, which increases with age during walking, is considered a neuromuscular defense against age-associated deficits in balance control. The purpose of this study was to investigate the effects of age and falls history on antagonist leg muscle coactivation during walking with and without optical flow perturbations of different amplitudes.

Methods: Eleven young adults [mean (standard deviation) age: 24.8 (4.8) years], eleven older non-fallers [75.3 (5.4) years] and eleven older fallers [age: 78 (7.6) years] participated in this study. Participants completed 2-minute walking trials while watching a speed-matched virtual hallway that, in some conditions, included mediolateral optical flow perturbations designed to elicit the visual perception of imbalance.

Findings: We first found that lower leg antagonist muscle coactivation during normal walking increased with age, independent of falls history. We also found that older but not young adults increased antagonist leg muscle coactivation in the presence of optical flow perturbations, with more pervasive effects in older adults with a history of falls.

Interpretation: Our findings allude to a greater susceptibility to optical flow perturbations in older fallers during walking, which points to a higher potential for risk of instability in more complex and dynamic everyday environments. These findings may also have broader impacts related to the design of innovative training paradigms and neuromuscular targets for falls prevention.

Paper Accepted (August 2018)

August 20, 2018

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Our newest publication represents a wonderful new and productive collaboration with Dr. Jessica Allen, Professor of Chemical and Biomedical Engineering at West Virginia University.

Allen JL and Franz JR. The motor repertoire of older adult fallers may constrain their response to balance perturbations. Journal of Neurophysiology (In press).

Abstract. Older adults are at a high risk of falls, and most falls occur during locomotor activities like walking. This study aimed to improve our understanding of changes in neuromuscular control associated with increased falls risk in older adults in the presence of dynamic balance challenges during walking. Motor module (a.k.a. muscle synergy) analyses identified changes in the neuromuscular recruitment of leg muscles during walking with and without perturbations designed to elicit the visual perception of lateral instability. During normal walking we found that falls history (but not age) was associated with reduced motor module complexity, and that age (but not falls history) was associated with increased step-to-step variability of module recruitment timing. Further, motor module complexity was unaltered in the presence of optical flow perturbations. The specific effects of falls history on leg muscle recruitment included an absence and/or inability to independently recruit motor modules normally recruited to perform biomechanical functions important for walking balance control. These results suggest that fallers do not recruit the appropriate motor modules necessary for well-coordinated walking balance control even in the presence of perturbations. The identified changes in the modular control of walking balance in older fallers may either represent a neural deficit that leads to poor balance control, or a prior history of falls results in a compensatory motor adaptation. In either case, our study provides initial evidence that a reduced motor repertoire in older adult fallers may be a constraint on their ability to appropriately respond to balance challenges during walking.

New and noteworthy: This is the first study to demonstrate a reduced motor repertoire during walking in older adults with a history of falls but without any overt neurological deficits. Further, using virtual reality during walking to elicit the visual perception of lateral instability, we provide initial evidence that a reduced motor repertoire in older adult fallers may be a constraint on their ability to appropriately respond to balance challenges during walking.



ABL attends ASB2018 in Rochester, MN

August 20, 2018

The Applied Biomechanics Lab had an incredible presence at the 2018 Annual Meeting of the American Society of Biomechanics in Rochester, MN. We were especially excited to have two finalists for the PhD student award competition and one finalist for the undergraduate student competition. Their hard work and commitment to exceptional science definitely paid off.


Conway KA, Bissette RG, Franz JR, Older adults overcome their deficits to young adults when propulsive demands of walking are increased to their maximum.

Browne MG and Franz JR, Older adults reverse their distal-to-proximal redistribution using ankle power biofeedback. *Finalist: Doctoral Student Presentation Competition

Browne MG and Franz JR, Restoring propulsive forces in elderly gait does not impair dynamic stability.

Clark WH and Franz JR, Activation-dependent changes in soleus length-tension behavior augment ankle joint quasi-stiffness.

Clark WH and Franz JR, Triceps surae muscle-subtendon interaction differs between young and older adults.    *Finalist: Doctoral Student Presentation Competition

Qiao M, Truong KN, and Franz JR, Does local dynamic stability during unperturbed walking predict the response to balance perturbations? An examination across age and falls history.

Qiao M, Richards JT, and Franz JR, Visuomotor error augmentation affects mediolateral head and trunk stabilization during walking.

Khanchandani A, McKenney H Arnold B, Clark WH, Franz JR, The Achilles tendon moment arm exhibits independent and combinatory effects of joint rotation and muscle loading. *Finalist: Undergraduate Student Presentation Competition



Paper Accepted (July 2018)

July 17, 2018

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Browne MG and Franz JR. More push from your push-off: joint-level modifications to modulate propulsive forces in old age. Plos One (In press).


Introduction: Compared to young adults, older adults walk with smaller propulsive forces and a redistribution to more proximal leg muscles for power generation during push-off. Despite this deficit in propulsive function, older adults can increase push-off intensity when encouraged to via real-time biofeedback. However, the specific joint-level modifications used by older adults to enhance propulsive force generation has yet to be elucidated. The purpose of this study was to identify the joint-level modifications used by young and older adults to modulate propulsive forces when walking at their preferred speed.

Methods: 9 young and 16 older adults walked at their preferred speed while visual biofeedback prompted them to modulate their propulsive forces using targets prescribed at ±10% and ±20% of their preferred value. Older adults were then divided into groups exhibiting relatively larger or smaller baseline redistribution to more proximal leg muscles for power generation.

Results: Neither young nor either older adult cohort modulated propulsive forces by altering their peak ankle power generation. Instead, subjects increased trailing limb extension and attenuated mechanical power demands at the hip during push-off. Older adults that had a larger baseline redistribution exhibited larger responses to enhanced push-off intensity than their peers – for example, walking with 11% less hip flexor power and 10% more trailing limb extension during push-off when exerting larger than preferred propulsive forces.

Conclusion: Propulsive force biofeedback that elicits larger than preferred propulsive forces also increases trailing limb extension and attenuates mechanical power demands at the hip in older adults most exhibiting a distal-to-proximal redistribution. Our results suggest that considering baseline redistribution may be important in the personalized prescription of interventions aimed at enhancing walking performance by improving push-off intensity.

ABL attends World Congress of Biomechanics

July 17, 2018

The Applied Biomechanics Lab recently traveled to Dublin, Ireland to present our research at the 8th World Congress of Biomechanics. Congratulations to all our students and trainees! Thanks for the great time!


Conway KA, Bissette RG, Franz JR, Increasing the propulsive demands of walking to their maximum elucidates functionally limiting impairments in elderly gait.

Waanders JB, Hortobágyi T, Murgia A, DeVita P, Franz JR, The distal-to-proximal shift of muscle function during gait in old age is absent for negative work.

Franz JR and Clark WH, Triceps surae muscle-subtendon interaction differs between young and older adults.

DeVita, P, Moulder A, Akindahunsi O, Curran C, Bell E, Knaus K, Ebrahimi A, Kuhman D, Drazen J, Paquette M, Miller R, Willy R, McNitt-Gray J, Dufek J, Franz JR, Darkenwald T, Breloff S, Carpes F. National Biomechanics Day: STEM Outreach for High School Students through the 21st Century’s Breakthrough Science.

Browne MG and Franz JR, Older adults reverse their distal-to-proximal redistribution and walk faster with ankle power biofeedback.

Paper Accepted (June 2018) 4

June 19, 2018

Clark WH and Franz JR. Do triceps surae muscle dynamics govern non-uniform Achilles tendon tissue displacements? PeerJ (In press).

Abstract. The human Achilles tendon (AT) consists of sub-tendons arising from the gastrocnemius and soleus muscles that exhibit non-uniform tissue displacements thought to facilitate some independent actuation. However, the mechanisms governing non-uniform displacement patterns within the AT, and their relevance to triceps surae muscle contractile dynamics, have remained elusive. We used a dual-probe ultrasound imaging approach to investigate triceps surae muscle dynamics (i.e., medial gastrocnemius-GAS, soleus-SOL) as a determinant of non-uniform tendon tissue displacements in the human AT. We hypothesized that superficial versus deep differences in AT tissue displacements would be accompanied by and correlate with anatomically consistent differences in GAS versus SOL muscle shortening. Nine subjects performed ramped isometric contractions at each of five ankle joint angles spanning 10° dorsiflexion to 30° plantarflexion. For all conditions, SOL shortened by an average of 78% more than GAS during moment generation. This was accompanied by, on average, 51% more displacement in the deep versus superficial region of the AT. The magnitude of GAS and SOL muscle shortening positively correlated with displacement in their associated sub-tendons within the AT. Moreover, and as hypothesized, superficial versus deep differences in sub-tendon tissue displacements positively correlated with anatomically consistent differences in GAS versus SOL muscle shortening. We present the first in vivo evidence that triceps surae muscle dynamics may precipitate non-uniform displacement patterns in the architecturally complex AT.

Paper Accepted (June 2018) 3

June 18, 2018

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Luc-Harkey BA, Franz JR, Losina E, Pietrosimone B. Association between Kinesiophobia and Walking Gait Characteristics in Individuals with Anterior Cruciate Ligament Reconstruction. Gait & Posture (In press).


Background: Individuals with anterior cruciate ligament reconstruction (ACLR) demonstrate persistent alterations in walking gait characteristics that contribute to poor long-term outcomes. Higher kinesiophobia, or fear of movement/re-injury, may result in the avoidance of movements that increase loading on the ACLR limb. Research Question: Determine the association between kinesiophobia and walking gait characteristics in physically active individuals with ACLR. Methods: We enrolled thirty participants with a history of unilateral ACLR (49.35±27.29 months following ACLR) into this cross-sectional study. We used the Tampa Scale for Kinesiophobia (TSK-11) to measure kinesiophobia. We collected walking gait characteristics during a 60-second walking trial, which included gait speed, peak vertical ground reaction force (vGRF), instantaneous vGRF loading rate, peak internal knee extension moment (KEM), and knee flexion excursion. We calculated lower extremity kinetic and kinematic measures on the ACLR limb, and limb symmetry indices between ACLR and contralateral limbs (LSI= [ACLR/contralateral]*100). We used linear regression models to determine the association between TSK-11 score and each walking gait characteristic. We determined the change in R2 (ΔR2) when adding TSK-11 scores into the linear regression model after accounting for demographic covariates (sex, Tegner activity score, graft type, time since reconstruction, history of concomitant meniscal procedure). Results: We did not find a significant association between kinesiophobia and self-selected gait speed (ΔR2 0.038, P=0.319). Kinesiophobia demonstrated weak, non-significant associations with kinetic and kinematic outcomes on the ACLR limb and all LSI outcomes (ΔR2 range = 0.001 to 0.098). Significance: These data do not support that kinesiophobia is a critical factor contributing to walking gait characteristics in physically active individuals with ACLR.

Paper Accepted (June 2018) 2

June 13, 2018

00219290_20160610Rasske K and Franz JR. Aging effects on the Achilles tendon moment arm during walking. Journal of Biomechanics (In press).

Abstract. The Achilles tendon (AT) moment arm transforms triceps surae muscle forces into a moment about the ankle which is critical for functional activities like walking. Moreover, the AT moment arm changes continuously during walking, as it depends on both ankle joint rotation and triceps surae muscle loading (presumably due to bulging of the muscle belly). Here, we posit that aging negatively effects the architecturally complex AT moment arm during walking, which thereby contributes to well-documented reductions in ankle moment generation during push-off. We used motion capture-guided ultrasound imaging to quantify instantaneous variations in the AT moment arms of young (23.9±4.3 years) and older (69.9±2.6 years) adults during walking, their dependence on triceps surae muscle loading, and their association with ankle moment generation during push-off. Older adults walked with 11% smaller AT moment arms and 11% smaller peak ankle moments during push-off than young adults. Moreover, as hypothesized, these unfavourable changes were significantly and positively correlated (r2=0.38, p<0.01). More surprisingly, aging attenuated load-dependent increases in AT moment arm (i.e., that between heel-strike and push-off at the same ankle angle); only young adults exhibited a significant increase in their AT moment arm due to triceps surae muscle-loading. Age-associated reductions in triceps surae volume or activation, and thus muscle bulging during force generation, may compromise the mechanical advantage of the AT during the critical push-off phase of walking in older adults. Thus, strategies to restore and/or improve locomotor performance in our aging population should consider these functionally important changes in musculoskeletal behavior.

Paper Accepted (June 2018) 1

June 2, 2018

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Luc-Harkey BA, Franz JR, Blackburn JT, Padua DA, Hackney AC, Pietrosimone B. Real-time Biofeedback Can Increase and Decrease Vertical Ground Reaction Force, Knee Flexion Excursion, and Knee Extension Moment during Walking in Individuals with Anterior Cruciate Ligament Reconstruction. Journal of Biomechanics (In press).

Abstract: Individuals with anterior cruciate ligament reconstruction (ACLR) often exhibit a “stiffened knee strategy” or an excessively extended knee during gait, characterized by lesser knee flexion excursion and peak internal knee extension moment (KEM). The purpose of this study was to determine the effect of real-time biofeedback (RTBF) cuing an acute change in peak vertical ground reaction force (vGRF) during the first 50% of the stance phase of walking gait on: 1) root mean square error (RMSE) between actual vGRF and RTBF target vGRF; 2) perceived difficulty; and 3) knee biomechanics. Acquisition and short-term recall of these outcomes were evaluated. Thirty individuals with unilateral ACLR completed 4 separate walking sessions on a force-measuring treadmill that consisted of a control (no RTBF) and 3 experimental loading conditions using RTBF including: 1) 5% vGRF increase (high-loading), 2) 5% vGRF decrease (low-loading) and 3) symmetric vGRF between limbs. Bilateral biomechanical outcomes were analyzed during the first 50% of the stance phase, and included KEM, knee flexion excursion, peak vGRF, and instantaneous vGRF loading rate (vGRF-LR) for each loading condition. Peak vGRF significantly increased and decreased during high-loading and low-loading, respectively compared to control loading. Instantaneous vGRF-LR, peak KEM and knee flexion excursion significantly increased during the high-loading condition compared to low-loading. Perceived difficultly and RMSE were lower during the symmetrical loading condition compared to the low-loading condition. Cuing an increase in peak vGRF may be beneficial for increasing KEM, knee flexion excursion, peak vGRF, and vGRF-LR in individuals with ACLR. Clinical Trials Number:NCT03035994