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The Applied Biomechanics Laboratory, in collaboration with the UNC Division of Physical Therapy and the Department of Chemical and Biomedical Engineering at West Virginia University, has been awarded a pilot research grant from the NIH-funded North Carolina Translational and Clinical Sciences Institute for our project titled “The peripheral motor repertoire as a neuromuscular constraint on walking balance integrity in age-related falls risk”. The scientific premise of the project is that all individuals rely on a principal number of peripheral neuromuscular commands – a “peripheral motor repertoire” – to accomplish everyday walking tasks during which falls may occur. Our overall objective is to test the hypothesis that a reduced peripheral motor repertoire used for everyday walking tasks represents a neuromuscular constraint on older adults’ ability to successfully respond to walking balance perturbations and prevent falls in the community. Our long-term goal is to introduce a novel neuromuscular mechanism for age-associated balance impairment as a target for diagnostic testing and rehabilitation to prevent falls in older adults.

 

 

Effects of Gait Biofeedback on Cartilage Oligomeric Matrix Protein in Individuals with ACL Reconstruction

Brittney A. Luc-Harkey, Jason R. Franz, Anthony C. Hackney, J. Troy Blackburn, Darin A. Padua, Todd A. Schwartz, and Brian Pietrosimone

 

 

Context: Gait biomechanics are linked to biochemical changes that contribute to the development of posttraumatic knee osteoarthritis in individuals with anterior cruciate ligament reconstruction (ACLR). It remains unknown if modifying peak loading during gait using real-time biofeedback will result in acute biochemical changes related to cartilage metabolism.

Objective: Determine if acutely manipulating peak vertical ground reaction force (vGRF) during gait influences acute changes in serum Cartilage Oligomeric Matrix Protein (sCOMP) concentrations in individuals with an ACLR.

Design: Crossover Study

Patients or Other Participants: Thirty individuals with an unilateral ACLR participated (70% Female, 20.4±2.9 years old, 24.4±4.2 body mass index (BMI), 47.8±27 months post-ACLR). Additionally, a subgroup was identified as those participants who demonstrated an increase in sCOMP following the control or natural loading condition (sCOMP_CHANGE >0ng/mL; n=22, 70% Female, 20.3±3 years old, 24.7±4.3 BMI, 47.3±29.3 months post-ACLR).

Main Outcome Measure(s): Serum was collected before and immediately following each condition to determine sCOMP_CHANGE.

Intervention: All participants attended four sessions involving 20 minutes of walking on a force-measuring treadmill consisting of a control condition (natural loading) followed by a random ordering of 3 loading conditions prescribed using real-time biofeedback: 1) a 5% increase in vGRF (high-loading), 2) a 5% decrease in vGRF (low-loading), and 3) symmetric vGRF between limbs. A general linear mixed model was used to determine differences in sCOMP_CHANGE between each altered loading condition and control in the entire cohort and subgroup.

Results: sCOMP_CHANGE was not different across all loading conditions for the entire cohort (F_3,29=1.34, P=0.282). Within the subgroup, sCOMP_CHANGE was significantly less during high-loading (1.95±24.22ng/mL, t₂₁=-3.53, P=0.005) and symmetrical loading (9.93±21.45ng/mL; t₂₁=-2.86, P=0.025) compared to the control (25.79±21.40ng/mL).

Conclusions: Increasing peak vGRF during gait decreases sCOMP in ACLR individuals who naturally demonstrate an increase in sCOMP following 20 minutes of walking.

Shorter gastrocnemius fascicle lengths in older adults associate with worse capacity to enhance push-off intensity in walking

Katie A. Conway and Jason R. Franz

Background: Reduced push-off intensity during walking is thought to play an important role in age-related mobility impairment. We posit that an age-related shift toward shorter plantarflexor operating lengths during walking functionally limits force generation, and thereby the ability of those muscles to respond to increased propulsive demands during walking. Research Question: To determine whether gastrocnemius muscle fascicle lengths during normal walking: (1) are shorter in older than young adults, and (2) correlate with one’s capacity to increase the propulsive demands of walking to their maximum. Methods: We used in vivo cine B-mode ultrasound to measure gastrocnemius fascicle lengths in 9 older and 9 young adults walking at their preferred speed, their maximum speed, and with horizontal impeding forces that increased in a ramped design at 1%BW/s to their maximum. A repeated measures ANOVA tested for effects of age and walking condition, and Pearson correlations assessed the relation between fascicle outcomes and condition performance. Results: A tendency toward shorter medial gastrocnemius muscle fascicle lengths in older versus young adults was not statistically significant. However, older adults walked with reduced peak fascicle shortening during all conditions compared to young adults – an outcome not explained by reduced muscle-tendon unit shortening and exacerbated during tasks with greater than normal propulsive demand. As hypothesized, we found a strong and significant positive correlation in older subjects between gastrocnemius fascicle lengths during normal walking and performance on the ramped impeding force condition (p=0.005, r²=0.704), even after controlling for isometric strength (p=0.011, r²=0.792) and subject stature (p=0.010, r²=0.700). Significance: Our findings provide muscle-level insight to develop more effective rehabilitation techniques to improve push-off intensity in older adults and assistive technologies designed to steer plantarflexor muscle fascicle operating behavior during functional tasks.

Can shank acceleration provide a clinically feasible surrogate for individual limb propulsion during walking?

Noah L. Pieper, Michael D. Lewek, Jason R. Franz

Abstract: Aging and many pathologies that affect gait are associated with reduced ankle power output and thus trailing limb propulsion during walking. However, quantifying trailing limb propulsion requires sophisticated measurement equipment at significant expense that fundamentally limits clinical translation for diagnostics or gait rehabilitation. As a component of joint power, our purpose was to determine if shank acceleration estimated via accelerometers during push-off can serve as a clinically feasible surrogate for ankle power output and peak anterior ground reaction forces (GRF) during walking. As hypothesized, we found that young adults modulated walking speed via changes in peak anterior GRF and peak ankle power output that correlated with proportional changes in shank acceleration during push-off, both at the individual subject (R²≥0.80, p<0.01) and group average (R²≥0.74, p<0.01) levels. In addition, we found that unilateral deficits in trailing limb propulsion induced via a leg bracing elicited unilateral and relatively proportional reductions in peak anterior GRF, peak ankle power, and peak shank acceleration. These unilateral leg bracing effects on peak shank acceleration correlated with those in peak ankle power (braced leg: R²=0.43, p=0.028) but those in both peak shank acceleration and peak ankle power were disassociated from those in peak anterior GRF. In conclusion, our findings in young adults provide an early benchmark for the development of affordable and clinically feasible alternatives for assessing and monitoring trailing limb propulsion during walking.

How age and surface inclination affect joint moment strategies to accelerate and decelerate individual leg joints during walking.

Jeroen B. Waanders, Alessio Murgia, Tibor Hortobágyi, Paul DeVita, Jason R. Franz

Abstract. A joint moment also causes motion at other joints of the body. This joint coupling-perspective allows more insight into two age-related phenomena during gait. First, whether increased hip kinetic output compensates for decreased ankle kinetic output during positive joint work. Second, whether preserved joint kinetic patterns during negative joint work in older age have any functional implication. Therefore, we examined how age and surface inclination affect joint moment strategies to accelerate and/or decelerate individual leg joints during walking. Healthy young (age: 22.5±4.1 years, n=18) and older (age: 76.0±5.7 years, n=22) adults walked at 1.4 m/s on a split-belt instrumented treadmill at three grades (0%, 10%, -10%). Lower-extremity moment-induced angular accelerations were calculated for the hip (0% and 10%) and knee (0% and -10%) joints. During level and uphill walking, both age groups showed comparable ankle moment-induced ipsilateral (p=0.774) and contralateral (p=0.047) hip accelerations, although older adults generated lower ankle moments in late stance. However, ankle moment-induced contralateral hip accelerations were smaller (p=0.001) in an older adult subgroup (n=13) who showed larger hip extension moments in early stance than young adults. During level and downhill walking, leg joint moment-induced knee accelerations were unaffected by age (all p>0.05). These findings suggest that during level and uphill walking increased hip flexor mechanical output in older adults does not arise from reduced ankle moments, contrary to increased hip extensor mechanical output. Additionally, results during level and downhill walking imply that preserved eccentric knee extensor function is important in maintaining knee stabilization in older age.

Visuomotor error augmentation affects mediolateral head and trunk stabilization during walking

Mu Qiao, Jackson T. Richards, and Jason R. Franz

Abstract. Prior work demonstrates that humans spontaneously synchronize their head and trunk kinematics to a broad range of driving frequencies of perceived mediolateral motion prescribed using optical flow. Using a closed-loop visuomotor error augmentation task in an immersive virtual environment, we sought to understand whether unifying visual with vestibular and somatosensory feedback is a control goal during human walking, at least in the context of head and trunk stabilization. We hypothesized that humans would minimize visual errors during walking – i.e., those between the visual perception of movement and actual movement of the trunk. We found that subjects did not minimize errors between the visual perception of movement and actual movement of the head and trunk. Rather, subjects increased mediolateral trunk range of motion in response to error-augmented optical flow with positive feedback gains. Our results are more consistent with our alternative hypothesis – that visual feedback can override other sensory modalities and independently compel adjustments in head and trunk position. Also, aftereffects following exposure to error-augmented optical flow included longer, narrower steps and reduced mediolateral postural sway, particularly in response to larger amplitude positive feedback gains. Our results allude to a recalibration of head and trunk stabilization toward more tightly regulated postural control following exposure to error-augmented visual feedback. Lasting reductions in mediolateral postural sway may have implications for using error-augmented optical flow to enhance the integrity of walking balance control through training, for example in older adults.

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Third year Ph.D. Candidate Billy Clark has been awarded an NIH National Research Service Award (F31) from the National Institute on Aging for his proposal titled “The role of muscle dynamics in governing Achilles subtendon behavior across the lifespan.” Billy will be co-advised on the project by Dr. Silvia Blemker, a Professor of Biomedical Engineering at the University of Virginia, and a mentoring committee spanning Engineering, Orthopedics, Geriatrics, and Exercise Science. Anticipated outcomes from his research will have immediate impact on our understanding of musculoskeletal mechanisms underlying age-related mobility impairment toward improving the health and welfare of our aging population. Moreover, his technological advancements in musculoskeletal imaging will revolutionize the use of in vivo ultrasound during functional locomotor behavior. More broadly, the knowledge gained from this study has the potential to accelerate the development of engineered tissues, regenerative medicine approaches and therapies, and orthopaedic surgical intervention.

Congratulations on this wonderful accomplishment!

 

Third year Ph.D. Candidate Katie Conway was recently awarded a Dissertation Completion Fellowship for the 2019-2020 academic year. Katie’s research in the lab focuses on the biomechanics of elderly gait and mobility impairment in our aging population. Currently, she is developing and using novel approaches for the functional assessment and restoration of push-off intensity during walking. Faculty reviewers on the Fellowship Committee of The Graduate School were impressed with the quality of her research and with the exceptional progress she is making toward completion of her degree and dissertation. Congratulations, Katie!!

Richards JT, Selgrade BP, Qiao M, Plummer P, Wikstrom EA, Franz JR. Time-dependent tuning of balance control and aftereffects following optical flow perturbation training in older adults. Journal of NeuroEngineering and Rehabilitation.

Abstract

Background: Walking balance in older adults is disproportionately susceptible to lateral instability provoked by optical flow perturbations. The prolonged exposure to these perturbations could promote reactive balance control and increased balance confidence in older adults, but this scientific premise has yet to be investigated. This proof of concept study was designed to investigate the propensity for time-dependent tuning of walking balance control and the presence of aftereffects in older adults following a single session of optical flow perturbation training.

Methods: 13 older adults participated in a randomized, crossover design performed on different days that included 10 minutes of treadmill walking with (experimental session) and without (control session) optical flow perturbations. We used electromyographic recordings of leg muscle activity and 3D motion capture to quantify foot placement kinematics, lateral margin of stability, and antagonist coactivation during normal walking (baseline), early (min 1) and late (min 10) responses to perturbations, and aftereffects immediately following perturbation cessation (post).

Results: At their onset, perturbations elicited 17% wider and 7% shorter steps, higher step width and length variability (+171% and +132%, respectively), larger and more variable margins of stability (MoS), and roughly twice the antagonist leg muscle coactivation (p-values<0.05). Despite continued perturbations, most outcomes returned to values observed during normal, unperturbed walking by the end of prolonged exposure. After 10-min of perturbation training and their subsequent cessation, older adults walked with longer and more narrow steps, modest increases in foot placement variability, and roughly half the MoS variability and antagonist lower leg muscle coactivation as they did before training.

Conclusions: Findings suggest that older adults: (i) respond to the onset of perturbations using generalized anticipatory balance control, (ii) deprioritize that strategy following prolonged exposure to perturbations, and (iii) upon removal of perturbations, exhibit short-term aftereffects that indicate a lessening of anticipatory control, an increase in reactive control, and/or increased balance confidence. We consider this an early, proof-of-concept study into the clinical utility of prolonged exposure to optical flow perturbations as a training tool for corrective motor adjustments relevant to walking balance integrity toward reinforcing task-specific, reactive control and/or improving balance confidence in older adults.