Our ongoing work combining virtual reality and optical flow perturbations to investigate mechanisms governing walking balance control has led to a recently accepted publication in the journal IEEE Transactions on Neural Systems & Rehabilitation Engineering.

 

Franz JR, Francis CA, Allen MS, Thelen DG (In Press). Visuomotor entrainment and the frequency-dependent response of walking balance to perturbations.

Abstract. Visuomotor entrainment, or the synchronization of motor responses to visual stimuli, is a naturally emergent phenomenon in human standing. Our purpose was to investigate the prevalence and resolution of visuomotor entrainment in walking and the frequency-dependent response of walking balance to perturbations. We used a virtual reality environment to manipulate optical flow in ten healthy young adults during treadmill walking. A motion capture system recorded trunk, sacrum, and heel marker trajectories during a series of 3-min conditions in which we perturbed a virtual hallway mediolaterally with systematic changes in the driving frequencies of perceived motion. We quantified visuomotor entrainment using spectral analyses and changes in balance control using trunk sway, gait variability, and detrended fluctuation analyses (DFA). ML kinematics were highly sensitive to visual perturbations, and instinctively synchronized (i.e., entrained) to a broad range of driving frequencies of perceived ML motion. However, the influence of visual perturbations on metrics of walking balance was frequency-dependent and governed by their proximity to stride frequency. Specifically, we found that a driving frequency nearest to subjects’ average stride frequency uniquely compromised trunk sway, gait variability, and step-to-step correlations. We conclude that visuomotor entrainment is a robust and naturally emerging phenomenon during human walking, involving coordinated and frequency-dependent adjustments in trunk sway and foot placement to maintain balance at the whole-body level. These findings provide mechanistic insight into how the visuomotor control of walking balance is disrupted by visual perturbations and important reference values for the emergence of balance deficits due to age, injury, or disease.

The UNC/NCSU Applied Biomechanics Lab had a highly successful week presenting at the 40th annual meeting of the American Society of Biomechanics. Congratulations to all our students and trainees!

Our work using motion-capture guided ultrasound imaging to measure dynamic variation in the Achilles tendon moment arm in vivo during walking has been accepted for publication in the journal Computer Methods in Biomechanics and Biomedical Engineering. This work was performed in collaboration with our colleagues at the University of Wisconsin-Madison.

 

 

Rasske K, Thelen DG, Franz JR. Variation in the Human Achilles Tendon Moment Arm during Walking (In Press).

Abstract. The Achilles tendon (AT) moment arm is an important determinant of ankle moment and power generation during locomotion. Load and depth-dependent variations in the AT moment arm are generally not considered, but may be relevant given the complex triceps surae architecture. We coupled motion analysis and ultrasound imaging to characterize AT moment arms during walking in 10 subjects. Muscle loading during push-off amplified the AT moment arm by 10% relative to heel strike. AT moment arms also varied by 14% over the tendon thickness. In walking, AT moment arms are not strictly dependent on kinematics, but exhibit important load and spatial dependencies.

Our review paper investigating the prevalence of and mechanisms governing age-associated reductions in propulsive power generation during walking has been accepted for publication in Exercise and Sports Sciences Reviews.

Franz JR. The age-associated reduction in propulsive power generation in walking (In Press).

 

Abstract. Propulsive power generation during push-off in walking decreases with advancing age. A common explanation is an accommodation for sarcopenia and muscle weakness. Yet, muscle strengthening often yields disappointing outcomes for walking performance. We examine the hypothesis that declines in force or power generating capacity of propulsive leg muscles cannot fully explain the age-related reduction in propulsive power generation during walking.

 

The Applied Biomechanics Laboratory and collaborators from the University of Wisconsin-Madison and the University of Virginia have been awarded a five-year NIH R01 award to study the role of age-related changes in tendon on motor performance. Dr. Franz’ lab will combine dynamic ultrasound imaging, quantitative motion capture, and biofeedback to investigate changes in localized Achilles tendon mechanics across the lifespan, as well as the effects on leg muscle contractile behavior and motor coordination during walking. Collaborators at the University of Wisconsin-Madison will employ dynamic MRI and shear wave elastography to characterize triceps surae muscle-tendon architecture and elasticity, and both sites will contribute their imaging work to the development and validation of multi-scale computational models of 3D muscle and tendon tissue mechanics at the University of Virginia.

The Applied Biomechanics Laboratory is very excited to have had SIX research abstracts accepted for presentation at the annual meeting of the American Society of Biomechanics this summer in Raleigh, NC! Congratulations to all of the students on this big accomplishment!!

 

List of ABL abstracts at the American Society of Biomechanics Meeting:

Browne MG and Franz JR, Biofeedback decouples the effects of speed and propulsive force on joint power generation in walking.

Francis CA, Franz JR, Acuna S, Thelen DG, Gait and balance training improves gait variability in old adults.

Rasske K, Thelen DG, Franz JR, Aging effects on the Achilles tendon moment arm in vivo during walking.

Franz JR, Francis CA, Allen MS, Thelen DG, Visuomotor entrainment and the control of balance in walking.

Stokes HE, Thompson JD, Franz JR, The association between kinematic variability and muscle activity during perturbed walking.

Thompson JD, Thelen DG, Franz JR, Does walking balance control adapt to perturbed optical flow?

 

 

The Applied Biomechanics Laboratory had a wonderful time participating in the very first National Biomechanics Day on April 7! We had a terrific group of students and faculty involved at both UNC and NC State.

http://www.unc.edu/spotlight/exploring-new-discipline/

The Applied Biomechanics Laboratory was awarded a two year grant from the University Research Council titled “The role of propulsive capacity reserves in age-related mobility impairment.” We will collaborate on the project with the Drs. Pietrosimone and Ryan in the UNC Dept. of Exercise and Sports Science.

Drs. Jason Franz, Caterina Gallippi and Xiaogang Hu have been awarded a seed grant from the UNC/NC State Rehabilitation Engineering Core to fund their new collaboration, which aims to enhance understanding of neurological, functional, and mechanical non-uniformity in muscle following stroke.

The Applied Biomechanics Laboratory, in a collaboration spanning UNC and NC State, was awarded a one year seed grant from the UNC/NC State Rehabilitation Engineering Core titled “Electrocortical activity governing human balance control.” This work will be performed in collaboration with Prof. CS Nam from the NC State Dept. of Industrial and Systems Engineering.