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Paper Accepted (August 2022)

August 2, 2022

Quantifying Relations Between Walking Speed, Propulsive Force, and Metabolic Cost

Richard E. Pimentel, Jordan N. Feldman, Michael D. Lewek, Jason R. Franz

Archive of "Frontiers in Sports and Active Living". - PMC


Walking speed is a useful surrogate for health status across the population. Walking speed appears to be governed in part by interlimb coordination between propulsive (FP) and braking (FB) forces generated during step-to-step transitions and is simultaneously optimized to minimize metabolic cost. Of those forces, FP generated during push-off has received more significant attention as a contributor to walking performance. Our goal was to first establish empirical relations between FP and walking speed and then to quantify their effects on metabolic cost in young adults. To specifically address any linkage between FP and walking speed, we used a self-paced treadmill controller and real-time biofeedback to independently prescribe walking speed or FP across a range of condition intensities.  Walking with larger and smaller FP led to instinctively faster and slower walking speeds, respectively, with about 80% of variance in walking speed explained by FP. We also found that comparable changes in either FP or walking speed elicited predictable and relatively uniform changes in metabolic cost, together explaining ~53% of the variance in net metabolic power and ~14% of the variance in cost of transport. These results provide empirical data in support of an interdependent relation between FP and walking speed, building confidence that interventions designed to increase FP will translate to improved walking speed. Repeating this protocol in other populations may identify other relations that could inform the time course of gait decline due to age and disease.

Paper Accepted (July 2022)

July 23, 2022

Quadriceps Muscle Action and Association with Knee Joint Biomechanics in Individuals with ACL Reconstruction

Amanda E. Munsch, Alyssa Evans, Hope C. Davis-Wilson, Brian Pietrosimone, Jason R. Franz

Journal of Applied Biomechanics on Twitter: "Anterior Cruciate Ligament Injury Risk Variables During Unanticipated Cutting and Decelerating Tasks #biomechanics" / TwitterAbstract. Insufficient quadriceps force production and altered knee joint biomechanics after anterior cruciate ligament reconstruction (ACLR) may contribute to a heightened risk of osteoarthritis (OA). Quadriceps muscles lengthening dynamics affect force production and knee joint loading; however, no study to our knowledge has quantified in vivo quadriceps dynamics during walking in individuals with ACLR or examined correlations between quadriceps dynamics and joint biomechanics. Our purpose was to quantify bilateral vastus lateralis (VL) fascicle length change behavior and the association thereof with gait biomechanics during the weight acceptance phase of walking (i.e., between heel-strike and the instant of pKEM) in individuals with ACLR. We hypothesized that ACLR limbs would exhibit more fascicle lengthening than contralateral limbs. We also hypothesized that ACLR limbs would exhibit positive correlations between VL fascicle lengthening and knee joint biomechanics during weight acceptance in walking. We quantified bilateral VL contractile dynamics via cine B-mode ultrasound imaging in 18 individuals with ACLR who walked on an instrumented treadmill and compared outcomes between limbs. In partial support of our hypothesis, ACLR limb VL fascicles activated without length change on average during early stance while fascicle length on the contralateral limb decreased. We found a positive association between fascicle lengthening and increase in KEM in both limbs in individuals following ACLR. Together, our results suggest that examining quadriceps muscle dynamics may elucidate underlying mechanisms relevant to OA.

Paper Accepted (July 2022)

July 6, 2022

Slowing Down to Preserve Balance in the Presence of Optical Flow Perturbations

Andrew D. Shelton, Ellora M. Mctaggart, Jessica L. Allen, Vicki S. Mercer, Jason R. Franz

Gait & Posture | Journal | by Elsevier

Background: The use of sensory and mechanical perturbations applied during walking has grown in popularity due to their ability to elicit instability relevant to falls. However, the vast majority of perturbation studies on walking balance are performed on a treadmill at a fixed speed. Research question: The aim of the study was to quantify the effects of mediolateral optical flow perturbations on walking speed and balance outcomes in young adults walking with fixed-speed and self-paced treadmill controllers. Methods: Fifteen healthy young adults (8 female, age: 23.1±4.6 yrs) completed four five-minute randomized walking trials in a speed-matched virtual reality hallway. In two of the trials, we added continuous mediolateral optical flow perturbations to the virtual hallway. Trials with and without optical flow perturbations were performed with either a fixed-speed or self-paced treadmill controller. We measured walking speed, balance outcomes (step width, margin of stability, local dynamic instability) and gait variability (step width variability and margin of stability variability). Results: We found significant increases in step width (+20%, p=0.004) and local dynamic instability (+11%, p = 0.008) of participants while responding to optical flow perturbations at a fixed treadmill speed. We found no significant differences in these outcome measures when perturbations were applied on a self-paced treadmill. Instead, participants walked 5.7% slower between the self-paced treadmill controller conditions when responding to optical flow perturbations (1.48±0.13 m/s vs. 1.57±0.16 m/s, p=0.005). Significance: Our findings suggest that during walking, when presented with a balance challenge, an individual will instinctively reduce their walking speed in order to better preserve stability. However, comparisons to prior literature suggest that this response may depend on environmental and/or perturbation context. Cumulatively, our results point to opportunities for leveraging self-paced treadmill controllers as a more ecologically-relevant option in balance research with potential clinical applications in diagnostics and rehabilitation.