Virtual Poster Session

Welcome to the Virtual Poster Session, a new and powerful tool for networking and information exchange. Here you can share your work, search though the poster library, and start a dialogue with others in your field. Each uploaded poster that pertains to force measurement and testing can currently be used to apply for an academic travel scholarship; please see the Scholarships page for application details and deadlines.

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Name: kuhmand15

Old versus young adults exhibit increased hip and decreased ankle joint mechanical output during level and incline walking. This distal-to-proximal redistribution of joint torques and powers is now a well-established age-related gait adaptation and has been termed biomechanical plasticity. The effect of physical capacity, which varies greatly in old adults, on this gait adaptation remains unclear. For example, high capacity old adults (i.e. those with fast walking speeds) might either retain a more youthful gait strategy or adopt larger magnitudes of plasticity in order to walk well. The purpose of this study was to quantify the relationships between physical capacity and biomechanical plasticity in old adults during level and incline walking. We conducted 3D gait analyses on 32 old adults (>70 yrs) as they walked over level ground and up a 10° incline at self-selected speeds. We used motion capture (Qualisys AB) and force platforms (AMTI) to collect kinematic and ground reaction force data, respectively. To measure physical capacity, we used the SF-36 Physical Component score and to define biomechanical plasticity we created ratios of hip extensor to ankle plantarflexor peak torques, angular impulses, peak positive powers, and work. We conducted correlation analyses between SF-36 PC scores and the biomechanical plasticity ratios. Positive relationships existed between SF-36 PC scores and all biomechanical plasticity ratios during level walking. Similar results were observed during incline walking, however only three of these four relationships reached statistical significance. Our results suggest that old adults of higher physical capacities exhibit larger magnitudes of biomechanical plasticity.

Listed In: Biomechanics, Gait
Name: mgbrowne

Even prior to walking slower, older adults walk with a diminished push-off – decreased propulsive forces (FP) accompanied by reduced ankle moment and power generation. The purpose of this study was to identify age-related differences in the joint-level modifications used to modulate FP generation during walking. We posit that there are two possibilities for older adults to enhance FP generation. First, older adults may increase ankle power generation and thereby alleviate compensatory demands at the hip. Alternatively, older adults may opt to exacerbate their distal to proximal redistribution by relying even more on the hip musculature.
10 healthy young adults and 16 healthy older adults participated in this study. Subjects walked at their preferred speed while watching a video monitor displaying their instantaneous FP while instructed to modify their FP to match target values representing normal and ±10% and ±20% of normal. For all trials, we estimated lower extremity joint kinematics and kinetics.
During normal walking, older adults exerted smaller FP and ankle power than young adults. Enhancing FP via biofeedback alleviated mechanical power demands at the hip, without changes in ankle power. Further, older adults walked with increased FP without increasing their total positive joint work. Thus, given the same total requisite power generation, older adults got ‘more bang for their ankle power buck’ using biofeedback.

Name: chrismccrum

Bilateral vestibular hypofunction (BVH) is a bilateral reduction or loss of vestibular function resulting in balance deficits and an increased falls risk. As part of a larger study, this experiment aimed to assess how spatiotemporal gait characteristics and their variability change across different walking speeds in patients with BVH. Nine patients (55±15y) with BVH have participated thus far. Experiments were conducted on the CAREN Extended system (Motekforce Link, Amsterdam, The Netherlands). Following multiple familiarisation trials, the participants completed five recorded two minute walking bouts at different speeds (0.6m/s, 0.8m/s, 1.0m/s, 1.2m/s and 1.4m/s). 60 strides per speed were analysed and the means, standard deviations and coefficients of variation (CV) of stride length and time, step length and width, double support time and swing phase toe clearance were calculated. Stride length, step length and toe clearance all increased with increases in walking speed (P<0.001). Stride and double support time decreased with increased walking speed (P<0.0001). No walking speed effect was found for step width (P=0.25). Significant reductions in variability with increases in walking speed were found for stride length, stride time, step length, toe clearance (P<0.01) and double support time (P<0.05). A significant increase in step width variability was observed with increases in walking speed (P=0.0033). These preliminary data suggest that while anteroposterior gait characteristics may improve in terms or variability with increases in walking speed in these patients, mediolateral motions may become more variable, which may have implications for mediolateral stability and falls risk in patients with BVH.

Name: meadowkd

Disc function is mechanical, and measures of disc mechanical function are important to address spine function, degenerative disc disease, and low back pain. In vivo measures of disc mechanical function are needed, however the current standard in disc imaging is to acquire a single static image and classify the disc’s appearance using qualitative integer scales for degree of degeneration. Current grading standards are acknowledged as insufficient to identify symptomatic discs for treatment. In addition, static T2 weighted MRI cannot provide mechanical function information – mechanics must be measured as the change following a load or deformation perturbation. Because the disc experiences significant compression and height loss throughout the day, and because flexion-extension postures are often associated with low back pain, these physiological mechanical perturbations have potential to be used to quantify disc mechanics in vivo. The objective of this study was to use MRI-based methods to quantify in vivo disc function by measuring changes in disc geometry and T2 relaxation time with diurnal changes and with controllable posture. Quantification of in vivo disc mechanics by using diurnal loading or prescribed posture changes has potential to improve our ability to identify, evaluate, and treat degenerative disc disease. Symptomatic discs may have aberrant mechanics; if so, in vivo measurements of mechanical function may, with continued development, facilitate diagnosis of pathological discs.

Name: deluccaj27

Residual stresses are known to exist in human intervertebral discs but have not been incorporated in finite element models. A multigeneration model was applied to the annulus fibrosus of the intervertebral disc to simulate residual stresses arising from growth and remodeling. The intervertebral disc shape and compressive creep were used to verify that the multigeneration approach generates realistic values of residual stress. The model was then validated by comparing its 6 degree-of-freedom mechanical response to experimental data. Human intervertebral discs were tested in a custom-built hexapod in all 6 degrees-of-freedom (lateral shear, anterior-posterior shear, torsion, bending, flexion, and compression). Incorporating residual stresses resulted in a finite element model which can predict 4 degrees-of-freedom while excluding residual stresses produces a finite element model that can only predict 2 degrees-of-freedom.

Name: danialkia

Knowledge of ligamentous contributions to joint stability is essential to restore normal joint range of motion and functionality through reconstruction procedures. Although, there has been numerous studies on the pathomechanics of the elbow joint, there have been very few rigorous and systematic attempts to characterize the roles of soft tissues during clinically relevant motions.
Five fresh frozen cadaveric elbows from three male subjects were used for this study. In-vitro simulations were performed using a VIVO six degree-of-freedom (6-DOF) joint motion simulator (AMTI, Watertown, MA) capable of virtually simulating the effects of soft tissue constraints (virtual ligaments). This study introduces a unique, hybrid experimental-computational technique for measuring and simulating the biomechanical contributions of ligaments to elbow joint kinematics and stability. In vitro testing of cadaveric joints is enhanced by the incorporation of fully parametric virtual ligaments, which are used in place of the native joint stabilizers to characterize the contribution of elbow ligaments during simple flexion-extension motions using the principle of superposition.
our results demonstrate the importance of AMCL and RCL structures as primary stabilizers under valgus and varus loading respectively. Virtual ligaments demonstrate the ability to restore the VV stability of the joint in the absence of any soft tissues attached to the osseous structures. This demonstrates the effectiveness of “virtual” ligaments for in vitro testing of elbow joint biomechanics, with applications in pre-clinical assessment of elbow implants.

Name: mcdonaac

The relationship between EMG and muscle force changes with muscle fatigue, making interpretation of load sharing between muscles over time challenging. The purpose of this investigation was to evaluate the efficacy of normalizing EMG data to repeated, static, submaximal exertions to mitigate the fatigue artifact in EMG amplitude. Participants completed simulated repetitive work tasks, in 60-second work cycles, until exhaustion and surface EMG was recorded from 11 muscles. Every 12 minutes, participants completed a series of 4 submaximal reference exertions. Reference exertion EMG data were used in 6 normalizing methods including 1 standard (normalized to initial reference exertion) and 5 novel methods: (i) Fatigue Only, (ii) Linear Model, (iii) Cubic Model, (iv) Points Forward, and (v) Points Forward/Backward. EMG data were normalized to each novel methods and results were compared to the Standard Method. The significant differences between the novel methods and the Standard Method were dependent on the muscle and the number of time points in the analysis. Correlation analysis showed that the predicted cubic model points correlated better to the actual data points than the linear predicted values. This novel method to create “fatigue debiased” ratios may better reflect the changing muscular loads during repetitive work. This method was evaluated with a novel data set examining the effects of repetitive shoulder exertions, in multiple axes, on load sharing in the shoulder over time. The normalizing method was effective at distinguishing between the effects of fatigue artifact on EMG amplitude and load sharing between muscles over time.

Listed In: Biomechanics

Falls due to slippery conditions are among the primary causes of disabling workplace injuries. Despite the extensive amount of human slip studies in the literature, only a handful of studies have reported ground reaction forces at the instant of slip initiation. The purpose of this study was to quantify the vertical ground reaction forces (VGRF) at slip initiation during unexpected human slips across different footwear-contaminant conditions. Forty-seven healthy subjects were unexpectedly exposed to a liquid–contaminant, while the vertical force was measured at the moment that the foot began to start slipping. The average VGRF were between 100 and 300 N and varied significantly across the footwear. These forces were significantly less than the typical forces (400-700 N) applied during slip-resistance measurements. This finding may suggest that available coefficient of friction (ACOF) measurements should use lower force levels in order to achieve higher relevance to the onset of slipping.

Listed In: Biomechanics, Gait
Name: dgroulx

Lateral ankle sprains are common orthopedic injuries and often result in chronic ankle instability (CAI). Studies have shown that the CAI population typically has decreased ankle proprioception and possibly a greater reliance on visual feedback when compared to healthy controls. However, little is known about how the postural control characteristics change in those with and without CAI when external visual feedback is manipulated. Purpose: To compare postural control characteristics of persons with CAI, Copers and healthy adults when performing a single leg balance test with and without external feedback. Method: The definition for CAI used for this study includes persons who have experienced recurrent ankle sprains, in addition to self-reported “feelings of instability” and “giving way,” and a score on the Identification of Functional Ankle Instability (IdFAI) of 11 or greater. 18 participants with CAI, 15 Copers, and 18 healthy controls (mean age of all groups: 22 years) performed the Athlete Single Leg Test on the Biodex Balance System (BBS) at Level 4 which involved a high degree of platform instability. All participants completed 2 trials without and with feedback in that order. Center of pressure position was recorded and the two trial mean was used for further analysis. Overall stability index (OSI) defined as the mean distance of the center of pressure from the center of the platform was obtained from the system. Sway area was calculated using custom Matlab script. Separate 3 (Group) x 2 (Feedback) mixed ANOVAs were run using overall stability index (OSI), and sway area as dependent variables. Results: Significant feedback main effect showed participants had significantly lower (better) OSI value with feedback (1.4±0.1) compared to without feedback (2.6±0.2; P < 0.001) but sway area with feedback (8.61±2.33cm2) was similar to without feedback (10.94±2.43 cm2). There was no significant group main effect or interaction observed for either of the variables. Conclusion: Results suggest that external visual feedback may not play a significant role in helping persons with CAI improve their postural control.

Name: kaconway

The age-associated decline in propulsive push off power generated during walking plays a central role in the reduction of mobility and independence in older adults. Previous work suggests that this population retains an underutilized propulsive reserve during normal walking that dynamometry assessments fail to effectively assess. This is especially notable when assessing plantarflexor mechanical output, which often yield implausible (i.e., ≥100%) values of ‘functional capacity utilized (FCU)’, most frequently defined as the ratio of the peak ankle moment during the push-off phase of walking to that during a maximum isometric voluntary contraction. Therefore, the extent to which we utilize our propulsive capacity, how utilization changes as we age, and the factors that govern utilization and maximum propulsive capacity remain unclear. Utilizing a feedback controlled, motor driven horizontal impeding force system and a novel maximum force condition which systematically increases applied force, we can find a participant’s maximum propulsive capacity. During this condition, we find that younger adults retain a reserve of 48% in terms of ground reaction force, 22% in terms of ankle moment and 43% in terms of ankle power, which may not be effectively predicted using dynamometry assessments. As an important first step, we present data showing that a more functional task, walking with horizontal impeding forces, could potentially more effectively assess propulsive reserves in younger adults.

Listed In: Biomechanics