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: wkorgan

Following amputation, an amputee must learn to walk again using a prosthesis. A goal of prosthetic rehabilitation is to reduce and eliminate asymmetries between the prosthetic leg and sound leg which may decrease the negative effects of long term force and work demands on the sound leg. An amputee-specific physical therapy program provides structured motor learning to aid in developing proper gait mechanics. However, physical therapy is not standard of care for all individuals receiving their first prosthesis due to limited evidence showing improved gait. Thus, the purpose of this study was to determine whether amputees receiving physical therapy have better gait mechanics than those that do not. It was hypothesized that those who underwent an amputee-specific physical therapy program would display a more symmetrical gait pattern. Transtibial amputees walked overground at self-selected pace while kinetic (600Hz) and kinematic (60Hz) data were collected. The therapy group had previously received 2-3 therapy sessions per week for 3 months. Asymmetries were determined through dependent t-tests (α=0.05) comparing sound leg and prosthetic leg kinetic variables. Of the 23 kinetic variables tested, 17 variables showed significant difference between the sound leg and prosthetic leg for the group that did not receive the amputee-specific physical therapy. For the group that had previously received the therapy, only 4 variables showed differences between the sound and prosthetic leg. Thus, we showed that individuals partaking in amputee-specific physical therapy have a more symmetrical gait which results on less force and energy demands on the sound leg.

Name: alexandros.chri...

Victims of improvised explosive devices (IEDs) that have presented spinal injury in recent conflicts have been shown to have a high incidence of lumbar spine fractures. Previous studies have shown that the initial positioning of spinal bone-disc-bone complexes affects their biomechanical response when loaded quasi-statically; such a correlation, however, has not been explored at appropriate high loading rate scenarios that simulate injury. This study aims to investigate the response of lumbar spine cadaveric segments in different postures under axial impact conditions. Three T11-L1 bi-segments were dissected and tested destructively in a drop tower under flexed/neutral/extended postures. Strains were measured on the vertebral body and the spinous process of T12. Forces were measured cranially using a 6-axis load cell, and a high-speed camera was used to capture displacements and fracture. The impacted specimens were CT-scanned to identify the fracture pattern. Whilst axial force to failure was similar for flexed and extended postures, the non-axial forces and the bending moments, however, were dissimilar between postures. Although all specimens showed a burst fracture pattern, the extended posture failed more posteriorly. This suggests that axial force alone is not adequate to predict injury severity in the lumbar spine. This insight would not have been possible without the use of the 6-axis load cell. As metrics for spinal injury in surrogates take into account only the axial force, this programme of work may provide data for a better injury criterion and allow for a mechanistic understanding of the effects of posture on injury risk.

Name: sson2

Background: Knee joint pain (KJP) independently alters motor function and gait mechanics, and these alterations may accelerate chronic knee joint disease. While TENS restores motor function deficits, it is unclear whether TENS restores compensatory gait mechanics. The purpose was to examine the effects of KJP on lower-extremity joint moments, and the effects of TENS on the aforementioned variables. We hypothesized that KJP will result in altered gait patterns, and TENS will help restore these mechanical alterations.
Methods: We randomly selected 15 subjects for the TENS group, after which subjects were matched for the placebo group. Subjects underwent 3 sessions (hypertonic, isotonic, control). A 20-gauge flexible catheter was inserted into the right infrapatellar fat pad, and an infusion pump infused a saline of 0.154 mL•min¯¹ for 50 min (total = 7.7 mL). A TENS protocol was set at a biphasic mode with 120 µs and 180 Hz for 20 min. To blind placebo treatment, subjects in the placebo group was told that an electrical stimulation had been set to sub-sensory level. High-speed video (240 Hz) and an instrumented treadmill (1200 Hz) were used for gait analysis. Functional analysis of variance were used to evaluate differences between groups over time for joint moments. The mean curve with 95% CIs is represented by polynomial functions, showing us the entire stance, rather than identifying discrete peak points. If 95% CIs did not cross zero, significant difference existed (P < 0.05).
Discussion: KJP independently increase internal knee varus moments, which were consistent with previous finding using patients with osteoarthritic knee pain. These compensatory gait patterns may be a result of a pain-avoidance motor deficits strategies. Since observed patterns can create altered mechanical and biological stress patterns on articular surface, it may increase the risk of degenerative knee disease. However, attempting to reduce perceived pain and increase neuron activation through TENS can help overcome deficits in knee and hip joint moments.

Name: AndreaA

Strength measurements are popular in the clinical practice to evaluate the health status of patients and quantify the outcome of training programs. Currently a common method to measure strength is based on Hand Held Dynamometers (HHD) which is operator-dependent. Some studies were conducted on repeatability of strength measurements but they were limited to the statistical analysis of repeated measurements of force. In this work, the authors developed a methodology to study the quality of knee flexion/extension strength measurements by measuring the effective HHD position and orientation with respect to the patient. HHD positioning attitude was measured by means of an Optoelectronic System for which a marker protocol was defined ad-hoc. The approach allowed to assess quality of measurements and operator’s ability by means of quantitative indices. The protocol permitted the evaluation of: angles of HHD application, angular range of motion of the knee and range of motion of the HHD. RMSE parameters allowed to quantify the inaccuracy associated to the selected indices. Results showed that the operator was not able to keep the subject’s limb completely still. The force exerted by the subject was higher in knee extension and the knee range of motion was higher than expected, however the operator had more difficulties in holding the HHD in knee flexion trials. This work showed that HHD positioning should be as accurate as possible, as it plays an important role for the strength evaluation. Moreover, the operator should be properly trained and should be strong enough to counteract the force of the subject.

Name: rlkrup

Calculating and interpreting joint moments using marker position and ground reaction force (GRF) data is a fundamental part of gait biomechanics research. Due to noise in marker positions, these data are low-pass filtered prior to performing inverse dynamics. Traditionally, kinematic data are filtered at low cutoff frequencies (~6 Hz) and kinetic data are filtered at high frequencies (~30-100 Hz). This technique can result in joint moment impact peaks, particularly during high-impact movements. Filtering marker and GRF data at the same cutoff frequency has been suggested to attenuate these impact artefacts. The effect of various filtering approaches on joint moments in walking is unknown. The purpose of this study was to compare the effect of low-pass filtering cutoff frequencies on joint moments during walking. We hypothesized that filtering would not affect peak joint moments during walking due to smaller violations of the rigid body assumption compared to high-impact movements. Kinetic and kinematic data were collected for twenty-four health adults walking at self-selected speed. Marker position and GRF were smoothed using a 4th-order dual-pass Butterworth filter with cutoff frequencies of 6/45 Hz, 6/6 Hz, 10/10 Hz, for markers and GRF, respectively. A one-way repeated measures ANOVA tested for the effect of filter frequency on peak hip and knee joint moments. Peak hip and knee moments were greater when filtered at 10/10 Hz compared to 6/45 Hz. Although there were differences between cutoff frequency conditions, the effect sizes were small, suggesting that the differences are not large enough to have a meaningful effect.

Listed In: Biomechanics
Name: Michelle Norris

The purpose of this study was to investigate stride rate (SR) dynamics of a recreational runner participating in his debut marathon. Tibial accelerometry data obtained during a half marathon (R1) and marathon (R2) were utilised. SR data were extracted utilising novel computational methods and descriptive statistics were utilised for analysis of R2, and comparison of the first half of the marathon (R2half) to R1. Results indicate that the participant employed comparable SR strategy in R1 and R2half. For R2 a combined decreasing trend in SR and increased variance in SR from 30 km (R2 =0.0238) was observed. Results indicate that the participant had the ability to maintain SR strategy for the first half of the marathon, however as fatigue onset occurred this ability decreased. Running strategies on SR during fatigue may be of future use to recreational runners.

Name: lmtennan

INTRODUCTION: Workers in industry wear steel toe boots; however, these boots are inflexible and may restrict foot movement. Occupational kneeling is also associated with an increased risk of knee osteoarthritis. Examination of the effects of work boots in kneeling is needed to better understand potential injury risk. Therefore, the purpose of this study was to analyze the center of pressure (COP) at the knee during kneeling when shod and barefoot.
METHODS: Fifteen, young, healthy males completed five 10-second static kneeling trials in each condition. Lower body kinematics were obtained using the Optotrak system (Certus and 3020, NDI, Waterloo, ON, CA). Force data were measured from a force plate under the knee of the dominant leg (OR6-7, AMTI, Watertown, MA, USA).
The mean COP location was determined with respect to the medial tibial plateau (normalized to tibial width) and the tibial tuberosity (normalized to tibial length) for the medial/lateral and longitudinal directions, respectively.
RESULTS: COP was located more medially in the shod condition (34% (±10.6%) tibial width) compared to the barefoot condition (40% (±11.9%) tibial width) (p=0.0485). COP was located above the tibial tuberosity, with no difference between conditions (shod 11% (±3.2%) tibial length, barefoot: (7%) (±8.8%) tibial length) (p=0.97).
DISCUSSION: There is a difference in COP location in shod compared to barefoot kneeling. A COP location farther from the joint center of rotation, as occurred in the frontal plane of the shod condition, would increase the moment arm of the ground reaction force and thus the moment at the knee.

Listed In: Biomechanics
Name: chrismccrum

Unilateral peripheral vestibular disorder (UPVD) negatively affects upper and lower body motor performance, but postural control during quiet stance in UPVD patients has not been directly compared with dynamic stability control after an unexpected perturbation during locomotion. We analysed centre of pressure (COP) characteristics during static posturography in UPVD patients and healthy controls and compared this with performance of a trip recovery task. 17 UPVD patients and 17 healthy controls were unexpectedly tripped while walking on a treadmill. The margin of stability (MoS) was calculated at touchdown (TD) of the perturbed step and the first six recovery steps. Posturography was used to assess postural stability during 30 seconds of standing with eyes open and closed using a force plate. The trip reduced the MoS of the perturbed leg (p<0.05) with no significant differences in MoS between the groups. Controls returned to MoS baseline level in five steps and patients did not return within the six steps. UPVD patients showed a greater total COP sway path excursion (closed eyes only), anterior-posterior range of COP distance and a more posterior COP position in relation to the posterior boundary of the base of support. There were no significant correlations between COP sway path excursion and MoS values. We concluded that UPVD patients have a diminished ability to control and recover dynamic gait stability after an unexpected trip and lower static postural stability control compared to healthy matched controls, but that trip recovery and static postural control rely on different control mechanisms.

Name: TDick

Introduction and Objectives: Traditional motion analysis provides limited insight into muscle and tendon forces during movement. This study used B-mode ultrasound, in combination with measured joint angles and scaled musculoskeletal models, to provide subject-specific estimates of in vivo Achilles tendon (AT) force. Previous studies have used ultrasound images, tracked in 3D space, to estimate AT strains during walking, running, and jumping [1,2]. Our approach extends this work in one novel way. Specifically, we characterized AT stiffness on a subject-specific basis by recording subjects’ ankle moments and AT strains during a series of isometric tests. We then used these data to estimate AT force during movement from in vivo measurements of tendon strain.
To demonstrate this approach, we report AT forces measured during cycling. Cycling offers a unique paradigm for studying AT mechanics. First, because the crank trajectory is constrained, joint angles and muscle-tendon unit (MTU) lengths of the gastrocnemius (MG, LG) and soleus (SOL) are also constrained. By varying crank load, subjects’ ankle moments can be altered without imposing changes in MTU lengths. For this study, 10 competitive cyclists were tested at 4 different crank loads while pedaling at 80 rpm. Based on published EMG recordings (e.g., [3]) and on in vivo tendon force buckle data from one subject [4], we hypothesized that the cyclists’ AT forces would increase systematically with crank load.

Methods: We coupled B-mode ultrasound with motion capture, EMG, and pedal forces to estimate in vivo AT forces non-invasively during cycling and during a series of isometric ankle plantarflexion tests. Marker trajectories were tracked using an optical motion capture system. Joint angles and MTU lengths were calculated based on scaled musculoskeletal models [5] using OpenSim [6]. A 50 mm linear-array B-mode ultrasound probe was secured over the distal muscle-tendon junction (MTJ) of the MG and was tracked using rigid-body clusters of LEDs. AT lengths were calculated as the distance from a calcaneus marker to the 3D coordinates of the MG MTJ. Subject-specific AT force-strain curves were obtained from isometric tests using ultrasound to track the MTJ, markers to track both the ultrasound probe and the AT insertion, and a strain gauge to measure the net ankle torques generated by each of the subjects at ankle angles of -10° dorsiflexion, 0°, +10° plantarflexion, and +20° plantarflexion. AT strain during cycling was converted to AT force using each subject’s force-strain relation. Subject-specific tendon slack lengths were calculated as the mean tendon length at 310° over all pedal cycles, based on examination of the AT length changes and on published data showing that this position in the pedal cycle precedes tendon loading across multiple pedalling conditions [4].

Results: Peak AT forces during cycling ranged from 1320 to 2160 N ± 400 N (mean± SD) and increased systematically with load (p<0.001; Fig. 1A/B). At the highest load, the peak AT forces represented, on average, 50 to 70 % of the combined MG, LG, and SOL muscles’ maximum isometric force-generating capacity, as estimated from the muscles’ scaled volumes [7], the muscles’ scaled optimal fiber lengths [5], and a specific tension of 20-30 N/cm2. Peak AT forces occurred midway through the pedaling downstroke, at about 80°, which is consistent with the AT forces directly measured from one subject [4] and with patterns of EMG during cycling [3]. Peak AT strains during cycling were uncoupled from the MG MTU strains and ranged from 3 to 5 % across the different loads examined, measured at the MG MTJ.

Conclusion: Our results are consistent with published data from a single subject in which AT force was measured using an implanted tendon buckle [8]; however, our results were obtained non-invasively using ultrasound and motion capture. These methods substantially augment the experimental tools available to study muscle-tendon dynamics during movement.

[1]Lichtwark and Wilson, 2005, J Exp Biol, 208(24), 4715-4725.
[2]Lichtwark et al., 2007, J Biomech, 40(1), 157-164.
[3]Wakeling and Horn, 2009, J Neurophysiol, 101(2), 843-854.
[4]Gregor et al., 1987, Int J Sports Med, 8(S1), S9-S14.
[5]Arnold et al., 2010, Ann Biomed Eng, 38(2), 269-279.
[6]Delp et al., 2007, IEEE Trans Bio Med Eng, 54(11), 1940-50.
[7]Handsfield et al., 2014, J Biomech, 47(3),631-638.
[8]Gregor et al. 1991, J Biomech, 24(5), 287-297

Name: ktsong

One in three individuals who suffer a lateral ankle sprain (LAS) subsequently develop chronic ankle instability. However, our inability to properly treat acute LAS is not surprising given our limited understanding of post-LAS consequences. 12 patients (21.6±2.9yrs; 172.9±13.1cm; 79.1±21.4kg) with an acute LAS participated. All participants were evaluated for dorsiflexion range of motion (DFROM), time-to-boundary (TTB) in single limb balance (SLB), and self-reported function (SRF) at 1-week, 2-weeks, 4-weeks, 6-weeks, and 8-weeks post injury. Both the involved and uninvolved limbs were measured during the patients first test session. DFROM was assessed using the weight-bearing lunge test and all participants performed 3, 10s of single limb stance with eyes open on a force plate to measure their single limb balance. SRF was measured using the Foot and Ankle Ability Measure (FAAM) and FAAM-Sport (FAAM-S). Post injury time points were compared to a control condition using multivariate ANOVAs (α=0.05). Relative to the control condition, FAAM and FAAM-S were significantly lower at 1-week and 2-weeks post injury. The FAAM-S was also significantly lower score compare to control condition at 4-weeks post-injury. Both FAAM and FAAM-S were not significant different at 6-weeks post-injury. Post-injury TTB measures and DFROM were not significantly different from the control condition. Non-significant declines in DFROM and TTB were observed as in this sample of acute LAS and appear to present with unique recovery patterns. Different recovery patterns among the tested outcomes indicate the need for further research with a larger cohort and for a longer post-injury duration.