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: 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: bryappie

Pain, tingling, or numbness in the calves, thighs, and/or buttocks brought on by physical activity is called intermittent claudication (IC). IC is the primary symptom of peripheral arterial disease (PAD) that occurs because blockages in the lower extremity arteries hinder blood flow to the legs. Current conservative treatment for patients with PAD consists of supervised treadmill walking exercise (STW). After STW, patients with PAD exhibit improvement in maximum walking distances(1), but little is known regarding gait biomechanics. This study was conducted to determine the effectiveness of the current conservative treatment on gait biomechanics and lower extremity strength in patients with PAD.

Fifteen patients (total of 26 claudicating limbs; age: 66±1.9 years, height: 1.75±2.24 m, weight: 89.23± 5.01 kg), diagnosed with PAD were recruited from the Omaha Veterans’ Affairs Medical Center. Patients visited the lab prior to and after completing a prescribed 12-week, 3 times/week STW. Five over-ground walking trials for each leg were performed while kinematics (60 Hz; Motion Analysis Corp., USA) and kinetics (600 Hz; Kistler Instruments, USA) were recorded pre and post 12-weeks STW. Absolute claudication distance (max walk distance) was determined through a progressive, graded treadmill protocol (2 miles/hour, 0% grade with 2% increase every 2 minutes) until maximal claudication pain. Inverse dynamics was used to calculate peak joint torques and powers for the ankle, knee, and hip (Visual 3D, C-Motion, Inc., USA). Peak plantar flexor strength was assessed using an isokinetic dynamometer (Biodex Medical Systems, USA). Differences pre to post STW were determined using paired t-tests (α=0.05).

In agreement with the previous literature, absolute claudication distance significantly increased post STW. No significant differences between baseline and post STW were detected for joint torques and powers, or lower extremity strength. Supervised treadmill walking appears to address a cardiovascular mechanism in PAD. STW may only be helping to improve stamina. The lack of any functional training may be reinforcing poor mechanics, which will continue to hinder patient function with a poor chance for long term benefits to be realized. Future investigation should include functional exercises in patients with PAD.

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: rakshatha

Multisensory integration is driven by a process of sensory reweighting during which each input is assigned a weight depending on the current functional state of a particular sensory system, the task itself and the context in which it is being performed. The primary aim of this study was to determine which of the two inputs between ankle proprioception and vision is upweighed during a postural control task when the two inputs provide conflicting information pertaining to direction of body sway. Achilles tendon vibration and visual flow were used to create sensory conflict, which produced center of pressure (COP) sway in opposite directions when applied independently. The baseline conditions (1) consisted of eyes open quiet stance condition, eyes closed with vibration applied on the Achilles tendons (2) and eyes open with visual flow (3). The experimental condition simultaneously combined vibration and visual flow. COP excursions were recorded in 10 healthy young adults to evaluate the magnitude and direction of sway produced by vibration and/or visual flow. Additionally, lower body joint kinematics were evaluated to understand the multi-segmental strategies and their adaptation to the various sensory manipulations. The results showed that visual flow moderated the extent of backward COP and ankle angular displacement produced when vibration was applied independently. Additionally, visual flow was also found to reduce the extent of predominant hip strategy generated by ankle vibration. The findings show that visual input plays a significant role in maintaining stability and that ankle proprioception is downweighed during conflicts between vision and proprioception. This has important implication for balance training using controlled visual flow in patients with balance disorders and elderly.

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: 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.

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: ADiffendaffer

Peripheral arterial disease (PAD) is a vascular disease characterized by atherosclerotic blockages restricting blood flow to the lower extremities causing pain and discomfort with physical activity. Several studies have previously found decrements in ambulation associated with PAD, such as decreased joint moments and powers before and after the onset of claudication pain [1]. With decreases in moments and powers, the joint work may also be decremented as well. Thus, the purpose of this study was to investigate the positive and negative work at the ankle, knee and hip of PAD patients in a pain-free condition and compare them to gait-velocity matched controls.

Five patients with PAD and five healthy older controls were consented for participation. Subjects walked along a 10-meter walkway at their own self-selected speed while kinematics and kinetics were recorded. Each subject rested one minute between trials to mitigate fatigue and prevent ischemic pain. The positive and negative joint work for the PAD patients’ affected limb and the right limb of each control were analyzed and compared through independent t-tests (α=0.05).

Five PAD patients (66.6 + 6.2 years; 178.2 + 9.3 cm; 102.6 + 18.5 kg; 1.16 + 0.07 m/s) and five controls (69 + 4.6 years; 174.5 + 1.6 cm; 79.4 + 8.14 kg; 1.30 + 0.09 m/s) were used for analysis.

From this study it was found that patients with PAD exhibit a 26% reduction in positive ankle joint work during stance phase than their healthy counterparts (p=0.012).

Listed In: Biomechanics
Name: sson2

Knee pain is 1 of 5 leading causes of disability by altering lower-extremity muscle function and gait mechanics. While transcutaneous electrical nerve stimulation (TENS) mitigates deficits of muscle function due to pain, it is unclear whether TENS improves gait mechanics. Each of 15 participant (24±3yrs, 71±12kg, 178±7cm) was assigned to the TENS or matched placebo group (23±2yrs, 72±14kg, 177±9cm). Participants underwent 3 different experimental saline infusion sessions (hypertonic, isotonic, control) in a counterbalanced order, separated by 48-h. Hypertonic (5% NaCl) or isotonic (0.9% NaCl) saline was infused into the infrapatellar fat pad for 50-min. No infusion was administered to the control session. Participants and investigators were blinded to the saline solution. A 20-min TENS or placebo treatment was administered, which was blinded to participants. Gait kinematic data were collected using the high-speed video (240 Hz) and force-sending tandem treadmill (1200 Hz) at each time interval (baseline, infusion, treatment, post-treatment). Functional ANOVA (α=0.05) were used to evaluate difference between 2 groups (TENS, placebo) over time. Pairwise comparison functions with 95% confidence interval were plotted to determine specific difference. Hypertonic saline infusion (pain) resulted in increased (1) ankle dorsiflexion (38-75% of stance), (2) knee valgus (20-40%), (3) knee flexion (40-90%), (4) hip adduction (72-100%), (5) hip flexion (50-90%). However, there was no group x time interaction for all kinematics. Altered gait strategies due to pain may play a role in long-term compensation that could have consequences for the joint. TENS treatment, however, did not acutely reduce the deficits in aforementioned kinematic variables.

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.