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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Submitted by Michael Browne

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.


Submitted by Danilo Catelli

INTRODUCTION: Cam femoroacetabular impingement (FAI) is characterized by an osseous overgrowth on the femoral head-neck junction [1], leading to pain and limited range of motion (ROM) during daily life activities [2]. Corrective surgery is highly recommended and performed in order to reduce or eliminate pain and further development of osteoarthritis (OA). However, it is still unclear whether it would lead to improved functional mobility. The purpose was to compare kinematic variables of the operated limb between FAI patients when performing a squat task pre-surgery and at around 2-year follow-up. A secondary objective consisted of express the results in a biomechanical functional score to quantify the joint kinematics of FAI patients compared to healthy control (CTRL) participants.
METHODS: Eleven male patients (7 arthroplasty: 34.6±8.1 years, 25.7±3.2 kg/m2; 4 open: 33.3±7.1 years, 24.9±1.9 kg/m2) and 21 CTRL (2F/19M, 33.4±6.7 years, 25.4±3.3 kg/m2) participants were recruited from the orthopaedic surgeon’s clinical practice. Patients were assigned to either an arthroplasty or open FAI surgery correction. The participants signed prior to their participation a consent form approved by the hospital and university ethics board. Patients agreed to undergo motion analysis prior to and 2 years after the surgery. The CTRL were selected based on similar age and BMI as the FAI group and underwent the same motion analysis protocol.
At the local hospital, CT scan was performed in all participants to confirm an alpha-angle higher than 55º and also establish their pelvic and knee bony landmarks. At the motion laboratory, the participants were outfitted with 45 reflective markers and performed a minimum of five trials of deep squat at a self-selected pace. Three-dimensional joint kinematics (200 Hz) of the lower limbs were captured using a ten-camera motion analysis system (Vicon, UK). Kinematics data were processed in Nexus 1.8.3 (Vicon, UK) using a modified Plug-In-Gait model and exported with a custom MATLAB script (Mathworks, USA) to calculate group averages and extract relevant variables. All trials were time-normalized based on a full squat cycle (descent and ascent phases) and individual averages for each participant were calculated across the trials.
Four kinematic variables were included in the analysis: pelvis, hip, knee, and ankle sagittal angles. The normalized root-mean-square deviation (nRMSD) was calculated between the FAI and the CTRL groups for both pre- and post-surgery conditions, expressed by


Submitted by Arian Iraqi

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
Submitted by Alison McDonald

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
Submitted by Ali Falaki

Over the past years, we have developed a test for postural stability based on the theory of synergies stabilizing salient performance variables. In this study, effects of Parkinson's disease (PD) and dopamine-replacement therapy on multi-muscle synergies stabilizing the center of pressure (COP) coordinate were explored between: (1) a cohort of 11 patients without clinically identifiable postural problems (Hoehn-Yahr stage II) and 11 age-matched controls, and (2) a cohort of 10 patients tested off- and on-medication, with and without postural problems (stage II and III, n = 5 per stage). Participants stood on a force platform and performed cyclical body sway at 0.5 Hz along the anterior-posterior direction. Electromyographic signals from 13 leg and trunk muscles were used to compute: (1) the amount of inter-cycle variance that did not affect (VUCM) and affected (VORT) COP coordinate, and (2) the magnitude of the cycle-to-cycle motion that did not change (motor equivalent: ME) and changed (non-motor equivalent: nME) the COP coordinate. We hypothesized that both methods would produce indices sensitive to PD and dopaminergic medications. Compared to controls, patients showed significantly smaller inter-cycle VUCM and ME components suggesting a less flexible, and hence less stable, behavior. Moreover, inter-cycle variance within/orthogonal to the UCM correlated with ME/nME displacements. Results suggest clinical utility of variance and motor equivalence analyses of postural instability in early stages of PD and quantifying the effects of dopamine-replacement drugs. The analysis of motor equivalence is particularly attractive because it requires only a handful of trials (observations).


Listed In: Neuroscience
Submitted by Sunku Kwon

Chronic ankle instability (CAI) patients often exhibit altered walking mechanics, due to strength and proprioceptive deficits associated with CAI. Reduced strength and proprioception function may alter walking energetic patterns, by reducing energy absorption and generation capability. It is unclear whether strength and proprioceptive training can affect walking energetics for CAI patients. PURPOSE: To examine the effect of a 6-week ankle and hip rehab program on ankle, knee, and hip joint energetic patterns during walking in CAI patients. METHODS: 15 CAI patients (23 ± 2 yrs, 178 ± 8 cm, 76 ± 9 kg, 83 ± 7% FAAM ADL, 56 ± 10% FAAM Sports, 3.6 ± 1.1 MAII, 4.7 ± 2.0 ankle sprains) performed ankle and hip strength and proprioceptive exercises (i.e., theraband, wobble board, etc.) 3 times per week, for 6 weeks (rehab group). 14 CAI patients (22 ± 2 yrs, 177 ± 9 cm, 75 ± 12 kg, 81 ± 9% FAAM ADL, 56 ± 12% FAAM Sports, 3.4 ± 1.2 MAII, 5.9 ± 3.3 sprains) performed no rehab exercises (control group). We measured ankle, knee, and hip joint power during walking for all patients before and after 6 week duration. Functional statistics (α = 0.05) were used to evaluate the influence of the rehab exercises on joint power for both groups across the entire stance phase of walking. RESULTS: The rehab intervention resulted in up to 0.07 W/kg more positive ankle power (concentric) between 19 and 26% of stance and up to 0.06 W/kg more positive knee power (concentric) between 40 and 48% of stance. No changes were detected in hip joint power during the stance phase of walking. CONCLUSION: Strength and proprioceptive training resulted in an improved gait energetic efficiency via increased ankle and knee power generation during mid-stance. As greater muscular strength can lead to an increase in power absorption and generation, the intervention focusing on strength could be beneficial in improving walking energetics in a CAI population.


Listed In: Biomechanics, Gait
Submitted by Gregory Tierney

Rugby is intrinsically an impact sport which results in concussions being a frequent injury within the game. Repeated concussion is linked to early-onset dementia and depression, and the rules for limiting repeated concussion are an ongoing controversy. Therefore a greater understanding of the dynamics of head impacts in rugby and the mechanism of concussion is required. Accordingly, this study focuses on assessing the use of Model Based Image Matching (MBIM) and multi-camera view video for measuring six degree of freedom head kinematics during an impact event in rugby union. The matching is performed on video evidence using 3-D animation software Poser 4. The surroundings are built in the virtual environment based on the real dimensions of the sport field. A skeleton model is then used to fit the player’s anthropometry for each video frame thus allowing player kinematics to be measured. The results from this initial study suggest that the MBIM method can be applied to head impact cases in rugby union. The head kinematics results from this case are similar to those reported in literature. The MBIM method should be applied to a number of head impact cases to establish thresholds for concussion injuries in rugby. The data gained from the MBIM method can allow for more reliable kinematic data to be inputted into finite element analysis and rigid body simulations of concussion impacts. This can allow multi-axis force measurements to be measured within the brain and neck. This can ultimately lead to an improvement in concussion injury prevention and management.


Submitted by Christopher McCrum

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.


Submitted by Daniel Kuhman

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
Submitted by Elizabeth Bell

Objectives: The conventional push-up is a popular exercise used by the American College of Sports Medicine to test participant muscular endurance. Push-ups require changes in the ground reaction forces generated at each point of contact with the ground (all four extremities) which are achieved through muscular contractions. Although this exercise is common, the motor control mechanisms used in this motion are relatively unknown. We investigated whether humans adjust individual limb forces (push-up synergies) as they reached volitional fatigue and evaluated the hypothesis that muscular fatigue influences synergistic actions between the forces produced at the hand contact points. Approach: Twenty-one volunteers participated in a single motion capture trial where they performed as many push-ups as possible, stopping at self-determined failure. Push-ups were completed to a controlled three-beat rhythm (down, up, hold plank) at a rate of 24 repetitions per minute. Participants were instructed to arrange themselves in a plank position with each extremity within the bounds of an embedded force platform and analog data was collected at a frequency of 1000Hz. An index of synergy, defined as correlations between vertical forces, was calculated for every downward and upward motion within the push-up trial. Findings: Between-arm vertical forces were positively correlated during upward and downward motion. Positive correlation indicates that limbs worked together to produce increases or decreases needed for center of mass movement. Upward limb synergy significantly (p ≤ 0.00) decreased as participants neared volitional fatigue while downward limb synergy did not significantly change (p = 0.77). Conclusions: We found that muscular fatigue affected the synergistic actions between limbs in upward motion but not in downward motion. After muscular fatigue, between arm synergy was reduced only during concentric muscle contractions. Public Health Significance: Better understanding the synergistic changes produced by fatigue could be used to evaluate or better understand control changes behind pathologic gait or movement adaptations.