11:30
MSK & Sweat sensing
Chair: Richard Lopata
11:30
15 mins
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Stretch hyperreflexia during Gait in children with cerebral palsy using dynamic ultrasound imaging
Eline Flux, Babette Mooijekind, Lynn Bar-On, Edwin van Asseldonk, Annemieke Buizer, Marjolein van der Krogt
Abstract: Stretch hyperreflexia is often assessed passively, but can express itself differently during dynamic activities such as gait (1). Studies assessing dynamic stretch hyperreflexia typically compare muscle activity to modeled musculotendon lengthening (1, 2), while fascicle lengthening is more directly related to stretch reflex activity (3). We hypothesized that children with stretch hyperreflexia display dynamic hyperreflexia during gait, which is more pronounced when measuring fascicle lengthening compared to musculotendon lengthening.
3D-gait analysis including electromyography (EMG) was performed on fourteen children with spastic cerebral palsy (CP) and fifteen typically developing (TD) children walking on an instrumented treadmill. Medial gastrocnemius fascicle lengthening was imaged using dynamic ultrasound and musculotendon lengthening was simulated using OpenSim.
Dynamic stretch hyperreflexia was identified during late swing and early stance, and defined as a sudden EMG peak preceded by a manually detected increased lengthening velocity within a reflex window of 40-120 ms. As a proxy for stretch reflex magnitude, the ratio between RMS EMG and maximum fascicle or musculotendon velocity within the reflex window was calculated, and compared between CP and TD using independent t-tests.
62.5% of CP showed clearly increased fascicle velocity preceding increased EMG activity in late swing, compared to 50% for musculotendon velocity. For early stance, this was 53.8% and 46.2% respectively. EMG/velocity ratios were significantly larger in children with CP compared to TD children, for both fascicle (91.5±57.4 vs. 28.6±14.5 for swing and 362.0±329.0 vs 96.7±135.6 for early stance, p<0.001) and musculotendon velocity (50.9±26.6 vs 15.0±8.4 for swing and 120.9±52.1 vs 29.2±16.8 for early stance, p<0.001). This difference was more pronounced when measuring musculotendon velocity instead of fascicle velocity, both in swing (240% and 220% larger ratio respectively) and in stance (315% and 275% respectively).
The increased EMG/velocity ratio suggests that children with CP indeed have increased dynamic stretch reflexes during gait compared to TD, which can be more frequently attributed to fascicle lengthening. Notwithstanding, increased activity was not always preceded by a clear peak in fascicle velocity. Therefore, other triggers might be involved in causing the increased activity, such as fascicle or tendon acceleration or other tissue dynamics, which requires further research.
1. Flux, J NeuroEngineering Rehabil 18:151 (2021) 1-17
2. van der Krogt, Clin Biomech 24:5 (2009) 422-428
3. Cronin, J Electromyogr Kinesiol 21:8 (2011) 197-207
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11:45
15 mins
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Determining stress relaxation of trabecular bone to simulate realistic press-fit conditions of cementless orthopaedic implants
Thomas Gersie, Thom Bitter, David Wolfson, Robert Freeman, Nico Verdonschot, Dennis Janssen
Abstract: INTRODUCTION
The success of orthopaedic implants designs mainly depends on the initial fixation. The accurate modelling of this primary stability relies on accurate material properties. To our knowledge, nonlinear stress relaxation of trabecular bone has not been quantified in relation to bone mineral density and strain level. In this work, we present preliminary data of multiple stress relaxation experiments.
METHODS
32 Trabecular femoral bovine bone cylinders were harvested. Stress relaxation experiments on 16 samples were conducted by applying a uniaxial compressive strain (0.2-0.8%) for 24 hours to determine the optimal test duration. The other samples, divided over four BMD groups, the samples were compressed with 0.2% strain for 30 minutes, after which they were stored to recover for 24 hours. This sequence was repeated for 0.4%, 0.6, and 0.8% strain.
RESULTS
After 24 hours, stress relaxation ranging from 41.0% to 68.7% was observed. Up to 52.9% of this stress relaxation occurred in the first 10 minutes . Moreover, stress relaxation did not level off after 24 hours. At last, it was shown that samples with a lower BMD displayed a lower peak force than samples with a higher BMD, with similar stress relaxation behavior.
DISCUSSION
Most of the stress relaxation occurs within 10 minutes, which in clinical practice is still during surgery. However, stress relaxation continued even after 24 hours of testing. It is therefore important to model the viscoelastic behavior up to 24 hours. Moreover, performing an experiment for 30 minutes provides an ideal tradeoff between fit accuracy and experimental testing time. Furthermore, it was shown that the BMD has an influence on the peak force, but no significant effect on the relative stress relaxation.
Further testing will illuminate the relation between BMD and the viscoelastic response for both bovine and human trabecular bone. The next step is to incorporate the viscoelastic behavior in simulations of primary fixation in total knee arthroplasty components to demonstrate the influence of bone relaxation on primary fixation.
SIGNIFICANCE
This work contributes to improving analytical tools to study the initial fixation of orthopaedic implants to allow testing of new designs in a preclinical phase.
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12:00
15 mins
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Musculoskeletal shoulder loads during different bench press variations
Lisa Noteboom, Marco Hoozemans, DirkJan Veeger, Frans Van der Helm
Abstract: Introduction: While shoulder injuries as result of the bench press exercise are commonly reported [1], no biomechanical evidence regarding the technique with the lowest injury risk is currently available. Therefore, the aim of the present study was to compare musculoskeletal shoulder loads during several variations of the bench press.
Methods: Ten experienced strength athletes performed 21 technical variations of the barbell bench press, including variations in grip width of 1,1.5 and 2 bi-acromial widths (BAW), shoulder abduction angles of 45, 70 and 90, and scapula poses including neutral, retracted, and released conditions. Motions and forces were recorded by an opto-electronic measurement system and an instrumented barbell. An OpenSim musculoskeletal shoulder model was employed to estimate net shoulder moments, muscle forces, and joint reaction forces for all technique variations. Within-subject ANOVAs with Bonferroni Post-hoc’s were performed to reveal the effects of the technique variations.
Results: First results revealed that for all abduction angles, net shoulder moments were significantly larger with retracted shoulders, compared to neutral and released shoulders (p<0.05). For grip width, shoulder moments were significantly higher at 2 BAW compared to 1.5 BAW (at 70 and 90) and significantly higher for 1.5 BAW compared to 1.0 BAW (at 70). Moreover, shoulder moments were significantly larger for 90 compared to 45 abduction. No interactions were found. The highest mean shoulder moment (SD over subjects) of 37.317.3 Nm was found for a combination of retracted shoulders, 2 BAW and 70 abduction, whereas the lowest mean shoulder moment of 20.611.0 Nm was found for a combination of released shoulders, 1 BAW and 70 abduction. Results of muscle forces and joint reaction forces in the glenohumeral and acromioclavicular joints will be added before the conference.
Discussion/Conclusion: The first results indicate that more load is placed at the shoulder during wide grips and retracted shoulders. Loads can be reduced by applying a technique with a small grip and released or neutral scapulae. However, other parameters including the muscle forces and joint reaction forces during the varying techniques need to be evaluated before final conclusions regarding the technique with the lowest injury risk can be drawn.
References
1. Bengtsson, V., Berglund, L., & Aasa, U. (2018). Narrative review of injuries in powerlifting with special reference to their association to the squat, bench press and deadlift. BMJ open sport & exercise medicine, 4(1), e000382.
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12:15
15 mins
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Blood glucose prediction based on sweat sensing by modeling the transport mechanism of glucose
Xiaoyu Yin, Elisabetta Peri, Eduard Pelssers, Jaap den Toonder, Massimo Mischi
Abstract: Introduction: Monitoring blood glucose levels is of utmost importance to improve the health and quality of life of patients affected by diabetes. Sweat sensing could be a non-invasive alternative to conventional invasive blood sampling for glucose monitoring. To achieve clinical relevance, models that can predict glucose levels in blood from measured glucose levels in sweat are necessary. However, such models are under-investigated. In this paper, we present a novel method based on biophysical modeling of the transport mechanism of glucose through a sweat gland and we propose a strategy to predict blood glucose levels by sweat sensing.
Methods: The strategy we propose is based on a forward model that builds on the work of La Count et al. [1], and it numerically simulates the transport process of glucose from the blood to sweat using COMSOL Multiphysics. The main innovations in our model are in the transport mechanism of glucose from the interstitial space into the secretory coil, where the influx of glucose and water are combined. For making a backward prediction that gives an estimate of blood glucose levels from known sweat values, we used a sequential quadratic programming optimization algorithm based on the forward model. We used five datasets from the literature [1], including experimental glucose levels in blood and sweat, for both the forward model and backward strategy and validated them in terms of root-mean-square-error (RMSE) and root-mean-square-percentage-error (RMSPE).
Results and Discussion: The average RMSE and RMSPE obtained by our forward model was 10±13 μmol/L and 10%±6%, smaller than for the original model (RMSE=15±18 μmol/L, RMSPE=20%±8%). This suggests that the proposed modifications improve the prediction accuracy of the model. The average RMSE and RMSPE of the backward model were 0.55±0.50 mmol/L and 6%±4% respectively, showing satisfactory prediction accuracy. Altogether, our study enables a more precise forecast of blood glucose changes based on known sweat glucose levels, possibly contributing to an overall improvement in diabetes monitoring via non-invasive sweat sensing.
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12:30
15 mins
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Analysis of sweat gland activity for improved monitoring of sweat biomarkers
Jelte Haakma, Elisabetta Peri, Simona Turco, Emma Moonen, Eduard Pelssers, Jaap Den Toonder, Massiom Mischi
Abstract: Sepsis is a life-threatening condition that affects 30 million people every year [1]. Currently, sepsis monitoring is performed by measuring blood lactate levels via regularly repeated blood draws.
Sweat is a relatively unexplored bio-fluid containing information that can provide broad insights into the metabolic activity of the human body [2], and that enables semi-continuous monitoring of biomarkers. In particular, sweat lactate may be a valuable biomarker for the detection of sepsis.
The relationship between blood and sweat lactate levels, however, is debated.
Previous studies suggested that the main contributor to the lactate in sweat is the lactate produced by the sweat gland metabolism itself. It is hypothesized that an estimation of the sweat rate per gland could be used to determine the amount of lactate produced by the sweat glands, thereby elucidating the relationship between blood and sweat lactate.
However, currently, no accurate methods to determine the sweat rate per gland are available.
We are developing a microfluidic sweat sensing patch that can determine the sweat rate per gland. To guide the design of the patch, we developed a deterministic model of the sweat generation process as well as the sweat sensing patch to simulate the signals produced by such a sweat patch. An analysis of the obtained signals should enable the estimation the number of active sweat glands as well as the sweat rate per gland. To make this possible, the analysis algorithm decomposes the signal into the contributions of the individual glands, based on the signature of each gland.
Interpretation of the results shows that the predominant cause possible errors and uncertainties in determining the number of active glands and sweat rate per sweat gland relates to signals that cannot be decomposed uniquely. When only one gland is simulated, an error-rate of 0% is obtained, while larger numbers of simulated glands yield errors up to 10%. Future studies will include the simulation of different sweat rates, the reduction of the current error-rates by using a probabilistic approach and the addition of stochastic elements to the model to realize a more realistic simulation of the sweat gland activity.
[1] Bauer et al. Critical care 2020
[2] Ghaffari et al. Sensors and Actuators B: Chemical 2021
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12:45
15 mins
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Joint stiffness estimation via EMG-driven muscoloskeletal modeling
Christopher Pablo Cop, Alfred Schouten, Bart Koopman, Massimo Sartori
Abstract: The simultaneous modulation of joint torque and stiffness enables humans to perform large repertoires of movements, while adapting to external mechanical demands in a versatile way. Multi-muscle force control is key for joint torque and stiffness modulation. However, the inability to directly measure muscle force in the intact moving human prevents understanding how muscle force causally links to joint torque and stiffness. Joint stiffness is predominantly estimated via joint perturbation-based experiments in combination with system identification techniques. However, these techniques provide joint-level stiffness estimations with no causal link to the underlying muscle forces. Moreover, the need for joint perturbations limits the generalisability and applicability to study natural movements.
We present an electromyography (EMG)-driven musculoskeletal modelling framework that can be calibrated to match reference joint torque and stiffness profiles simultaneously via a multi-term objective function.
EMG-driven models calibrated on less than 2 s of reference torque and stiffness data could blindly estimate reference profiles across 100 s of data not used for calibration. Model calibrations using an objective function comprising torque and stiffness terms always provided less feasible solutions than an objective function comprising solely a torque term, thereby reducing the space of feasible muscle-tendon parameters. Results also showed the proposed framework’s ability to estimate joint stiffness in unperturbed conditions, while capturing differences against stiffness profiles derived during perturbed conditions.
The proposed framework may provide new ways for studying causal relationships between muscle force and joint torque and stiffness during movements in interaction with the environment, with broad implications across biomechanics, rehabilitation and robotics.
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