nils-herrmann/clean_scirepeval huggingface dataset:
Effects of vibrotactile feedback on postural sway in trans-femoral amputees: A wavelet analysis.
Venue: Journal of biomechanics

Loss of somatosensory feedback after amputation inflicts a serious challenge to achieve postural stability. Improving motor skills by incorporating sensory feedback in rehabilitation protocols for persons with lower limb amputation has been gaining traction over time. However, the control mechanisms involved in this regarding time-frequency analysis have not been investigated yet. The purpose of this study was to explore the frequencies/time-scales responsible for postural stability in trans-femoral amputees with vibrotactile feedback. Center of Pressure (COP) signals were collected from 5 trans-femoral amputees and 10 healthy subjects during weight shifting balance tasks. A customized foot insole was used to estimate the COP for actuation of vibratory feedback. The evaluation of postural sway fluctuations by means of COP excursions with vibrotactile feedback was computed by wavelet transform method. Vibrotactile feedback was found to be effective in controlling low frequency postural sway in amputees. We found significantly higher energy (p = 0.004, 0.0007) at shorter time-scales (j = 6,7, freq. = 0.6-1.25 Hz) and lower energy (p = 0.0006) at longer time-scale (j = 10, freq. = 0.078 Hz) in amputees with vibrotactile feedback in comparison to healthy subjects using Coif 1 wavelet. We also found significant increase in energy (p = 0.003) during forward weight shifting with vibrotactile feedback in the sound limb of amputees in comparison to no feedback session at frequency/time-scales corresponding to somatosensory acuity (j = 6-8, freq. = 0.3-1.5 Hz) using Haar wavelet. These findings reflect the higher contribution of somatosensory receptors in amputees with vibrotactile feedback and may provide a better understanding of the mechanisms associated with standing balance in terms of time-frequency analysis.
The stretch-shortening cycle effect is prominent in the inhibited force state.
Venue: Journal of biomechanics

It has been suggested that residual force enhancement (RFE) contributes to the work enhancement observed in stretch-shortening cycles (SSC). Based on recent findings that RFE was preserved in the reduced force state, one may speculate that the SSC effect may be preserved in the reduced force state as well. The purpose of this study was to examine the magnitude of the SSC effect in inhibited skeletal muscle force states. Normal and inhibited force conditions were analyzed using skinned rabbit soleus fibres (N = 18). The inhibited force condition was achieved by adding 2,3-Butanedione monoxime into the activating solution. For both conditions, a SSC test and a pure shortening test were performed. In the SSC tests, fibres were activated at an average sarcomere length of 2.4 μm, and then stretched to 3.0 μm. Immediately after the end of the stretch, fibres were shortened to 2.4 μm. In the pure shortening tests, fibres were activated at an average sarcomere length of 3.0 μm and then shortened to 2.4 μm. The relative increase in mechanical work in the shortening phase of the SSC compared to the pure shortening condition was defined as the SSC effect index, and the magnitude of the SSC effect was compared between the normal and the inhibited force condition. The SSC effect was greater in the inhibited compared to the normal force condition (p < 0.001). We conclude that the SSC effect is at least in part preserved in the reduced force state.
Cell aggregation on nanorough surfaces.
Venue: Journal of biomechanics

The ability to control adhesion and the spatial organization of cells over nanoscale surfaces is essential in tissue engineering, regenerative medicine, the growth of organoids and spheroids as an in-vitro-model of human development and disease. Nonetheless, despite the several different works that have explored the influence of nanotopography on cell adhesion and clustering, little is known about how the forces arising from membrane conformational change developing during cell adaptation to a nanorough surface, and the cell-cell adhesion forces, interact to guide cell assembly. Here, starting from the works of Decuzzi and Ferrari, who examined how the energy of a cell varies while adhering to a nanoscale surface, and of Armstrong and collaborators, who developed a continuous model of cell-cell adhesion and morphogenesis, we provide a description of how nanotopography can modulate cellular clustering. In simulations where the parameters of the model were varied over large intervals, we found that nanoroughness may induce cell aggregation from a homogenous, uniform state, also for weak cell-cell adhesion. Results of the model are relevant in bio-engineering and biomedical nanotechnology, and may be of interest for those involved in the design and fabrication of biomaterials and scaffolds for tissue formation and repair.
Ureterovesical junction deformation during urine storage in the bladder and the effect on vesicoureteral reflux.
Venue: Journal of biomechanics

The motivation behind this study is to understand how ureterovesical junction (UVJ) deformation during urine storage in the bladder affects vesicoureteral reflux (VUR), when urine flows backward from the bladder toward the kidneys. Using nonlinear, large deformation finite element simulations, the deformation of the bladder wall during urine storage is modeled in this study. The bladder wall is assumed to be a homogeneous, isotropic, hyperelastic spherical shell with a finite thickness. The UVJ is defined as a straight elliptical cylindrical hole through the bladder wall at the reference configuration before inflation. Broad parametric studies on different UVJ configurations are performed as the bladder inner surface stretches by a factor of 2.2 from an initial radius corresponding to bladder volumes of 10% to slightly over physiologic capacity. For each considered UVJ configuration, a simple fluid analysis of the tunnel flow resistance compares different bladder inner surface stretch ratios. Our model shows that the deformation of the UVJ depends on its orientation with respect to the bladder wall radial and circumferential directions. We show that as the UVJ insertion angle increases, the UVJ cross section decreases and its tunnel length increases during urine storage causing the closure of the UVJ and a rise in its flow resistance. The modeling results indicate that UVJ closure could be explained by bladder wall deformation rather than the local differential pressure. Our findings are consistent with the accepted primary anti-reflux mechanism of the UVJ being dependent on the tunnel length-to-diameter ratio and consequently the UVJ insertion angle.
Knee joint biomechanics of patients with unilateral total knee arthroplasty during stationary cycling.
Venue: Journal of biomechanics

Stationary cycling is typically recommended following total knee arthroplasty (TKA) operations. However, knee joint biomechanics during cycling remains mostly unknown for TKA patients. Biomechanical differences between the replaced and non-replaced limb may inform applications of cycling in TKA rehabilitation. The purpose of this study was to examine the knee joint biomechanics of TKA patients during stationary cycling. Fifteen TKA participants cycled at 80 revolutions per minute and workrates of 80 W and 100 W while kinematics (240 Hz) and pedal reaction forces using a pair of instrumented pedals (1200 Hz) were collected. A 2x2 (limb × workrate) repeated measures ANOVA was run with an alpha of 0.05. Peak knee extension moment (KEM, p = 0.034) and vertical pedal reaction force (p = 0.038) were significantly reduced in the replaced limbs compared to non-replaced limbs by 21.3% and 5.3%, respectively. Peak KEM did not change for TKA patients with the increased workrate (p = 0.750). However, both peak hip extension moment (p = 0.009) and ankle plantarflexion moment (p = 0.017) increased due to increased workrate. Patients following TKA showed similar decreases in peak KEM and vertical pedal reaction force in their replaced compared to non-replaced limbs, as previously seen in gait. Patients of TKA may rely on their hip and ankle extensors to increases in workrate. Increasing intensity by 20 W did not exacerbate any inter-limb differences for peak KEM and vertical PRF.
Hospital bed height influences biomechanics during bed egress: A comparative controlled study of patients with Parkinson disease.
Venue: Journal of biomechanics

Although a significant proportion of patient falls occur during egress from the hospital bed, the biomechanical adaptations during egress from different bed heights are still largely unknown. The purpose of this study was to evaluate the effect of hospital bed height on natural transition during egress in patients with Parkinson disease (PD). Twelve patients with PD and fourteen healthy elderly adults (HEA) were recruited and the natural transition during egress from three different bed heights (low, medium and high) were recorded for each participant using a motion capture system and force plates. The bed egress time, joint kinematics, ground reaction force and center of mass (CoM) were compared using a two-factor repeated ANOVA to determine the effects of three bed heights and two groups. The results showed that patients with PD had a significantly increased bed egress time, decreased peak of pelvis anterior tilt, hip flexion, and anteroposterior distance between pelvis center and CoM compared to HEA. Additionally, both PD and HEA groups increased the peak of trunk, hip and knee flexions to generate forward CoM momentum and joint torque to rise from a low bed height. These findings indicated that patients with PD invoked a more conservative movement pattern than HEA during egress to improve postural stability. The low bed height increased demands of balance and postural control during egress which exacerbates the risk of falls for patients with PD.
Reorienting the tibial baseplate improves the registration accuracy of model-based radiostereometric analysis.
Venue: Journal of biomechanics

Accuracy of model-based radiostereometric analysis (MBRSA) in calculating tibial baseplate migration depends on baseplate shape and orientation relative to the imaging planes. The primary objectives were to introduce a new method for determining the optimal baseplate orientation to minimize bias error during MBRSA and to demonstrate the clinical usefulness of the method using a knee positioning guide to repeatably orient the baseplate. A tibia phantom was rotated to achieve 24 different orientations with three pairs of radiographs acquired at each orientation. Radiographs were processed in MBRSA software and the mean maximum total point motion (MTPM), an indicator of bias error during model registration, was plotted as a function of the rotation angles to determine the optimal orientation and a range of acceptable orientations. The bias error decreased 85% between the reference orientation and the optimal orientation. An acceptable range of orientations was defined by a decrease in bias error more than 50%. Future researchers can use this method to determine the optimal orientation and a range of acceptable orientations for their specific baseplate to minimize bias error. Clinical usefulness was demonstrated by repeatedly imaging a knee model placed in a knee positioning guide (simulated clinical positioning) and demonstrating that the mean orientation ± one standard deviation fell within the acceptable range of orientations. Thus, use of a knee positioning guide was an effective tool for repeatable patient positioning and should be considered for future RSA studies to maintain consistent positioning during a longitudinal study.
Altered stress field of the human lens capsule after cataract surgery.
Venue: Journal of biomechanics

The lens capsule of the eye is important in focusing light onto the retina during the process of accommodation and, in later life, housing a prosthetic lens implanted during cataract surgery. Though considerable modeling work has characterized the mechanics of accommodation, little has been done to understand the mechanics of the lens capsule after cataract surgery. As such, we present the first 3-D finite element model of the post-surgical human lens capsule with an implanted tension ring and, separately, an intraocular lens to characterize the altered stress field compared to that in a model of the native lens capsule. All finite element models employed a Holzapfel hyperelastic constitutive model with regional variations in anisotropy. The post-surgical lens capsule demonstrated a dramatic perturbation to the stress field with mostly large reductions in stresses (except at the equator where the implant contacts the capsule) compared to native, wherein maximal changes in Cauchy stress were -100% and -145% for the tension ring and intraocular lens, respectively. However, implantation of the tension ring produced a more uniform stress field compared to the IOL. The magnitudes and distribution of the perturbed stress field may be an important driver of the fibrotic response of inhabiting lens epithelial cells and associated lens capsule remodeling after cataract surgery. Thus, the mechanical effects of an implant on the lens capsule could be an essential consideration in the design of intraocular lenses, particularly those with an accommodative feature.
Lower-limb stiffness mediates speed but not turning angle during unplanned side-step cutting.
Venue: Journal of biomechanics

An inability to pre-plan a side-step cutting maneuver results in a greater reduction in speed and shallower cut angle. Although leg stiffness has not been directly quantified in cutting, indirect evidence suggest that greater stiffness may benefit cutting speed, but lower stiffness may benefit cut angle. No studies have investigated if stiffness causally mediates the relationship between anticipation, cutting speed and angle. The aims of the present study were to determine the influence of anticipatory cues on leg stiffness, and quantify the mediation effects of stiffness on cutting speed and angle. Seventeen healthy participants performed a 45° cut at an approach speed of 4 m/s. Leg stiffness (% bodyweight/leg length [BW/LL]), cutting angle and change in running speed between initial contact and toe-off of the cut were calculated. Causal mediation analysis was performed with anticipatory cues as the independent variable, cutting speed and angle as the dependent variables, and stiffness as the mediator. Unanticipated cutting significantly increased leg stiffness (β=3.82%BW/LL,P=0.005) compared to anticipated cutting. The average causal mediation effect of stiffness on cutting angle was not significant (P = 0.68). The average causal mediation effect of stiffness on cutting speed was significant (-0.02 m/s [95%CI -0.04 to 0.00 m/s, P = 0.016). Reduced preplanning time in cutting increased leg stiffness. Alterations in leg stiffness only explained the change in speed, and not angle, associated with cutting under different anticipatory cues. Loss of speed when cutting is unplanned may be mitigated by improving leg stiffness.
Gait regularity assessed by wearable sensors: Comparison between accelerometer and gyroscope data for different sensor locations and walking speeds in healthy subjects.
Venue: Journal of biomechanics

Inertial measurement units (IMU), including accelerometers and gyroscopes, can support the assessment of gait regularity, relevant for an effective walking. Gait regularity is typically quantified by an autocorrelation analysis of trunk/pelvis accelerations. A methodological upgrade fosters a multi-sensor approach including upper and lower limbs. Very few studies dealt with gait regularity using gyroscope data and no comparison between the two inertial sensors has been published. Therefore, this study compares gait regularity assessment by autocorrelation analyses performed on accelerometer and gyroscope data simultaneously acquired. Twenty-five adult healthy subjects walked steady-state on treadmill at three speeds (3.6, 5.0, 6.4 km/h), with rest between. Four IMUs were firmly attached on the trunk, pelvis, wrist and ankle. The autocorrelation method was applied to time-windows of the signal vector magnitude and resulted, on average for each trial, in its regularity index (RI) and periodicity index (PI), i.e. the stride time. Results showed that both sensors identified the same PI (Spearman correlation coefficient = 0.999), and evidenced that, for matched sensor locations and gait speeds, the accelerometer-based RI was larger/equal to the gyroscope-based RI on 86.3% of all conditions (overall median of gyroscope-to-accelerometer RI ratio was 91.1%). The two sensors gave always statistically different RI, with the exception of the ankle at the lowest speed and wrist at higher speeds. Such results help remove potential confounders from analyses performed with different sensors and support the use of accelerometers for gait regularity assessment, not excluding that gyroscopes may be more suitable for other human movements.
The effects of exterior boundary conditions on a internally heated tumor tissue with a thermoporoelastic model.
Venue: Journal of biomechanics

Modeling flow field in tumor regions interstitial space is of primary importance, because of the importance of advection in macromolecule drug delivery. Its deformation has also to be taken into account because of the forces caused by the fluid; if the tumor region is not isothermal, this deformation can be also strongly affected by temperature fields. In this paper, the effects of thermal boundary conditions on a tumor region periphery with an internal heat source are investigated. The tumor region is modeled as a deformable sphere, in which two phases can be distinguished. The fluid phase is the interstitial fluid, while the rest of the tumor is modeled as the solid phase, including also capillaries and tissues. Transient-state governing equations for mass, momentum and energy are written for both phases, by also considering tumor deformation under the linear elastic material assumption. A situation of Tumor Blood Flow (TBF) rapid decay, in which vascular pressure rapidly approaches to zero, is considered, while the heat source is modeled as a fourth-grade radial-decay function. Boundary conditions for the energy equation are varied on the external surface of the sphere, in order to appreciate the effects of the surrounding on flow and temperature fields inside the tumor. After scaling equations, a finite-element scheme is employed for the numerical solution. Comparisons with analytical solutions from literature show a good agreement. Results are shown for different dimensionless parameters that are referred to temperature, volumetric strain, pressure and velocity, showing in which case external boundary conditions strongly affect tumor region flow fields and a third-kind boundary condition is needed.
Joint fatigue-failure: A demonstration of viscoelastic responses to rate and frequency loading parameters using the porcine cervical spine.
Venue: Journal of biomechanics

Fatigue-failure in low back tissues is influenced by parameters of cyclic loading. Therefore, this study quantified the effect of loading rate and frequency on the number of tolerated compression cycles. Energy storage and vertical deformation were secondarily examined. Thirty-two porcine spinal units were randomly assigned to experimental groups that differed by loading rate (4.2 kN/s, 8.3 kN/s) and loading frequency (0.5 Hz, 1 Hz). Following preload and range-of-motion tests, specimens were cyclically loaded in a neutral posture until fatigue-failure occurred or 10800 cycles were tolerated. Macroscopic dissection was performed to identify the fracture morphology, and measurements of energy storage and vertical displacement were calculated throughout the specimen lifespan (1%, 10%, 50%, 90%, 99%). Given the differences in compression dose-force-time integral-between experimental conditions, the number of sustained cycles were assessed following linear and nonlinear dose-normalization via correction factors calculated from existing risk-exposure approximations. Without dose-normalization, an 8.3 kN/s loading rate and 0.5 Hz loading frequency reduced the fatigue lifetime by 3541 and 5977 cycles, respectively (p < 0.001). Linear and nonlinear dose-normalization resulted in a significant rate × frequency interaction (p < 0.001). For a 1 Hz loading frequency, the number of sustained loading cycles did not differ between loading rates (padj ≥ 0.988), but at 0.5 Hz, spinal units compressed at 8.3 kN/s sustained 99% (linear) and 97% (nonlinear) fewer cycles (padj < 0.001). These findings demonstrate that the interacting effects of loading frequency and loading rate on spinal fatigue-failure depend on the normalization of dose discrepancies between experimental groups.
Measurement of pubic symphysis width in different birthing positions using ultrasound.
Venue: Journal of biomechanics

Studies have shown that some vertical birthing positions, such as squatting and standing, may influence labour and childbirth. However, a rigorous biomechanical understanding of how different positions affect a woman's pelvis during labour is currently lacking. It was hypothesized that the position of pubic bones is affected in different positions, and thus the pubic symphysis width changes. Therefore, we measured pubic symphysis width on eleven women in their seventh to ninth months of pregnancy in different positions through three-dimensional (3D) reconstruction of pubic symphysis ultrasound images. Positions studies included those used in clinics like supine and lithotomy positions, in addition to squatting and standing, which are recommended by midwives. The results showed that the average superior and inferior pubic symphysis widths in lithotomy, squatting and standing positions were approximately 1 mm larger than those in the supine position. However, no significant difference between lithotomy, squatting and standing positions was found. The results were consistent with those of two comparable studies. A significant difference was only found between standing and squatting, standing and lithotomy in the rotation angle about the medio-lateral axis. The results suggest that positions with thigh hyperflexion and gravity effect make a difference in pubic symphysis width and might have a positive effect in childbirth. However, due to the small sample size, no definite conclusion can be drawn.