nils-herrmann/clean_scirepeval huggingface dataset:
Mechanical misconceptions: Have we lost the "mechanics" in "sports biomechanics"?
Venue: Journal of biomechanics

Biomechanics principally stems from two disciplines, mechanics and biology. However, both the application and language of the mechanical constructs are not always adhered to when applied to biological systems, which can lead to errors and misunderstandings within the scientific literature. Here we address three topics that seem to be common points of confusion and misconception, with a specific focus on sports biomechanics applications: (1) joint reaction forces as they pertain to loads actually experienced by biological joints; (2) the partitioning of scalar quantities into directional components; and (3) weight and gravity alteration. For each topic, we discuss how mechanical concepts have been commonly misapplied in peer-reviewed publications, the consequences of those misapplications, and how biomechanics, exercise science, and other related disciplines can collectively benefit by more carefully adhering to and applying concepts of classical mechanics.
Biomechanical testing of various suture techniques for Achilles tendon repair with and without augmentation by using synthetic polyester grafts.
Venue: Journal of biomechanics

Following surgical Achilles tendon reconstruction surgery, there is a distinct trend towards an early and faster rehabilitation protocol to avoid muscle atrophy. However, this procedure involves the risk of a higher complication rate. In order to reduce the occurrence of re-ruptures and pathological tendon extensions, a tendon reconstruction with the highest possible primary stability is desirable. Therefore, the aim of this study was to determine if augmentation using synthetic polyester tapes (QuadsTape™) could provide greater primary stability in case of different tendon suture techniques. 90 tendons of the superficial toe flexor of pigs were divided into 9 groups. The reconstruction method was combined using the factors suture technique (Kessler and Bunnell), augmentation (non-augmented and augmented with QuadsTape™) and defect type (end-to-end and 10 mm gap). The biomechanical measurements were performed on a material testing machine and consisted of a creep test, a cyclic test and a tear-off test. This study compared creep strain, ultimate load failure, maximum stress and stiffness. Irrespective of the type of defect involved, augmentation of the tendon sutures led to a significant increase of the maximum force (not augmented: 82.30 ± 25.48 N, augmented: 135.73 ± 30.69 N, p < 0.001) and the maximum stress (not augmented: 2.26 ± 0.83 MPa, augmented: 4.13 ± 1.79 MPa, p < 0.001). Furthermore, there was a non-significant increase in stiffness and no significant differences were observed with respect to creep strain. Augmentation of Achilles tendon reconstruction using QuadsTape™ increases composite strength and stiffness in the in vitro model, thus potentially contributing to the feasibility of early rehabilitation programs. Biological factors still need to be investigated in order to formulate appropriate indications.
Magnetic resonance imaging based modeling of microvascular perfusion in patients with peripheral artery disease.
Venue: Journal of biomechanics

Peripheral artery disease (PAD) is associated with an increased risk of adverse cardiovascular events, impaired lower extremity blood flow and microvascular perfusion abnormalities in the calf muscles which can be determined with contrast-enhanced magnetic resonance imaging (CE-MRI). We developed a computational model of the microvascular perfusion in the calf muscles. We included 20 patients (10 PAD, 10 controls) and utilized the geometry, mean signal intensity and arterial input functions from CE-MRI calf muscle perfusion scans. The model included the microvascular pressure (pv), outflow filtration coefficient (OFC), transfer rate constant (kt), porosity (φ), and the interstitial permeability (Ktissue). Parameters were fitted and the simulations were compared across PAD patients and controls. Intra-observer reproducibility of the simulated mean signal intensities was excellent (intraclass correlation coefficients >0.995). kt and Ktissue were higher in PAD patients compared with controls (4.72 interquartile range (IQR) 3.33, 5.56 vs. 2.47 IQR 2.10, 2.85; p = 0.003; and 3.68 IQR 3.18, 4.41 vs. 1.81 IQR 1.81, 1.81; p < 0.001). Conversely, porosity (φ) was lower in PAD patients compared with controls (0.52 IQR 0.49, 0.54 vs. 0.61 IQR 0.58, 0.64; p = 0.016). Porosity (φ) was correlated with the ankle brachial index (r = 0.64, p = 0.011). The proposed computational microvascular model is robust and reproducible, and essential model parameters differ significantly between PAD patients and controls.
Development and validation of subject-specific pediatric multibody knee kinematic models with ligamentous constraints.
Venue: Journal of biomechanics

Computational knee models that replicate the joint motion are important tools to discern difficult-to-measure functional joint biomechanics. Numerous knee kinematic models of different complexity, with either generic or subject-specific anatomy, have been presented and used to predict three-dimensional tibiofemoral (TFJ) and patellofemoral (PFJ) joint kinematics of cadavers or healthy adults, but not pediatric populations. The aims of this study were: (i) to develop subject-specific TFJ and PFJ kinematic models, with TFJ models having either rigid or extensible ligament constraints, for eight healthy pediatric participants and (ii) to validate the estimated joint and ligament kinematics against in vivo kinematics measured from magnetic resonance imaging (MRI) at four TFJ flexion angles. Three different TFJ models were created from MRIs and used to solve the TFJ kinematics: (i) 5-rigid-link parallel mechanism with rigid surface contact and isometric anterior cruciate (ACL), posterior cruciate (PCL) and medial collateral (MCL) ligaments (ΔLnull), (ii) 6-link parallel mechanism with minimized ACL, PCL, MCL and lateral collateral ligament (LCL) length changes (ΔLmin) and (iii) 6-link parallel mechanism with prescribed ACL, PCL, MCL and LCL length variations (ΔLmatch). Each model's geometrical parameters were optimized using a Multiple Objective Particle Swarm algorithm. When compared to MRI-measured data, ΔLnull and ΔLmatch performed the best, with average root mean square errors below 6.93° and 4.23 mm for TFJ and PFJ angles and displacements, respectively, and below 2.01 mm for ligament lengths (<4.32% ligament strain). Therefore, within these error ranges, ΔLnull and ΔLmatch can be used to estimate three-dimensional pediatric TFJ, PFJ and ligament kinematics and can be incorporated into lower-limb models to estimate joint kinematics and kinetics during dynamic tasks.
Statistical shape modelling reveals large and distinct subchondral bony differences in osteoarthritic knees.
Venue: Journal of biomechanics

Knee osteoarthritis (OA) results in changes such as joint-space narrowing and osteophyte formation. Radiographic classification systems group patients by the presence or absence of these gross anatomical features but are poorly correlated to function. Statistical-shape modelling (SSM) can detect subtle differences in 3D-bone geometry, providing an opportunity for accurate predictive models. The aim of this study was to describe and quantify the main modes of shape variation which distinguish end-stage OA from asymptomatic knees. Seventy-six patients with OA and 77 control participants received a CT of their knee. 3D models of the joint were created by manual segmentation. A template mesh was fitted to all meshes and rigidly aligned resulting in a set of correspondent meshes. Principal Component Analysis (PCA) was performed to create the SSM. Logistic regression was performed on the PCA weights to distinguish morphological features of the two groups. The first 7 modes of the SSM captured >90% shape variation with 6 modes best distinguishing between OA and asymptomatic knees. OA knees displayed sub-chondral bone expansion particularly in the condyles and posterior medial tibial plateau of up to 10 mm. The model classified the two groups with 95% accuracy, 96% sensitivity, 94% specificity, and 97% AUC. There were distinct features which differentiated OA from asymptomatic knees. Further research will elucidate how magnitude and location of shape changes in the knee influence clinical and functional outcomes.
Responsiveness to rehabilitation of balance and gait impairment in elderly with peripheral neuropathy.
Venue: Journal of biomechanics

Elderly people with peripheral neuropathy of the lower limbs (PNLL) demonstrate a typical balance and gait impairment because of sensory ataxia. There is evidence that rehabilitation produces important gains on balance and gait. However, responsiveness to rehabilitation of balance and gait measures is unknown in PNLL. Aim of the current work is to evaluate the responsiveness to rehabilitation of balance, gait and sensory ataxia measures in elderly with PNLL. Twenty-five elderly with PNLL attending physiotherapy and occupational therapy during inpatient rehabilitation were recruited. Balance and gait measures (including static posturography, TUG test and the 10 m walking test) were administered on admission and discharge. An accelerometer secured to the trunk was used for TUG recording and static balance assessment. Static balance was tested with open and closed eyes, so as to assess sensory ataxia. Following rehabilitation, patients improved gait [admission vs discharge, mean(SD): 0.86(0.33) vs 0.98(0.32) m/s], TUG [18.7(7.8) vs 15.1(5.2) s] and turning [46.2(15.3) vs 53.3(15.3) °/s]. However, none of 12 static balance parameters derived from trunk acceleration significantly changed. Principal component analysis showed that before training, eyes closed and eyes open balance correlated with orthogonal components (one and two vs. three and four). After training, eyes open and eyes closed balance were more similar to each other being both correlated with component one. Responsiveness to rehabilitation is larger for gait than static balance measured by trunk acceleration. However, exercise can also have a beneficial effect on sensory ataxia by making eyes closed balance more similar to eyes open balance.
Optimal marker set assessment for motion capture of 3D mimic facial movements.
Venue: Journal of biomechanics

Nowadays, facial mimicry studies have acquired a great importance in the clinical domain and 3D motion capture systems are becoming valid tools for analysing facial muscles movements, thanks to the remarkable developments achieved in the 1990s. However, the face analysis domain suffers from a lack of valid motion capture protocol, due to the complexity of the human face. Indeed, a framework for defining the optimal marker set layout does not exist yet and, up to date, researchers still use their traditional facial point sets with manually allocated markers. Therefore, the study proposes an automatic approach to compute a minimum optimized marker layout to be exploited in facial motion capture, able to simplify the marker allocation without decreasing the significance level. Specifically, the algorithm identifies the optimal facial marker layouts selecting the subsets of linear distances among markers that allow to automatically recognizing with the highest performances, through a k-nearest neighbours classification technique, the acted facial movements. The marker layouts are extracted from them. Various validation and testing phases have demonstrated the accuracy, robustness and usefulness of the custom approach.
Evaluation of 4D flow MRI-based non-invasive pressure assessment in aortic coarctations.
Venue: Journal of biomechanics

Severity of aortic coarctation (CoA) is currently assessed by estimating trans-coarctation pressure drops through cardiac catheterization or echocardiography. In principle, more detailed information could be obtained non-invasively based on space- and time-resolved magnetic resonance imaging (4D flow) data. Yet the limitations of this imaging technique require testing the accuracy of 4D flow-derived hemodynamic quantities against other methodologies. With the objective of assessing the feasibility and accuracy of this non-invasive method to support the clinical diagnosis of CoA, we developed an algorithm (4DF-FEPPE) to obtain relative pressure distributions from 4D flow data by solving the Poisson pressure equation. 4DF-FEPPE was tested against results from a patient-specific fluid-structure interaction (FSI) simulation, whose patient-specific boundary conditions were prescribed based on 4D flow data. Since numerical simulations provide noise-free pressure fields on fine spatial and temporal scales, our analysis allowed to assess the uncertainties related to 4D flow noise and limited resolution. 4DF-FEPPE and FSI results were compared on a series of cross-sections along the aorta. Bland-Altman analysis revealed very good agreement between the two methodologies in terms of instantaneous data at peak systole, end-diastole and time-averaged values: biases (means of differences) were +0.4 mmHg, -1.1 mmHg and +0.6 mmHg, respectively. Limits of agreement (2 SD) were ±0.978 mmHg, ±1.06 mmHg and ±1.97 mmHg, respectively. Peak-to-peak and maximum trans-coarctation pressure drops obtained with 4DF-FEPPE differed from FSI results by 0.75 mmHg and -1.34 mmHg respectively. The present study considers important validation aspects of non-invasive pressure difference estimation based on 4D flow MRI, showing the potential of this technology to be more broadly applied to the clinical practice.
Intermediate fenestrations reduce flow reversal in a silicone model of Stanford Type B aortic dissection.
Venue: Journal of biomechanics

Pulsatile, three-dimensional hemodynamic forces influence thrombosis, and may dictate progression of aortic dissection. Intimal flap fenestration and blood pressure are clinically relevant variables in this pathology, yet their effects on dissection hemodynamics are poorly understood. The goal of this study was to characterize these effects on flow in dissection models to better guide interventions to prevent aneurysm formation and false lumen flow. Silicone models of aortic dissection with mobile intimal flap were fabricated based on patient images and installed in a flow loop with pulsatile flow. Flow fields were acquired via 4-dimensional flow MRI, allowing for quantification and visualization of relevant fluid mechanics. Pulsatile vortices and jet-like structures were observed at fenestrations immediately past the proximal entry tear. False lumen flow reversal was significantly reduced with the addition of fenestrations, from 19.2 ± 3.3% in two-tear dissections to 4.67 ± 1.5% and 4.87 ± 1.7% with each subsequent fenestration. In contrast, increasing pressure did not cause appreciable differences in flow rates, flow reversal, and vortex formation. Increasing the number of intermediate tears decreased flow reversal as compared to two-tear dissection, which may prevent false lumen thrombosis, promoting persistent false lumen flow. Vortices were noted to result from transluminal fluid motion at distal tear sites, which may lead to degeneration of the opposing wall. Increasing pressure did not affect measured flow patterns, but may contribute to stress concentrations in the aortic wall. The functional and anatomic assessment of disease with 4D MRI may aid in stratifying patient risk in this population.
Experimental analysis of the lower cervical spine in flexion with a focus on facet tracking.
Venue: Journal of biomechanics

Cervical traumas are among the most common events leading to serious spinal cord injuries. While models are often used to better understand injury mechanisms, experimental data for their validation remain sparse, particularly regarding articular facets. The aim of this study was to assess the behavior of cervical FSUs under quasi-static flexion with a specific focus on facet tracking. 9 cadaveric cervical FSUs were imaged and loaded under a 10 Nm flexion moment, exerted incrementally, while biplanar X-rays were acquired at each load increment. The relative vertebral and facet rotations and displacements were assessed using radio-opaque markers implanted in each vertebra and CT-based reconstructions registered on the radiographs. The only failures obtained were due to specimen preparation, indicating a failure moment of cervical FSUs greater than 10 Nm in quasistatic flexion. Facet motions displayed a consistent anterior sliding and a variable pattern regarding their normal displacement. The present study offers insight on the behavior of cervical FSUs under quasi-static flexion beyond physiological thresholds with accurate facet tracking. The data provided should prove useful to further understand injury mechanisms and validate models.
Compressive mechanical properties of rat and pig optic nerve head.
Venue: Journal of biomechanics

Glaucoma is the leading cause of irreversible blindness worldwide. Elevated intraocular pressure (IOP), the primary risk factor for glaucoma, is thought to induce abnormally high strains in optic nerve head (ONH) tissues, which ultimately result in retinal ganglion cell damage and vision loss. The mechanisms by which excessive deformations result in vision loss remain incompletely understood. The ability of computational and in vitro models of the ONH to provide insight into these mechanisms, in many cases, depends on our ability to replicate the physiological environment, which in turn requires knowledge of tissue biomechanical properties. The majority of mechanical data published to date regarding the ONH has been obtained from tensile testing, yet compression has been shown to be the main mode of deformation in the ONH under elevated IOP. We have thus tested pig and rat ONH tissue using unconfined cyclic compression. The material constants C1, obtained from fitting the stress vs. strain data with a neo-Hookean material model, were 428 [367, 488] Pa and 64 [53, 76] Pa (mean [95% Confidence Interval]) for pig and rat optic nerve head, respectively. Additionally, we investigated the effects of strain rate and tissue storage on C1 values. These data will inform future efforts to understand and replicate the in vivo biomechanical environment of the ONH.
On-field player workload exposure and knee injury risk monitoring via deep learning
Venue: Journal of biomechanics

In sports analytics, an understanding of accurate on-field 3D knee joint moments (KJM) could provide an early warning system for athlete workload exposure and knee injury risk. Traditionally, this analysis has relied on captive laboratory force plates and associated downstream biomechanical modeling, and many researchers have approached the problem of portability by extrapolating models built on linear statistics. An alternative approach would be to capitalize on recent advances in deep learning. In this study, using the pre-trained CaffeNet convolutional neural network (CNN) model, multivariate regression of marker-based motion capture to 3D KJM for three sports-related movement types were compared. The strongest overall mean correlation to source modeling of 0.8895 was achieved over the initial 33% of stance phase for sidestepping. The accuracy of these mean predictions of the three critical KJM associated with anterior cruciate ligament (ACL) injury demonstrate the feasibility of on-field knee injury assessment using deep learning in lieu of laboratory embedded force plates. This multidisciplinary research approach significantly advances machine representation of real-world physical models with practical application for both community and professional level athletes.
A quasi three-dimensional visualization of unsteady wake flow in human undulatory swimming.
Venue: Journal of biomechanics

Human undulatory underwater swimming (UUS) is an underwater propelling technique in competitive swimming and its propulsive mechanism is poorly understood. The purpose of this study was to visualize the three-dimensional (3D) flow field in the wake region during human UUS in a water flume. A national level male swimmer performed 41 UUS trials in a water flume. A motion capture system and stereo particle image velocimetry (PIV) equipment were used to investigate the 3D coordinates of the swimmer and 3D flow fields in the wake region. After one kick cycle was divided into eight phases, we conducted coordinate transformations and phase averaging method to construct quasi 3D flow fields. At the end of the downward kick, the lower limbs external rotations of the lower limbs were observed, and the feet approached towards each other. A strong downstream flow, i.e. a jet was observed in the wake region during the downward kick, and the paired vortex structure was accompanied by a jet. In the vortex structure, a cluster of vortices and a jet were generated in the wake during the downward kick, and the vortices were subsequently shed from the feet by the rotated leg motion. This suggested that the swimmer gained a thrust by creating vortices around the foot during the downward kick, which collided to form a jet. This paper describes, illustrates, and explains the propulsive mechanism of human UUS.
Using smart garments to differentiate among normal and simulated abnormal gaits.
Venue: Journal of biomechanics

Detecting and assessing an individual's gait can be important for medical diagnostic purposes and for developing and guiding follow-on rehabilitation protocols. Thus, an accurate, objective gait classification system has the potential to facilitate earlier diagnosis and improved clinical decision-making. Systems using smart garments represent an emerging technology for physical activity assessment and that may be relevant for gait classification. The objective of this study was to assess the accuracy of one such system - comprised of commercial instrumented socks and a custom instrument shirt - for differentiating among normal gait and four distinct simulated gait abnormalities. Eleven participants completed an experiment in which they completed several gait trails on a single day. Gait types were classified using diverse modeling approaches (K-nearest neighbors, linear discriminant analyses, support vector machines, and artificial neural networks). High classification accuracy could be obtained, both when classification models were developed and tested using data from each participant separately and grouped together, particularly using the k-nearest neighbor method (>98% accuracy). Some gaits were more often "confused" with other gaits, especially when they shared underlying kinematic aspects. These results support the potential of using "smart" garments for detecting and identifying abnormal gaits, and for future implementation in diagnosis and rehabilitation.
Viscoelastic properties of the central region of porcine temporomandibular joint disc in shear stress-relaxation.
Venue: Journal of biomechanics

In this study, shear relaxation properties of the porcine temporomandibular joint (TMJ) disc are investigated. Previous studies have shown that, in fatigue failure and damage of cartilage and fibrocartilage, shear loads could be one of the biggest contributors to the failure. The aim of the present study is to develop an evaluation method to study shear properties of the disc and to do a mathematical characterization of it. For the experiments, twelve porcine discs were used. Each disc was dissected from the TMJ and, then, static strain control tests were carried out to obtain the shear relaxation modulus for the central region of the discs. From the results, it was found that the disc presents a viscoelastic behavior under shear loads. Relaxation modulus decreased with time. Shear relaxation was 10% of the instantaneous stress, which implies that the viscous properties of the disc cannot be neglected. The present results lead to a better understanding of the discs mechanical behavior under realistic TMJ working conditions.