Soft-bodied organisms offer a fertile ground for uncovering fundamental principles of locomotion, yet direct mechanical access to their microscale muscles has remained elusive due to their fragility, compliance, and limited experimental accessibility. Here, we introduce a single-axis in situ tensile framework based on scanning probe microscopy (SPM), enabling direct cyclic stress-stretch measurements of individual muscles in Drosophila larvae with high spatial and force resolution. We reveal that these microscale muscles exhibit a distinctive cycle-dependent mechanical response, characterized by evolving J-shaped nonlinearity, progressive hysteresis modulation, and stiffness adaptation during repeated loading. Remarkably, this behavior is quantitatively captured by a minimal pseudo-elastic model, which links the observed hysteresis evolution to energy dissipation and potential structural adaptation at the sarcomeric scale. These findings provide new insights into the intrinsic passive mechanics of soft-bodied locomotion and establish a high-resolution experimental framework for investigating the mechanical behavior of biological soft tissues.
Drop jump tasks are complex whole-body movements requiring multi-joint control to meet mechanical demands. Unlike drop vertical jumps (DVJs), drop lateral jumps (DLJs) require medial–lateral GRF components that may introduce asymmetry between limbs and increase multi-planar joint demands. The purpose of this study was to compare limb- and joint-level mechanical demands between DVJs and DLJs. Eighteen female athletes performed three drop jump tasks, landing with each foot on separate force plates before jumping vertically or laterally (left or right) with full-body kinematics recorded. Limb-level (resultant GRF and 3D support moment [SM]) and joint-level (angles and net joint moments [NJMs]) demands were compared across conditions. The resultant GRF (p < 0.001, η2 = 0.29), SM (p < 0.001, η2 = 0.27), and NJMs (p < 0.001, η2 = 0.20) were greatest in the DLJ contralateral limb, followed by DVJ limbs, and then the DLJ ipsilateral limb. Within each condition, hip and knee resultant NJMs were not significantly different (p = 0.099, d = 0.30) and both were greater than the ankle (p < 0.01, d = 1.24–0.48). No joint-by-condition interaction was observed for resultant NJMs (p = 0.76, η2 = 0.001). Relative hip (33–34%), knee (36–37%), and ankle (30–31%) contributions to the SM remained consistent, facilitated by alignment (>99%) of the GRF with the lower limb plane (LLP). GRF–LLP alignment was maintained via changes in ankle kinematics, and, with the feet relatively fixed on the ground, frontal plane ankle NJMs differed significantly between conditions but were not propagated proximally to the knee or hip. These findings demonstrate that invariant multi-joint control strategies were utilized across conditions, despite differences in absolute limb- and joint-level mechanical demands.
Acute alterations on patellar tendon properties following an isokinetic knee extension task with a fatigue protocol remains unknown. To investigate this, nineteen (11♂, 8♀) physically active individuals participated in this study. Patellar tendon was assessed using ultrasonography in B-mode and shear wave elastography modes with the knee at 30° of flexion (0° = full extension). Tendon and subcutaneous fat tissue thickness, and echo intensity (EI) were analyzed from the extended field of view B-mode images. Mean shear wave velocity (SWV) was analyzed from the SWE images. This process was performed before and immediately after the isokinetic task, which included a fatigue protocol. Mechanical work was calculated for the first and last five repetitions to assess performance fatigability. Pre-post comparisons were performed using paired t-tests, and correlations between tendon EI and SWV were assessed using Pearson's correlation. Reliability was evaluated using the intraclass correlation coefficient (ICC), standard error of measurement (SEM) and minimum detectable change (MDC). Statistical significance was set at α = 0.05, and Cohen's d was calculated for effect size. While no differences in tendon thickness were observed (p = 0.208), EI increased 9% (p < 0.001, ES = 0.73) and SWV decreased 5% (p = 0.031, ES = 0.23) after the isokinetic task. Although EI and SWV correlated before the isokinetic task (r = 0.468, p = 0.043), no correlations were observed after it (r = 0.279, p = 0.247) and between EI and SWV variation (r = -0.419, p = 0.074). Very high reliability was seen before and after the isokinetic task (ICC ≥ 0.922, p < 0.001). However, SWV mean difference pre-post task was lower than MDC.
Despite advances in treatment, mortality rates for advanced heart failure and cardiogenic shock remain unchanged due to delays in identifying shock types and challenges in choosing the right therapy. Accurate patient phenotyping can help clarify the patient's condition and guide better treatment. In this study, we used in silico modeling to investigate the dynamic relationships among power, efficiency, and the shock phenotype in six advanced heart failure hypothetical phenotypes and a healthy control. We simulated phenotype-specific Starling curves by changing volume loading. We calculated advanced hemodynamic and energetic variables-pulsatility index, power output, myocardial performance score, and efficiency for the left and right ventricles. We proposed composite cardiac indices for energetic phenotyping. Adding a dynamic energetic assessment with volume loading showed that cardiac efficiency limits cardiac performance in each heart failure phenotype, but not in healthy controls. Advanced hemodynamic and energetic phenotyping-both at rest and during volume loading-especially with biventricular assessment, can accurately distinguish clinical shock phenotypes. This approach offers mechanistic insight into the causes of cardiac underperformance and helps guide optimal therapeutic interventions.
Meniscus allografts must be transplanted shortly after harvest or be preserved until transplantation, typically by freezing. However, the effects of preservation on the structure-function relationship of the meniscus are not well understood. The objective of this study was to propose a physical mechanism by which preservation affects the tensile properties of the meniscus. It is hypothesized that the separation of collagen fibres from voids formed during freezing and fresh storage decrease tensile strength and modulus. Medial and lateral porcine menisci were dissected on the day of slaughter and allocated into four groups: processed immediately (controls), fresh storage (4 °C, 21 days), or frozen with (-140 °C, 21 days) and without cryoprotectant (-80 °C, 21 days). Tensile tests were performed in the circumferential and radial directions to measure tensile modulus, ultimate tensile strength (UTS), and ultimate strain in the circumferential and radial directions. Area void fractions of collagen fibre bundles were estimated from scanning electron microscopy images. All preservation groups had a significantly lower modulus, UTS and a significantly greater void fraction than controls. Menisci frozen with cryoprotectant had a significantly greater modulus, UTS and a significantly lower void fraction than those frozen without. No significant differences in mechanical or structural properties were found between the freezing without cryoprotectant and fresh storage groups. Decreases in tensile properties may result from interfibrillar changes such as fibril spacing and crosslinking. Future tensile studies should include dynamic mechanical analysis, physiological strain rates, and a physically representative material model.
This study presents a modular adaptation of the Drift-Free 3D Orientation and Displacement (DFOD) estimation method for estimating lower-extremity kinematics using independent inertial measurement units (IMU) during steady-state walking and running without calibration procedures or biomechanical models. The adapted DFOD was evaluated in ten healthy recreational runners during walking (2.5 and 5 km/h) and running (9, 11, and 13 km/h), using optical motion capture as reference. Good accuracy was achieved for the feet and lower legs in the sagittal plane (orientation) and forward direction (displacement), with mean errors below 7.2 and 4.2 cm, respectively, and Pearson correlations above 0.97. Accuracy was lower in other movement directions and for the upper legs, with mean errors up to 12.8 and 6.5 cm. However, Pearson correlations for the upper legs in the sagittal plane (orientation) and forward direction (displacement) exceeded 0.87, suggesting that waveform characteristics can be captured. Statistical analysis confirmed that movement axis and body segment were the dominant factors explaining estimation accuracy, with speed having a significant but smaller effect. Overall, larger errors were observed for movements with smaller RoM, for the upper legs, and for the slowest walking speed (2.5 km/h). These findings indicate that the adapted DFOD provides promising single-IMU–based estimates of lower-extremity orientation and displacement during walking and running for distal segments and primary movement directions.
The cervical spine is highly vulnerable to injury during high-acceleration emergency ejection because of its flexibility, head-torso inertial lag, and dependence on coordinated muscle function. This study investigated the biomechanical effects of selective neck muscle deactivation on cervical spine kinematics under vertical acceleration loading using a validated C0-T1 finite element model based on a Hill-type muscle model. A 10-G vertical acceleration was applied, and individual muscle deactivation was simulated by reducing muscle activation to 0.005 at 80 ms. The results showed all muscular effects became prominent after 100 ms. Among the 12 neck muscle deactivations, longus capitis, semispinalis capitis, trapezius, splenius capitis, and scalenus anterior produced substantial alterations in upper cervical (C0-C2) and global cervical (C0-C7) motion patterns. Rotation analysis showed C0-C3 flexion and C3-C7 extension, forming S-shaped and C-shaped curvatures during 0-100 ms and 100-150 ms, respectively. Except under longus capitis deactivation, rapid motion reversal of flexion to extension at approximately 135 ms, the entire cervical C0-C7 segments formed two unique S- and C-shaped curvatures in the loading phase, with a 27.5% reduction in overall C0-C7 flexion of overall C0-C7 segment. These motion patterns caused stress concentration and altered load transfer at the C2-C3 and C6-C7 intervertebral discs and elongation of ligaments. The findings highlight the critical role of coordinated neck muscle function in cervical spine stability during high-G ejection and may contribute to the development of targeted muscle training and protective cockpit systems.
A 3D bicuspid venous valve model is used to investigate the biomechanical role of leaflet buckling in achieving efficient, low-pressure opening. The model is parameterized to represent the femoral vein, common femoral vein, and popliteal vein, with sizes and flow rates scaled to match in vivo conditions. Using a body-fitted numerical method with semi-implicit predictor-corrector coupling, we demonstrate that leaflet buckling enables opening through low-energy bending rather than energetically costly elastic stretching. This design ensures a maximum opening pressure loss of 42 Pa in the cases tested, significantly lower than previously reported values and compatible with the physiologically observed pressure loss, highlighting the importance of excess surface area in minimizing flow resistance while maintaining valve competence. Even with thickened leaflets and the resulting reduced effective opening area, the pressure loss for this model remains largely below physiological pressure loss compared to other numerical studies on venous valves. Finally, complex downstream flow patterns suggest potential interactions with proximal valve dynamics, even under bed-rest conditions.
Musculoskeletal model generation often requires scaling a generic adult skeleton, which is fast but generally inaccurate. Statistical shape models have been developed to scale musculoskeletal models based on the population of interest, improving personalisation. Low-cost 3D surface scanning presents a new opportunity to scale musculoskeletal models directly from external body shape, such as SKEL. This study assessed the accuracy of 1) a combined shape model to predict tibia/fibula geometry from skin surface in a typically developed paediatric population and 2) the output from the generic scaling through SKEL. The left tibia/fibula bones and shank skin surface were segmented from 318 full-body CT scans. Principal component analysis captured the combined morphological variations between the shank surface and tibia/fibula geometry. A combined shape model was then developed to predict tibia/fibula geometry from the external shank surface using Principal Component fitting. The model was validated using a leave-one-out analysis. The combined shape model predicted the tibia and fibula with a root-mean-square error of 2.00 ± 0.90 mm, whereas the surface error from SKEL fitting was 2.98 ± 0.62 mm. Clinical bone measurement derived from predicted bones showed low error when compared to the segmented bones, except for tibial length and the mechanical medial proximal tibial angle. These results were repeatable across three prediction rounds, demonstrating robust and accurate prediction of bone shape and clinical measurements from the external skin surface. This proof-of-concept demonstrates the feasibility of inferring bones from the skin, paving the way for full-body models to enhance paediatric clinical gait analysis.
The chemical composition, structure, and mechanical properties of mature bone are well established. However, predictive models for the mechanical properties of developing bone-characterized by active mineralization and structural remodeling-remain incomplete. This study integrated high-resolution Micro-CT, high-throughput nanoindentation, and confocal Raman spectroscopy to systematically map the spatial heterogeneity of structure, chemical composition, and mechanical properties in tibiae from 6-week-old female C57BL/6J mice. Multi-parameter composite factor models were proposed to predict the elastic modulus and hardness. The results indicated that single structural or chemical composition parameters exhibited limited explanatory power for elastic modulus (R2 ≤ 0.346) and hardness (R2 ≤ 0.37). In contrast, integrating structural and chemical descriptors significantly improved model performance, achieving R2 values of 0.746 for elastic modulus and 0.814 for hardness, underscoring a coordinated structure-chemistry interplay during bone development. Notably, significant gradients in the circumferential direction of mineralized matrix ratio and carbonate substitution degree (p < 0.01) did not result in heterogeneous mechanical properties, reflecting a dynamic balance mechanism that supports structural growth while maintaining mechanical integrity. This work provides mechanistic insight into the developmental adaptation of immature bone and establishes a theoretical foundation for advanced fracture treatment strategies and biomimetic bone repair materials.
Hydrosalpinx significantly reduces the success rate of in vitro fertilization-embryo transfer; however, the absence of dedicated tubal occlusion devices in current clinical practice limits the standardization of its treatment. Here, we designed and fabricated a dual-disc shape-memory alloy occluder for interventional embolization of hydrosalpinx, with structural density defined as the circumferential wire coverage fraction (48-96 NiTi wires across three configurations). The effects of structural density on occlusion performance and inflammatory response were systematically investigated through in vitro hydrodynamic testing and in vivo animal experiments. The results demonstrated that occlusion efficacy increased with structural density. Compared with a single occluder, double occluders exhibited more stable flow attenuation performance and reduced the equivalent permeability by 39.3 %. Histological evaluation indicated that all device configurations induced mild inflammatory responses; however, no observable aggravation of inflammation was associated with increasing structural density. Collectively, this study presents a shape-memory alloy-based occlusion strategy for hydrosalpinx and provides quantitative biomechanical evidence linking structural architecture to flow-resistance behavior, offering a potential engineering basis for device optimization and future translational development.
Pathological ankle conditions alter joint kinematics and contribute to degeneration in adjacent hindfoot and midfoot joints. Accurate in-vivo assessment of these motions is essential for understanding disease progression and guiding clinical interventions. Biplane videoradiography (BVR) is a tool for six-degree-of-freedom in-vivo bone kinematics, but validation against gold-standard radiostereometric analysis (RSA) is needed for each new joint of interest and BVR configuration. This study validated a BVR system using one participant instrumented with tantalum beads in the tibia, fibula, talus, calcaneus, cuboid, and navicular. Dynamic imaging was acquired during walking, step-up, step-down, and heel rise. Bone motions were tracked using model-based tracking (MBT) and compared to RSA. Root mean square (RMS) error and coefficient of multiple correlation analyses quantified accuracy and inter-/intra-rater variability, respectively. The mean angular MBT RMS error was 1.37 ± 0.23° across all joints. The greatest error was 1.66 ± 0.19° in the talonavicular joint and the smallest error was 0.97 ± 0.19° in the subtalar joint. The mean translational MBT RMS error was 2.05 ± 0.58 mm across all joints. The greatest error was 2.83 ± 0.21 mm in the calcaneocuboid joint, while the smallest error was 1.20 ± 0.29 mm in the subtalar joint. The coefficient of multiple correlations scores for intra-rater repeatability ranged from 0.545 to 0.996. Joint accuracy errors are more clinically relevant and exceeded bone accuracy errors, reflecting compounded tracking of multiple bones. These findings indicate that BVR MBT is accurate in assessing foot and ankle kinematics and can be translated to pathological research.
Effective locomotion depends on the ability to adapt to changing environmental constraints. Flexibility, defined as the ability of the locomotor system to adopt alternative movement solutions to achieve the same task outcome, is widely considered a fundamental property of adaptable movement. Despite its theoretical importance, flexibility in locomotion remains rarely characterized. This study investigated the relationship between implicit flexibility and explicit flexibility during perturbed walking.Healthy young males walked on a treadmill while unexpected unilateral perturbations were introduced via sudden belt accelerations or decelerations. Implicit flexibility was quantified using baseline Continuous Relative Phase variability (bCRPV). Explicit flexibility was quantified using joint angle relaxation time following perturbation. Spearman’s rank correlations were used to examine the relationship between implicit flexibility, represented by bCRPV, and explicit flexibility, represented by joint angle relaxation time.Moderate positive correlations were observed between bCRPV and relaxation time across three of the four segment couplings. Individuals exhibiting greater bCRPV required more strides to return to regular walking patterns following sudden perturbations.Contrary to the hypothesis, greater bCRPV was associated with longer joint angle relaxation times. Under the present operational definitions, greater implicit flexibility was associated with lower explicit flexibility during perturbed walking. These findings indicate that higher bCRPV does not necessarily correspond to faster locomotor reorganization following perturbation. The present study provides an empirical investigation of the relationship between implicit and explicit flexibility during human walking and demonstrates the value of characterizing flexibility using complementary measures derived from different levels of movement organization.
The heel fat pad plays a vital role in shock absorption during weight-bearing and may exhibit structural and textural differences associated with long-term mechanical loading. This study employed ultrasound radiomics to investigate the association between exercise volume and layer-specific radiomic features of the macrochamber and microchamber layers of the heel fat pad. Ultrasound images were obtained from 51 healthy young adults aged 18-35 years, who were classified into high-exercise-volume (HEV, n = 18), moderate-exercise-volume (MEV, n = 15), and low-exercise-volume (LEV, n = 18) groups according to weekly physical activity energy expenditure. A total of 101 radiomic features were extracted from each layer to characterize intensity, heterogeneity, and spatial texture patterns. Intergroup differences were analyzed using one-way analysis of variance or the Kruskal-Wallis test, followed by Bonferroni-adjusted pairwise comparisons. Significant radiomic differences were identified in the macrochamber layer, with 19 features differing among the three groups (P < 0.05), and six representative features retained after LASSO feature selection. The main pairwise differences occurred between the LEV group and the MEV or HEV groups, whereas no significant differences were detected between the MEV and HEV groups in the main distinguishing features. In contrast, the microchamber layer showed limited variation, with only Uniformity differing significantly between the LEV group and the MEV/HEV groups. These findings suggest that the macrochamber layer may be more sensitive to activity-associated radiomic texture differences than the microchamber layer. Overall, ultrasound radiomics shows potential as a non-invasive approach for quantifying subtle, layer-specific texture patterns in the heel fat pad.
In this work, an optimisation algorithm is employed to calibrate a quasi-brittle phase-field cohesive zone model against notched three-point bending experiments on bovine cortical bone using the force vs crack mouth opening displacement data. Calibration is performed both for individual specimens, to quantify parameter variability, and for groups of specimens from the same subject and crack propagation direction, to determine material parameters representative of the homogenised tissue.The proposed approach enables simultaneous identification of elastic modulus, strength and fracture toughness from a single specimen, yielding values consistent with ranges reported in the literature. Using the calibrated tissue material parameters, the model reproduces the experimental responses with good accuracy and captures key features of quasi-brittle fracture behaviour, including non-negligible crack advance prior to peak load. The good agreement suggests that a cohesive phase-field formulation provides a suitable framework for modelling fracture in cortical bone. This methodology can be applied to human bone in order to determine how fracture properties vary with age and disease, something that eventually could improve predictions of load-carrying capacity in subject-specific models.
