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Rotation of the cervical spine beyond its normal range of motion is a leading cause of fall-related spinal cord injuries (SCIs) in older adults. This rotation is constrained, in part, by the spinal ligaments. The experimentally measured properties of these ligaments are tabulated in literature, including sex-specific properties; however, their influence on the rotation kinematics of the cervical spine has not been compared. We examined how different mechanical properties of spinal ligaments, including sex-specific properties, affected the rotational kinematics of the cervical spine using finite element analysis (FEA). Ligament properties most influenced the rotation of the lower cervical spine, with increased ligament stiffness reducing rotation. Ligament deformation remained mostly in the toe region of their force-displacement curves, emphasizing the need to incorporate non-linear ligament behavior in FEA. Predictions made using one set of experimental properties (Property 1) better-matched experimental kinematic data. Using sex-specific properties had a moderate effect (6% in extension, –3% in flexion) on rotation, with a greater impact on extension. Ligament properties also affected the segmental distribution of rotation, causing a variability of 3–21% at different levels. We emphasized the need to incorporate tailored approaches to FEA to obtain clinically relevant results when modeling flexion/extension rotation.

Muscle strength may vary depending on the pathological issues and static life habits. These conditions lead to abnormal spinal loads and change muscle strength as well as activation patterns, thereby causing spinal disorders. In this study, the effects of muscle strength on the spine stabilization exercise were analyzed using a whole-body tilt device. Musculoskeletal modeling was performed and the results were validated through a comparison with the electromyography (EMG) analysis results. Based on the validated basic model, modeling was performed for the whole-body tilt device. To examine the exercise effect and muscle activation while the maximum muscle force capacity (MFC) was varied from 30N/cm² to 60N/cm² and 90N/cm², the muscle force was predicted through inverse dynamics analysis. When MFC was 30N/cm², the posterior direction of the tilt could not be analyzed (no solution found). When MFC was 60N/cm², it could be analyzed, but the muscle force was predicted to be higher compared to when MFC was 90N/cm². It was confirmed that muscle strength is a very important element for maintaining postural activities and performing exercise. Therefore, for rehabilitation patients and elderly people with weak muscle strength, hard or extreme exercise may cause musculoskeletal injuries.

Hyperpronation of the foot is believed to contribute to ankle hypermobility and associated stiffness reduction, but the underlying biomechanical mechanisms remain unknown. This study aimsed to investigate multidirectional ankle displacement and associated stiffness when a posterior–anterior impact force was applied to the posterior knee compartment. Forty healthy adults with and without foot hyperpronation were recruited. A three-dimensional motion capture system and force plates were used to acquire angular displacement and ankle joint moment data. The independent $t$-test and Mann–Whitney $U$ test were used to compare the group differences in ankle angular displacement, moment, and stiffness. Spearman’s rho test was performed to determine the relationship between ankle angular displacement and stiffness. The hyperpronation group demonstrated significantly greater sagittal ($p=0.003$) and frontal plane ($p=0.033$) angular displacements and reduced sagittal plane ankle stiffness ($p=0.026$) than the neutral group. The Spearman’s correlation analysis showed a close inverse relationship between the ankle angular displacement and stiffness, ranging from $r=-0.44$ to $-0.55$. The biomechanical data in our study suggest that individuals with foot hyperpronation present with multidirectional hypermobility and a reduction in ankle stiffness. These factors contribute to an increased risk of ankle-foot injury in individuals with foot hyperpronation.

This study investigated the quantitative scaling properties of the center of pressure (COP) as well as the spatial-temporal properties of the COP to elucidate the postural control behavior of healthy elderly (HE) adults and adults with Parkinson’s disease (PD) during quiet standing. Eighteen adults with PD and eighteen HE adults participated in this study. The COP movements were recorded while participants stood on either a firm surface or on a foam pad with their eyes either opened or closed. The sway ranges in the anterior–posterior (AP) ($R_x)$ and medio-lateral (ML) ($R_y)$ directions, the total length of the trajectory ($L)$, sway area ($A)$, and scaling exponents ($\alpha )$ from detrended fluctuation analysis were computed from the measured COP data. All temporal variables of the COP in all conditions were found to be significantly larger in the PD group than in the HE group. Low scaling exponents obtained for the PD group showed this group possessed diminished postural control ability compared to the HE group. The PD group showed unpredictable open-loop control in both the AP and ML directions. This proprioceptive control became predictable and the time scale relations decreased as the postural challenges increased. The AP and ML closed-loop control of the PD group was more predictable than that of the HE group only when proprioception was distorted using intact visual input, and the visual and proprioceptive inputs were both intact.

The use of finite element models has gained popularity in the field of foot and footwear biomechanics to predict the stress–strain distribution and the treatment effectiveness of therapeutic insoles for pathological foot conditions. However, a comprehensive evaluation of mesh quality is often ignored, meanwhile no golden standard exists for the mesh density and selection of element size at an acceptable accuracy. Here, we make a convergence test and established anatomically-realistic foot models at different mesh densities. The study compared the discrepancy in output variables to the changes of element type and mesh density under barefoot and footwear conditions with compressive and shear loads, which are commonly encountered in foot and footwear biomechanics simulations. For a range of loading conditions simulated in 125 finite element models, the peak plantar pressure consistently converged with optimal mesh size determined at 2.5mm. The convergence variable of principal strains and stress tensors, however, varies significantly. The max von-Mises stress showed strong sensitive behavior to the changes of the mesh density. The pattern for contact pressure distribution became less accurate when the element sizes increase to 6.0mm; in particular, the locations of the pressure peak do not show remarkable changes, but the size of the area of contact still changes. The current study could offer a general guideline when generating a reasonable accurate finite element models for the analysis of plantar pressure distributions and stress/strain states employed for foot and footwear biomechanics evaluations.

Hepatic injury induced by blunt abdominal impact is a major cause of death in vehicle crashes. However, few works have been done effectively in cadaver experiments to clarify the liver’s specific dynamic behavior and mechanical characteristics. This paper described the dynamic behavior and mechanical characteristics of the liver under blunt impacts to the upper abdomen with the finite element model (FEM) of the Chinese human body — the 50 percentile-sized male (CHUBM-M50). The simulation matrix, three directions (frontal, oblique, lateral), and four speeds included in each group were designed with a 23.4kg, rigid cylindrical impactor aligning the T11 level. The liver deformation contours displayed compression against the spine and rotation in the horizontal plane, which were the two main features in liver motion. Pressure distribution in the liver capsule and parenchyma was discussed to elucidate the biomechanical characteristics related to impact direction. Generally, the stress distribution in the capsule was 10 times higher than that in the parenchyma. A discussion of the injury mechanism of the liver capsule and parenchyma observed in the simulations was given upon the pressure distribution. It demonstrated that the capsule could protect liver parenchyma at low-speed impacts and should not be neglected for understanding liver injury mechanisms.

This study investigated the predictive ability of the skeletal muscle force model presented by Knodel et al. [Knodel NB, Lawson LB, Nauman EA, “An emg-based constitutive law for force generation in skeletal muscle-part i: Model development,” J Biomech Eng (in press), doi: 10.1115/1.4053568] on the knee joint. It has previously been validated on the ankle joint [Knodel NB, Calvert LB, Bywater EA, Lamia JP, Patel SN, Nauman EA, “An emg-based constitutive law for force generation in skeletal muscle-part ii: Model validation on the ankle joint complex,” Submitted for Publication] and this paper aimed to identify how well it, and the solution process, performed on a more complex articulation. The knee joint’s surrounding musculoskeletal tissue loading was also identified. Ten subjects (five male and five female) performed six exercises targeting the muscles that cross the knee joint. Motion capture, electromyography, and force plate data was collected during the exercises for use in the analysis program written in MATLAB and magnetic resonance images were used to observe subject-specific ligament and tendon data at the knee articulation. OpenSim [Delp, SL, Anderson FC, Arnold AS, Loan P, Habib A, John CT, Guendelman E, Thelen DG, “Opensim: Open-source software to create and analyze dynamic simulations of movement,” IEEE Trans Biomed Eng 54(11):1940–1950, 2007, doi: 10.1109/TBME.2007.901024] was used for scaling a generic lower extremity anatomical model of each subject. Five of the six exercises were used to calculate each muscle’s constant, $K_m$ [Knodel NB, Lawson LB, Nauman EA, “An emg-based constitutive law for force generation in skeletal muscle-part i: Model development,” J Biomech Eng (in press), doi: 10.1115/1.4053568; Knodel NB, Calvert LB, Bywater EA, Lamia JP, Patel SN, Nauman EA, “An emg-based constitutive law for force generation in skeletal muscle-part ii: Model validation on the ankle joint complex,” Submitted for Publication], and the sixth was used as a testing set to identify the model’s predictive ability. Average percent errors ranged from 9.4% to 26.5% and the average across all subjects was 20.6%. The solution process produced physiologically relevant muscle forces and the surrounding tissue loading behaved as expected between the various exercises without approaching respective tensile strength values.

This study examined the influence of running shoe center of gravity relative position shifting forward and backward in sagittal axis on male amateur runners. Twenty-three adult male runners were recruited through social media with paid to participate in this study. The experimental shoe used was the Li Ning Feidian Challenger 3. Forward center of gravity (FCG), defined as the shoe center of gravity located at 10.8cm (15% before midpoint) from shoe toe to heel. Intermediate center of gravity (ICG), defined as the shoe center of gravity, is located at 14.8cm (midpoint) from shoe toe to heel. Backward center of gravity (BCG), defined as the shoe center of gravity, is located at 23.1cm (15% after midpoint) from shoe toe to heel. Questionnaire collection was used to assess the perception of the center of gravity shifting. Ground contact temporal, peak force/pressure of plantar and kinetics indicators data were simultaneously captured by motion capture system and force platform. Three participants (13.04%) correctly perceived the shoe center of gravity shifting forward and backward simultaneously. Shoes ICG peak force underneath Meta 1 increased significantly than BCG by 7.59% ($p<0.05$). Shoes FCG peak force underneath Meta 2 decreased significantly compared to ICG and BCG by 13.62% and 8.96% ($p<0.05$). Shoes BCG peak force underneath Meta 5 decreased significantly compared to ICG and FCG by 18.18% and 23.78% ($p<0.05$). Shoes FCG peak pressure underneath Meta 2 decreased significantly compared to ICG and BCG by 13.02% and 9.19% ($p<0.05$). Shoes FCG peak pressure underneath Meta 2 decreased significantly compared to ICG and BCG by 11.18% and 9.16% ($p<0.05$). However, there are no significant differences in kinetic indicators. The findings suggest that a fraction of participants can correct perceived shoe center of gravity shifting. Shoes’ FCG reduces force and pressure in the middle metatarsal regions. Shoes’ BCG reduces force in the lateral and medial metatarsal region. Healthcare professionals can optimize the design of footwear accordingly to improve rehabilitation outcomes and reduce injury risks in runners.

The objective was to investigate the effects of running shoes with midsole hollow structure span and height on the biomechanics of the lower limbs during running. We collected 21 adults with running habits who wore two pairs of running shoes with different midsole hollow structures and ran at a speed of 3.3m/s on a force-measuring treadmill. The lower limb kinematics, ground reaction force (GRF) and lower limb muscle activation characteristics were simultaneously captured by a motion capture system, a 3D force treadmill, and a surface electromyography (sEMG) system. Paired t-tests were performed on data for the two shoe conditions that fit the normal distribution assumptions; otherwise, Wilcoxon signed-rank tests were used. The statistical parameter mapping (SPM) technology was used for the analysis of 1D parameters of kinematic, dynamic, and sEMG activation characteristics. The result showed that the time to the peak impact force at touchdown of Hollow shoe2 was significantly increased ($P<0.01$), the maximum loading rate ($P<0.01$) and average loading rate ($P<0.05$) were significantly reduced, braking time ($P<0.05$), push time ($P<0.05$), contact time ($P<0.01$) of Hollow shoe2 were significantly increased compared with Hollow shoe1. Hollow shoe2 push phase of the tibialis anterior muscle activation characteristics was significantly lower (SPM, $P<0.05$) than Hollow shoe1. Our conclusion is that running shoes offer the solution as they have the advantage of the complex structure of the hollow midsole.

The bending stiffness of footwear impacts running efficiency and lower-limb work redistribution. However, studies integrating both aspects are scarce. This study aimed to examine the impact of footwear stiffness on lower-limb biomechanics, joint work, and overall metabolic efficiency. This study was performed on 12 male recreational runners to complete an experimental protocol while wearing two different running shoes with varying degrees of longitudinal bending stiffness. Paired-sample t tests were applied in this research. The stiffer footwear decreased the range of motion (ROM), angular velocity, negative and positive work of the metatarsophalangeal (MTP) joint, and ROM of the ankle joint. The running economy significantly improved with the stiffer footwear. However, no significant difference was observed in the joint work of other lower limbs. Shoes with increased bending stiffness significantly reduced the MTP joint ROM and angular velocity, thereby reducing negative power and work at the MTP joint and improving running economy for runners. This study provided relevant information for shoe designers, developers, and scientists conducting research on footwear midsole structures and designs.

Fracture is one of the most important health problems in people’s life. Millions of people have fractures every year. However, there is no unified standard for fracture healing in the clinic. Most definitions of complete fracture healing are subjective evaluations based on X-ray films. However, it is not reliable to evaluate the biomechanical strength of bone according to the number of callus on X-ray, and the imaging time of callus lags behind the actual callus, which is not conducive to the evaluation of early fracture healing time. In addition, although more and more fracture patients have achieved imaging healing after injury, the bone quality and bone strength of the whole body and local fracture have not returned to the normal level, and the probability of re-fracture has increased significantly, which has brought great pain to their families. Fracture healing is affected by many factors, such as age, fracture site, whether to fix the fracture site, and osteoporosis. Therefore, when evaluating the fracture healing status of patients, we should not only evaluate whether the fracture is healed but also evaluate its healing. By analyzing the previous research methods of fracture healing, in this paper, we systematically summarize the evaluation methods of fracture healing from the perspectives of computer tomography, ultrasound, bone density, biosensors, and biomechanics by analyzing previous research methods of fracture healing, aiming to provide reference for researchers in related fields.

Objective: This study aimed to evaluate the effect of rehabilitation training combined with visual feedback balance training on motor functions in patients with knee injuries. Methods: A total of 80 patients with sports-related knee injuries from the outpatient and inpatient departments of Lishui City People’s Hospital were randomly divided into control and observation groups, with 40 patients in each group. The control group underwent rehabilitation training based on biomechanical principles, and the observation group underwent additional visual feedback balance training. Trunk control ability, limb motor function, and walking stability were compared between the two groups before, 1 month after, and 3 months after training. Results: After 1 month of training, the lower-limb function scores, trunk control ability scores in activities such as turning to the healthy side and the affected side on the bed, sitting and standing balance, and scores for Dynamic Gait Index and Berg balance scale were all higher in the observation group compared with the control group ($P<0.05$). After 3 months of training, the differences in scores between the two groups became more pronounced ($P<0.05$). Conclusions: Rehabilitation training based on biomechanical principles combined with visual feedback balance training effectively improved the limb motor function, enhanced the trunk control ability, and maintained the body balance and walking stability in patients with sports-related knee injuries. This study provided a more effective novel rehabilitation approach for the postoperative recovery of patients with knee injuries.

Elbow joint loading was evaluated during a forward fall at various elbow initial flexion angles, in order to determine which is the best elbow initial flexion angles to prevent the elbow injury during a fall. Subjects were asked to perform a forward fall and followed by a push-up motion in different elbow initial flexion angles: 0°, 20°, 40° and unrestricted group. Fall on the outstretched hand is the leading cause of upper extremity injury. There are far more extension type of supra-condylar fracture of the elbow than flexion type. Flexion of the elbow may represent the effects of damper and spring. Using the motion analysis system, the kinematics and kinetics of the elbow joint were investigated under various elbow initial flexion angles. The loading biomechanics of the elbow joint differed with various elbow initial flexion angles. The ground reaction forces decrease with increase of elbow flexion upon impact. Different initial elbow flexion angles would affect the biomechanics of upper extremities during falls. Forward fall with elbow in extension is more dangerous. Knowledge of elbow kinematics and kinetics may be helpful in preventing injuries by reducing the ground reaction force with changes of the elbow initial flexion angles during a fall.

The purposes of the present study were to (1) investigate the effects of the arm movement and initial knee joint angle employed in standing long jump by the ground reaction force analysis and three-dimensional motion analysis; and (2) investigate how the jump performance of the female gender related to the body configuration. Thirty-four healthy adult females performed standing long jump on a force platform with full effort. Body segment and joint angles were analyzed by three-dimensional motion analysis system. Using kinetic and kinematic data, the trajectories on mass center of body, knee joint angle, magnitude of peak takeoff force, and impulse generation in preparing phase were calculated. Average standing long jump performances with free arm motion were +1.5 times above performance with restricted arm motion in both knee initial angles. The performances with knee 90° initial flexion were +1.2 times above performance with knee 45° initial flexion in free and restricted arm motions. Judging by trajectories of the center mass of body (COM), free arm motion improves jump distance by anterior displacement of the COM in starting position. The takeoff velocity with 90° knee initial angle was as much as 11% higher than in with 45° knee initial angle. However, the takeoff angles on the COM trajectory showed no significant differences between each other. It was found that starting jump from 90° bend knee relatively extended the time that the force is applied by the leg muscles. To compare the body configurations and the jumping scores, there were no significant correlations between jump scores and anthropometry data. The greater muscle mass or longer leg did not correlated well with the superior jumping performance.

Degenerative osteoarthritis is the consequence of impact force applied to articular cartilage that results in surface fissuring. Soft cushions and flexed posture are two important factors to reduce the impact force; however, no quantitative information of how soft should the cushion be to prevent the injury and the mechanism of force attenuation of knee joint at neutral and flexed posture was not well documented yet. The objective of current study is hence to find the quantitative shock attenuation of knee joint using different stiffness of cushions when the knee is at neutral posture and flexed posture. A “drop-tower type” impact apparatus was used for testing. Nineteen fresh porcine knee joints were divided into two posture groups, i.e. neutral and flexed posture. All specimens were tested using stiff, medium, and soft cushions. The axial reaction force, anteroposterior shear force, and flexion bending moment were recorded for analysis. We found the flexed posture decreased the axial reaction force and anterior shear force but increased the flexion bending moment. The effect of stiffness of cushions on the mechanical response of knee joint during impact loading was significant for neutral posture but not for flexed posture.

The aim of this study was to evaluate the influence of implant length and bone quality on the biomechanical aspects in alveolar bone and dental implant using non-linear finite element analysis. Two fixture lengths (8 and 13mm) of Frialit-2 root-form titanium implants were buried in 4 types of bone modeled by varying the elastic modulus for cancellous bone. Contact elements were used to simulate the realistic interface fixation within the implant system. Axial and lateral (buccolingual) loadings were applied at the top of the abutment to simulate the occlusal forces. The simulated results indicated that the maximum strain values of cortical and cancellous bone increased with lower bone density. In addition, the variations of cortical bony strains between 13mm and 8mm long implants were not significantly as a results of the same contact areas between implant fixture and cortical bone were found for different implant lengths. Lateral occlusal forces significantly increased the bone strain values when compared with axial occlusal forces regardless of the implant lengths and bone qualities. Loading conditions were found as the most important factor than bone qualities and implant lengths affecting the biomechanical aspects for alveolar bone and implant systems. The simulated results implied that further understanding of the role of occlusal adjustment influencing the loading directions are needed and might affect the long-term success of an implant system.

The geometric shape and mechanical structure of RBFPD compared to conventional FPD are relatively complex and unstable. The low retention rate between the retainer and abutment affects the prosthesis/abutment interface de-bonding, and closely relates to the design of the prosthesis and varied occlusion status. This study used reverse engineering (RE) and computer-assisted design (CAD) to construct two solid models of anterior RBFPD with different span lengths. After mesh generation, biomechanical interactions of span length in RB prosthesis with two loading conditions (axial and lateral) were performed by FE analysis. The simulated results indicated that lateral occlusal force increased significantly 2-3 times maximum stress than that of axial occlusal force. For different span lengths simulation, the analysis on static movement finds that longer pontic would lead to high stress to the prosthesis. Thus, the length of the pontic has significant effect on the overall intensity of the prosthesis under static clenching loading, and the effect of lateral loading exceeds that of axial loading.

Recently, there are more people jogging with a treadmill at the gym or the home setting. The main available selected modes for treadmill jogging are speed and slope of incline. Increased speeds and incline slopes will not only increase the cardiopulmonary loading but may also alter the lower extremity (LE) movement patterns. There are few systematic investigations of the effect of the speed and incline on LE kinematics. Most studies have used 2D methods which focused on movements in sagittal plane only and this has limitations in the acquired data since lower extremity movements also include frontal and transverse planes. The current study aimed to investigate LE movement during jogging at different speeds and incline slopes using a high speed three-dimensional (3D) motion analysis system.

Eighteen young healthy males were recruited. The video-based motion capture system with six CCD cameras, HIRES Expert Vision System (Motion Analysis Corporation, CA, USA), was used to collect kinematic data at a sampling frequency of 120Hz. Nineteen passive reflective markers were attached to bilateral lower extremities of the subject. The joint angle is calculated by Euler angle using the rotation sequence: 2-1-3 (y-x′-z″). Four speeds were selected: 2 m/s, 2.5 m/s, 3 m/s, 3.5 m/s with the slope at 0, and four slopes were selected: 0%, 5%,10%,15% at a speed of 3 m/s. Repeated-measures ANOVA was used to test hypotheses regarding changes in jogging condition on LE kinematic variables. The significance level was set at 0.05.

As the jogging slope increased, the hip, knee and ankle demonstrated a significantly greater maximum flexion in swing phase (p<0.001), but the maximum extension angles in stance phase were relatively unchanged. Increased LE flexion during swing phase is important to ensure foot clearance with increased slope. For increased speed, the hip and ankle joints had significantly greater maximum joint extension angles during stance phase and the hip and knee joint had significantly larger maximum flexion angles in swing phase (p<0.001). Increased motion during swing phase account for a larger step length and increased motion during stance phase may facilitate the generation of power during forward propulsion as the jogging speed increased. As the slope and speed increased, LE movement patterns were changed in the transverse plane: the significantly increased (p<0.01) internal hip rotation at terminal stance, the increased toe-in of foot (p<0.001) during terminal stance phase and decreased (p<0.05) toe-out during swing phase. Increased hip motion in transverse plane could lengthen the stride distance and increase foot toe-in for providing a stable lever for push off to increase propulsion force as speed or slope is increased. By way of systematic 3D kinematic investigation of the LE in jogging, the results further elucidate the effect of changing speed and incline on LE joints movements. This information could provide guidelines for rehabilitation clinicians or coaches to select an appropriate training mode for jogging.