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Abstract:In recent years, the effects of the neuro-biomechanical ergogenic technology on improving and enhancing human function and physical movement performance have widely attracted certain attentions. This review summarized the recent achievements in the effects of non-invasive brain stimulation (NIBS) and biomechanical ergogenic technology based on sports equipment on human physical performance, and further explored the possible mechanisms for improving and promoting human physical performance. The obtained preliminary evidence based on animal experiments and biomechanical researches on neuromotor control under multi-joint movement were also summarized, so as to explain the coordinated development of human function enhancement at cerebral cortex regulation and neuromuscular coordinated control levels, and interpret its integration with sports equipment. This review ultimately provided certain references for the future frontier development and research position of neuro-biomechanics and human sports biomechanics.

Abstract:Objective To discuss rationality of the three-link model used in analysis on interactive dynamics of deep squatting, and clarify the source of differences in calculation of joint torque by three-link model and Visual 3D. Methods Eight subjects were selected to obtain kinematic data of the squat motion through Vicon. The second Lagrangian equation was used to establish the three-link dynamic equation. The joint torque was calculated based on the Mathematica programming. The results were compared with the calculation results of lower limb chain segment model by Visual 3D, and the similarity between the two results was evaluated by the coefficient of complex correlation (CMC). Results The CMC of hip joint and knee joint from 8 subjects was larger than 0.85, and the CMC of ankle joint was between 0.50-0.85. The joint torque calculated by three-link dynamic equation and Visual 3D was highly similar in hip joint and knee joint, and there was only a moderate similarity in ankle joint. Conclusions The three-link model can be used in further analysis on interactive dynamics of deep squatting, but the influence of interactive moment caused by ground reaction force (external moment) on ankle torque should be considered.

Abstract:Objective By establishing the intervention mode of 12-week gait retraining (GR) (with the specific aim of changing the habitual running gait), to determine the changes of vertical ground reaction force (vGRF), kinematics and dynamics of hip, knee, ankle joints, as well as stiffness of lower limbs in running before and after GR, and to explore the influence of running posture transformation on impact force and lower limb biomechanics. Methods Vicon motion capture system and Kistler 3D force measurement platform were used to collect the GRF and marker track of 30 runners (15 in experimental group and 15 in control group) before and after GR with the minimalist shoes at a speed of 12 km/h±5%. Results A total of 17 subjects (9 in experimental group and 8 in control group) completed the GR. After GR, the maximum loading rate of both groups decreased significantly, and the maximum loading rate of experimental group was lower than that of control group. The foot strike angle in experimental group decreased significantly after GR, and the plantarflexion angle and hip joint angular extension velocity increased in both groups. The force moment of ankle joint increased in experimental group, and the stiffness of lower limbs was significantly improved in both groups. Conclusions A 12-week GR exercise intervention model was successfully established, with 78% conversion rate (from rearfoot strike to forefoot strike). GR can effectively avoid the peak of impact force, reduce the maximum loading rate, increase the lower limb stiffness, and thus reduce or even avoid the risk of running injury caused by impact force and may provide a possibility for the improvement of running economy.

Abstract:Objective To study the sex-specific lower extremity biomechanics of amateur runners with patellofemoral pain (PFP). Methods Fifteen male and ten female amateur runners with PFP were identified and enrolled in PFP group, twenty-five healthy amateur runners matched with the PFP group were recruited as control group. The kinematics and kinetics, surface electromyography (EMG) data from all the subjects in the running task were collected.Two-way analysis of variance was performed to determine the influence of group and sex on lower extremity biomechanics during running. Results Compared with control group, male amateur runners with PFP showed a greater peak knee flexion angle during the landing phase of running. Compared with control group, male and female amateur runners with PFP showed a greater peak hip adduction angle during the landing phase of running, while the peak hip adduction angle of female participants was significantly greater than that of male participants. Conclusions Amateur runners with PFP showed sex-specific lower extremity biomechanics in the running task, and the clinical intervention for PFP should be sex-specific.

Abstract:Objective To study the effect of ankle taping (restriction of ankle varus and plantar flexion) on biomechanical characteristics of the knee during drop landing on the dominant leg. Methods Eighteen amateur athletes performed the dominant-legged drop landing under two different ankle conditions (with or without taping). Vicon three-dimensional (3D) motion capture system, Kistler force plate and Noraxon surface electromyography (sEMG) system were used to collect kinetic, kinematic and sEMG data for statistical analysis. Results Compared with control group, ankle taping significantly increased flexion angle at initial contact and maximum flexion angle, while significantly decreased the maximum valgus angle. Conclusions The restriction of varus and plantar flexion might reduce the risk of anterior cruciate ligament (ACL) injury. The intervention with ankle taping could modify biomechanical parameters of the knee during drop landing. The ankle taping by restriction of ankle varus and plantar flexion may be an effective measure to prevent ACL injury for collegiate athletes.

Abstract:Objective To study the effect of vibration training with adjusted frequency on changes in explosive force of lower limbs, balance and muscle function around ankle joints of patients with functional ankle instability (FAI), so as to provide an empirical basis for rehabilitation training of FAI patients in clinic. Methods Twenty-six FAI patients were randomly divided into the experimental group (n=14) and the control group (n=12). The experimental group received 8-week rehabilitation training with vibration intervention, while the control group only received 8-week rehabilitation training. Changes in maximum power, average power, maximum speed and average speed of the injured limb during vertical jump with single leg, changes in distances during long jump, changes in time during one-leg standing with eyes open and closed，changes in contract time (tc), relax time (tr) and displacement (Dm) of medial gastrocnemius (GM), lateral gastrocnemius (GL) and tibialis anterior (TA) muscles before and after training were measured and compared. Results In the experimental group, the maximum power and maximum speed of the injured limb during vertical jump with single leg, the distance during long jump with single leg and the time during one-leg standing with open and closed eyes were significantly improved, and the increase was higher than that of the control group. The increase of tc of all muscles in the experimental group was smaller than that of the control group, but tr and Dm did not show any regularity. Conclusions Vibration training with adjusted frequency can effectively improve the explosive force and balance ability of lower limbs of FAI patients, and promote the tc shortening of GL, GM and TA muscles, but whether vibration training with adjusted frequency can reduce muscle tension and promote muscle relaxation is still not clear.

Abstract:Objective To analyzes the biomechanical and dynamic characteristics of human body during exercise on elliptical cross trainer. Methods An elliptical cross trainer model and a human skeletal muscle model were built by three-dimensional (3D) modeling software and AnyBody software, respectively, which were then coupled and simulated. Results During exercise on elliptical cross trainer, the lumbar spine L5 was subjected to the maximum force 1023 kN, and the maximum activation of external oblique and internal oblique muscles were 80% and 40%, respectively. The maximum muscle activation in lower limb muscle groups did not exceed 40%, and the maximum plantar ground reaction force was 600 N. Conclusions The use of elliptical cross trainer can alleviate the pain of patients with chronic low back pain, and help to improve the trunk control and balance function of patients with stroke and hemiplegia. Compared with running exercise, exercise on elliptical cross trainer can protect the human knee joint.

Abstract:Objective The single leg support tree pose and Yan balace of yoga was selected to compare the biomechanical characteristics of lower limb joint angles, joint force and muscle strength for professional and non-professional yoga practitioners, so as to provide theoretical basis for scientific fitness of yoga beginners and exercise prescription determined by rehabilitation physicians. Methods BTS infrared motion capture system was used to collect kinematic data, Kistler forceplate was used to collect dynamic data, AnyBody 7.0 simulation software was used to calculate the joint force and muscle strength, and Biodex balance system was used to evaluate the stability of single support. Results In both tree pose and Yan balance, the muscle strength of lower limbs in professional group was greater than that in non-professional group. Support leg of tree pose: the muscle strength of the tibialis anterior, gluteus medius posterior, iliac medialis and sartorius in professional group was greater than that in non-professional group (P<0.05). Balance leg of tree pose: the muscle strength of the biceps femoris breve, sartorius, piriformis, gemellus inferior, iliac lateralis, iliac medialis, gluteus maximus inferior, obturator internus in professional group was greater than that in non-professional group (P<0.05). Support leg of Yan balance: the muscle strength of tibialis anterior, extensor digitorum longus, extensor hallucis longus, obturator internus, gluteus maximus superior in the professional group was greater than the non-professional group (P<0.05). Balance leg of Yan balance: The muscle strength of extensor hallucis longus in professional group was greater than that in non-professional group (P<0.05). The scores of front-rear, overall of PS-BI, overall, front-rear, left-right of athlete single leg (ASL) in professional group were significantly lower than those in non-professional group (P<0.05). Conclusions The joint angle will affect the degree of muscle exercise in lower limbs. During yoga practice, attention should be paid to the standard of postures and the exercise of corresponding muscles. In tree pose, the muscle strength of both legs in non-professional group was significantly different from that in professional group, and the difference in Yan balance was more obvious on the supporting leg. Yoga practice can improve the stability of single leg support in multiple directions.

Abstract:Objective To study the effects of collagen fiber bundle on mechanical properties of articular cartilage, so as to provide references for clinicians to guide the rehabilitation of patients with early cartilage injury. Methods The two-dimensional (2D) numerical model of fiber-reinforced porous viscoelasticity was established, with consideration of the relationship of fiber distribution, elastic modulus, porosity and permeability with cartilage depth. The influences from local fracture of the fiber bundle, the progressive fracture from the surface and the fiber bundle size on mechanical properties of the cartilage were studied, and the maximum principle strain of cartilage matrix was obtained. Results The maximum principal strain of the matrix occurred at a position in middle layer of the cartilage, about upper 1/3 of the cartilage, which was not affected by fiber breakage mode and fiber bundle size. The strain of the cartilage with thicker fiber bundles decreased. Conclusions The middle layer of the cartilage was prone to mechanical damage. The thicker fiber bundle could reduce the maximum principal strain of the matrix. Once the fiber bundle broke, the maximum principal strain of the cartilage matrix with thicker fiber bundle became larger, leading to an easier evolution of the cartilage damage.

Abstract:Objective To explore the influence of different model scopes on acetabular stress distribution and optimal osteotomy result in preoperative planning of Bernese acetabular osteotomy. Methods Two patients with hip dysplasia were established according to different model ranges. Model 1 included the affected hip and femur, and Model 2 included the complete pelvis and affected femur. Compare and analyze the acetabular cartilage contact pressure, area and distribution of the two models under single-leg standing conditions, and simulate osteotomy. Results Compared with Model 1 before surgery, Model 2 had higher contact pressure, smaller contact area and closer distribution to the meniscus edge of acetabulum. Compared with 11 postoperative plans, the variation amplitude of contact pressure and the optimal osteotomy angle for Model 1 were all smaller than those of Model 2. Conclusions The preoperative analysis result of the model with affected hip bone and femur would underestimate the degree of stress concentration and misjudge the location of stress concentration, and the obtained optimal osteotomy rotation angle would be relatively small. The research findings provide certain theoretical basis for preoperative planning and modeling of osteotomy.

Abstract:Objective To simulate the hemodynamic effects of different flow diverters (FD) parameters by using computational fluid dynamics (CFD) technology, so as to develop a more reasonable FD embolization strategy before operation. Methods The porous media model was used to simulate the process of FD implantation into aneurysms, and the initial values of its own unique porous media momentum source parameters (permeability and inertial resistance) were calculated for a specific FD (Tubridge).The changes of hemodynamic parameters such as blood flow velocity, wall shear stress (WSS), volume flow and pressure of aneurysm-roof were compared under different situations (initial values of 80%, 90%, 100%, 110% and 120%), and the sensitivity analysis on hemodynamic parameters of patient-specific intracranial aneurysms (IA) for the porous media model was further conducted. Results The sensitivity of IA hemodynamic parameters to the permeability of porous media model was as follows: WSSparent-artery＞WSSaneurysm＞paneurysmal-roof, but the sensitivity to inertia resistance was relatively lower. Conclusions By using the porous media model, different metal coverages (MC) of FD could be simulated by choosing different permeability parameters, so it is necessary to adjust specific permeability settings during modeling of FD with different MC.

Abstract:Objective To study the effects of different residual stromal bed thickness (RSBT) in laser-assisted in situ keratomileusis (LASIK) surgery on geometric deformation and stress changes of the cornea under different intraocular pressures (IOP), and evaluate safety of the three retention values (250, 280, 300 μm). Methods The models of normal cornea and corneas with different RSBT after surgery were established by the finite element software ABAQUS. Appropriate loading and boundary conditions were set and then the corresponding displacement and stress were calculated. Results The apical displacement of the postoperative cornea (RSBT=250 μm) under IOP=2.66 kPa was basically the same as that of the normal cornea (RSBT=550 μm) under IOP=5.32 kPa. RSBT=280 μm was in the low risk area of keratoconus, while RSBT=250 μm was in the high-risk area. At a value between 280 μm and 300 μm of RSBT, the stress distribution was nearly consistent with that of the normal cornea. With RSBT=300 μm, the stromal layer of the cornea lost 40% of the strongest strength against tissue tension. Conclusions RSBT=250 μm is the minimum retention value for LASIK surgery. RSBT=250 μm is the high risk value. With RSBT=330-340 μm, LASIK surgery is safe enough for most patients.

Abstract:Objective To simulate the biomechanical characteristics of pelvic-ligament-muscle during vaginal delivery and rest, and to explore the injury of levator ani muscles during vaginal delivery, pelvic organ prolapse and stress urinary incontinence. Methods The three-dimensional (3D) nonlinear finite element model of pelvis-ligament-muscle was established to calculate the stress and strain distributions and injury of levator ani muscles under different abdominal pressures and loads. The stress and strain distributions as well as damage of type I, Ⅱ, Ⅲ stress urinary incontinence and pelvic organ prolapse were also calculated. Results The highest equivalent stresses of levator ani were 14, 29, 43, 86, 144, 230 kPa, respectively, when the abdominal pressure was 1 kPa under the load of 3, 5, 8 kPa and the abdominal pressure was 1.5 kPa under the load of 3, 5, 8 kPa. The stresses of type I, Ⅱ, Ⅲ stress urinary incontinence and pelvic organ prolapse were 1.69, 1.01, 0.70, 1.58 MPa. Conclusions Vaginal delivery would result in the damage to the puborectalis and the middle of the pubococcipital muscle, which was consistent with the damage of the anal levator muscle with pelvic floor dysfunction. This study uses scientific method to find out the exact location of pelvic floor injury during vaginal delivery, which can provide references for clinicians to prevent pelvic floor disease and formulate post natal rehabilitation training.

Abstract:Objective To explore the effect of mechanical stimulation on polarity of macrophages. Methods RAW264.7 cells were stimulated with tensile stretch at various amplitude and time, then cell viability was assessed with cell count kit-8 (CCK-8) for determining the stimulation parameters. RAW264.7 cells were induced to M1 type, then tensile stretch at 10% amplitude and 2 Hz was applied to M1 cells. CCK-8 and flow cytometry were used to detect the effects of tensile stretch on cell activity and apoptosis. Quantitative real-time polymerase chain reaction (qRT-PCR) was used to detect the effect of tensile stretch on M1 type macrophage related gene expression. Results After stimulation for 3 hours, tensile stretch at 15% or 20% amplitude and 2 Hz significantly inhibited cell viability (P<0.05), while tensile stretch at 10% amplitude and 2 Hz did not inhibit the viability of RAW264.7 cells (P>0.05). Tensile stretch at 10% amplitude and 2 Hz neither inhibited viability nor cause apoptosis of M1 type macrophages. The expression of inflammation-related genes including interleukin-1β(IL-1β) and tumor necrosis factor-α (TNF-α) of M1 type macrophages was significantly down-regulated with tensile stretch at 10% amplitude and 2 Hz (P＜0.05). Conclusions Mechanical stimulation at 10% amplitude and 2 Hz can inhibit M1 type macrophages and promote the polarization from M1 to M2. Mechanical stimulation may become a method for treating inflammation-related diseases.

Abstract:Objective To analyze the correlation of the maximum myocardial stiffness (maxEav), maximum modulus of elasticity (Emax) with the E/A ratio of mltral annulus at the end of left ventricular systole for patients with essential hypertension. Methods 298 patients with essential hypertension were selected as research objects. The left ventricular mass index (LVMI) and relative wall thickness (RWT) of the patients were calculated. Based on LVMI and RWT indexes, the patients were divided into left ventricular normal (LVN) group, left ventricular concentric remodeling (LVCR) group, left ventricular eccentric hypertrophy (LVEH) group, left ventricular concentric hypertrophy (LVCH) group, respectively. In addition, 115 healthy subjects were selected into control group. The subjects were diagnosed by echocardiography, so as to analyze the correlation of maxEav, Emax with E/A. Results The maxEav, Emax and E/A in LVCR group, LVEH group and LVCH group were all negatively correlated. The differences of E/A between LVCR group, LVCH group and control group showed statistical significance. Compared with control groups, both the maxEav and Emax in hypertension group decreased, and the difference was statistically significant. Conclusions The maxEav and Emax are more sensitive and easy indexes to judge left ventricular diastolic function. The analysis on maxEav and Emax changes in patients with left ventricular remodeling and diastolic dysfunction in hypertension, as well as the exploration on pathogenesis of diastolic heart failure, can provide the theoretical basis for prevention and treatment of diastolic heart failure in the future.

Abstract:Objective To investigate biomechanical characteristics of the modified memory alloy internal fixator for separation of pubic symphysis. Methods The model of pubic symphysis separation injury was established based on 10 pelvic specimens. The control group was fixed with the dynamic compression plate after reduction, and the experimental group was fixed with the modified memory alloy internal fixator for separation of pubic symphysis after reduction. The biomechanical stability for two kinds of internal fixation was compared. Results There were no loosening and fracture of internal fixation in both groups. The displacement of pubic symphysis in horizontal, anterio-posterior and vertical direction in the experimental group was obviously reduced compared with the control group (P＜0.05). Conclusions Compared with the dynamic compression plate, the modified memory alloy internal fixator for separation of pubic symphysis shows better resistance to the tensile force against horizontal and anterio-posterior direction, as well as better resistance to the vertical shear force.

Abstract:Biomechanical factors play a crucial role in the steady-state maintenance of articular cartilage. The primary cilium (PC) is a kind of organelle which can sense mechanical and chemical signals at the same time. It is also distributed on the surface of chondrocyte membrane. It is involved in multiple signal transduction pathways as well as in the process of chondrocyte phenotype maintenance and material metabolism. Abnormalities in PC are also associated with a variety of human bone and joint diseases. This paper mainly discusses the mechanism of PC in mechanical microenvironment of chondrocytes and the interaction with other signaling pathways, and explores its relationship with bone and joint diseases, so as to provide some scientific basis for clinical and basic research in orthopedics.

Abstract:The angiogenic capacity of vascular endothelial cells is influenced by multiple mechanical factors. Mechanical factors guide the rearrangement of cytoskeleton, mediate intracellular signal transduction, affect cell migration, orientation and other behaviors, and then regulate their angiogenic capacity. However, different types of mechanical stimulation have different effects on their angiogenic capacity. This article summarizes and discusses the research work and progress of the influence of five mechanical factors （shear force, stretch stress, low-intensity pulsed ultrasound, microgravity, material properties） on vascular endothelial cell angiogenesis, which provides a basis and ideas for in-depth research of vascular biomechanics.