Abstract:Pilots are usually under various different mechanical loads during flights, which can affect their musculoskeletal and cardiovascular system and even bring them injuries. Biomechanics mainly studies the mechanics and mechanobiology in medicine and biology. Aviation biomechanics studies the physiological response to different complicated mechanical loads during flights and the countermeasures. The research fields of aviation biomechanics include: mechanical loads on human body injury and related countermeasures, durative loads, vibration and noise on the physiological effects of human body and related comtermeasures, etc.

Abstract:Objective To study effects of ankle stabilizer on electromyographic activities of lowerextremity muscles during the simulated halfsquat parachute landing and its gender differences. Method Eight male and eight female healthy adults were required to jump from a platform of 0.72 m high to simulate halfsquat parachute landing. The experiment was divided into 3 groups: the barefoot one as control group, the group wearing tapes and braces respectively. The electromyogram (EMG) of each subject’s tibial anterior, lateral gastrocnemius, biceps femoralis and rectus femoralis was measured. Twoway ANOVA was used to analyze and evaluate the effect of the stabilizers and genders on EMG variables. Results The use of brace significantly increased the prelanding EMG amplitude of the tibialis anterior for male (Control: 266 μV; Tape: 368 μV; Brace: 552 μV). The stabilizers had no significant effects on the other EMG parameters. Conclusions Semirigid ankle braces are capable of arousing more active EMG of male’s ankle flexor during halfsquat parachute landing, but female does not share this predominance. Ankle stabilizers have no significant effects on EMG activities for knee joints.

Abstract:Objective To numerically simulate the halfsquat parachute landing and analyze the mechanism of knee injuries with the finite element method based on the data of the simulated parachute landing experiment. Method The halfsquat parachuting experiment was performed by 16 healthy volunteers. The heights of simulated landing were 0.32 m, 0.52 m and 0.72 m respectively. A threedimensional finite element model of human knee joint was developed based on magnetic resonance images. The kinematical data of the knee and the data of the reaction force obtained by experiments were used to make a numerical simulation of the parachute landing process. Results The stress level of the knee increased with the increase of the height. The lateral meniscus and cartilage suffered greater loads than the medial ones. Obvious stress concentrations occurred in the anterior cruciate ligament and the medial collateral ligament when the knee flexion degree reached the peak value. Conclusions The severe impact in parachute landing is the direct cause of injuries in parachute landing. The lateral cartilage and meniscus are more likely to be injured, and the anterior cruciate ligament and the medial collateral ligament are easier to tear when the knee flexion degree reaches the peak value.

Abstract:Objective To compare the effects of location and orientation training on the improvement of visualmotor coordination under updown reversed vision, provide reference for the preventation of space motion sickness and the design of adaptation training for sensory conflict. Method Sixteen subjects were instructed to complete the maze task wearing the updown reversing prism spectacle before and after the location training and the orientation training. Both trainings lasted 30 minutes respectively. The error rate and the executing time during the maze test were analyzed and compared. Results Both trainings significantly decreased the error rate and the executing time. In addition, the results of different training methods had significant difference, and the effects of the orientation training was better than that of the location training under up-down reversed vision. Conclusions Under the sensory conflict environment arising from the visual change, the adaptation induced by some task training could also be of benefit to some other task training so as to improve the ability of visual-motor coordination and the adaption to the sensory conflict. However, different trainings could have various degrees of improvement.

Abstract:Objective To carry out quantitative investigation on application of emulational trunk dummy (ETD) in evaluating the opening shock of lifesaving parachute and provide a more reliable test method for further development. Method ETD equipped with parachute was tested in the impact experiment, where a 63.4 kg impact block was dropped from the height of 0.20 m，0.40 m，0.60 m，0.80 m respectively to simulate different opening shocks. The opening shocks were deducted by measured forces on harness and acceleration loads at the center of dummy's thorax. For comparison, 5 rigid trunk dummies (RTD) were tested under the equivalent impacts. As the contrast test, 24 male healthy subjects were also exposed under such impacts with standing and sitting posture respectively. Results Under the same impact, the peak impact value on harness exhibited maximum on RTD, minimum on subjects with sitting posture, and medium on ETD. There were significant differences between each experimental group (P<0.01). With different impact loads, the peak impact value on ETD was 2 795，3 873，4 816 and 5 736 N respectively, which was correspondingly close to that of subjects with standing posture(2 541，3 042，3 720 and 4250 N). Conclusions The result of opening shock gathered from ETD is closer to that from RTD due to ETD’s viscoelasticity, which shall certainly influence the measured opening shock. Therefore, ETD is suggested to be used in the development of livesaving parachute.

Abstract:Objective To provide data for establishing, driving and validating the inverse dynamics model of AnyBody Modeling System, the simulated halfsquat parachute landing experiment was designed and relevant data were collected. Method The subject was required to jump from a 0.32 m high platform to simulate the halfsquat parachute landing. The kinematic parameter of lower extremity joint, the ground reaction force and the surface electromyogram (SEMG) of four main muscles in the lower extremity joint were measured simultaneously. Results The angle changes of hip, knee and ankle along with time in three anatomical planes, the ground reaction force of right foot and the trajectory of the center of pressure were collected within 1 second just before and after the subject landing. These data would be used to drive the muscleskeletal model, while the data for measuring electromyogram activity would be used to validate the model. Conclusions The experiment meets the requirement of muscleskeletal model analysis, which can be used for further study of halfsquat parachute landing.

Abstract:Objective To investigate the present situation of neck injuries in military pilots, analyze possible factors that induce neck injuries and how such injuries could influence flight training, and provide suggestions for relevant physiological researches and engineering solutions. Method Questionnaires were carried out among 1 924 military pilots, including pilots of primary trainer, attacker, fighter, bomber, transporter and helicopter. The questionnaire consist of 2 parts: (1) pilots’ basic information, such as unit, age, type of aircraft, flying hours, height, weight, etc. (2) relevant issues on neck injuries, including symptoms and their influences on flight, reasons that cause the injuries, etc. Statistical analyses were conducted according to the questionnaire results. Results The investigation showed that 71.3% of the pilots had uncomfortable neck symptoms and 60.4% of them had befallen such symptoms during flight. 33.7% of the pilots had suffered neck pain and 19.2% of them reported that such pains took place during flight. Factors such as acceleration, weight of helmet and long duration of flight would be the main reasons resulting in the discomfort of neck. Bomber pilots showed the highest proportion either on the neck discomfort or on the neck pain. Conclusions Neck injuries have become the frequently occurring illness in Chinese military pilots and have affected their daily flight. The study also foresees an increased tendency on pilots’ neck injuries due to the growing requirements of flight load and training strength on fighter and attacker pilots. Therefore, great importance should be attached on neck injuries of military pilots and further studies should be conducted on physiological investigations and engineering solutions.

Abstract:Objective To study the stability of upper lumbar vertebra in spondylolysis by measuring the upper vertebra pressure on lumbar spondylolysis models. Method Nine freshfrozen human lumbar spinal specimens were used as experimental models. The pressure on upper vertebral discs of lumbar vertebrae was measured by the material testing machine (MTS858 Bionix test system)with extension, flexion and axial, bilateral compression being applied on two groups of specimens: 1) intact spine; 2) lumbar spondylolysis. Results Compared with the intact specimens, the pressure of upper lumbar vertebra in spondylolysis was increased by 1.3％，1.5％，1.7％ in axial compression with 600, 800, 1 000 N (the differences were not significant (P＞0.05)), by 20.97％，24.45％，28.79％ in 15°of extension with 300, 500, 700N (the differences were significant (P < 0.01)), by 14.15％，17.86％，24.92％ in 15°of flexion with 300, 500, 700N (the differences were significant (P < 0.01)), by 3.54％，2.12％，1.14％ in 15°of bilateral compression with 300, 500, 700N (the differences were not significant (P＞0.05)). Conclusions Lumbar spondylolysis has a significant mechanical influence on lumbar spine not only at the involved level but also at the upper adjacent level, which can affect the stability of lumbar spine correspondingly.

Abstract:Objective To investigate the influence of airway structural changes after reconstruction of nasal cavity structure on the airflow patterns within the whole upper airway and the movement of soft palate in patient with OSAHS accompanied by nasal abnormality. Method Based on the preoperative and postoperative CT data from the patient with OSAHS, the threedimensional finite element model of the upper airway and the soft palate were reconstructed. The preoperative and postoperative flow characteristics of the upper airway and movement of the soft palate were simulated by the fluidsolid interaction method. Results The surgical operation altered the abnormal anatomy of the nasal cavity. The nasal airway resistance and the whole upper airway resistance decreased significantly. Meanwhile, it was shown that the soft palate edema remitted obviously, and the motion amplitude of the free edge also decreased. The displacement of the soft palate increased with the decrease in elastic modulus of soft palate. Postoperative numerical results showed a good agreement with the experimental and computational results of the normal human in literature review. Conclusions The reconstruction of the nasal cavity structure influenced the airflow patterns and the movement of soft palate through altering the anatomy of the upper airway. The movement of soft palate was affected by the variations of elastic modulus under different pathophysiologic conditions.

Abstract:Objective To filter the noises in the experimental data of parallel plate flow chamber for observing more clearly the events occurring in the process of cell rolling adhesion and develop a new method to measure the elasticity of microvillus on cells based on the flow chamber experiment. Method The experiment of E-selectin regulated HL-60 cell rolling was performed by flow chamber system, and the data were denoised by wavelet analysis so that the high frequency thermal response signals were extracted from the data. Based on the equipartition theorem and equilibrium equations of tethered cell, the relationship between the cell microvillus spring constant and thermal fluctuations was constructed. Results Filtering noises from cell rolling time course by wavelet analysis, the events such as free rolling, slowing down, stopping and speeding up of rolling cell could be observed more easily; almost 80% of fluctuating energy of a rolling cell was involved in its high frequency fluctuation which was regarded as the thermal response of the cell to the Brown movement of water molecules, and the spring constant of microvillus on HL-60 cell was measured to be (13.7±7.4) μN/m at wall shear stress from 0.01～0.06 Pa. Conclusions The wavelet analysis can filter the thermal noises in cell rolling data of flow chamber experiment, and since the rigidity information of cell microvillus is involved in and can be extracted from the high frequency thermal fluctuation of the rolling cell, the parallel plate flow chamber experimental technique can be extended to measure the elasticity of microvillus on cells.

Abstract:Objective To judge the effect of hemodynamic characteristics on flow vessel of double bifurcation collateral by numerical calculation. Method A kind of double bifurcation collateral flow vessel’s hemodynamic characteristics such as blood flowing velocity vector, the shear stress and pressure at the vessel wall were calculated, studied and compared by the boundary element method. The lesions caused and developed by hemodynamic reasons were logically explained. Whether the hemodynamic characteristics of the branch would be affected by the lesion in the primary branch vessel was judged based on calculation results of the shear stress and the pressure at the branch vessel wall before and after the lesions. Results In the primary branch vessel, the blood velocity and shear stress increased obviously if the lesion appeared to narrow the vessel. Although the blood velocity and the shear stress in the branch vessel were not affected by the lesion, but its blood pressure became high. Conclusions The blood hydrokinetic characteristics play an important role in the cause and development of cardiovascular diseases. The atherosclerosis could be caused in the branch vessel of double bifurcation arterialvessel as the lesion becomes more serious in its primary branch vessel.

Abstract:Objective To explore the influence of integrin redistribution on hepatoma cell alignment and migration and the influence of cytoskeleton reassembly on integrin redistribution by the method of mechanical loadingunloading and fibronection(FN) coating. Method By using immuneofluescence staining, cofocal laser scanning microscopy and quantitative morphological analysis, integrin distribution change and crtoskeleton assembly adjustment were observed and the deformation of cell movement was tested and analyzed quantitatively. Results (1) cells with different forms have different integrin expressions and distribution features. The β1 integrin expression for spreading cells was higher than that for round (nonspreading) cells. For spreading cells, the strongest staining was found towards the attachment surface. While for round (nonspreading) cells, the integrin staining on the free surface towards medium was stronger than that towards the attachment surface. (2) After 5 hours of mechanical stretch, the β1 integrin expression for both spreading and round cells increased, and distribution peaks towards the attachment surface broadened. At 1 hour after unloading, the β1 integrin expression decreased and the distribution of integrin staining showed the tendency of dispersion, especially for round cells. (3) After coating the substrates with FN, the β1 integrin expression increased. The integrin staining for either spreading or round cells was more towards the attachment surface to reduce the migration of hepatoma cells. 4) After 5 hours of mechanical stretch, 60% of cells showed their orientation of major axes distributed between 70°～110° towards the stretching direction, and the cytoskeleton aligned vertically to the stretching direction. Cytoskeletons were found significantly depolymerized at 1 hour of unloading. Conclusions The change of integrin distribution is affected by cytoskeleton aligned and the number of ligand. The distribution feature of the whole integrin expression on the surface of individual round cells is related to their stronger invasion and metastasis capability.

Abstract:Objective To study the effects of cement base with different thickness on the stress distributions of restored tooth by finite element method. Method A threedimensional finite element model of a restored first mandibular molar with class 1 cavity was developed based on Micro CT. The thicknesses of cement base with lightcured glass ionomer (Vitrebond) and selfcured calcium hydroxide (Dycal) were chosen as 0.5 mm, 1.0 mm, 1.5 mm and 2.0 mm, respectively. Occlusal load of 250N was applied to compare the peak maximum and minimum principal stresses of the tooth, restoration and cement base in each model. Results With Dycal of 2mm, the peak maximum principal stress of the tooth was higher than its tensile strengths, and the peak maximum/minimum principal stress of the cement base was both higher than its tensile and compressive strength. Moreover, the peak maximum principal stress of the restoration was about 90% closer to its tensile strength with Dycal of 1.5 mm and 2 mm. With Vitrebond, it also showed that the peak maximum principal stress of the tooth, restoration and cement base appeared in the models with cement base of 1.5 mm and 2.0 mm. Conclusions To prevent the failure in restored tooth, it is advised to use thinner cement base, and the thickness of cement base should be considered from 0.5 mm to 1.0 mm in clinic.

Abstract:Objective To optimize the design of ballsocket of artificial cervical joint complexity. Method A threedimension model of the artificial cervical joint complexity was constructed by the finite element method. The height range of the ballsocket handle in the model was set. A simulation was manipulated to optimize the height under the physical load. The stress and strain of the joint complexity with different sizes was analyzed and the systematic safety factor was also evaluated. Results The simulation showed that the maximum Von mises stress appeared at the joint of handle and bottom in the anteflexion position. As the height of the handle increased, the maximum strain increased, and the graph of minimum safety factor was Parabola curve. Conclusions Considering the systematic stability and mobility, when the height of handle is 6 mm, the design of ballsocket is considered to be optimal.

Abstract:Objective To investigate effects of cold water stimulation on kinematic and dynamic characteristics of index finger. Method In order to reduce the influence on its flexion and extension, the index finger movement was recorded by a highspeed camera. Then a selfdeveloped MATLAB program was developed to obtain the trajectory with the help of the black speckles on index finger joints. Finally, a dynamic calculating model with FDS and FDP was set up to describe the relationship between the trajectory and muscle forces changed along with the time. Results After the cold water stimulation, the average angular velocity of the second joint in the index finger decreased in the process of fisting and stretching. Before and after the cold water stimulation, the force of FDP muscle changed little while the force of FDS muscle approximately doubled at the end of the fisting. Conclusions An optical method for obtaining the trajectory of index finger was applied, and a dynamic calculating model was developed to calculate the muscle forces during the finger movement. Therefore, the characteristics of the index finger before and after the cold stimulation could be further discussed.