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Abstract:Biomechanics, one important sub-discipline of mechanics, is an interdisciplinary subject involved in mechanics, biology and medical science, and it is closely associated with life health and clinic medicine. In this paper, applications and grants of normal projects and youth science foundation projects of National Natural Science Foundation of China (NSFC) on biomechanics from year 2012 to 2016 are introduced. Research directions and research teams of biomechanics are mainly discussed, and some suggestions are given for the development of biomechanics in China.

Abstract:The effect and significance of rehabilitation technical aids are growing with the population aging. Recently, the State Council of China has released several documents about the industrial development of Chinese rehabilitation technical aids, and proposed new requirements on the innovation in this field. Biomechanics plays an important role in rehabilitation technical aids, including exercise rehabilitation training system, orthotic device, artificial limb, walking aid, etc. In this special issue, several biomechanical papers about rehabilitation and rehabilitation technical aids are included，to provide references for rehabilitation engineering and rehabilitation technical aids.

Abstract:Objective To study the method of lower limb movement pattern recognition using the electromyographic (EMG) signals of the residual thigh muscles, and explore the possibility of lower limb prosthesis control based on the EMG signals. Methods Fifteen transfemoral amputees were selected as subjects, and the subjects were required to complete 5 kinds of motion, including level walking, stair ascent, stair descent, standing up and sitting down. The surface EMG signals from 6 muscles of the thigh stump were collected from each subject, including rectus femoris, vastus lateralis, tensor fascia lata, biceps femoris, semitendinosus and gluteus maximus. Six kinds of time-domain and frequency domain features of the EMG signals were extracted, and 5 kinds of motion patterns were recognized by the support vector machine. Results Five kinds of motion patterns could be recognized online by EMG signals of the residual thigh muscles. By single experimental data from one subject, the recognition rate was 94%; for the same subject, by the data mixed from two experiments, the recognition rate was 85%; for different subjects, the recognition rate was 74%. By feature optimization, using only two EMG features of 3 muscles, the recognition rate could reach 92% by single experimental data from one subject. For 3 kinds of motion patterns (level walking, stair ascent, stair descent), the recognition rate respectively was 100% using single experimental data from one subject, 98.33% using the data mixed from two experiments for the same subject, and 93.33% using the data from different subjects. Conclusions Simply using the thigh stump EMG signals to recognize movement intention is proved to be feasible. For each patient, by several times of training before using the EMG signals, the recognition rate is expected to reach an ideal state. The present work will lay a foundation for lower limb prosthesis control based on the EMG signals.

Abstract:Objective To explore the mechanism of ankle sprain varus, a kind of human ankle brace with asymmetric physiological structure which can protect the ankle effectively is designed. Methods The anatomic factors of ankle varus were analyzed firstly, and a kind of ankle brace with asymmetric structure was designed based on asymmetric structure of ankle joint by anatomy. Using Kinect system and Geomagic Studio software, 3D scanning and digital modeling on ankle joint of a male adult were performed, and the ankle model was established by 3D printing technology. With EVA film, silica gel film and wrapped edge copper network as raw materials, two kinds of ankle brace with asymmetric structure were prepared by 3D draping and composite materials processing technology. The shaping properties, tensile properties, fatigue performance, outer fabric breathability and friction of the designed brace were tested. Results The outside of ankle brace with asymmetric structure had good shaping property, low tensile elastic recovery rate. Under the effect of repeated small load, EVA composite materials and silicone composite materials could keep good elastic recovery and effectively bear external varus forces. The results from air permeability and grinding test showed that polyester material was a kind of suitable fabrics for the outer lining material. Conclusions The mechanical properties of ankle brace with asymmetric structure can meet the requirement of ankle varus protection. The fabric of ankle brace can improve moisture permeability and frictional properties.

Abstract:Objective To study the effect from different structures and material hardness of orthopedic insoles on flatfoot correction. Methods The contours of flatfoot under weight-bearing and non-weight-bearing conditions were scanned by Infoot system. The 3 kinds of medial longitudinal arch height (typeⅠ, Ⅱ, Ⅲ) and 3 kinds of material hardness (30°, 35°, 42°) from orthopedic insoles were used to compare their effects on flatfoot by the embedded insole test system. Results TypeⅠorthopedic insoles could significantly restore the anatomical position by improving the height of navicular bone, and redistribute the concentrated plantar pressure and increase the loading area of medial longitudinal arch with material hardness of 35°. Conclusions The appropriate insole shows a favorable orthopedic effect to ameliorate the foot deformity of flatfoot patients. The research findings lay a theoretical basis on design of the personalized orthopedic insoles.

Abstract:Objective By comparing the accuracy of different multi-rigid-body models used for simulating walking process of elderly women, to explore the effect of walking speed on the load of knee joints based on the obtained optimal model. Methods In human motion simulation software ADAMS/LifeMOD, the individualized human body models with 19 (M1), 16 (M2) or 12 (M3) links and the corresponding grounds were established, respectively. Then, the dynamic simulation of gait based on 3 models was conducted in turn. Results By comparing the vertical ground reaction force (vGRF), the walking time, the lower extremity joint angles among 3 models, M2 was the most applicable model to reproduce the real performance of gait. When elderly woman fastened their walking speed, the peak values of vGRF, the knee joint torque and power peak were all increased significantly. Conclusions It is suggested that elderly women should do more training for their quadriceps to improve their walking behavior. The research findings also provide references for rehabilitation treatment of knee osteoarthritis patients in clinic.

Abstract:Objective To simulate leg length discrepancy by unilateral increase in lower limb of normal person, analyze gait features in the case of leg length discrepancy and its effect on walking gait, so as to provide theoretical proofs for chronical musculoskeletal diseases in lower limb amputees due to leg length discrepency. Methods Leg length discrepancy was simulated by subjects wearing shoes to increase the unilateral height of one leg. The time-space parameters, ground reaction forces and joint angles of the subjects during normal walking gait and leg length discrepancy gait were obtained via the 3D motion capture system and the reaction force platform to make comparative analysis. Results Significant differences were found between leg length discrepancy gait and normal gait in terms of step length, stride time and single supporting period. In the case of leg length discrepancy gait, the ground reaction force of both feet significantly increased at heel-strike phase compared with normal gait, and obvious changes were observed in angles of hip, knee and ankle joints. Conclusions Leg length discrepancy is an important cause leading to gait abnormalities, and maybe a cause of leg joint diseases for trans-tibial amputees wearing prosthesis.

Abstract:Objective To study the changes of plantar pressure during backward walking, so as to explore its effects on balance ability of human gait. Methods Plantar pressure measurement system (Pedar-X pressure insoles) was used to collect the plantar pressure data from 10 subjects during forward walking and backward walking, respectively. The experiment was conducted on the treadmill, and the forward walking was set as the control group. According to the test conditions and intuitive feeling of test participants, 4 speed values (2.0, 2.5, 3.0, 3.5 km/h) were selected to carry out the experiment under two walking modes, respectively. The changes in parameters such as plantar pressure center trajectory, plantar pressure and foot-ground contact time under different speed were analyzed. Results Under two walking modes at different walking speed, subjects showed different plantar pressure during walking. During backward walking, the plantar pressure center transferred from the front foot to the heel and from inside to outside. Compared with forward walking, the plantar pressure during backward walking decreased significantly while the foot-ground contact time increased. Conclusions The study on pressure distribution during backward walking contributes to comprehensively understanding the mechanism of dynamic balance and provides a new perspective for related study on walking stability.

Abstract:Objective To propose a method for analyzing the hip joint signals during human walking based on Hilbert-Huang transform (HHT) method and verify its feasibility. Methods First, the hip joint angles of one healthy subject were measured by using the hip joint measuring platform composed of acceleration sensors and gyroscopes. Second, all intrinsic mode functions (IMFs) at different scales, which could be further analyzed and combined, were obtained by applying the ensemble empirical mode decomposition (EEMD) to original signals. Finally, the Hilbert spectrum of original signals were plotted and analyzed. Results The signals representing different motion modes as well as gait characteristics indicated by rotating track of the hip joint were obtained. The Hilbert spectrum could show the intra-wave frequency modulation in the main motion mode and the characteristics of walking frequencies. Conclusions This method can be used in rehabilitation and treatment of patients with gait diseases. By using this method, the characteristic signals of the hip joints at different frequency scales can be effectively decomposed, and the post-processing signals can be filtered and centrally corrected, so as to adaptively analyze gait signals of the patients.

Abstract:Objective To design a constant-force extrusion unit to meet the functional requirements of the prosthesis socket. Methods Based on the operational principle that the constant-force derives from offsetting of the positive and negative stiffness, the leaf spring was simulated based on the finite element analysis software. According to the simulation result of the leaf spring, the coefficient of spring stiffness was calculated. The constant-force unit after processing and assembling was tested by compression experiment. Results The simulation result was consistent with experimental result and the constant force of extrusion unit obtained an error about 2% within 3.5-mm range. Conclusions The constant-force characteristic is confirmed by experiment, which lays the foundation of realizing the time-shared and load-bearing hand prosthesis socket.

Abstract:Objective Aiming at solving the problem of the middle-aged and old women suffering from stress urinary incontinence (SUI), which can seriously affect their physical and mental health, the numerical study on urodynamics in pelvic floor of the female urinary system is conducted. Methods According to the characteristics of interaction coupled between urine and pelvic organizations, the SUI urine dynamics model was established based on computational fluid dynamics. Thus, the stress, strain and displacement of the urine system, and the pressure or velocity distributions in the urine flow, were analyzed. Results The stress, strain and displacement of elastic structure in the urinary system fluctuated with time，which played the important role in the mechanical mechanism of SUI. Conclusions It is not only necessary but also available to apply the fluid-structure interaction model to study the urinary system of SUI, and the urodynamic simulations can provide the theoretical foundation and technological method for the prediction and assessment of SUI diseases in clinic.

Abstract:Objective To construct a three-dimensional finite element model of human skull with anatomic structure and to study biomechanical responses of the head under various loading conditions. Methods The finite element model of high-precision human head with anatomic structure was reconstructed with the constitutive skull made from elastic-plastic material to simulate the fracture. This model was used to simulate frontal impact intracranial pressure testing, dynamic skull fracture testing and head drop testing reported by the literature, and the simulation reproduced the experimental process of head subjected to impact loads, skull fractures, and biomechanical responses of head fall at different speed. Results Under frontal impact loading, the model showed hedge-side positive-negative intracranial pressure distributions, and the occipital deformation was more serious than that in prefrontal, parietal under similar loading. The faster falling speed would cause more serious injuries. Conclusions To establish the accurate anatomic finite element model of human head can preferably simulate biomechanical responses of the head under the loading of impact and fall. Through quantifying parameters such as contact force and intracranial pressure, injury risks can be assessed to provide scientific references for design of protective devices.

Abstract:Objective To study the effects of different pressure boundary conditions and breathing patterns on the airflow of upper airway and related physiological status of the obstructive sleep apnea hypopnea syndrome (OSAHS) patient at sleep stage with eupnea and apnea, respectively. Methods The CT scan data of an OSAHS patient during natural sleep in supine position were acquired and used to reconstruct a three-dimensional finite element model of upper airway. Meanwhile the pressure changes in laryngeal cavity of the OSAHS patient were clinically measured and then used as the boundary conditions, and four typical breathing patterns (nasal inhaling and nasal exhaling, nasal inhaling and oral exhaling, oral inhaling and nasal exhaling, oral inhaling and oral exhaling) were considered for computational fluid simulation. Results The airflow of the OSAHS patient during sleep was an unstable, whorled and bidirectional flow, which was significantly affected by pressure boundary conditions and breathing patterns. Compared with nasal breathing, the maximum velocity of airflow by mouth breathing was increased, resulting in an increase of pressure drop in oral cavity, with was about 30% in inspiration and 100% in expiration. Conclusions It is significant to use CT data of an OSAHS patient during natural sleep for model reconstruction and the clinically measured pressure in laryngeal cavity as boundary conditions for finite element simulations, and the results will contribute to understand the characteristics of flow field in upper airway of the OSAHS patient during real natural sleep.

Abstract:Objective To compare biomechanical performance of four-part proximal humeral fractures fixed by novel locking plate or by AO-PHILOS plate. Methods The finite element fixation models of both the novel locking plate and AO-PHILOS plate for four-part proximal humeral fractures were established, respectively. The maximum Von Mises stress and displacement under 4 different functional positions of shoulder abduction in the two fixation models were compared by finite element analysis. Results The maximum displacement in shoulder abduction of 0°,30°,60°,90° were 6.644, 7.079, 5.850, 3.005 mm, respectively, in novel locking plate fixation model, and 6.293, 6.826, 5.774, 3.023 mm, respectively, in AO-PHILOS plate fixation model. Since the maximum displacements in both fracture fixation models were similar, it indicated that there was no significant difference in the stability for fixing proximal humeral fracture. The maximum Von Mises stress in shoulder abduction of 0°,30°,60°,90°were 1 033.0, 904.1, 888.1, 1 062.0 MPa in novel locking plate fixation model, while in AO-PHILOS plate fixation model, it showed 743.1, 692.4,486.4,393.5 MPa, respectively. During the process of shoulder abduction, the total stress in both fracture fixation models gradually decreased, but the new locking plate decreased in a larger range, showing an obvious stress dispersion. Conclusions Both the novel locking plate and AO-PHILOS plate can be used as internal fixation treatment for complex four-part proximal humeral fractures with no significant difference in stress distribution, and both showing a stable fixation effect. For fixing proximal humeral fractures with osteoporosis combined with the great and less tuberosity, the novel locking plate has an advantage over AO-PHILOS plate due to its unique anatomical wings and better fixing effect.

Abstract:Bone, acting as the main load-bearing organ in human body, is of mechanical adaptability. It is prevalent but perilous that under fatigue loading, bone suffers from fatigue damage characterized as the initiation, propagation of micro-cracks, deterioration of bone mechanical properties or even stress fracture, which is commonly seen in long distance running of athletes, fitness training of military recruits and daily activities of the elderly. Bone fatigue damages exist in multi-levels of ultra-micro structure, microstructure and macrostructure. The anti-fatigue units in cortical bone (osteons) and cellular components (osteocytes) inside have been proved to play important roles in fatigue damage prevention, micro-cracks recognition and bone-targeted remodeling activation. Therefore, a general review and summing-up of relative research findings can help to provide a systematic understanding of fatigue behavior and corresponding repair process, and to give some useful references and insights for subsequent clinical researches aiming at prevention and treatment for bone fatigue damage.

Abstract:Tuinan manipulation is one of common non-surgical treatment methods for the cervical vertigo, with a good anti-vertigo effect. However, the key factor affecting efficacy of cervical vertigo is the manipulation force (including force size, time, frequency), which is lack of Objective quantification criteria. There is still not any unified statement about the mechanism of anti-vertigo effect. In this study, based on the summary of previous research work, the shortcomings of current research are analyzed, and a possible solution for manipulation quantification is suggested, and normalization, standardization as well as the mechanism of nerve centers are also investigated.