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Activation of the muscles and reaction forces of the joints rely on the body posture. The aim of the present paper is to investigate the relationship between the kinematics of static postures and muscle activation and joint forces by means of predictive regression models. To cover a reasonable number of postures and muscle recruitment patterns in forward inclinations, 4096 postures were analyzed. The response surface method was used to estimate the results of optimization-based inverse dynamics analysis. Two sorts of input variables (three angular positions of the lower limb joints and optimized muscular activation levels) and two model responses (muscle activation and joint force) were designed. The predictive models showed adequate goodness-of-fit in average ($R^2>0.84$). The predictive models that applied on the feasible balanced postures revealed considerable reliance of the biomechanical efforts on the postural angles. The ankle force was majorly supported by activation of the calf muscles as $F_{\mathrm{\text{ank}}}=0.4+8.7{\alpha }_{\mathrm{\text{TS}}}-2.1{\alpha }_{\mathrm{\text{TS}}}^2+0.2{\alpha }_{\mathrm{\text{TA}}}^2$ (kN). The knee and the hip joint were dominantly influenced by the hamstring activation. Quantitative assessment of biomechanical parameters in the balanced standing postures may help researchers in finding standing information by knowing one type of experimental data such as the kinematic angles or the muscle electromyography.

Footwear is an extremely important clothing item worn by all individuals. Currently, there is insufficient research regarding the influence of dress shoes on standing stability and energy consumption while walking. Therefore, the aim of this study was to evaluate the influence of dress shoes on the performance of normal subjects based on stability and energy consumption analysis. Fifteen normal subjects were recruited in this research study to stand and walk with and without shoes. The stability of the subjects in quiet standing was measured by the use of a force plate based on center of pressure (COP) sway. The energy consumption was evaluated by a heart rate monitoring system (Polar Electro) based on the physiological cost index (PCI). The mean values of PCI while walking with and without shoes were 0.29 ± 0.117 and 0.265 ± 0.112 beats/m, respectively (p-value > 0.05). The amplitudes of COP sways in the mediolateral and anteroposterior directions were 10.4 ± 3.5 and 25 ± 6.92 mm while standing with shoes and 9.3 ± 2.84 and 22.5 ± 5.25 mm in barefoot standing, respectively (p-value > 0.05). It can be concluded that wearing dress shoes does not influence the performance of subjects while standing or walking.

Knee joint is the hub of human lower limb movement and it is also an important weight-bearing joint, which has the characteristics of load-bearing and heavy physical activities. So the knee joint becomes the predilection site of clinical disease. Once people have the cartilage lesions, their daily life will be affected seriously. The simulation of the knee joint lesions could provide help for clinical knee-joint treatment. Based on the complete model of knee joint, this paper use the finite element method to analyze the biomechanical characteristics of the defective knee joint. The results of simulation show that the stress of cartilages when standing on single leg is approximately doubled than that of standing on two legs. When standing on single leg, the 8-mm diameter osteochondral defect in femur cartilage can generate maximal changes in von-mises stress (by 36.74%), while the von-mises stress on tibia cartilage with 8-mm defect increase by 87%. The stress distribution of cartilages is almost the same, there is no obvious stress concentration when in defect. Increasing the defective diameter, femoral cartilage, meniscus and tibial all present an increasing trend towards stress. When increasing the applied load, the stress of the femoral cartilage, the meniscus and the tibial cartilage all increased.

Diabetic ulcers can lead to infection and amputation. Using insole can help to reduce and prevent foot ulceration and amputation in a diabetic patient. The aim of this study was to analyze the effect of wearing an insole with different density on standing and walking plantar pressure distribution. Methods: A group of 10 diabetic patients participated in this one-grouped before-after trial. Plantar pressure distribution was measured during walking and standing. Repeated Measure was used to test differences. Results: Repeated measure test showed that use of insole decreased foot pressure while walking significantly ($P=0.023$). Pairwise comparison showed that wearing shoe insole with shore 30 decreased pressure compared to wearing shoe insole with shore 50 ($P=0.004$) and walking without insole respectively ($P=0.06$). Conclusion: The insole has more effect on plantar pressure during walking than standing, it also concluded that insole with shore 30 decreased pressure during walking more than that of the insole with shore 50. It could be said that patients who suffer from pain and discomfort on hind and forefoot may benefit insole with shore 30 to relieve from plantar pressure on the hindfoot and forefoot regions during standing and walking.

Proprioception while standing is important for the balance control, but the proprioception has not been investigated in the unconstrained standing conditions. The purpose of this study was to investigate the effects of age and gender on the thresholds of perception and muscle response in response to the support surface rotation. The experiment was designed so that the thresholds depend mainly on the proprioception, i.e., quasistatic condition (0.2^∘/s rotation of the platform) with eyes closed. Fifty-two healthy subjects (half young and half elderly) participated in this study. A platform was developed which can be rotated in four directions. Perception threshold angle was registered from subjects’ pressing a button. Muscle response threshold angle was determined as the earlier onset of EMG in lower limb muscles. Two standing conditions (feet together and natural stance) were tested. Repeated-measures ANOVA showed that both thresholds increased with age. Post hoc tests revealed (1) that the perception threshold was greater for women than men in the elderly and (2) both thresholds of the elderly were greater for the feet-together stance than natural stance. Inferior perception sensitivity of platform rotation in elderly women may be associated with inferior performance in cortical postural control and greater fall ratio compared to elderly men, which suggests the need of proprioception trainings.

The consensus of the normal magnitude of lumbosacral curve has not been achieved. The Cobb's angle cannot depict the whole contour of this curve. For practical applications, a clearer image of these curves and their aging changes should be further investigated. This study aimed to provide a more consolidate concept of normal lumbosacral curves for clinician through a computerized reconstruction method.

Standing lateral radiographs of lumbosacral spine in 82 normal adults were used for reconstructing the sagittal lumbosacral curves. The geometric characteristics of these curves according to the gender and age groups were studied. Using standing lateral radiographs, reconstruction of the lumbosacral curves was performed through digitization, programming and computation. These curves and related parameters were normalized and averaged for analyzing the differences of gender and age.

The most anteriorward and horizontal vertebrae usually occurred on the L4 and L3 in any gender and age groups. The sacral inclination angle did not change obviously with the increasing ages. A tendency of L1 shifting backward was noted in the age groups of 40 to 60 and above 60 years old. The sagittal lumbosacral curves can be easily reconstructed by digitizing lateral radiographs, The aging changes of lumbosacral curves could be qualitatively described as the flattening of lower lumbar curve and the rearward inclination of upper lumbar curve. The changes occurred obviously above 40 years old. Although individual variations existed, the aging changes and the geometric characteristics such as the most anteriorward or horizontal vertebrae could be used as an important guideline during therapy or surgical correction.