ABSTRACT
Objective By establishing finite element model of the proximal femur, the injury risk of proximal femur under the conditions of self-selected speed rise and rapid rise at initial stage of standing during sit-to-stand (STS) transition was analyzed.Methods CT images of proximal femur in the elderly were processed with three-dimensional (3D) reconstruction and reverse modeling, so as to complete the solid model. The finite element model was established through material assignment and meshing. Based on the finite element analysis software ANSYS, the boundary conditions were constrained, and 1.733 kN and 1.837 kN loads were applied to obtain stress distributions and strain of proximal femur at different rising speeds. Results The stress concentrated at medial edge of the greater trochanter and the femoral neck. The peak stress and micro-strain appeared on inner edge of the larger rotor. The peak stress was 30.16 MPa and peak micro-strain was 2 553.5 at rapid rising speed. The peak stress and peak micro-strain at self-selected rising speed were 28.69 MPa and 2 430.4, respectively, which were relatively lower. For stress concentration area of femoral neck, the stress ranges at rapid rising speed and self-selected rising speed were 13.42-23.46 MPa and 12.76-25.51 MPa, respectively.Conclusions Frequent STS transition may increase the risk of fatigue fractures for proximal femur in the elderly. Rapid STS transition has a higher injury risk for proximal femur than STS transition at self-selected speed.
ABSTRACT
Objective To evaluate the difference of foot-ankle function for subjects with different foot types from both dynamic and static aspects by means of sports biomechanics, so as to provide theoretical support and references for the study of foot-ankle movement. Methods According to the arch index, 65 subjects were divided into three groups: flat foot, low arch foot and normal foot. One-way ANOVA was used to analyze the difference of static and dynamic foot-ankle function indexes among the three groups. Results In terms of static foot-ankle function, the malleolar valgus flexibility (MVF) of normal foot and ankle was significantly higher than that of low arch foot and flat foot (P<0.05), while in terms of arch height flexibility (AHF), the effect of weight bearing on normal foot was smaller than that of flat foot (P<0.05), but there was no significant difference in transverse arch flexibility (TAF) among the three groups. In terms of dynamic foot-ankle function, the force offset amplitude and time of normal foot at buffer stage were higher than those of the other two groups (P<0.05), and at transition stage, the transition time of normal foot was significantly lower than that of low arch foot and flat foot (P<0.05). At pedal-extension stage, the pedal-extension time and speed of normal foot were significantly higher than those of flat foot (P<0.05). Conclusions The posture maintenance ability and longitudinal arch shape maintenance ability of low arch foot and flat foot are worse than those of normal foot with the load increasing, and the arch rigidity and plantar elasticity of low arch foot and flat foot are worse than those of normal foot, and normal foot shows better load-bearing cushioning ability, elastic-to-rigid transition ability and pedal extension efficiency during walking. A systematic and comprehensive evaluation system is of great significance to the prediction of foot-ankle injury risk and the evaluation of sports ability.
ABSTRACT
BACKGROUND: Changes in the center of body weight during standing reflects the structure, function and muscles of the lower limbs and even the whole body. The relationship between standing posture control and foot type, balance ability, and muscle activation is rarely reported. OBJECTIVE: To investigate the effects of natural, lean forward and lean backward standing on foot arch, body balance and muscle activation. METHODS: Fifteen subjects without foot lesions and diseases related to foot function were selected. Three-dimensional foot scanner was used to test and analyze the foot arch in three standing postures. BTS FREEMG 300 surface electromyography tester and balance tester were used to test and analyze the maximum root mean square of muscle and two balance ability indexes (envelope area and average velocity of center of gravity) in three standing postures. RESULTS AND CONCLUSION: (1) For height index of foot arch: there was significant difference between natural standing and forward standing (P ＜ 0.05). There was significant difference between natural standing and backward standing (P ＜ 0.05), but there was no significant difference between forward standing and backward standing (P＞ 0.05). (2) The degree of muscle activation was as follows: when standing naturally, the medial peroneal muscles＞ erector muscles＞ rectus abdominis＞ gluteus medius＞ biceps femoris＞ external oblique femoris＞ anterior tibial muscle＞ rectus femoris muscle＞ gluteus maximus muscle. During forward standing: the medial of the peroneal muscle＞ medius gluteus＞ vertical ridge＞ long head of biceps femoris＞ anterior tibial muscle＞ rectus abdominis muscle＞ gluteus maximus. During backward standing: the obliquus externus femur＞ rectus femoris＞ long head of biceps femoris＞ erector spinae＞ musculus rectus abdominis＞ the medial of the peroneal muscle＞ gluteus medius＞ gluteus maximus. (3) Balance: there was no significant difference between natural standing and forward standing (P＞ 0.05); there was significant difference between natural standing and backward standing (P ＜ 0.05), but there was no significant difference between forward standing and backward standing (P＞ 0.05). (4) In summary, it is easy to maintain body stability at low muscle activation intensity when the human body is standing naturally. During the body backward standing, the muscle activation intensity is highest due to instability. When the center of gravity moves forward and backward, the contralateral muscle is mainly activated. The arch of the foot rises when it leans forward and backward. The slight anterior and posterior movements of the center of gravity in the standing posture can lead to changes in muscle activation degree and balance control.