The effect of sex and localised fatigue on triceps surae musculoarticular stiffness

Purpose: The main purpose of this study was to investigate the influence of fatigue on musculoarticular stiffness (MAS) of the ankle joint across sexes. Methods: Twenty-seven males and 26 females participated in the study. After baseline assessment of MAS and related variables, localised fatigue was induced in triceps surae using the standing heel-rise test during which the subjects were instructed to lift and drop the heel at a frequency of 0.5?Hz. When subjects were unable to continue due to exhaustion the test was terminated and another MAS test was performed soon after. Results: Significant higher triceps surae MAS was found in men compared to women (p?p??1 and from 14.5 to 13.9?KN?m^?1 in men and women, respectively. Percentage changes revealed, however, that in relative terms the changes in all the variables evaluated were similar (p?>?.01) between sexes, with MAS less than 5%. Conclusion: Despite the sex-related differences at baseline, fatigue seems to affect biomechanical properties of the ankle joint similarly in men and women.     

Effects of viscoelastic properties of tendon structures on stretch – shortening cycle exercise in vivo

The aim of the present study was to examine the effects of viscoelastic properties of human tendon structures during stretch?–?shortening cycle exercise. The elongation of tendon and aponeurosis of the medial gastrocnemius muscle of 26 participants was measured by ultrasonography while they performed ramp isometric plantar flexion up to the voluntary maximum, followed by a ramp relaxation. The relationship between estimated muscle force and tendon elongation during the ascending phase was fitted to a linear regression, the slope of which was defined as stiffness. The percentage of the area within the muscle force?–?tendon elongation loop relative to the area beneath the curve during the ascending phase was defined as hysteresis. In addition, maximal voluntary concentric contractions at 2.09 and 3.14 rad?·?s^?1 with and without prior eccentric contractions were performed. The difference in the concentric torque at equivalent joint angles with and without prior eccentric contractions (i.e. pre-stretch augmentation) was negatively correlated with stiffness (P <?0.05) and hysteresis (P <?0.05). Furthermore, there was a higher correlation between the pre-stretch augmentation and the viscoelastic properties index – that is, the sum of normalized score values of stiffness and hysteresis (P <?0.01) – than with either stiffness or hysteresis alone. The results of this study suggest that performance during stretch?–?shortening cycle exercise is significantly affected by the viscoelastic properties of the tendon structures.     

Repeatability of scores on a novel test of endurance running performance

Abstract

The aim of the present study was to determine the repeatability of a running endurance test using an automated treadmill system that requires no manual input to control running speed. On three separate occasions, 7 days apart, 10 experienced male endurance-trained runners (mean age 32 years, s = 10; [Vdot]O_2peak 61 ml · kg^?1 · min^?1, s = 7) completed a treadmill time trial, in which they were instructed to run as far as possible in 60 min. The treadmill was instrumented with an ultrasonic feedback-controlled radar modulator that spontaneously regulated treadmill belt speed corresponding to the changing running speed of each runner. Estimated running intensity was 70%[Vdot]O_2peak (s = 11) and the distance covered 13.5 km (s = 2), with no difference in mean performances between trials. The coefficient of variation, estimated using analysis of variance, with participant and trial as main effects, was 1.4%. In summary, the use of an automated treadmill system improved the repeatability of a 60-min treadmill time trial compared with time trials in which speed is controlled manually. The present protocol is a reliable method of assessing endurance performance in endurance-trained runners.     

Tensiomyography parameters and jumping and sprinting performance in Brazilian elite soccer players

Tensiomyography has been suggested as an indirect marker of muscle stiffness, which is associated with strength/power performance. Therefore, it is reasonable to suggest that tensiomyography parameters could be associated with power-related motor tasks. The purpose of this study was to investigate the association between tensiomyography parameters (from rectus and biceps femoris) and jumping and sprinting abilities in elite soccer players. In addition, we used tensiomyography parameters to compare the lateral symmetry between dominant and non-dominant legs. Twenty elite soccer players (age: 23.3 ± 4.8 years; height: 183.5 ± 6.6 cm; weight: 77.8 ± 7.5 kg) volunteered to participate in the study. Significant moderate negative correlations between biceps femoris displacement and contact time (r = –0.5, p = 0.03), rectus femoris displacement and contact time (r = –0.51, p = 0.02), and a significant moderate correlation between biceps femoris displacement and reactive strength index (r = 0.5, p = 0.03) were found. There were no correlations between tensiomyography parameters and power-related motor tasks. In addition, no differences in tensiomyography parameters between dominant and non-dominant legs were found. Our data suggest that tensiomyography parameters are not associated with power-related motor tasks performance in elite soccer players.     

Sex differences in lower extremity stiffness and kinematics alterations during double-legged drop landings with changes in drop height

The aim of this study was to determine whether sex differences and effect of drop heights exist in stiffness alteration of the lower extremity during a landing task with a drop height increment. Twelve male participants and twelve female participants performed drop landings at two drop heights (DL40 and DL60; in cm). The leg and joint stiffnesses were calculated using a spring–mass model, and the joint angular kinematics were calculated using motion capture. Ground reaction forces (GRFs) were recorded using a force plate. The peak vertical GRF of the females was significantly increased when the drop height was raised from 40 to 60 cm. Significantly less leg and knee stiffness was observed for DL60 in females. The ankle, knee, and hip angular displacement during landing were significantly increased with drop height increment in both sexes. The knee and hip flexion angular velocities at contact were significantly greater for the 60 cm drop height relative to the 40 cm drop height in males. These sex disparities regarding the lower extremity stiffness and kinematics alterations during drop landing with a drop height increment would predispose females to lower extremity injury.     

基于Morph功能的改款车模态刚度分析

基于ANSA中的Morph功能,在某改款车型的概念设计阶段,对标杆车的有限元模型进行快速的结构调整,通过仿真手段,对改款车的模态刚度进行分析;然后,对原型车白车身结构进行模态实验,获取其模态频率及对应振型,进而与改款车进行对比,提前对改款车结构的合理性做出评价。     

The role of shoe design on the prediction of free torque at the shoe–surface interface using pressure insole technology

The goal of the current study was to expand on previous work to validate the use of pressure insole technology in conjunction with linear regression models to predict the free torque at the shoe–surface interface that is generated while wearing different athletic shoes. Three distinctly different shoe designs were utilised. The stiffness of each shoe was determined with a material’s testing machine. Six participants wore each shoe that was fitted with an insole pressure measurement device and performed rotation trials on an embedded force plate. A pressure sensor mask was constructed from those sensors having a high linear correlation with free torque values. Linear regression models were developed to predict free torques from these pressure sensor data. The models were able to accurately predict their own free torque well (RMS error 3.72 ± 0.74 Nm), but not that of the other shoes (RMS error 10.43 ± 3.79 Nm). Models performing self-prediction were also able to measure differences in shoe stiffness. The results of the current study showed the need for participant–shoe specific linear regression models to insure high prediction accuracy of free torques from pressure sensor data during isolated internal and external rotations of the body with respect to a planted foot.     

滑动运动副接触刚度控制研究

设计并制造了基于NiTi形状记忆合金驱动的间隙可调整（或接触刚度可控）运动副．实验结果表明：这种运动幅间隙可控性好，其接触动刚度变化范围大（最大动刚度是原始动刚度的11倍），具有理想的自适应抗振特性．     

获取＂动力硬化＂的一般程式

阐述一种获取＂动力硬化＂的一般程式。基于凯恩方程导出做大范围运动任意柔体的运动方程。用几何非线性应变一位移关系和角速度的非线性表达式正确实现线性化，一般情况下可自然获取＂动力硬化＂项。休斯敦方法中偏速度和偏角速度阵列的概念和推导拓宽到柔体，并做为分析的基础。通过用于梁和板模型数值计算的结果证实了所述程式是普遍有效的。     

基于Plaxis 2D的基坑支护中内支撑对支护桩的影响分析

借助Plaxis 2D的有限元分析程序,计算不同支撑刚度下的支护桩变形及内力,揭示了支护桩支撑轴力与支撑刚度之间的变化规律,分析了两者比值对支护桩的影响曲线,并得出近似比值,用以指导工程实际。