The role of the entry-and-stretch phase at the different paces of race in front crawl swimming

The aim of this study was to determine the role played by the entry-and-stretch phase in the coordination of swimming, at the different paces of race. Three national level swimmers (two men and one woman) were recorded, in lateral and bottom views, in three swimming paces: sprint (50 m and 100 m), middle-distance (200 m and 400 m) and long-distance (800 m and 1500 m). Anatomical landmark positions were obtained by manual digitalisation of the videos. Computational fluid dynamics and experimental studies (with a strain gauge balance and particle image velocimetry method) were used to measure and to calculate the external forces applied to the hand and to the forearm and to visualise the flow around the profile. Entry-and-stretch is the phase which varies the most according to the swimming pace. This phase can be decomposed into two sub-phases: one, the extension forward coordinated with the insweep of the opposite arm, and another one, the rotation downward coordinated with the upsweep. Results show that, at the three paces, this phase is not propulsive and could contribute essentially to maintain the horizontal balance of the body.     

运动员腘绳肌损伤危险因素的Meta分析

目的:腘绳肌拉伤是体育运动中最常见的损伤之一,且康复难度大复发率高。通过对腘绳肌损伤的危险因素进行综合的Meta分析,有助于深入了解影响腘绳肌拉伤的危险因素,为有效地预防和康复腘绳肌拉伤提供科学依据。方法:收集1992-2014年间国内外公开发表的关于腘绳肌损伤危险因素的研究文献,根据入选标准与排除标准纳入文献并对其质量进行评价,根据入选文献的异质性检验结果,对各危险因素进行随机效应模型或固定效应模型的Meta分析。结果:本次Meta分析结果显示,腘绳肌损伤的主要危险因素为年龄(SMD=0.68,95%CI 0.12~1.25;RR=4.04,95%CI 2.08~7.84),股四头肌最大力矩(SMD=0.58,95%CI 0.19~0.96),腘绳肌损伤史(RR=2.56,95%CI 1.93~3.40;OR=2.98,95%CI 1.30~6.81)。结论:与腘绳肌损伤关联度最大危险因素为年龄的增大,有腘绳肌损伤史和股四头肌最大力矩过大。运动员的身高,体重,腘绳肌最大力矩,腘绳肌肌力与股四头肌肌力比,腘绳肌柔韧性与腘绳肌损伤的发生关联不明显,是否为腘绳肌损伤的主要危险因素尚不确定,还需要进一步的研究证实。     

高分子膜性质及其印刷特性（英文）

<正>It is recently obvious a wide use of printing on polymer films.This is bound up most of all with a rapid development of the industry for production of goods in colorful packaging made of polymer materials.The interest in printing on polymer films increases significantly in view of the application of new technological processes of electronic microchips manufacturing by printing methods[1-4].At     

The Properties and Printing Functions of Polymer Films

It is recently obvious a wide use of printing on polymer films. This is bound up most of all with a rapid development of the industry for production of goods in colorful packaging made of polymer mate-rials.     

Is there really an eccentric action of the hamstrings during the swing phase of high-speed running? Part II: Implications for exercise

We have previously argued that there may actually be no significant eccentric, but rather predominantly an isometric action of the hamstring muscle fibres during the swing phase of high-speed running when the attachment points of the hamstrings are moving apart. Based on this we suggested that isometric rather than eccentric exercises are a more specific way of conditioning the hamstrings for high-speed running. In this review we argue that some of the presumed beneficial adaptations following eccentric training may actually not be related to the eccentric muscle fibre action, but to other factors such as exercise intensity. Furthermore, we discuss several disadvantages associated with commonly used eccentric hamstring exercises. Subsequently, we argue that high-intensity isometric exercises in which the series elastic element stretches and recoils may be equally or even more effective at conditioning the hamstrings for high-speed running, since they also avoid some of the negative side effects associated with eccentric training. We provide several criteria that exercises should fulfil to effectively condition the hamstrings for high-speed running. Adherence to these criteria will guarantee specificity with regards to hamstrings functioning during running. Practical examples of isometric exercises that likely meet several criteria are provided.     

Comparison of estimates of Achilles tendon loading from inverse dynamics and inverse dynamics-based static optimisation during running

Tendon stress may be one of the important risk factors for running-related tendon injury. Several methods have been used to estimate Achilles tendon (AT) loading during a human performance such as inverse dynamics (ID) and inverse dynamics-based static optimisation (IDSO). Our purpose was to examine differences between ID and IDSO estimates of AT loading during running. Kinematic data were captured simultaneously with kinetic data. Imaging of the AT cross-sectional area was performed with ultrasound for 17 healthy runners (height: 170.2 ± 6.2 cm, mass: 63.9 ± 11.0 kg, age: 21.8 ± 1.4 years). AT stress, strain, and force were estimated from both ID and IDSO approaches. The two methods resulted in minimal differences (3.6–4.7%) in estimated peak AT stress, strain, and force (P = 0.051–0.054); however, IDSO estimates were greater (32.7–36.8%) during early-stance phase of running (P = 0.000–0.008). This difference in AT load during early-stance may be due to the inability of the ID to account muscle coactivation. The similarity between the peak AT loading for ID and IDSO methods revealed that the advantage of IDSO used to estimate muscle forces had little effect on the ankle plantar flexor peak forces during running. Therefore, the use of IDSO with a higher computational cost compared with ID may not be necessary for estimating AT stress during running.     

Continuous and intermittent heat acclimation and decay in team sport athletes

The aim of this study was to compare the impact of continuous (CON) and intermittent (INT) heat acclimation protocols on repeat-sprint performance, and to also assess the degree of performance decay following acclimation. Using a pair-matched, between subjects design, 16 trained male team sport athletes were allocated to either INT (8 sessions over 15 days) or CON acclimation (8 sessions over 8 days) groups. Participants performed a heat tolerance test (HTT) involving 60-min of repeat-sprint cycling with a 10-min half time break (in 35.3?±?0.7°C, 60.1?±?4.0%; RH) two days pre- (pre-HTT) and post-acclimation (post-HTT1). Decay was investigated with two further HTT's completed over the next two weeks (post-HTT2 and post-HTT3). Results showed the post-HTT1 performance variables [mean power (pre-HTT; INT?=?1002.07?±?173.74, CON?=?1057.10?±?180.07 / post-HTT1; INT?=?1097.11?±?186.85, CON?=?1163.77?±?184.65 W), mean power (W.kg^?1), total work (kJ) and work (J.kg^?1)] were greater than pre-HHT (p?p?相似文献   

Gender influence on the adaptation of atrial performance to training

Background: High-intensity training has been associated with atrial remodelling and arrhythmias in men. Our purpose was to analyse atrial performance in female endurance athletes, compared to male athletes and controls. Methods: This was a cross-sectional study. We included four groups: female athletes, females controls, male athletes and male controls. Left (LA) and right atrial (RA) volumes and function were assessed using 2D and speckle-tracking echocardiography to determine peak atrial strain-rate at atrial (SRa) and ventricular contraction (SRs), as surrogates of atrial contractile and reservoir function, respectively. ANOVA and Bonferroni’s statistical tests were used to compare variables among groups. Results: We included 82 subjects, 39 women (19 endurance athletes, 20 controls) and 43 men (22 endurance athletes, 21 controls). Mean age was similar between groups (36.6?±?5.6 years). Athletes had larger bi-atrial volumes, compared to controls (women, LA 27.1 vs. 15.8?ml/m², p?<?0.001; RA 22.31 vs. 14.2?ml/m², p?=?0.009; men, LA: 25.0 vs. 18.5?ml/m², p?=?0.003; RA 30.8 vs. 21.9?ml/m², p?<?0.001) and lower strain-rate (women, LASRa ?1.60 vs. ?2.18?s^?1, p?<?0.001; RASRa ?1.89 vs. ?2.38?s^?1, p?=?0.009; men, LASRa ?1.21 vs. ?1.44?s^?1, p?=?1; RASRa ?1.44 vs. ?1.60?s^?1, p?=?1). However, RA indexed size was lower and bi-atrial deformation greater in female athletes, compared to male athletes. Conclusions: The atria of both male and female athletes shows specific remodelling, compared to sedentary subjects, with larger size and less deformation at rest, particularly for the RA. Despite a similar extent of remodelling, the pattern in women had greater bi-atrial myocardial deformation and smaller RA size.     

木糖渣发酵料栽培糙皮侧耳优良菌株的选育

新选育的PL -AD2 8属于早熟型品种。该菌株菌丝在 5 - 37℃温度范围内均能生长 ,菌丝生长适温为 1 8- 30℃ ,最适温度为 2 5 - 2 8℃。在木糖渣发酵料培养基上 ,菌丝粗壮、洁白、整齐 ,爬壁能力强 ,满袋天数为 2 2d± 1d。经栽培证明 ,PL -AD2 8是高产优质菌株。     

应变势能的意义与表达方式

从势能的基本概念出发,对应变势能的表达形式及其所代表的物理意义提出了看法,并提出了与传统作法不同的计算模式.