Impact loading in female runners with single and multiple bone stress injuries during fresh and exerted conditions

Background:Bone stress injuries(BSIs)are common in female runners,and recurrent BSI rates are high.Previous work suggests an association between higher impact loading during running and tibial BSI.However,it is unknown whether impact loading and fatigue-related loading changes discriminate women with a history of multiple BSIs.This study compared impact variables at the beginning of a treadmill run to exertion andthe changes in those variables with exertion among female runners with no history of BSI as well as among those with a history of single or multiple BSIs.Methods:We enrolled 45 female runners(aged 18-40 years)for this cross-sectional study:having no history of diagnosed lower extremity BSI(N-BSI,n=14);a history of 1 lower extremity BSI(1-BSI,n=16);and diagnosed by imaging,or a history of multiple(>3)lower extremity BSIs(M-BSI,n=15).Participants completed a 5-km race speed run on an instrumented treadmill while wearing an Inertial Measurement Unit.The vertical average loading rate(VALR),vertical instantaneous loading rate(VILR),vertical stiffness during impact via instrumented treadmill,and tibial shock determined as the peak po sitive tibial acceleration via Inertial Measurement Unit were measured at the beginning and the end of the run.Results:There were no differences between groups in VALR,VILR,vertical stiffness,or tibial shock in a fresh or exerted condition.However,compared to N-BSI,women with M-BSI had greater increase with exertion in VALR(-1.8%vs.6.1%,p=0.01)and VILR(1.5%vs.4.8%,p=0.03).Similarly,compared to N-BSI,vertical stiffness increased more with exertion among women with M-BSI(-0.9%vs.7.3%,p=0.006)and 1-BSI(-0.9%vs.1.8%,p=0.05).Finally,compared to N-BSI,the increase in tibial shock from fresh to exerted condition was greater among women with M-BSI(0.9%vs.5.5%,p=0.03)and 1-BSI(0.9%vs.11.2%,p=0.02).Conclusion:Women with 1-BSI or M-BSIs experience greater exertion-related increases in impact loading than women with N-BSI.These observations imply that exertion-related changes in gait biomechanics may contribute to risk of BSI.

How does high-intensity intermittent training affect recreational endurance runners? Acute and chronic adaptations: A systematic review

Objective: This systematic review aimed to critically analyze the literature to determine how high-intensity intermittent training(HIIT) affects recreational endurance runners in the short-and long-term.Methods: Electronic databases were searched for literature dating from January 2000 to October 2015. The search was conducted using the key words "high-intensity intermittent training" or "high-intensity interval exercise" or "interval running" or "sprint interval training" and "endurance runners" or "long distance runners". A systematic approach was used to evaluate the 783 articles identified for initial review. Studies were included if they investigated HIIT in recreational endurance runners. The methodological quality of the studies was evaluated using the Physiotherapy Evidence Database(PEDro) scale(for intervention studies) and the modified Downs and Black Quality Index(for cross-sectional studies).Results: Twenty-three studies met the inclusionary criteria for review. The results are presented in 2 parts: cross-sectional(n = 15) and intervention studies(n = 8). In the 15 cross-sectional studies selected, endurance runners performed at least 1 HIIT protocol, and the acute impact on physiological, neuromuscular, metabolic and/or biomechanical variables was assessed. Intervention studies lasted a minimum of 4 weeks, with 10 weeks being the longest intervention period, and included 2 to 4 HIIT sessions per week. Most of these studies combined HIIT sessions with continuous run(CR) sessions; 2 studies' subjects performed HIIT exclusively.Conclusion: HIIT-based running plans(2 to 3 HIIT sessions per week, combining HIIT and CR runs) show athletic performance improvements in endurance runners by improving maximal oxygen uptake and running economy along with muscular and metabolic adaptations. To maximize the adaptations to training, both HIIT and CR must be part of training programs for endurance runners.

Heart Rate Variability, Standard of Measurement, Physiological Interpretation and Clinical Use in Mountain Marathon Runners during Sleep and after Acclimatization at 3480 m

Fluctuations in autonomic cardiovascular regulation during exposure to high altitude may increase the risk of heart attack during waking and sleep. This study compared heart rate variability (HVR) and its components during sleep at low altitude and after 30 - 41 hours of acclimatization at high altitude (3480 m) in five mountain marathon runners controlled for diet, drugs, light-dark cycle and jet lag. In comparison to sea level, RR-intervals during sleep at high altitude decreased significantly (P 0.001). The significant increase in sympathetic autonomic cardiovascular modulation at high altitude protects against excessive oxygen deprivation during sleep. Increases in R-R intervals can require longer periods of acclimatization at3480 m to mitigate the effects of altitude/hypoxia on sympathetic tone, thus reducing cardiovascular distress at rest during waking and sleep and probably before during and after athletic performance at altitude.

Effects of age on marathon finishing time among male amateur runners in Stockholm Marathon 1979–2014

Purpose: The purpose of the present study was to investigate the age-related changes in the endurance performance among male amateur marathon runners.Methods: Subjects were taken from the 36 Stockholm Marathons held from 1979 through 2014, and age and finishing time were analyzed for a total of 312,342 male runners.Results: The relation was found to be a second-order polynomial, t = a + bx + cx^2, which models 99.7% of the variation in the average running time t as a function of age x. The model shows that the marathon performance of the average runner improves up to age 34.3 ± 2.6 years, thereafter,the performance starts to decline. A quantification of the age's influence on running time shows that it accounts for 4.5% of the total variance seen in the performance data.Conclusion: These outcomes indicate that the effect of age on performance in endurance running events is clearly measurable, quantifiable, and possible to describe. At the same time the findings indicate that other factors, such as training, affect the performance more. A comparison with the elite showed peak performance at the same age, but the rates of change in performance with age, improvement as well as degradation, was found to be higher among the elite.

Kinematic alterations after two high-intensity intermittent training protocols in endurance runners

Purpose:This study aimed to evaluate running kinematic characteristics during the early and late stages of 2 high-intensity intermittent training(HIIT)protocols with similar external load but different average running pace,as well as to compare the fatigue-induced changes during both HIIT protocols at a kinematic level.Methods:Eighteen endurance runners were tested on a track on 2 occasions:10 runs of 400 m with 90-120 s recovery between running bouts(10 × 400 m),and 40 runs of 100 m with 25-30 s recovery between running bouts(40 × 100 m).Heart rate was monitored during both protocols;blood lactate accumulation and rate of perceived exertion were recorded after both exercises.A high-speed camera was used to measure sagittalplane kinematics at the first and last runs during both HIIT protocols.The dependent variables were spatial-temporal parameters(step length and contact and flight time),joint angles during support(relative angles of the hip,knee,and ankle),and foot strike pattern.Results:High levels of exhaustion were reached by the athletes during both workouts(blood lactate accumulation>12 mmol/L,rate of perceived exertion>15;peak heart rate(HRpeak)>176 bpm).A within-protocol paired t test(first vs.last run)revealed no significant changes(p≥0.05)in kinematic variables during any of the HIIT sessions.A between-protocol comparison with the first run of each protocol revealed the effect of running speed on kinematics:+2.44 km/h during the 40 × 100 m:shorter contact and flight time(p<0.01)and longer step length(p= 0.001);greater hip flexion(p = 0.031)and ankle extension(p = 0.001)at initial contact;smaller knee and ankle flexion(p<0.001)at midstance;and greater hip extension at toe-off(p<0.001).Conclusion:HIIT sessions including runs for 15-90 s and performed at intensity above the velocity associated with maximal oxygen uptake did not consistently perturb the running kinematics of trained endurance runners.

Study of Radio-Sensitivity of Strawberry Runners <i>cv. Fortuna</i>under Moroccan Conditions

In recent years, strawberry is being successfully cultivated in Loukkos perimeter of Morocco and a wide range of varieties are being grown. The strawberry crop also generates 3 million working days per year. In fact, all plants are imported and prices are exorbitant. Varietal improvement is essential if a new impetus is to be given to the morocco strawberry. We have accordingly started a mutation breeding program by bud irradiation. Strawberry runners of cv. Fortuna were exposed to increasing doses of acute gamma rays. The physiological effects induced by irradiation were evaluated from cutting survival and growth. It has been determined that the doses of gamma and the varieties used are significant on the number of surviving plants and plant growth parameters. It was determined that low doses gamma irradiation respectively affected plant height, leaf length, leaf width and the number of leaves. These results allowed us, in the first instance, to fix the optimal dose range for cutting irradiated at 62 Grays.

Medication Use by Runners in Self-Care Situations

The benefits of running for cardiovascular health have long been established, but no relationship between runners/non-runners and their usage of prescription and over-the-counter (OTC) medications has been established. A comprehensive survey was sent out via Facebook, Inc., to self-identified runners to assess runners’ first response to 5 common self-care situations. The results were compared to the national average of the U.S. population who take prescription and OTC medications. What was also assessed was the relationship between average weekly miles run and the likelihood to choose OTC medications. 714 runners, residing predominately in the St. Louis, Missouri metropolitan area, completed the survey and their results were drastically different than the national average use for prescription and OTC medication in the general (non-runners) population. Approximately 30% of the runners in this study are on daily prescription medications versus a national average of 70% of the U.S. population. In each of the 5 common self-care situations, less than 50% of runners chose an OTC medication as their first option for self-care vs. the national average of 80%. Results of the study also showed that runners with a weekly mile average of 30 miles or more were less likely to choose an OTC option for self-care than runners with a weekly average of 15 miles or less. Overall, results of this survey suggest that runners are less likely to take medications and may be healthier than the average U.S. citizen overall.

A master-slave generalized predictive synchronization control for preheating process of multi-cavity hot runner system

As a key component of injection molding,multi-cavity hot runner(MCHR)system faces the crucial problem of polymer melt filling imbalance among the cavities.The thermal imbalance in the system has been considered as the leading cause.Hence,the solution may rest with the synchronization of those heating processes in MCHR system.This paper proposes a’Master-Slave’generalized predictive synchronization control(MS-GPSC)method with’Mr.Slowest’strategy for preheating stage of MCHR system.The core of the proposed method is choosing the heating process with slowest dynamics as the’Master’to track the setpoint,while the other heating processes are treated as‘Slaves’tracking the output of’Master’.This proposed method is shown to have the good ability of temperature synchronization.The corresponding analysis is conducted on parameters tuning and stability,simulations and experiments show the strategy is effective.

Changes in balance ability,power output,and stretch-shortening cycle utilisation after two high-intensity intermittent training protocols in endurance runners

Purpose：This study aimed to describe the acute effects of 2 different high-intensity intermittent trainings（HIITs） on postural control,countermovement jump（CMJ）,squat jump（SJ）,and stretch-shortening cycle（SSC） utilisation,and to compare the changes induced by both protocols in those variables in endurance runners.Methods：Eighteen recreationally trained endurance runners participated in this study and were tested on 2 occasions：10 runs of 400 m with 90 s recovery between running bouts（10×400 m）,and 40 runs of 100 m with 30 s recovery between runs（40 × 100 m）.Heart rate was monitored during both HIITs;blood lactate accumulation and rate of perceived exertion were recorded after both protocols.Vertical jump ability（CMJ and SJ） and SSC together with postural control were also controlled during both HIITs.Results：Repeated measures analysis revealed a significan improvement in CMJ and SJ during 10 × 400 m（p〈0.05）,whilst no significan changes were observed during 40×100 m.Indexes related to SSC did not experience significan changes during any of the protocols.As for postural control,no significan changes were observed in the 40×100 m protocol,whilst significan impairments were observed during the 10×400 m protocol（p〈0.05）.Conclusion：A protocol with a higher number of shorter runs（40×100 m） induced different changes in those neuromuscular parameters than those with fewer and longer runs（10×400 m）.Whereas the 40×100 m protocol did not cause any significan changes in vertical jump ability,postural control or SSC utilisation,the 10×400 m protocol impaired postural control and caused improvements in vertical jumping tests.

Blood Chemistry, Acid-Base, Electrolyte, Blood Lactate Metabolism and Sleep at 3480 m in Mountain Marathon Runners

Altered blood chemistry, acid-base and electrolyte are suggested determinants of sleep disturbance, with frequent arousal at high altitude even in well and long-trained altitude marathon runners. In this sample of experienced altitude marathon runners with maximal aerobic power at sea level of 61.4 ± 2.7 ml/kg-1·min-1 we found that pO2 and percent of oxygen saturation (%SO2) were lower at2050 mand3480 mthan at sea level;pO2 was higher after 38 - 41 hours than after 30 - 31 hours of acclimatization at3480 m(P 2 decreased (P 2 and (P 2 at a sleeping altitude of3480 mwas lower (P Simple regression analysis disclosed a significant correlation between the changes in TST and the percent of REM sleep and the changes in %SpaO2 recorded during sleep (P 2 at higher altitude and the percent of W and of TST (P 2, tCO2 and [HCO3-] correlated negatively and significantly with the percent of REM sleep changes at high altitude (P 2 and pH and correlated negatively with the changes in %SO2, pCO2, tCO2, and [HCO3-] (P ++] and [BE] and negatively with the changes in buffered bases [BB] and [BEeffective] (P 2 and significantly and negatively with the changes in [K+] (P 2, tCO2, [HCO3-] and [K+]

The Effect of a Chocolate Bar Supplementation on Moderate Exercise Recovery of Recreational Runners

To study the effects of a chocolate bar supplementation before exercise on improving recovery of physiological and metabolic changes induced by exercise, 16 male students aged 18-20 years voluntarily served as subjects. A crossover design was employed. Each subject took part in two trials and ran an hour on a treadmill with the intensity of keeping heart rate at 148-150 min for each trial. Results showed that plasma glucose levels of subjects increased significantly (5.42±0.83 mmol/L) at 15 min after ingestion of a chocolate bar and maintained in moderate high levels (4.92 ±0.57 mmol/L) until 30 min after an hour's running while the glucose levels were low and dropped to under normal ranges (3.84 ± 0.31 mmol/L) at 30 min after exercise as they were with a supplement of placebo. Results of plasma FFA, blood lactate and plasma urea nitrogen levels and RPE all indicated that chocolate bar supplementation before exercise benefits to create the necessary prerequisite for exercise and recovery

Early Prevention of Exercise-induced Tibia Periostitis for Long-Distance Runners in China＇ s Regular Universities

Exercise-induced tibia periostitis is one of the most common sports injuries in the sports training of athletics in regular institutions of higher learning. It often occurs. When it is serious, periosteal proliferation would occur, It will result in fatigue fi^cture sometimes. This is relevant to tibialis anterior muscle restrained contraction in the events in the sports process. If measures are not adopted, early prevention should be strengthened. This would not only affect seriously the sports achievement of long-distance runners, but also affects their future ordinary lives. Through analysis and summaries, the main reasons for the occurrence of tibia periostitis for long-distance runners are shown. From the perspectives of reasonably arranging the exercise load, strengthening the field management and strengthening the self-protection and so on, the prevention of tibia periostitis for long-distance runners has been explored. It also helps the long-distance runners to train scientifically, which can effectively avoid and lessen the occurrence of tibia periostitis and the adverse effect it brings.

Nutrition For Marathon Runners In Competition Season

The week or ten days before competition is the time to cut down the amount of training,but the quality of the food must be improved, i.e.comprehensive nutrient must be supplied so as to increase the energy reserve and speed up the recovery form the pre-competition training.Calories in the food supply should be reduced lest it causes the increase of body fat and weight.In pre-competition food, glycogen reserve Should be fully guaranteed, acid food of protein of fat must be replenished exceessively. Runners should eat fruit and vegetables as much as possible to fill up various vitamins and inorganic salts.

热流道板真空钎焊有限元模拟与分析

采用BNi-2镍基钎料对热流道板进行真空钎焊,须根据钎焊件设定加热工艺曲线。加热工艺曲线的设定是钎焊过程最重要的环节之一,决定着钎焊的质量和效率。该文结合真空加热的特点及钎焊要求,运用Ansys有限元软件数值模拟的方法,对壁厚、体积较大的多层热流道板真空钎焊进行仿真分析,通过对比不同工艺方案及不同钎焊件的模拟结果,探究真空钎焊过程升温规律,从而调整各阶段的相关参数及制定合理的加热工艺曲线,避免了现场反复调试参数造成的资源浪费,节约了时间和成本,提高了效率。此外,通过在实际钎焊试验过程中布置热电偶对钎焊件测量温度,并与数值模拟结果对比,两者基本吻合,验证了有限元分析的准确性,能为之后其他零部件的真空钎焊提供参考。

轴流式水轮发电机组不对中-碰摩耦合故障振动特性分析

针对轴流式水轮发电机组因联轴器偏角不对中引起的碰摩转子-转轮系统振动问题,基于修正的LuGre摩擦模型,该研究推导了联轴器不对中故障下转轮叶片碰摩力表达式。在此基础上,搭建了综合考虑不平衡磁拉力等外激励作用下系统动力学模型。采用数值方法研究了不对中角度对系统振动特性的影响,并结合Floquet理论分析了以转速为控制变量的系统周期解稳定性。结果表明,不对中的存在增大了系统发生失稳可能性,显著改变了系统动态特性。此外,不对中角度对转子与转轮振动响应的影响具有较大差异,随着不对中角度的增加,转轮振动变化明显且碰摩程度较为恶劣。该研究结果可为轴流式水轮发电机组安全运行及稳定性分析提供有益借鉴。

中长跑运动员穿不同鞋垫跑步时的足底压力探究

目的:选取参与训练与教学课程的27名中长跑运动员,通过在相同速度下穿着不同类型鞋垫跑步时的实验测试,揭示跑步时足底压力、压强生物力学参数指标特征,为中长跑运动员提供生物力学的理论依据。方法:采用实验法、文献资料法、专家访谈法、数理统计法,利用足底压力测试系统与处理软件进行数据整理分析。结果:中长跑运动员穿着不同类型测试鞋垫跑步时左脚和右脚足底平均压力、最大压强在8个分布区域情况不一,两两对比重复测量方差分析存在不同差异,表现为足跟区是跑步时落地缓冲阶段足部主要的受力区域。结论:①无鞋垫时,左、右脚的M2、M4、M5、M6区足底压力均大于其他3种鞋垫;而无鞋垫时足底除M3区外,其他区域内的足底压强均大于其他3种鞋垫。②M5(第2~4跖骨区)、M6(第1跖骨区)是跑步蹬地发力阶段主要受力区域。M1(足跟区)是跑步时落地缓冲阶段足部主要的受力区域。③无鞋垫时,左、右脚的M2、M5、M6区的足底压力值以及左、右脚的M2、M4、M5、M6区的最大压强值均与其他3种鞋垫存在显著性差异。④足底压力值和足底压强值显示A型鞋垫在减压、抗震方面的功能较好。

痛并快乐:资深马拉松业余跑者良性自虐的现象学研究

为了深入探讨资深马拉松业余跑者良性自虐的表现形式、动机来源和认知特点,运用现象学研究方法以13名资深马拉松业余跑者为访谈对象,并对访谈文本进行分析。研究结果表明:(1)良性自虐现象普遍存在于资深马拉松业余跑者群体中;(2)资深马拉松业余跑者良性自虐的表现形式主要体现在环境、生理和心理等3个方面;(3)资深马拉松业余跑者良性自虐的动机来源主要包括挑战自我、过往经历、同伴激励、追求刺激和探索未知等5个方面;(4)资深马拉松业余跑者良性自虐在认知上反映出追求认同接纳、能力体现和利弊权衡的结果。研究认为良性自虐行为对于资深马拉松业余跑者利弊共存,需要积极引导宣传、正确教育和制度合理管控,保障马拉松跑者安全科学运动,促进身心健康。

PEMFC船形堵块阴极流场的性能

建立流体体积(VOF)两相流模型,研究船形堵块流道的排水性能。建立不同开孔率的船形堵块流道三维模型,研究船形堵块及开孔率对质子交换膜燃料电池(PEMFC)性能的影响。船形堵块流道峰值净功率密度相较于传统直流道可提升9.4%,相较于同堵塞率下的梯形堵块流道可提高2.9%,具有较好的强化传质作用。通过提高船形堵块流道的开孔率,PEMFC可以获得更好的性能。在相同开孔率下,船形堵块流道的氧气摩尔浓度较直流道和梯形堵块流道分别提高28.6%和14.0%。结果表明,相较于传统直流道,船形堵块流道可降低排水周期和流道内平均水含量,具有更好的排水性能。

基于MRD优化布置的水轮发电机组碰摩系统振动抑制

针对水轮发电机组转子-转轮系统碰摩故障问题,采用磁流变液阻尼器(magneto-rheological damper,MRD)对轴系振动进行抑制,旨在探究MRD对机组轴系振动的影响规律及其对系统碰摩故障的抑制效果。首先,将机组轴向位置函数引入MRD非线性动力学模型,推导了碰摩故障下含轴向分布参数的MRD-转子-转轮系统动力学方程。其次,基于数值模拟方法,以机组转速为控制参数对比分析了是否考虑MRD的转子-转轮系统非线性动力学行为。最后,研究了不同MRD轴向布置参数对碰摩转子-转轮系统动力学行为的影响。研究结果表明:MRD的加入对转子、转轮非稳态运动具有良好约束作用,能够显著减小转子、转轮振动幅值,有效避免了机组轴系碰摩故障的发生;当阻尼器位置参数s_(1)、s_(2)分别取0.25与0.95时,MRD对系统的减振效果最佳。通过在机组轴系合理布置MRD,可有效改善系统振动情况,从而为水轮发电机组振动控制提供有益指导。

左右后雾灯边框的顺序阀热流道注塑模设计

结合新能源汽车的左右后雾灯边框注塑时易产生熔接痕和脱模时易变形的问题,设计了1模2腔的侧浇口二板式热流道注塑模具。基于Moldflow模拟分析结果,确定了左右后雾灯边框的最佳浇口位置、浇口数量,通过综合分析塑件尺寸、生产技术和效率等设计了模具的浇注系统、冷却系统、抽芯机构、脱模机构等结构。为合理控制塑件的熔接痕,采用冷流道与热流道相结合的复合流道,利用顺序阀控制进浇点的进浇时间;为了实现高效脱模,将模具引入了斜顶机构、倒装的斜导柱侧抽芯的组合式脱模结构,替代了传统注塑推杆式脱模,采用两侧油缸驱动推板运动的脱模方式。最后,利用UG软件对模具的导向机构、复位机构和其他辅助机构进行分析,完成了模具设计。