Errors in the estimation of hydration status from changes in body mass

Hydration status is not easily measured, but acute changes in hydration status are often estimated from body mass change. Changes in body mass are also often used as a proxy measure for sweat losses. There are, however, several sources of error that may give rise to misleading results, and our aim in this paper is to quantify these potential errors. Respiratory water losses can be substantial during hard work in dry environments. Mass loss also results from substrate oxidation, but this generates water of oxidation which is added to the body water pool, thus dissociating changes in body mass and hydration status: fat oxidation actually results in a net gain in body mass as the mass of carbon dioxide generated is less than the mass of oxygen consumed. Water stored with muscle glycogen is presumed to be made available as endogenous carbohydrate stores are oxidized. Fluid ingestion and sweat loss complicate the picture by altering body water distribution. Loss of hypotonic sweat results in increased osmolality of body fluids. Urine and faecal losses can be measured easily, but changes in the water content of the bladder and the gastrointestinal tract cannot. Body mass change is not always a reliable measure of changes in hydration status and substantial loss of mass may occur without an effective net negative fluid balance.     

The use of dietary supplements by athletes

Many athletes use dietary supplements as part of their regular training or competition routine, including about 85% of elite track and field athletes. Supplements commonly used include vitamins, minerals, protein, creatine, and various "ergogenic" compounds. These supplements are often used without a full understanding or evaluation of the potential benefits and risks associated with their use, and without consultation with a sports nutrition professional. A few supplements may be helpful to athletes in specific circumstances, especially where food intake or food choice is restricted. Vitamin and mineral supplements should be used only when a food-based solution is not available. Sports drinks, energy bars, and protein-carbohydrate shakes may all be useful and convenient at specific times. There are well-documented roles for creatine, caffeine, and alkalinizing agents in enhancing performance in high-intensity exercise, although much of the evidence does not relate to specific athletic events. There are potential costs associated with all dietary supplements, including the risk of a positive doping result as a consequence of the presence of prohibited substances that are not declared on the label.     

Alcohol and football

The use of alcohol is often intimately associated with sport, and the association is particularly strong in football. As well as providing a source of energy, alcohol (ethanol) has metabolic, cardiovascular, thermoregulatory, and neuromuscular actions that may affect exercise performance. Its actions on the central nervous system, however, result in decrements in skill and behavioural changes that may have adverse effects on performance. There is also evidence of dose-dependent decrements in aerobic capacity. Although the mechanisms are not well understood, the aftermath of alcohol use (hangover) may also adversely affect performance for many hours after intoxication. Alcohol intoxication may adversely affect the player's dietary choices by displacing carbohydrate from the diet at a time when restoration of glycogen stores should be a priority.     

Physiological variables and performance markers of serving soldiers from two "elite" units of the British Army

The aim of this study was to compare selected physiological variables and performance markers of soldiers from two "elite" units of the British Army. Ten soldiers from each of the two units were recruited for this study (n = 20). All participants completed three tests while carrying a 20 kg backpack load: (1) a maximal treadmill test using the Bruce protocol; (2) a 2 mile backpack run test specific to Unit A on a consistently flat tarmac road; and (3) a 29 km time-trial over hilly terrain typical of a mountainous area used by Unit B for performance assessment. Heart rate, maximal blood lactate concentration and performance (run time) were assessed during all three tests, with peak oxygen uptake also being measured during the maximal treadmill test. Measurements of anthropometry, isokinetic strength and mental toughness (MT48) were also recorded. There were no significant differences in terms of performance markers between the units (P > 0.05). Performance on the maximal treadmill test correlated with performance on the 2 mile backpack run test (r = -0.57) and 29 km time-trial (r = -0.66). Performance on the 2 mile backpack run test in turn correlated with 29 km time-trial performance (r = -0.77), accounting for 59% of the variance. In conclusion, the maximal treadmill test and the 2 mile backpack run test are useful indicators of performance on the arduous hill march and could be employed in the screening and selection of potential recruits.     

Kinematic analysis of three water polo front crawl styles

During water polo matches, players use different front crawl styles. The purpose of this study was to conduct a kinematic analysis of three water polo front crawl styles: front crawl with head under water, front crawl with head above water, and front crawl when leading the ball. Ten proficient water polo players performed 3 × 15 m sprints in each front crawl style, which were recorded three-dimensionally by two surface and four underwater cameras. The results showed no differences in performance and several kinematic characteristics among the water polo front crawl styles. However, front crawl when leading the ball showed shorter stroke length and greater stroke frequency. Front crawl with head underwater presented greater maximal finger depth and elbow angle at mid-stroke position. Front crawl with head above water and when leading the ball showed greater trunk obliquity and maximal depth of right and left foot, and shorter kick stroke frequency. The findings suggest that proficient players learn to master front crawl with head above water to achieve top velocity. Despite the common use of the front crawl with head underwater as the basis for water polo fast displacement, coaches should emphasize the use of the specific water polo styles to attain high performance.     

Health Services Technology Assessment Research (HSTAR): an introduction

The National Information Center on Health Services Research and Health Care Technology (NICHSR), located at the National Library of Medicine (NLM), mounted a database called Health Services Technology Assessment Research (HSTAR). HSTAR pulls together a number of online resources which cover topics such as clinical practice guidelines, technology assessments, and clinical trials. This article gives a brief overview of the database and some hints for effective searching.     

教师与声音艺术表现

教师与声音艺术表现郭建民，赵世兰（三）授讲之术──语言表达形象化教师讲课不同于读，因而不能照本宣科，也不能用公式化，概念化，始终一模式一种腔调；应根据教学内容所提供的一切可能借助发挥的条件，用生动、通俗形象的语言进行授课艺术的再创造。比如：鲁迅先生的...     

Want to Improve Undergraduate Thesis Writing? Engage Students and Their Faculty Readers in Scientific Peer Review

One of the best opportunities that undergraduates have to learn to write like a scientist is to write a thesis after participating in faculty-mentored undergraduate research. But developing writing skills doesn't happen automatically, and there are significant challenges associated with offering writing courses and with individualized mentoring. We present a hybrid model in which students have the structural support of a course plus the personalized benefits of working one-on-one with faculty. To optimize these one-on-one interactions, the course uses BioTAP, the Biology Thesis Assessment Protocol, to structure engagement in scientific peer review. By assessing theses written by students who took this course and comparable students who did not, we found that our approach not only improved student writing but also helped faculty members across the department--not only those teaching the course--to work more effectively and efficiently with student writers. Students who enrolled in this course were more likely to earn highest honors than students who only worked one-on-one with faculty. Further, students in the course scored significantly better on all higher-order writing and critical-thinking skills assessed.     

Continuity and change in inhibited and uninhibited children

After screening 368 toddlers and selecting 77 into extremely inhibited, extremely uninhibited, and intermediate groups, 63 children (82%) were followed up at 4 and 7 years. Minority subgroups of both the inhibited and uninhibited children showed continuity on outcomes consisting of questionnaire measures of shyness, inhibitory control, and impulsivity, as well as multiepisode observational measures of behavioral inhibition and exuberance. Change from both inhibited and uninhibited status from the toddler age was more common than remaining extremely inhibited or uninhibited, but that change was largely constrained to the middle of the distribution.     

中西歌剧演唱艺术迥然相异的美学品格

中国歌剧演唱艺术“戏剧唱法”由于受到传统戏曲的影响，其美学价值是达意之情，美学理想是韵味。韵味又包含着字、声、情、神韵，四合一达到塑造人物、表达故事情节、感染观众之目的，这种独特的美学品格具有鲜明民族特色的审美风貌和精神。西洋歌剧演唱艺术“美声唱法”由于受到音乐创作观念和演唱家本身对歌唱技巧的审美追求，其美学价值是华声之情，美学理想是唯美。它用一种均匀、统一、华丽、完美的声音艺术达到感染观念之目的。