水代谢与运动能力

水代谢与人体的运动能力有着密切的关系.剧烈运动会使机体脱水,严重影响运动能力.所以,运动前、中、后都应该正确合理地补充水分.通过查阅大量文献资料,对此问题进行综述.     

Glucose Polymer Ingestion during Ultraendurance Bicycling

ABSTRACT

Purpose: The purpose of this study was to examine the predictive relationship among physical activity, health-related fitness, and on-task classroom behavior in children using a discriminant function analysis. Method: Participants were a convenience sample of children (N = 533; M_age = 8.8 ± 1.9 years) recruited from 77 1st- through 5th-grade classrooms at 3 low-income schools in a capital city in the Southwest United States. Percent of the school day spent in sedentary behavior (%SED), moderate-to-vigorous physical activity (%MVPA), and health-related fitness scores (body mass index [BMI] and Progressive Aerobic Cardiovascular Endurance Run [PACER] laps) were assessed during school hours. Classrooms were observed for on-task behavior during the academic year with the use of 5-s momentary time sampling methodology. A discriminant function analysis was performed using a binary on-task behavior outcome, stratified by an 80% on-task behavior cut point. Results: The results yielded 1 function (r² = .26, F = 13.1) explaining approximately one quarter of the total variance. The standardized function coefficients were ?.29, .29, ?.48, and .48 for %SED, %MVPA, BMI, and PACER laps, respectively. The sensitivity and specificity of the derived function for classifying a child into an on-task or off-task classroom were .79 and .73, respectively. Children who belonged to classrooms that achieved 80% on-task behavior displayed shorter times in sedentary behaviors (d = 1.01), lower BMI (d = 0.13), and higher PACER scores (d = 0.22) compared with children who belonged to off-task classrooms. Conclusion: School-day physical activity behaviors and health-related fitness scores can moderately discriminate children who belong to classrooms from low-income schools that are categorized as being sufficiently on task.     

The effect of hydration status on appetite and energy intake

This study investigated the effect of hypohydration produced by exercise and sub-optimal rehydration on appetite and energy intake. Ten males lost ~2% body mass through evening exercise in the heat (35°C). Over the next 13 h, participants were re-fed and either rehydrated (RE: water equal to 175% of body mass loss (BML)) or remained hypohydrated (HYPO: 200 ml water), until the following morning. Urine samples, blood samples and subjective feelings were collected pre-exercise, post-exercise and 13 h post-exercise, with an ad libitum breakfast provided 13 h post-exercise. Total BML at 13 h post-exercise was greater during HYPO (2.8 (0.5)%) than RE (0.5 (0.5)%). Energy intake at the ad libitum breakfast was similar between trials (RE: 4237 (1459) kJ; HYPO: 4612 (1487) kJ; P = 0.436), with no difference in energy consumed in foods (P = 0.600) or drinks (P = 0.147). Total water ingestion at the ad libitum breakfast meal was greater during HYPO (1641 (367) ml) than RE (797 (275) ml) (P < 0.001), with this being explained by increased water intake through fluids (P < 0.001). Thirteen hours post-exercise, participants reported greater thirst (P < 0.001) and lower fullness (P < 0.01) during HYPO. Alterations in hydration status produced by exercise are unlikely to influence post-exercise food intake and consequently other aspects of recovery or adaptation.     

Hydration status affects mood state and pain sensation during ultra-endurance cycling

Laboratory-based studies indicate mild dehydration adversely affects mood. Although ultra-endurance events often result in mild to moderate dehydration, little research has evaluated whether the relationship between hydration status and mood state also exists in these arduous events. Therefore, the purpose of this study was to evaluate how hydration status affected mood state and perceptual measures during a 161 km ultra-endurance cycling event. One hundred and nineteen cyclists (103 males, 16 females; age = 46 ± 9 years; height = 175.4 ± 17.9 cm; mass = 82.8 ± 16.3 kg) from the 2011 and 2013 Hotter’N Hell events participated. Perceived exertion, Thermal, Thirst, and Pain sensations, Brunel Profile of Mood States, and urine specific gravity (USG) were measured pre- (~1 h before), mid- (~97 km), and post-ride. Participants were classified at each time point as dehydrated (USG ≥ 1.022) or euhydrated (USG ≤ 1.018). Independent of time point, dehydrated participants (USG = 1.027 ± 0.004) had decreased Vigour and increased Fatigue, Pain, Thirst, and Thermal sensations compared to euhydrated participants (USG = 1.012 ± 0.004; all P < 0.01). USG significantly correlated with Fatigue (r = 0.36), Vigour (r = ?0.27), Thirst (r = 0.15), and Pain (r = 0.22; all P < 0.05). In conclusion, dehydrated participants had greater Fatigue and Pain than euhydrated participants. These findings indicate dehydration may adversely affect mood state and perceptual ratings during ultra-endurance cycling.     

运动员减体重的医学监控

从生理生化角度对运动员减体重所产生的影响进行了分析。探讨了减体重造成脱水，蛋白质、矿物质的丢失以及降低免疫系统功能所产生的影响。     

Exercise in the heat: challenges and opportunities

Exercise in the heat poses a formidable challenge to the body's ability to control its internal environment due to the high rates of metabolic heat production and heat gain by physical transfer from the environment. In an attempt to restrict the rise in core temperature, an increased rate of sweat secretion onto the skin is invoked. This may limit the rise in core temperature, and can prolong the time before a limiting temperature is attained, but it does so at the cost of a loss of body water and electrolytes. The effects of the diminished blood volume are offset to some extent by cardiovascular adaptations, including an increased heart rate and an increased peripheral resistance, but these are insufficient to maintain functional capacity when blood volume is reduced. Prior dehydration will impair performance in both prolonged exercise and short-term high-intensity exercise. Athletes living and training in the heat may experience chronic hypohydration due to inadequate replacement of fluid losses. The negative consequences of exercise in the heat are attenuated to some extent by a period of adaptation, and by the ingestion of water or other appropriate fluids. Optimum fluid replacement strategies will depend on the exercise task, the environmental conditions and the individual physiological characteristics of the athlete. Manipulation of pre-exercise body temperature can also influence exercise performance and may be a strategy that can be used by athletes competing in stressful environments.     

醋酸/水分离研究进展

醋酸是一种重要的化工原料，其水溶液广泛存在于各类工业过程中,由于醋酸／水体系的相对挥发度不大，生产中用于分离醋酸／水的普通精馏和共沸精馏工艺能耗较高，因此研究者和工业界都在寻求更好的分离方法,目前醋酸／水的分离方法有精馏法、萃取法、醋化法、中和法、吸附法、膜分离法等，其中有些方法已经工业化，具有成熟的生产工艺；有些则处于研究阶段,本文对这些方法的研究现状及应用前景进行了介绍和评述，提出了萃取精馏法将是一很有前途的分离方法。     

含水矿物电导率研究进展

含水矿物对于地球内部水循环非常重要,通过研究典型含水矿物的电导率可以获得地球内部水循环的路径和物质成分的变化。归纳高温高压下典型含水矿物脱水前后的电导率结果、导电机制、脱水机制和地球物理应用。含水矿物脱水前电导率普遍在10^-4 S/m,脱水后电导率显著增加,不同含水矿物电导率存在差异。脱水机制与导电机制耦合可能决定了含水矿物脱水过程的电导率,而脱水后体系的电导率一般取决于流体的成分和连通度。含水矿物脱水前后电导率的变化可以为解释俯冲带不同深度的高导异常提供实验依据;确定含水矿物分解产生的流体的成分可以为认识俯冲带物质循环带来启示。在已有研究基础上,展望了含水矿物电导率未来的研究方向。     

影响饱水古木加固进程因素的实验研究

分别测定了用加填充物法脱水加固饱水古木时加固液渗透量受木材含水率的影响以及浸渍温度、添加溶剂对处理周期的影响。结果表明：高含水率古木由于内部木纤维素几乎全部降解,在相同浓度加固液中,加固剂的尖一增加,在实际自理中采用高浓度加固液更有利于器物定型,温度升高和添加溶剂,有利于降你加固液的黏度和表面张力,提高渗透速度,缩短处理时间。     

The Influence of Hydration on Anaerobic Performance

This review examines the influence of dehydration on muscular strength and endurance and on single and repeated anaerobic sprint bouts. Describing hydration effects on anaerobic performance is difficult because various exercise modes are dominated by anaerobic energy pathways, but still contain inherent physiological differences. The critical level of water deficit (～ 3–4%; mode dependent) affecting anaerobic performance is larger than the deficit (～ 2%) impairing endurance performance. A critical performance-duration component (> 30 s) may also exist. Moderate dehydration (> 3% body weight; precise threshold depends on work/recovery ratio) impairs repeated anaerobic bouts, which place an increased demand on aerobic metabolism. Interactions between dehydration level, dehydration mode, testing mode, performance duration, and work/recovery ratio during repeated bouts make the dehydration thresh-old influencing anaerobic performance mode dependent.