排球跳传技术的研究

跳传是排球运动中一项重要技术,在排球比赛中运用跳传技术组织进攻有许多优点,熟练地掌握跳传技术对比赛获胜具有重要作用,文中对跳传的移动取位、起跳和空中动作的要求、传球的时机、击球点和传球手型、击球部位和用力方向、落地的技术等方面均从理论与实践结合上作了科学的剖析。     

The effect of pre-exercise carbohydrate feedings on the intensity that elicits maximal fat oxidation

The aim of the present study was to examine the effect of ingesting 75 g of glucose 45 min before the start of a graded exercise test to exhaustion on the determination of the intensity that elicits maximal fat oxidation (Fatmax). Eleven moderately trained individuals (VO2max: 58.9 +/- 1.0 ml x kg(-1) x min(-1); mean +/- sx), who had fasted overnight, performed two graded exercise tests to exhaustion, one 45 min after ingesting a placebo drink and one 45 min after ingesting 75 g of carbohydrate in the form of glucose. The tests started at 95 W and the workload was increased by 35 W every 3 min. Gas exchange measures and heart rate were recorded throughout exercise. Fat oxidation rates were calculated using stoichiometric equations. Blood samples were collected at rest and at the end of each stage of the test. Maximal fat oxidation rates decreased from 0.46 +/- 0.06 to 0.33 +/- 0.06 g min(-1) when carbohydrate was ingested before the start of exercise (P < 0.01). There was also a decrease in the intensity which elicited maximal fat oxidation (60.1 +/- 1.9% vs 52.0+3.4% VO2max) after carbohydrate ingestion (P < 0.05). Maximal power output was higher in the carbohydrate than in the placebo trial (346 +/- 12 vs 332 +/- 12 W) (P < 0.05). In conclusion, the ingestion of 75 g of carbohydrate 45 min before the onset of exercise decreased Fatmax by 14%, while the maximal rate of fat oxidation decreased by 28%.     

Physical activity and situational motivation in physical education: influence of the motivational climate and perceived ability

The influence of perceptions of the motivational climate and perceived ability on situational motivation and the physical activity behavior of 213 male and 229 female adolescent physical education students (M age = 12.56 years; SD = 0.96) was examined over a 3-day period. A significant age by gender interaction emerged, with physical activity declining from the sixth to eighth grade. The decline was more pronounced among female than male students. Perceptions of a mastery climate were strongly related to more self-determined forms of situational motivation. In contrast, perceptions of a performance climate were strongly related to less self-determined forms of situational motivation. Results of a hierarchical regression analysis revealed gender, perceived ability, and perceptions of a mastery climate to explain a significant amount of variance in physical activity. These findings suggest that promoting a mastery oriented motivational climate in physical education will foster self-determined situational motivation and physical activity.     

Gender typing of sports: an investigation of Metheny's classification

The purpose of this study was to investigate if children perceived certain sports to be masculine, feminine, or neutral. Students attending a University Laboratory school (grades K-12) were asked to fill out a survey about sports during a class period, Children in grades K-6 were given a sport (such as baseball) and asked if a boy named David would play it, if a girl named Jane would play it, or if both David and Jane would play the sport. Students in grades 7-12 were asked to name their favorite athlete or team and sport and indicate what sports they felt was best for a girl and a boy. Then they were given a list of sports and asked to indicate, using a 5-point Likert-type scale, whether they believed the sport was masculine, neutral, or feminine. Results from loglinear analyses indicated that students sex-typed certain sports, such as aerobics and football. Additionally, although some responses from students in grades 7-12 indicated that individuals should be able to play any sport they wanted, there were many gendered rsponses in terms of what sport(s) girls and boys should participate in. The results are discussed with reference to Metheny's categories of permissible sports for girls and in the framework of the gender typing of sport.     

Arousal, anxiety, and performance: a reexamination of the Inverted-U hypothesis

Until recently, the traditional Inverted-U hypothesis had been the primary model used by sport psychologists to describe the arousal-performance relationship. However, many sport psychology researchers have challenged this relationship, and the current trend is a shift toward a more "multidimensional" view of arousal-anxiety and its effects on performance. In the current study, 104 college-age participants performed a simple response time task while riding a bicycle ergometer. Participants were randomly assigned to one of eight arousal groups (between 20 and 90% of heart rate reserve) and were told they were competing for a cash prize. Prior to the task, the Competitive State Anxiety Inventory-2 and Sport Anxiety Scale (SAS) were administered to assess the influence of cognitive and somatic anxiety. As hypothesized, regression analysis revealed a significant quadratic trend for arousal and reaction time. This accounted for 13.2% of the variance, F change (1, 101) = 15.10, p < .001, in performance beyond that accounted for by the nonsignificant linear trend. As predicted by the Inverted-U hypothesis, optimal performance on the simple task was seen at 60 and 70% of maximum arousal. Furthermore, for the simple task used in this study, only somatic anxiety as measured by the SAS accounted for significant variance in performance beyond that accounted for by arousal alone. These findings support predictions of the Inverted-U hypothesis and raise doubts about the utility theories that rely on differentiation of cognitive and somatic anxiety to predict performance on simple tasks that are not cognitively loaded.     

Validation of a stages of exercise change questionnaire

The purpose of this study was to examine evidence for the validity of a stages of change measure of the Transtheoretical Model for exercise behavior. Participants were 152 university students (53.3% women, 71.6% Caucasian, M age = 19.18 years) who completed processes of change, self-efficacy, decisional balance, stages of change, and exercise behavior questionnaires as well as a maximal treadmill test. Participants in the action and maintenance stages had the highest strenuous (PC/C/P < A/M) and moderate (PC/C < A/M) self-reported exercise behavior. Those in the maintenance stage had the highest estimated aerobic fitness (PC/P < MA). The differences between the early stages (PC, C, and P) and the later stages (A and M) as described by the first function were primarily due to the behavioral process of change. The differences between the extreme stages (PC and M) and the middle stages (C, P, and A) were due to the experiential processes of change and the pros of decisional balance. The hypothesized patterns of stage differences were partially supported. Failure to obtain full support may have been due to methodological issues or inherent difficulties in detecting evidence for the validity of stages of change measures.     

The Region 4 collaborative virtual reference project

In May 2002, the Denison Memorial Library at the University of Colorado Health Sciences Center and the J. Otto Lottes Health Sciences Library at the University of Missouri-Columbia, with funding from the National Network of Libraries of Medicine-Midcontinental Region, embarked on a collaborative, real-time reference project using the 24/7 Reference, Inc., software package. This paper describes how the project was conceived, and includes details on the service hours, staffing, training, marketing, lessons learned, and future plans for the service.     

"Ask A Librarian": the experiences of four hospital libraries

The librarians at four hospital libraries describe the electronic reference service, "Ask A Librarian," offered at their institutions. The hospitals are vastly different in size and in number of library staff, and offer the "Ask A Librarian" service to different clientele. The article illustrates that both large hospitals with a large library staff and small hospitals with a solo librarian and some volunteers can offer this type of service.