Power output of field-based downhill mountain biking

The purpose of this study was to assess the power output of field-based downhill mountain biking. Seventeen trained male downhill cyclists (age 27.1 +/- 5.1 years) competing nationally performed two timed runs of a measured downhill course. An SRM powermeter was used to simultaneously record power, cadence, and speed. Values were sampled at 1-s intervals. Heart rates were recorded at 5-s intervals using a Polar S710 heart rate monitor. Peak and mean power output were 834 +/- 129 W and 75 +/- 26 W respectively. Mean power accounted for only 9% of peak values. Paradoxically, mean heart rate was 168 +/- 9 beats x min(-1) (89% of age-predicted maximum heart rate). Mean cadence (27 +/- 5 rev x min(-1)) was significantly related to speed (r = 0.51; P < 0.01). Analysis revealed an average of 38 pedal actions per run, with average pedalling periods of 5 s. Power and cadence were not significantly related to run time or any other variable. Our results support the intermittent nature of downhill mountain biking. The poor relationships between power and run time and between cadence and run time suggest they are not essential pre-requisites to downhill mountain biking performance and indicate the importance of riding dynamics to overall performance.     

Effects of muscle-tendon length on joint moment and power during sprint starts

The aim of this study was to examine the effects of muscle-tendon length on joint moment and power during maximal sprint starts. Nine male sprinters performed maximal sprint starts from the blocks that were adjusted either to 40 degrees or 65 degrees to the horizontal. Ground reaction forces were recorded at 833 Hz using a force platform and kinematic data were recorded at 200 Hz with a film camera. Joint moments and powers were analysed using kinematic and kinetic data. Muscle - tendon lengths of the medial gastrocnemius, soleus, vastus medialis, rectus femoris and biceps femoris were calculated from the set position to the end of the first single leg contact. The results indicated that block velocity (the horizontal velocity of centre of mass at the end of the block phase) was greater (P < 0.01) in the 40 degrees than in the 65 degrees block angle condition (3.39 +/- 0.23 vs. 3.30 +/- 0.21 m . s(-1)). Similarly, the initial lengths of the gastrocnemius and soleus of the front leg in the block at the beginning of force production until half way through the block phase were longer (P < 0.001) in the 40 degrees than in the 65 degrees block angle condition. The initial length and the length in the middle of the block phase were also longer in the 40 degrees than in the 65 degrees block angle condition both for both the gastrocnemius (P < 0.01) and soleus (P < 0.01-0.05) of the rear leg. In contrast, the initial lengths of the rectus femoris and vastus medialis of the front leg were longer (P < 0.05) in the 65 degrees than in the 40 degrees block angle condition. All differences gradually disappeared during the later block phase. The peak ankle joint moment (P < 0.01) and power (P < 0.05) during the block phase were greater in the 40 degrees than in the 65 degrees block angle condition for the rear leg. The peak ankle joint moment during the block phase was greater (P < 0.05) in the 40 degrees block angle for the front leg, whereas the peak knee joint moment of the rear leg was greater (P < 0.01) in the 65 degrees block angle condition. The results suggest that the longer initial muscle-tendon lengths of the gastrocnemius and soleus in the block phase at the beginning of force production contribute to the greater peak ankle joint moment and power and consequently the greater block velocity during the sprint start.     

Pedometer reliability, validity and daily activity targets among 10- to 15-year-old boys

The aims of this study were to: (1) determine whether the number of pedometer counts recorded by adolescents differs according to the adiposity of the participant or location on the body; (2) assess the accuracy and reliability of pedometers during field activity; and (3) set adolescent pedometer-based physical activity targets. Seventy-eight 11- to 15-year-old Boy Scouts completed three types of activity: walking, fast walking and running. Each type was performed twice. Participants wore three pedometers and one activity monitor during all activities. Participants were divided into groups of normal weight (BMI < 85th percentile) and at risk of being overweight (BMI > or = 85th percentile). Intra-class correlations across the three activities indicated reliability (r = 0.51 - 0.92, P < 0.001). This conclusion was supported by narrow limits of agreement that were within a pre-set range that was practically meaningful. Multivariate analysis of covariance indicated adiposity group differences, but this difference was a function of the increased stature among the larger participants (P < 0.001). Ordinary least-squares regression models and multi-level regression models showed positive associations between the number of pedometer and activity monitor counts recorded by the three groups of participants during all activities (all P < 0.001). The mean number of counts recorded for all participants during the fast walk was 127 counts per minute. In conclusion, the pedometers provided an accurate assessment of adolescent physical activity, and a conservative estimate of 8000 pedometer counts in 60 min is equivalent to 60 min of moderate to vigorous physical activity.     

Youth exercise intention and past exercise behavior: examining the moderating influences of sex and meeting exercise recommendations

The study purposes were to examine: (a) the determinants of exercise intention and past exercise behavior (PEB) using the theories of reasoned action and planned behavior, and (b) the moderating influences of sex and exercise group (meeting or not meeting exercise guidelines). Participants (n = 676 adolescents) completed self-reported measures of their exercise attitude, subjective norm, perceived behavioral control (PBC), intention, and PEB. We found that attitude, subjective norm, and PBC explained 55% of the variance in intention, and intention and PBC explained 51% of the variance in PEB. While we found sex and exercise group differences across the study measures, we did not find evidence of significant moderation. Thus, the theory constructs predicted intention and PEB similarly across sex and exercise groups.     

Teachers' perspectives on the challenges of teaching physical education in urban schools: the student emotional filter

The purpose of this study was to analyze how the challenges of urban schools influence physical education teachers' emotional understanding and connections with their students and the implications on their teaching. Sixty-one elementary physical educators from an urban school district in the midwestern U.S. were interviewed multiple times (N = 136) over 3 years using interpretive methodology. Teachers reported five unique challenges that significantly shaped their thinking about students and their careers, along with strategies they used to overcome or manage those challenges. The challenges were: (a) insufficient instructional resources, (b) implementing culturally relevant pedagogy, (c) dealing with community violence, (d) integrating more games in curricula, and (e) teaching in a culture of basketball. Implications centered on the guilt-inducing nature of urban teaching, developing an informed and realistic vision of urban physical education, and the role of teacher preparation and professional development.     

体育课教学的困惑与变式

众所周知,升学率作为学校办学质量的代表性标志,它的高低直接与学校的生存发展,社会声望相关联。在这种事实面前,凡做为升学考试的科目以及该科目的教师,在人们（学生、家长、领导等）的心目中,就获得较高的身价。而与升学考试相关不大的课程及教师就处于无足轻重的尴尬境地。在这样一种不合理的体系中,学校体育的改革,路在何方？体育课教学的价值究竟怎么去体现？这是无法回避的障碍与困惑。     

对我国职业篮球联赛13年发展演变的研究

采用文献资料、访谈调查、数理统计和逻辑分析等方法,对我国职业篮球联赛——CBA联赛13年发展过程中影响竞赛质量主导因素——球队、教练员、队员和外援的发展变化历程进行分析,将对提高联赛水平和质量具有重要的指导意义。结果表明：CBA联赛13年发展过程中,球队数量保持稳定增长,国内球员平均身高和体重呈稳定增长趋势,年龄结构趋向年轻化,引进外援整体水平较高,教练员团队逐渐壮大,一批优秀的年轻教练员逐渐成熟,聘请的外籍教练员普遍水平较高,但整体效果不佳。     

国外富翁如何“调教”富二代

近期社会上接连出现"富二代"违法犯罪的新闻,这一社会现象越发引起人们的关注.在西方国家,也有富二代的问题.国外的富二代同样有类似不劳而获、有此生花不完的金山银山、普遍责任感比较差等特点.如何让富二代有所担当?是富二代的上辈思虑和挠头的问题,由此衍生出五花八门的"调教"富二代的方法. 诺兰公爵,一位拥有三亿英镑的贵族,其家产源于继承.但其父的遗嘱中,竟然有一条,规定诺兰的儿子希伯来16岁这年继承100万遗产,18岁开始,每年从他父亲那里支取25万英镑的生活费.这项遗嘱,当然体现了祖父对孙儿的爱.     

Evaluation of a university course to promote physical activity: project GRAD

Project GRAD (Graduate Ready for Activity Daily) evaluates a university course to promote physical activity. In a randomized study, 338 university seniors participated in either an intervention or control course for academic credit, and posttest data were collected on 321. The control course was knowledge-oriented. The intervention course taught behavior change skills in weekly lectures and peer-led labs. Physical activity was assessed with 7-Day Physical Activity Recall interviews. The intervention had no significant effects on men. Among women, the intervention increased total physical activity during leisure, strengthening exercises, and flexibility exercise. This university course had the intended effects of promoting healthful patterns of physical activity among women, but no effects were observed on men, who were more active than women at baseline.     

The comparative importance of books: clinical psychology in the health sciences library

Clinical psychology has received little attention as a subject in health sciences library collections. This study seeks to demonstrate the relative importance of the monographic literature to clinical psychology through the examination of citations in graduate student theses and dissertations at the Fordham Health Sciences Library, Wright State University. Dissertations and theses were sampled randomly; citations were classified by format, counted, and subjected to statistical analysis. Books and book chapters together account for 35% of the citations in clinical psychology dissertations, 25% in nursing theses, and 8% in biomedical sciences theses and dissertations. Analysis of variance indicates that the citations in dissertations and theses in the three areas differ significantly (F = 162.2 with 2 and 253 degrees of freedom, P = 0.0001). Dissertations and theses in biomedical sciences and nursing theses both cite significantly more journals per book than the dissertations in clinical psychology. These results support the hypothesis that users of clinical psychology literature rely more heavily on books than many other users of a health sciences library. Problems with using citation analyses in a single subject to determine a serials to monographs ratio for a health sciences library are pointed out.