Effects of a 12-week physical activity protocol delivered by YMCA after-school counselors (Youth Fit for Life) on fitness and self-efficacy changes in 5-12-year-old boys and girls

To address reduced physical education (PE) in elementary schools, a 12-week physical activity protocol was tested on 5-12-year-old, primarily African American, girls (n = 226) and boys (n = 344) at 14 YMCA after-school care sites. The 3 times/week, 45-min session curriculum included cardiovascular, resistance, and flexibility training, in which all children could participate simultaneously, and a behavioral skills education component. After-school counselors, formerly untrained in PE methods, administered the sessions, with periodic supervision by YMCA wellness staff members. Analyses of the eight Age x Sex subsamples indicated significant improvements on body composition, strength, and endurance, both within-groups and when predicted changes due to maturation were accounted for. Exercise barriers self-efficacy significantly increased in subsamples of 9-10- and 11-12-year-old girls only. The need for replication across ethnic groups was suggested. Limitations and the need for extension of research on supplementation of elementary school PE were discussed.     

Acute effects of static stretching on characteristics of the isokinetic angle - torque relationship, surface electromyography, and mechanomyography

The aims of this study were to examine the acute effects of static stretching on peak torque, work, the joint angle at peak torque, acceleration time, isokinetic range of motion, mechanomyographic amplitude, and electromyographic amplitude of the rectus femoris during maximal concentric isokinetic leg extensions at 1.04 and 5.23 rad x s(-1) in men and women. Ten women (mean +/- s: age 23.0 +/- 2.9 years, stature 1.61 +/- 0.12 m, mass 63.3 +/- 9.9 kg) and eight men (age 21.4 +/- 3.0 years, stature 1.83 +/- 0.11 m, mass 83.1 +/- 15.2 kg) performed maximal voluntary concentric isokinetic leg extensions at 1.04 and 5.23 rad x s(-1). Following the initial isokinetic tests, the dominant leg extensors were stretched using four static stretching exercises. After the stretching, the isokinetic tests were repeated. Peak torque, acceleration time, and electromyographic amplitude decreased (P< or = 0.05) from pre- to post-stretching at 1.04 and 5.23 rad . s(-1); there were no changes (P > 0.05) in work, joint angle at peak torque, isokinetic range of motion, or mechanomyographic amplitude. These findings indicate no stretching-related changes in the area under the angle - torque curve (work), but a significant decrease in peak torque, which suggests that static stretching may cause a "flattening" of the angle - torque curve that reduces peak strength but allows for greater force production at other joint angles. These findings, in conjunction with the increased limb acceleration rates (decreased acceleration time) observed in the present study, provide tentative support for the hypothesis that static stretching alters the angle - torque relationship and/or sarcomere shortening velocity.     

Prediction of fat and fat-free mass in male athletes using dual X-ray absorptiometry as the reference method

The ability of bioelectrical impedance analysis and anthropometry to predict fat mass and fat-free mass was compared in a sample of 82 male athletes from a wide variety of sports, using dual-energy X-ray absorptiometry (DXA) as the reference method. The percent fat measured by DXA was 10.9+/-4.9% (mean +/- s), and fat mass was predicted with a standard error of the estimate of 1.7 kg for skinfolds and 2.8 kg for bioelectrical impedance analysis (P < 0.001). Fat-free mass was predicted with a standard error of the estimate of 1.7 kg for anthropometry and 2.6 kg for bioelectrical impedance analysis (P < 0.001). Regression of various individual skinfolds and summed skinfolds, to examine the effect of skinfold selection combinations by stepwise regression, produced an optimal fat mass prediction using the thigh and abdominal skinfold sites, and an optimal fat-free mass prediction using the thigh, abdominal and supra-ilium sites. These results suggest that anthropometry offers a better way of assessing body composition in athletes than bioelectrical impedance analysis. Applying the derived equations to a separate sample of 24 athletes predicted fat and fat-free mass with a total error of 2.3 kg (2.9%) and 2.2 kg (2.7%), respectively. Combining the samples introduced more heterogeneity into the sample (n = 106), and the optimal prediction of fat mass used six skinfolds in producing a similar standard error of the estimate (1.7 kg), although this explained a further 4% of the variation in DXA-derived fat. Fat-free mass was predicted best from four skinfolds, although the standard error of the estimate and coefficient of determination were unchanged.     

Comparison of 1 and 2 days per week of strength training in children

The purpose of this study was to compare the effects of 1 and 2 days per week of strength training on upper body strength, lower body strength, and motor performance ability in children. Twenty-one girls and 34 boys between the ages of 7.1 and 12.3 years volunteered to participate in this study. Participants strength trained either once per week (n = 22) or twice per week (n = 20) for 8 weeks at a community-based youth fitness center. Each training session consisted of a single set of 10-15 repetitions on 12 exercises using child-size weight machines. Thirteen children who did not strength train served as age-matched controls. One repetition maximum (1RM) strength on the chest press and leg press, handgrip strength, long jump, vertical jump, and flexibility were assessed at baseline and posttraining. Only participants who strength trained twice per week made significantly greater gains in 1RM chest press strength, compared to the control group (11.5 and 4.4% respectively, p < .05). Participants who trained once and twice per week made gains in 1RM leg press strength (14.2 and 24.7%, respectively) that were significantly greater than control group gains (2.4%). On average, participants who strength trained once per week achieved 67% of the 1RM strength gains. No significant differences between groups were observed on other outcome measures. These findings support the concept that muscular strength can be improved during the childhood years and favor a training frequency of twice per week for children participating in an introductory strength training program.     

Heat acclimation improves intermittent sprinting in the heat but additional pre-cooling offers no further ergogenic effect

The aim of this study was to determine the effect of 10 days of heat acclimation with and without pre-cooling on intermittent sprint exercise performance in the heat. Eight males completed three intermittent cycling sprint protocols before and after 10 days of heat acclimation. Before acclimation, one sprint protocol was conducted in control conditions (21.8 ± 2.2°C, 42.8 ± 6.7% relative humidity) and two sprint protocols in hot, humid conditions (33.3 ± 0.6°C, 52.2 ± 6.8% relative humidity) in a randomized order. One hot, humid condition was preceded by 20 min of thigh pre-cooling with ice packs (-16.2 ± 4.5°C). After heat acclimation, the two hot, humid sprint protocols were repeated. Before heat acclimation, peak power output declined in the heat (P < 0.05) but pre-cooling prevented this. Ten days of heat acclimation reduced resting rectal temperature from 37.8 ± 0.3°C to 37.4 ± 0.3°C (P < 0.01). When acclimated, peak power output increased by ～2% (P < 0.05, main effect) and no reductions in individual sprint peak power output were observed. Additional pre-cooling offered no further ergogenic effect. Unacclimated athletes competing in the heat should pre-cool to prevent reductions in peak power output, but heat acclimate for an increased peak power output.     

关于技术援助项目的管理问题

一、前言在七十年代和八十年代撒哈尔[sahel]地区发生两次旱灾期间,为阻止该地区旱情继续发展的援助项目就花费了75亿美元。其结果,该地区变得更贫困,饥饿程度更为严重。现在的非洲,仍然是在技术上主要依赖于外国的唯一大陆,每年支付给外国专家的各项技术服各费用就达40亿美元以上。     

中国与欧盟科技合作评述

在世界范围高技术产业技术革命推动世界经济结构发生深刻变化,围绕技术创新和技术贸易在全球激烈竞争的今天,欧联盟在经济政治方面表现出特有的凝聚力。欧联盟围绕统一大市场,货币同盟及政治同盟三大举措展开的空前的经济一体化战略正在给欧洲带来投资、消费和科技创新...     

Autonomy and children's reactions to being controlled: evidence that both compliance and defiance may be positive markers in early development

This study examined reactions of 1-year-olds and young 2-year-olds to being controlled by mothers. Mothers' supportive behavior predicted children's willing compliance. However, contrary to research with older children, defiance was also associated with variables linked to maternal competence, specifically, mothers' supportive behavior, autonomy-granting controls, and low depressive symptoms. At this age high-defiant children initiated positive interaction with mothers more than did low-defiant children. With age, children displayed more willing compliance and more active resistance (defiance, low passivity). However, developmental increases in active resistance were absent when mothers were high in depressive symptoms. Findings are consistent with the proposal that in early development active resistance to parents often reflects children's motivation to control events, not poor parenting or strained parent-child relationships.     

Perceptions and functions of play and real fighting in early adolescence

The hypothesis is tested that adolescent boys' (mean age of 12.8 years) intrasexual rough-and-tumble play (R&T) is used for dominance and intersexual R&T is used to establish heterosexual relationships. In Study 1, boys' observed R&T was related to both dominance and aggression. In the first half of the school year, R&T occurred primarily between males, possibly to establish dominance. In the second half of the year, both boys and girls engaged in R&T, possibly to establish heterosexual relationships. Counter to the hypothesis, observed aggression increased across the year. In Study 2, youngsters viewed taped R&T bouts in which they were participants or nonparticipants. Participant, more than nonparticipant, males saw R&T as related to dominance whereas participant, more than nonparticipant, females saw it as playful.     

内部社会资本、知识整合与核心能力

以北京和广州的133家企业为调查对象,对内部社会资本是否以及如何通过知识整合影响核心能力进行了实证研究。结果表明,内部社会资本需要通过知识整合对核心能力产生影响,知识整合在内部社会资本与核心能力之间起着部分中介的作用。