Associations of accelerometer-measured sedentary time,sedentary bouts,and physical activity with adiposity and fitness in children

ABSTRACT

Sedentary time (ST) has been inconsistently associated with adiposity and cardiorespiratory fitness in children in previous studies. We studied cross-sectional associations of ST, light physical activity (LPA), and moderate-to-vigorous physical activity (MVPA) with fat mass index (FMI) and cardiorespiratory fitness (estimated VO₂max). Associations were evaluated with and without considering pattern of ST by bout length. We measured ST and activity by a wrist-worn accelerometer, FMI by bioelectrical impedance, and VO₂max by Pacer test in 443 children (51.2% girls, 10.2 ± 0.6 years). Isotemporal substitution regression models estimated the effects of substituting ST, LPA, and MVPA on FMI and VO₂max. Further models repeated analyses separating ST into short (<10 min) and long (≥10 min) bouts. Only replacing ST or LPA with MVPA was consistently associated with lower FMI and greater VO₂max. When separated by bout length, only one unique association was found where replacing long ST bouts with short ST bouts was associated with lower FMI in girls only. In conclusion, activity pattern is associated with adiposity in girls and fitness in boys and girls. Separating ST into long and short ST bouts may be of minimal importance when assessing associations with adiposity and fitness using wrist-worn accelerometry in children.     

带缓冲器的多入口串行生产线的无阻塞最优控制

本文讨论了带缓冲器的串行生产线的无阻塞最优控制问题,给出了多入口情况下串行生产线的加工状态方程及其最优控制。     

不同水平赛艇运动员2000m模拟划中心功能及血乳酸的变化

本文研究了不同训练水平男子赛艇运动员与健康大学生进行2000m模拟划中心功能及血乳酸的变化,比较了武汉体院优秀赛艇选手与国外优秀选手存在的差距。     

O_2max速度的不同间歇训练对运动员有氧能力和3000m跑成绩的影响

最大耗氧量速度(vV.O2max)作为中长跑训练的一个强度指标可以有效地用来制定中长跑间歇训练和持续训练的训练计划和评定日常的训练效果。研究目的:通过4周vV.O2max强度的间歇训练和持续跑训练的实效性研究,首先是验证高强度的间歇训练对于提高受试者的有氧耐力方面是否优于持续跑训练;其次来评价高强度的间歇训练跑30/15组与15/15组在4周训练后对提高运动员有氧耐力和3000m跑成绩的效果优劣。研究方法:男性田径运动员18名,随机分成3组:1)40min70%v.VO2max持续跑训练组(A组);2)间歇跑15/15训练组(B组);3)间歇跑30/15训练组(C组)。训练前、后测试指标:vV.O2max、V.O2max、3000m成绩测定。研究结果:1).VO2max:间歇跑组(B组和C组)训练前、后均有显著性升高(P<0.05;P<0.01);A组训练前后无统计学意义的变化。2)vV.O2max:间歇跑组训练前后均有非常显著性的的提高(P<0.01),而A组训练前后无显著性差异。4)3000m跑成绩:C组训练前后有非常显著性的升高(P<0.01),A组和B组均有显著性升高(P<0.05)。结论:用vV.O...     

非精英篮球运动员Yo Yo间歇耐力跑和运球Yo Yo跑与最大摄氧量的关系

探讨了非精英男子篮球运动员Yo-Yo间歇耐力跑测试成绩、运球Yo-Yo间歇耐力跑测试成绩的再测信度,以及与最大摄氧量的关系。受试者为31名年龄13—18岁的非精英篮球运动员。结果显示Yo-Yo跑测试速度、运球Yo-Yo跑测试速度的再测信度和典型误分别为ICC=0.76(p=0.012),TE=0.31,ICC=0.90(p=0.000 1),TE=0.23。最大摄氧量与Yo-Yo跑测试速度、运球Yo-Yo跑测试速度相关度分别为r=0.54(p=0.01),r=0.60(p=0.002)。运球Yo-Yo跑速度与Yo-Yo跑速度相关度为r=0.72(p=0.000 1),第二次运球Yo-Yo跑和Yo-Yo跑测试成绩的一致性界限范围是(-2.50,-0.93)。结果说明Yo-Yo跑测试成绩、运球Yo-Yo跑测试成绩1周内进行重测,具有较高的再现性,且Yo-Yo跑测试成绩和运球Yo-Yo跑测试成绩与最大摄氧量都具有中度相关,Yo-Yo跑测试成绩与运球Yo-Yo跑测试成绩高度显著相关。     

The effect of training on aerobic power characteristics of young cross‐country skiers

The influences of growth, training and various training methods were investigated by analysing long‐term training effects in young cross‐country and biathlon skiers (n = 129). Some athletes (n = 49) were studied six times in three years and some at least once a year during a four year period (n = 48). During three summer training periods skiers emphasized either intensive training or distance training or continued to train normally. The results indicated that maximal oxygen uptake (VO₂ max) and heart volume increased between 15 and 20 years of age and the most significant changes in heart volume were observed between 16 and 18 years of age. International level skiers were able to increase their VO₂ max and heart volume even after 20 years of age. Anaerobic threshold (AT, ml kg^‐1 min^‐1) increased like VO₂ max but when expressed as a percentage of VO₂ max, the AT was similar in every age group over 16 years of age. Intensive training at the intensity of anaerobic threshold or higher was observed to be most effective in producing improvements in VO₂ max. Low‐intensity distance training was more effective in producing improvements in anaerobic threshold.     

An Analysis of the Validity of the Three-Mile Run as a Field Test of Aerobic Capacity in College Males

Abstract

The purpose of the present investigation was to examine the concurrent and construct validity of the three-mile (4.83 km) run as afield test of aerobic capacity. Subjects included 109 college-aged males whose three-mile run time (M = 1310.31 ± 184.48 s) was measured. Fifty of the subjects were given a maximal treadmill stress test, and their peak oxygen consumption (VO₂peak) (M = 54.23 ± 7.08 ml.kg^?1.min^?1) was measured. The three-mile run was conducted on an outdoor 0.25 mile (0.425 km) track, and split tunes were recorded each 110 yds (100.32 m) for the first and last laps and total time was recorded for laps 2 through 11. The correlation coefficient between the run time and VO₂peak was -.58, indicating only moderate concurrent validity for the run as afield test for aerobic capacity. A factor analysis conducted on the split time data revealed a three-factor structure of a stable pace phase, an initial sprint, and a final sprint with the stable pace factor accounting for most of the common factor variance (69%). The three-mile run time was used to discriminate successfully between two known groups of subjects in aerobic capacity. These data provide a degree of support for the construct validity of the three-mile run as afield test of aerobic capacity.     

Effect of Optimized and Standard Cycle Ergometry on VO2max in Trained Cyclists and Runners

Abstract

This study contrasted prepractice modeling with either the perceptual component (perceptual modeling) or the motor component (movement pattern) of a coincident-timing task to determine whether experiencing the modalities singly or in combination enhanced timing performance on initiation of active practice. The motor component was a 60-cm right-to-left arm movement coincident with the illumination of lights on a Bassin timer runway to displace a barrier as the final runway light was illuminated. Four groups were compared (n = 12 per group). A perceptual modeling group passively viewed stimulus runway lights prior to attempting the task. A motoric modeling group viewed a videotape prior to practice of a model performing the motor component of the skill with zero timing error. A perceptual modeling plus motoric modeling group experienced both modeling modalities prior to performance. Finally, a no modeling group simply initiated practice on the task without modeling. Results indicated that the groups experiencing perceptual modeling initiated practice with significantly less average timing error and variability. Thus, perceptual modeling appeared to be at least as important as motoric modeling as a source of prepractice information to make available to a learner to optimize coincident-timing skill acquisition.     

Effect of Toe Clips during Bicycle Ergometry on [Vdot]O2 max

Abstract

Previous investigators have yielded conflicting results in testing the hypothesis that the use of toe clips during bicycle ergometry produces a higher maximal oxygen uptake ([Vdot]O ₂ max) than testing without toe clips. Eight men, four competitive cyclists and four competitive distance runners volunteered to participate in three randomized [Vdot]O ₂ max tests: 1) a treadmill running lest, 2) a bicycle ergometer test using standard toe clips, and 3) a test on the same ergometer without toe clips. The highest mean [Vdot]O ₂ max was observed in the treadmill condition as expected. However, no statistically significant difference in mean [Vdot]O ₂ max or performance time was observed between the toe-clip and no toe-clip conditions. Based on these results, the research hypothesis was rejected and no favorable physiological effect may be attributed to the use of toe clips.     

Effect of Caffeine Ingestion on Cardiorespiratory Endurance in Men and Women

Abstract

The effect of caffeine ingestion on submaximal endurance performance of 15 females and 13 males was investigated. After completing a [Vdot]O ₂ max test, each subject performed two submaximal cycling tests at approximately 75% of [Vdot]O ₂ max to exhaustion. For the caffeine (C) trials, 300 mg of caffeine was added to 250 ml of decaffeinated coffee and ingested one hour prior to the exercise. The decaffeinated (D) trial involved consuming 250 ml of decaffeinated coffee an hour prior to the test. The C and D trials were administered randomly using a standard double blind design. Physiological parameters were monitored each 9, 10, and 11 minute intervals throughout each trial and averaged. As expected the [Vdot]O ₂ (L · min ^?1 ), [Vdot]E and work outputs (kgm) were significantly (p < 0.001) higher for the males than the females. All other variables, time to exhaustion, [Vdot]O ₂ (ml · kg · min ^?1 ), R, HR, and rating of perceived exertion (RPE) were not significantly (p > 0.05) different between the sexes for either the C or D trials. Time to exhaustion was 14.4 and 3.1% longer for the C trials for the females and males, respectively, however these increases were not significant (p > 0.05). Furthermore, there were no significant differences (p > 0.05) for any of the measured variables during successive 10 minute work intervals between the C and D trials for either sex. These results do not support the general use of caffeine in moderate amounts as an ergogenic aid for either males or females, but from a practical point it appears that caffeine may have an ergogenic effect on specific individuals.