A comparison of four treadmill protocols for determination of maximum oxygen uptake in 10- to 12-year-old boys

Little information is available regarding the relative effectiveness of various treadmill exercise protocols in eliciting maximal oxygen consumption (VO2 max) values in children. In this study of 10- to 12-year-old boys, running protocols produced significantly higher VO2 max levels compared with walking, but there were no important differences in continuous, intermittent, and handrail-supported running schedules. The intermittent run protocols, however, prolonged the test duration. Studies examining VO2 max in children should utilize standard criteria for demonstrating peak oxygen intake. In this study criteria of VO2 plateau, peak heart rate over 198 and respiratory quotient exceeding 1.0 were satisfied most commonly with running protocols.     

Validity of a physical activity computer questionnaire in 12- to 18-year-old boys and girls

The reliability and validity of a physical activity computer questionnaire of a usual week were studied in 33 adolescents between 12 and 18 years of age. Intraclass correlation coefficients and Kappa values were calculated to verify test-retest reliability. Validity was investigated by calculating Pearson correlation coefficients between the questionnaire and the Computer Science and Applications uniaxial accelerometer (CSA). Accelerometer data were obtained during seven successive days (sum and mean counts, estimated MET). Intraclass coefficients generally exceeded 0.70 and all Kappa values but one varied between 0.44 and 1.00. Transport variables (active transport from and to school, and during leisure time) showed no relationship with CSA. Sport participation during leisure time, sport participation summed with total transport, and the frequencies of moderate and hard activity were significantly correlated with CSA (r between 0.48 and 0.78). These data indicate that the physical activity computer variables provide reliable information. Moreover, sport participation (and summed with total transport) and the frequencies of moderate and hard activity provide valid data about adolescents' usual week physical activity, based on CSA comparison.     

Development of motor abilities of trained Indian boys of 9-16 years of age.

A study was conducted on 294 north Indian boys of 9-16 years of age. The boys were studying in a sports school and were doing systematic sports training twice a day. The following tests were conducted on the subjects: Standing broad jump, standing shot put (4 kg), 40 m sprint, zig-zag run, forward bend and reach and endurance run. The results indicated that the spurt in height, weight and motor abilities of Indian boys is less pronounced than in boys of Europe and America.     

Effect of 12 weeks of strenuous physical training on hematological changes

It is well known that sports and physical exercise affect the hemoglobin (Hb) concentrations; however, the factors affecting the hematological changes after intense exercise are still not fully elucidated. In the present study, we examined the hematological and biochemical parameters of nine young male soldiers participating in a 12-week ranger training program. The platelet counts before the training showed a strong in-verse correlation with the Hb concentrations after the training (r = -0.829, p < 0.01). Furthermore, the Hb concentrations of the subjects whose platelet counts were more than 25.0 x 10(4)/microL decreased significantly after the training (p < 0.05). Our findings suggest that an association exists between high platelet counts even within the normal range before strenuous physical training and the risk of a subsequent decrease in the Hb concentrations.     

Changes in gait patterns in 10-year-old boys with increasing loads when walking on a treadmill

This study examined the gait pattern, heart rate and blood pressure in children carrying school bags of 0 (as control), 10, 15 and 20% of their own body weight whilst walking on a treadmill. When compared to the 0% load condition, the 20% load condition induced a significant increase in trunk forward lean, double support and stance duration, and decreased trunk angular motion and swing duration and a prolonged blood pressure recovery time. The 15% load condition induced a significant increase in trunk forward lean and prolonged blood pressure recovery time. No significant difference was found in the measured parameters between the 10 and 0% load conditions. We concluded that back pack weight should not exceed 10% of body weight in 10-year-old boys.     

Intraindividual allometric development of aerobic power in 8- to 16-year-old boys

PURPOSE: The aims of this study are two-fold: first, to analyze intraindividual allometric development of aerobic power of 73 boys followed at annual intervals from 8 to 16 yr, and second, to relate scaled aerobic power with level of habitual physical activity and biological maturity status. METHODS: Peak VO2 (treadmill), height, and body mass were measured. Biological maturity was based on age at peak height velocity (PHV) and level of physical activity was based on five assessments between 11 and 15 yr and at 17 yr. Interindividual and intraindividual allometric coefficients were calculated. Multilevel modeling was applied to verify if maturity status and activity explain a significant proportion of peak VO2 after controlling for other explanatory characteristics. RESULTS: At most age levels, interindividual allometry coefficients for body mass exceed k = 0.750. Intraindividual coefficients of peak VO2 by body mass vary widely and range from k' = 0.555 to k' = 1.178. Late maturing boys have smaller k' coefficients than early maturing boys. CONCLUSION: Peak VO2 is largely explained by body mass, but activity level and its interaction with maturity status contribute independently to peak VO2 even after adjusting for body mass.     

The relative contribution of strength and physique to running and jumping performance of boys 7-11.

The purpose of this study was to determine the association of static strength with motor performance of 7 through 11 year old boys (N = 60) after accounting for differences in physique, i.e., body size, shape, and composition. Static strength measures included thigh extension, leg extension and plantar flexion measured by electronic transducer and back lift, leg lift, and right and left grips measured by spring dynamometer. Measures of body composition consisted of fat estimated from triceps, subscapsular and calf skinfolds, and fat-free body weight estimated from potassium-40 measurements. Body structure consisted of skeletal widths, and segment girths, lengths and volumes. The dependent variables were vertical jump, standing broad jump, 50-yard dash, 600-yard run and mile run. The measures of strength increased the variance accounted for from 10 to 23% over that when body size, composition and structure were used without strength. An exception was vertical jump where no increase in the variance accounted for was found with the addition of strength variables. The regression equations determined for the sample of 60 boys rendered multiple R's ranging from 0.64 (mile run) to 0.75 (50-yard dash). It was concluded that strength has a significant relation to motor performance and that its contribution can be better assessed after accounting for differences in body size, shape, and composition.     

Evaluation of specific anaerobic power in 12–14-year-old male rowers

No previous study had applied the modified Wingate rowing test to young athletes (i.e. children and adolescents). The aims of this study were to evaluate the trial-to-trial reliability of a rowing-modified Wingate test in a group of 12–14-year-old rowers (n = 98) and to compare anaerobic power values among the 12-, 13-, and 14-year-old rowers after accounting for differences in physical maturity and body size. Each subject performed two “all-out” 30-s trials on a Concept II rowing ergometer. The trials were separated by a 15-min active recovery period, which included walking and stretching and ensured the participants’ full recovery. The test proved to be highly reliable, with coefficients of variations of 2.4 and 2.9% (CI = 2.1–3.4%) and intraclass correlation coefficients of 0.994 and 0.996 (CI = 0.991–0.997) for mean power and peak power, respectively. The ANCOVA analyses accounting for differences in body size and level of physical maturity (assessed using indices of pubic hair) and the Bonferroni post hoc tests identified the 14-year-olds as having significantly greater adjusted mean power and peak power values (P < 0.01) than the other two age groups, while the differences between the 12- and 13-year-olds in terms of mean power and peak power were not significant. Our findings indicate (1) that the rowing-modified Wingate test may be reliably used for the assessment of specific anaerobic performance in 12–14-year-old rowers and (2) that factors other than physical maturity and body size are partly responsible for the increase in anaerobic power during growth.     

不同走跑锻炼方案对中老年人血脂异常的调节作用

目的:探讨改善血脂异常的适宜运动方案.方法:以中老年血脂异常患者为研究对象,以走跑锻炼为主要运动方式,根据受试者年龄、性别及功能能力(F.C.),将其随机分为对照组和锻炼组,其中锻炼组又按F.C.和血清总胆固醇含量测定值进行配伍,分为中等强度长时间(60～70%F.C.,60分钟/天)锻炼组(ML)、中等强度短时间(60～70%.F.C,30分钟/天)锻炼组(MS)、低强度长时间(50～60%.F.C,60分钟/天)锻炼组(LL)和低强度短时间(50～60%.F.C,30分钟/天)锻炼组(LS).观察实施不同走跑锻炼方案后各锻炼组血脂的变化情况.每周5天,锻炼期为2个月.结果:2个月后,对照组血清TG、TC、LDL-C和ApoB水平显著升高,ApoAL/ApoB比值显著下降(P＜0.01,P＜0.05).各锻炼组血清VLDL-C和TC/HDL-C比值均显著下降(P＜0.05,P＜0.01),ML、MS、LL和LS组血清VLDL-C下降幅度分别为26%、27%,34%、21%.ML、LL和LS组血清HDL-C含量显著升高(P＜0.05),分别较锻炼前升高10%、7%和6%.低强度锻炼组血清ApoAI/ApoB比值显著升高(P＜0.05,P＜0.01).结果表明:走跑锻炼是改善血脂异常的有效运动方式,走跑锻炼的运动强度不是影响血脂异常改善效果的主要因素,中等强度(60～70%F.C.)和低强度(50～60%F.C.)走跑锻炼均可改善血脂异常.     

Effect of 14 weeks of resistance training on lipid profile and body fat percentage in premenopausal women

OBJECTIVES: To study the effects of a supervised, intensive (85% of one repetition maximum (1-RM)) 14 week resistance training programme on lipid profile and body fat percentage in healthy, sedentary, premenopausal women. SUBJECTS: Twenty four women (mean (SD) age 27 (7) years) took part in the study. Subjects were randomly assigned to either a non-exercising control group or a resistance exercise training group. The resistance exercise training group took part in supervised 45-50 minute resistance training sessions (85% of 1-RM), three days a week on non-consecutive days for 14 weeks. The control group did not take part in any structured physical activity. RESULTS: Two way analysis of variance with repeated measures showed significant (p < 0.05) increases in strength (1-RM) in the exercising group. There were significant (p < 0.05) decreases in total cholesterol (mean (SE) 4.68 (0.31) v 4.26 (0.23) mmol/1 (180 (12) v 164 (9) mg/dl)), low density lipoprotein (LDL) cholesterol (2.99 (0.29) v 2.57 (0.21) mmol/l (115 (11) v 99 (8) mg/dl), the total to high density lipoprotein (HDL) cholesterol ratio (4.2 (0.42) v 3.6 (0.42)), and body fat percentage (27.9 (2.09) v 26.5 (2.15)), as well as a strong trend towards a significant decrease in the LDL to HDL cholesterol ratio (p = 0.057) in the resistance exercise training group compared with their baseline values. No differences were seen in triglycerides and HDL cholesterol. No changes were found in any of the measured variables in the control group. CONCLUSIONS: These findings suggest that resistance training has a favourable effect on lipid profile and body fat percentage in healthy, sedentary, premenopausal women.     

Tissue Doppler assessment of ventricular function during cycling in 7- to 12-yr-old boys

PURPOSE: Studies utilizing submaximal supine exercise have indicated that tissue Doppler imaging (TDI) may be useful for assessing ventricular systolic and diastolic function during exercise and might offer a means of detecting patients with early myocardial dysfunction. This investigation of 14 healthy boys ages 7-12 yr was designed to assess measures of inotropic and lusitropic function during maximal upright cycle exercise. METHODS: Color tissue Doppler imaging (S and E' waves, indicative of systolic and diastolic function, respectively), stroke volume, and mitral peak inflow velocity (E wave) were recorded at rest and during a progressive upright cycle test to exhaustion. RESULTS: Values of TDI-S and TDI-E' were obtained at exhaustive exercise in all but one subject. Mean value of S rose 163% (3.8+/-1.2 to 10.0+/-2.5 cm.s), and average E' increased by 92% (-6.3+/-2.2 to -12.1+/-3.2 cm.s). No significant changes were observed in the ratio of E' to mitral peak flow velocity (E), suggesting that left ventricular end-diastolic pressure remained stable. CONCLUSIONS: These data indicate that measurement of TDI is feasible during maximal upright exercise, and velocities obtained may provide insights into ventricular systolic and diastolic functional capacity.     

Influence of ethnic origin on predictive parameters of performance in sprint running in prepubertal boys

Afro-American and Caribbean athletes have long dominated sprint running, although the reasons for their disproportionate success remain unclear. The studies of sprinting ability in blacks versus whites have shown contradictory results. This study compared the anthropometric measurements and the physical test results (vertical jump and sprint) of Caucasian and Afro-Caribbean prepubertal boys. Seventeen healthy untrained prepubertal boys, 8 Caucasians and 9 Afro-Caribbeans (11.49 +/- 0.74 years) performed vertical jump tests (a countermovement jump according to the Sargent method, using Abalakov material) and short sprints (30 m). Age, height, weight, and fat mass percentage were also recorded. The sprints were filmed to determine the number of strides over the 30 m. No significant difference was noted for sprint performance between the Caucasians and Afro-Caribbeans (respectively, 5.59 seconds +/- 0.44 vs. 5.51 s +/- 0.50). The predictors of sprint performance differed between the two groups: the vertical jump test was the main predictor for the Caucasian group, whereas the stride number/height ratio was the main predictor for the Afro-Caribbean group. This last group had better ratio (0.14 +/- 0.15 vs. 0.16 +/- 0.02, p < 0.05) and better jump test results (36.77 cm +/- 2.90 vs. 31.12 cm +/- 4.76, p < 005). The prepubertal Afro-Caribbeans seemed to be endowed to run faster but they did not. We hypothesize that they were unable to use their greater leg strength to develop an optimal stride. Further study is needed to investigate what occurs at other maturational stages.