Aerobic power and pubertal peak height velocity in Belgian boys

To determine the cardiorespiratory response to maximal exercise before, during and after the pubescent growth spurt, thirty boys were tested at yearly intervals over a period of six consecutive years. For each individual, peak height velocity (PHV) was determined. The age at PHV (X = 13.6 years) was taken as a standard of maturation. The results from all subjects at 1.5 and 0.5 years before and 0.5 and 1.5 years after PHV are presented. The highest oxygen uptake (VO2) obtained during an incremental bicycle ergometer test to voluntary exhaustion was taken as peak oxygen uptake (VO2 peak). Across each of the four years studied, mean VO2 peak (min = 49.6; max = 52.5 ml.kg-1.min-1) and mean heart rate (HR) at VO2 peak (min = 190; max = 192) did not change significantly as a function of PHV. On the other hand, the respiratory quotient at VO2 peak increased considerably from mean minima and maxima of 0.99 and 1.01 before PHV to 1.07 and 1.10 after PHV. Ventilatory equivalent for VO2 (VE/VO2), taken as an indicator of ventilatory economy, seemed to be unaffected by the maturation process. The steepest increase in circumpubertal oxygen pulse was found one year after PHV. Average stability coefficients (r), calculated from the inter-years correlations were high for height (r = 0.95), weight (r = 0.92), HR at VO2 peak (r = 0.74), VO2 peak in 1/min (r = 0.71), oxygen pulse (r = 0.68) and tidal volume (r = 0.64).     

Longitudinal study of ventilation threshold and maximal O2 uptake in athletic boys

Ventilation threshold (VET) and peak O2 uptake (VO2max) were determined annually from ages 11 to 15 yr in 18 athletic boys. The treadmill protocol consisted of a constant-run speed with grade increments every second minute. Ventilation, VO2, and CO2 production were measured using online open-circuit spirometry. Coefficients of variation for determination of VO2max and VET were 3.4 and 5.6%, respectively. VO2max increased across age 11-15 yr, from 60.8 to 68.0 ml X kg-1 X min-1. VET at 11 yr was 34.4 and at 15 yr 41.9 ml X kg-1 X min-1, thus increasing from 56 to 62% of VO2max. Previous studies of children have shown a decline of VET relative to VO2max across age; however, in the present study the increase may have been due to the training of the boys in competitive athletics. However, the trained youth did not achieve the high relative threshold of trained adults. Across age, both VO2max and VET scaled to weight to the power 1 (in a log-log transformation). The increase in VO2max (l/min) showed greatest increments corresponding to gains in size (a growth curve), whereas increases of VET were consistent year to year. Thus VET was altered independently of VO2max. Factors other than size (and presumably muscle mass) such as the maturation of an enzymatic profile of fast glycolytic fibers might have an important influence on the threshold during youth.     

Aerobic power as related to body growth and training in Japanese boys: a longitudinal study

Maximal aerobic power was measured for 5-6 successive years in 50 Japanese schoolboys starting from the age of 9 or 13 yr. and for 2-3 yr in 6 superior junior runners from the age of 14 yr. A large increase in aerobic power was observed during the adolescent growth spurt for 7 schoolboys who trained between the ages of 9 and 14 yr. Aerobic power for 43 average schoolboys increased from 45.0 to 52.2 ml/kg.min between the ages of 13 and 17 yr. The aerobic power of 6 superior junior runners increased from 63.4 to 73.4 ml/kg.min between the ages of 14 and 17 yr. A remarkable increase in aerobic power was not observed in trained boys before the age of peak height growth velocity (PHV). Beginning approximately 1 yr prior to the age of PHV and thereafter, training effectively increased aerobic power above the normal increase attributable to age and growth. The highly developed aerobic power found in superior junior runners may have been derived from strenuous training and partially by genetically superior endowment.     

Modeling growth and maturation changes in peak oxygen uptake in 11-13 yr olds.

The influence of gender, growth, and maturation on peak O(2) consumption (VO(2 peak)) in 11-13 yr olds were examined by using multilevel regression modeling. Subjects were 119 boys and 115 girls, aged 11.2 +/- 0.4 (SD) yr at the onset of the study. Sexual maturation was classified according to Tanner's indexes of pubic hair. VO(2 peak) was determined annually for 3 yr. The initial model identified body mass and stature as significant explanatory variables, with an additional positive effect for age and incremental effects for stage of maturation. A significant gender difference was apparent with lower values for girls, and an age-by-gender interaction indicated a progressive divergence in boys' and girls' VO(2 peak). Subsequent incorporation of the sum of two skinfold thicknesses into the model negated stature effects, reduced the gender term, and explained much of the observed maturity effects. The body mass exponent almost doubled, but the age-by-gender interaction term was consistent with the initial model.     

Scaling peak VO2 to body mass in young male and female distance runners.

This study examined age- and sex-associated variation in peak oxygen consumption (VO2) of young male and female distance runners from an allometric scaling perspective. Subjects were from two separate studies of 9- to 19-yr-old distance runners from the mid-Michigan area, one conducted between 1982 and 1986 (Young Runners Study I, YRS I) and the other in 1999-2000 (Young Runners Study II, YRS II). Data from 27 boys and 27 girls from YRS I and 48 boys and 22 girls from the YRS II were included, and a total of 139 and 108 measurements of body size and peak VO2 in boys and girls, respectively, were available. Subjects were divided into whole year age groups. A 2 x 9 (sex x age group) ANOVA was used to examine differences in peak VO2. Intraindividual ontogenetic allometric scaling was determined in 20 boys and 17 girls measured annually for 3-5 yr. Allometric scaling factors were calculated using linear regression of log-transformed data. Results indicated that 1) absolute peak VO2 increases with age in boys and girls, 2) relative peak VO2 (ml x kg(-1) x min(-1)) remains relatively stable in boys and in girls, 3) relative peak VO2 (ml x kg(-0.75) x min(-1)) increases throughout the age range in boys and increases in girls until age 15 yr, and 4) peak VO2 adjusted for body mass (ml/min) increases with age in boys and girls. The overall mean cross-sectional scaling factor was 1.01 +/- 0.03 (SE) in boys and 0.85 +/- 0.05 (SE) in girls. Significant age x sex interactions and significant scaling factors between sexes identify the progressive divergence of peak VO2 between adolescent male and female distance runners. Mean ontogenetic allometric scaling factors were 0.81 [0.71-0.92, 95% confidence interval (CI)] and 0.61 (0.50-0.72, 95% CI) in boys and girls, respectively (P = 0.002). There was considerable variation in individual scaling factors (0.51-1.31 and 0.28-0.90 in boys and girls, respectively). The results suggest that the interpretation of growth-related changes in peak VO2 of young distance runners is dependent upon the manner of expressing peak VO2 relative to body size and/or the statistical technique employed.     

Forty years trends in timing of pubertal growth spurt in 157,000 Danish school children

Background

Entering puberty is an important milestone in reproductive life and secular changes in the timing of puberty may be an important indicator of the general reproductive health in a population. Too early puberty is associated with several psychosocial and health problems. The aim of our study was to determine if the age at onset of pubertal growth spurt (OGS) and at peak height velocity (PHV) during puberty show secular trends during four decades in a large cohort of school children.

Methods and Findings

Annual measurements of height were available in all children born from 1930 to 1969 who attended primary school in the Copenhagen Municipality. 135,223 girls and 21,612 boys fulfilled the criteria for determining age at OGS and age at PHV. These physiological events were used as markers of pubertal development in our computerized method in order to evaluate any secular trends in pubertal maturation during the study period (year of birth 1930 to 1969). In this period, age at OGS declined statistically significantly by 0.2 and 0.4 years in girls and boys, respectively, whereas age at PHV declined statistically significantly by 0.5 and 0.3 years in girls and boys, respectively. The decline was non-linear with a levelling off in the children born between 1940 and 1955. The duration of puberty, as defined by the difference between age at OGS and age at PHV, increased slightly in boys, whereas it decreased in girls.

Conclusion

Our finding of declining age at OGS and at PHV indicates a secular trend towards earlier sexual maturation of Danish children born between 1930 and 1969. Only minor changes were observed in duration of puberty assessed by the difference in ages at OGS and PHV.     

Kinetics of oxygen uptake and heart rate at onset of exercise in children

Requirements for cellular homeostasis appear to be unchanged between childhood and maturity. We hypothesized, therefore, that the kinetics of O2 uptake (VO2) in the transition from rest to exercise would be the same in young children as in teenagers. To test this, VO2 and heart rate kinetics from rest to constant work rate (75% of the subject's anaerobic threshold) in 10 children (5 boys and 5 girls) aged 7-10 yr were compared with values found in 10 teenagers (5 boys and 5 girls) aged 15-18 yr. Gas exchange was measured breath to breath, and phases I and II of the transition and phase III (steady-state exercise) were evaluated from multiple transitions in each child. Phase I (the VO2 at 20 s of exercise expressed as percent rest-to-steady-state exercise VO2) was not significantly correlated with age or weight [mean value 42.5 +/- 8.9% (SD)] nor was the phase II time constant for VO2 [mean 27.3 +/- 4.7 (SD) s]. The older girls had significantly slower kinetics than the other children but were also found to be less fit. When the teenagers exercised at work rates well below 75% of their anaerobic threshold, phase I VO2 represented a higher proportion of the overall response, but the phase II kinetics were unchanged. The temporal coupling between the cellular production of mechanical work at the onset of exercise and the uptake of environmental O2 appears to be controlled throughout growth in children.     

A survey on growth and sexual development of adolescent students in Changhua City: growth of body height and weight

In order to understand the physical growth and sexual development of contemporary adolescents, a cross-sectional survey was conducted during the period September 1983 to May 1984. The population came from all the pupils from 4th grade up, and all the junior and senior high students of Changhua City. By using stratified cluster sampling, 1419 boys and 1599 girls participated, ranging in age from 8 to 19 years. Body weight and height were measured. Growth spurt is a unique event during adolescence. It is well shown in the distance curves and pseudo-velocity curves of body height and weight. In boys, the growth spurt of height spanned from 12.0 to 14.8 years, with peak height velocity (PHV) at 13.5 years. In girls it was from 10.0 to 12.6 years and peaked at 11.5 years. The growth spurt of weight occurred from 12.0 to 15.9 years in boys with peak weight velocity (PWV) at 14.5 years, while girls had a growth spurt at 10.0-12.7 years with PWV at 11.5 years. Girls entered into the growth spurt about 2 years earlier, and also entered into PHV, PWV, two and three years earlier respectively than boys, while boys had a more intense and longer growth during the growth spurt than girls. Between 10.0-13.0 years girls were taller than boys, and between 12.0-13.0 years they were heavier than boys. However, from 13.5 years onward girls were soon surpassed by boys both in height and weight. Growth in height after 16.5 years in boys and after 15.5 in girls was minimal. Growth in weight in boys also became minimal after 16.5 years while girls weight even dropped a little bit after 16.5 years. At the mean age of 17.5 years, boys were 168.1 cm, girls were 156.2 cm in average, boys being 12 cm taller than girls after reaching their final height.     

Age-related augmentation of plasma catecholamines during dynamic exercise in healthy males

Although plasma norepinephrine (NE) increases with age in response to a variety of submaximal adrenergic stimuli, the effect of age on plasma catecholamine levels during maximal aerobic effort and during submaximal work at a fixed percent of peak O2 consumption (VO2) is unknown. We therefore measured NE, epinephrine (E), and VO2 at rest and during graded maximal treadmill exercise in 24 healthy male volunteers (ages 22-77 yr) from the Baltimore Longitudinal Study of Aging who were rigorously screened to exclude the presence of cardiovascular disease. At rest neither heart rate (HR) nor VO2 were age related. Resting NE (pg/ml) was not age related, but resting E (pg/ml) was higher in male subjects 68-77 yr old (group III) than in those aged 22-37 (group I) or 44-55 yr (group II), P less than 0.01. Maximal HR (beats/min) showed a strong inverse relationship to age (203.5 - 0.65 age, r = -0.80, P less than 0.001). Peak VO2 in milliliters per kilogram total body weight per minute decreased with age (47.7 - 0.23 age, r = -0.71, P less than 0.001). At maximal effort both NE (P less than 0.01) and E (P less than 0.05) were higher in group III than in either of the younger groups. At submaximal work levels NE and E also increased with age, and when normalized for relative effort at loads between 45 and 80% of peak VO2 both NE and E were higher in the group III male subjects, although statistical significance was reached for NE (P less than 0.01) but not for E (P = 0.09).(ABSTRACT TRUNCATED AT 250 WORDS)     

Sexual dimorphism in growth in the relative length of the forearm and relative knee height during adolescence

There are numerous studies concerning sexual dimorphism in body proportions, but only a few have investigated growth in the relative length of particular segments of the upper and lower limbs during adolescence. The aim of the study is an assessment of sex differences of longitudinal growth in the relative length of the forearm and knee height among adolescents. Sample involved 121 boys and 111 girls, participants of the Wroclaw Growth Study, examined annually between 8 and 18 years of age. Sexual dimorphism in six ratios: forearm length and knee height relatively to: trunk, height, and limb length were analyzed using a two‐way analysis of variance with repeated measurements. The sex and age relative to an estimate of maturity timing (3 years before, and after age class at peak height velocity [PHV]) were independent variables. All of the ratios showed significant sex differences in interaction with age relative to age at PHV. The relative length of the forearm, in boys, did not change significantly with the years relative to age at PHV, whereas in girls, was the lowest in the two first age classes and afterward significantly increased just 1 year before and during the adolescent growth spurt, remaining unchanged in further age classes. For relative knee height no clear pattern for sex differences was noticed. It is proposed that relatively longer forearms, particularly in relation to the trunk in girls, could have evolved as an adaptation to more efficient infant carrying and protection during breastfeeding.     

Metabolic and cardiovascular adjustment to arm training

Maximal and submaximal metabolic and cardiovascular measures and work capacity were studied in control (n = 7) and experimental (n = 9) subjects (S's) during arm work prior to and following 10 wk of interval arm training. These measures were oxygen uptake (VO2), minute ventilation (VE), heart rate (HR), respiratory exchange ratio (R), cardiac output (Q), stroke volume (SV), and arteriovenous oxygen difference ((a--v)O2 diff). In addition, maximal oxygen uptake (VO2max) was measured in both groups during treadmill running. Experimental S's showed significant increases (P less than 0.01) in peak VO2 (438 ml.min-1), max VE (17.7 l.min-1), max (a--v)O2 diff (20.8 ml.l-1), and work time (9.2 min) during arm ergometry, while maximum values of Q, SV, HR, and R remained unchanged. In addition, submaximal heart rates were significantly lower during arm ergometry after training. VO2max during treadmill running remained essentially unchanged. No changes in metabolic and physiological measures were noted for the controls after the 10-wk training period. The results support the concept of training specificity for VO2max, and indicate that the improvement in peak VO2 in arm ergometry reflects enhanced oxygen utilization due to an expanded (a--v)O2 diff.     

A comparison of the point of deflection from linearity of heart rate and the ventilatory threshold in the determination of the anaerobic threshold in Indian boys

The purpose of the study was to assess whether the point of deflection from linearity of heart rate (HRD) could be used as an alternative method to determine the ventilatory threshold (VT) in Indian (Bengali) boys that represents the determination of the anaerobic threshold (AT), and also to standardize an exercise test to be effective in eliciting AT in Indian (Bengali) boys by using HRD. Twenty six (26) boys with a mean age of 12.8 (+/-1.18) years performed a graded maximal exercise test on a treadmill to determine peak VO(2), HRD and VT. The mean peak VO(2), weight related peak VO(2), peak pulmonary ventilation, and peak heart rate of the boys were found to be 1.75 l/min, 47.1 ml/kg/min, 66.9 l/min and 200.2 beats/min respectively. There were no significant differences between mean VO(2), weight related VO(2), pulmonary ventilation (VE), heart rate and respiratory exchange ratio (RER) that were measured at VT and HRD. The mean VO(2) measured at VT and HRD was found to be 1.46 and 1.45 l/min, which were about 84% and 83% of their respective peak values. Linear regression analysis revealed a correlation of 0.94 (p<0.01) between VO(2) measured at VT and VO(2) measured at HRD, so the present study indicates that the point of deflection from linearity of heart rate (HRD) may be an accurate predictor of VT in most but not all boys.     

The influence of training on physical and functional growth before, during and after puberty

In boys, the ages at which growth rates for body weight, height, VO2max, maximum O2 pulse and VImax reached their peaks were approximately the same (means and SD: 14.64 +/- 0.98, 14.67 +/- 0.99, 14.71 +/- 1.59, 14.38 +/- 1.36 and 14.64 +/- 1.42 years respectively). There was a positive relationship between the peak velocities of functional capacity indicators (VO2max 0.79 +/- 0.19 1.min-1.year-1, O2 pulse max 4.1 +/- 1.20 ml.year-1, VImax 27.3 +/- 7.15 l.min-1.year-1) and the peak growth velocity of weight and/or height (weight 9.1 +/- 1.92 kg.year-1, height 9.8 +/- 1.92 cm.year-1). A positive relationship between the age at peak velocity of VO2max and O2 pulse max with the age at peak velocity for body weight was also found (r = 0.524 and 0.400 respectively). No relationship was revealed between the age at peak velocity on the one hand and the peak velocities of body weight, height, VO2max, O2 pulse or VImax on the other. Moderate training did not influence acceleration in growth--the age at peak velocity and the peaks of the growth rate did not differ in groups with a different regime of exercise (higher - n = 8, medium - n = 9, lower - n = 12; the peak velocity of VO2max--means and SD--being 0.85 +/- 0.15, 0.76 +/- 0.22 and 0.78 +/- 0.17.min-1.year-1 respectively).     

Ventilatory anaerobic threshold in healthy children. Age and sex differences

The ventilatory anaerobic threshold (VAT) during graded exercise was defined as the oxygen uptake (VO2) immediately below the exercise intensity at which pulmonary ventilation increased disproportionally relative to VO2. Since VAT is considered to be a sensitive and noninvasive measure for evaluating cardiorespiratory endurance performance, the purpose of the present study was to determine normal values in children. We examined 257 healthy children (140 boys and 117 girls) varying in age from 5.7 to 18.5 years, during treadmill exercise. The data were analyzed in relation to sex and age. In boys the lowest VO2max (ml X min-1 X kg-1) was found in the youngest age group (5-6 year). In girls, on the other hand, no significant increase occurred with age. For VAT, expressed as ml O2 X min-1 X kg-1 or as a percent of VO2max, a significant decrease was found in boys and girls with age. This suggests an increase in lactacid anaerobic capacity during growth. In contrast to observations in adults, only low correlations were found between VO2max and VAT (r = 0.28 in boys and r = 0.52 in girls), which suggests that the development of the underlying physiological mechanism does not occur at the same rate in growing children. These data provide normal values for VAT that can be used for clinical exercise testing in the pediatric age group.     

Growth attainments of well-off chandigarh children: A mixed longitudinal study

Distance and velocity pattern of growth for body weight and height of 134 well-off Chandigarh boys aged 9–17 years, and 109 girls aged 9 to 16 years were studied following a mixedlongitudinal growth study design. For both body weight and height pattern-wise, Chandigarh boys showed close similarity with their American counterparts up to about 13 years of age, while girls did so till 12 years. Where after, Chandigarh children remained lighter and shorter than those of American origin and this differential may be explained on racial grounds rather than nutritional ones since all children included in this study remained free from dietary and other health related constraints. Marginally, higher height growth attainments noticed in Chandigarh children in contrast to their other Indian counterparts during initial years of adolescence shows that Chandigarh children are in process of expressing their genetic growth potential to its full which has not yet been fully achieved. The rate (velocity) of weight and height growth in Chandigarh children remained substatially lower than their sex-matched British counterparts throught the period of study. PHV in boys measured 6.4 cm/yr. and 5.4 cm/yr. in girls. It was attained at the age of 11.5 years in girls and 12.5 years in boys. Peak weight velocity in boys averaged 3.7 kg/yr., while it measured 4.6 kg/yr. in girls. In girls (11.5 yr.), PWV too was attained earlier than boys (13.5 yr.) by two years. The shorter height and lighter weight growth attainments noticed in Chandigarh children in contrast to their Western counterparts may be attributed to slower and lesser magnitude peak growth velocities recorded in Chandigarh children. The use of values presented has been recommended to monitor and assess growth attainments of Indian children residing in the Union Territory of Chandigarh.     

Cardiovascular responses to military antishock trouser inflation during standing arm exercise

Military antishock trousers (MAST) inflated to 50 mmHg were used with 12 healthy males (mean age 28 +/- 1 yr) to determine the effects of lower-body positive pressure on cardiac output (Q), stroke volume (SV), heart rate (HR), systolic blood pressure (SBP), diastolic blood pressure (DBP), mean arterial blood pressure (MABP), total peripheral resistance (TPR), and O2 uptake (VO2) during graded arm-cranking exercise. Subjects were studied while standing at rest and at 25, 50, and 75% of maximal arm-cranking VO2. At each level, rest or work was continued for 6 min with MAST inflated and for 6 min with MAST deflated. Order of inflation and deflation was alternated at each experimental rest or exercise level. Measurements were obtained during the last 2 min at each level. Repeated-measures analysis of variance revealed significant increases (P less than 0.001) in Q, SV, and MABP and a consistent decrease in HR with MAST inflation. There was no apparent change in Q/VO2 between inflated and control conditions. There was no effect of MAST inflation on VO2 or TPR. MAST inflation counteracts the gravitational effect of venous return in upright exercise, restoring central blood volume and thereby increasing Q and MABP from control. HR is decreased consequent to increased MABP through arterial baroreflexes. The associated decrease in TPR is not observed, being offset by the mechanical compression of leg vasculature with MAST inflation.     

Gender differences in the endocrine and metabolic responses to hypoxic exercise.

This study tested the hypothesis that women would have blunted physiological responses to acute hypoxic exercise compared with men. Fourteen women taking oral contraceptives (28 +/- 0.9 yr of age) and 15 men (30 +/- 1.0 yr of age) with similar peak O(2) consumption (VO(2 peak)) values (56 +/- 1.1 vs. 57 +/- 0.8 ml x kg fat-free mass(-1) x min(-1)) were studied under hypoxic (H; fraction of inspired oxygen = 13%) vs. normoxic (fraction of inspired oxygen = 20.93%) conditions. Cardiopulmonary, metabolic, and neuroendocrine measures were taken before, during, and 30 min after three 5-min consecutive workloads at 30, 45, and 60% VO(2 peak). In women compared with men, glucose levels were greater during recovery from H (P < 0.05) and lactate levels were lower at 45% VO(2 peak), 60% VO(2 peak), and up to 20 min of recovery (P < 0.05), regardless of trial (P < 0.0001). Although the women had greater baseline levels of cortisol and growth hormone (P < 0.0001), gender did not affect these hormones during H or exercise. Catecholamine responses to H were also similar between genders. Thus the endocrine response to hypoxia per se was not blunted in women as we had hypothesized. Other mechanisms must be at play to cause the gender differences in metabolic substrates in response to hypoxia.     

Recovery O2 and blood lactic acid: longitudinal analysis in boys aged 11 to 15 years

Nineteen boys were tested annually from age 11 to 15 years. Recovery O2 (or O2 debt in l and ml X kg-1) and blood lactate ([La], mmol X l-1) were measured following supramaximal treadmill tests (20% grade) designed to stress the anaerobic energy systems maximally. The purpose was to describe the rate of development of anaerobic capacity (AnC) from pre-puberty to adolescence. AnC improved from age 11 to 15 years, as indicated by a tripling of recovery O2 (l), 80% increase in recovery O2 per kg and 45% in [La]. Changes were similar from year to year with average yearly increments in recovery O2 of 0.8 l or 9 ml X kg-1 and in [La] of 0.9 mmol X l-1. Individual data also were plotted in relation to age of peak height velocity (PHV, 12.9 +/- 1.2 years). Changes in the measures of AnC were not significantly different when related to biological rather than chronological age. Development of AnC did not show a growth function curve and was not closely correlated with size, nor was the development of AnC enhanced immediately following maturation. Thus, in this longitudinal study, recovery O2 and [La] as measures of AnC showed large increases from age 11 to 15 years, but the gains were similar year to year rather than related to size growth, per se, or hormonal influences at maturation postulated to induce qualitative changes in glycolytic potential of muscle.     

儿童身高生长追踪研究

以北京市106名儿童为样本 ,为研究各年龄生长速度的集中趋势、变异状况以及与生长速度有关的参数 ,追踪观察这些儿童自6、7岁至 18岁时共12年的身高变化 ,并做有关参数分析。报告了各年龄组身高生长速度的均值及标准差 ,该组儿童身高生长突增开始年龄 (男10.73±1 .12岁 ,女 9.00± 1.18岁 )及速度 (男4.51± 0.65cm/年 ,女 4.95± 0.79cm/年 ) ;身高生长高峰发生年龄 (男 1 3.0 7±1.08岁 ,女11.32± 1.32岁 )及速度高峰值 (男10 .01± 1.59cm/年 ,女8.13± 1.03cm/年 ) ;以及生长突增结束年龄 (男16.18± 1.02岁 ,女 13.96± 1.09岁 )。分析了最终身高与生长突增有关指标的相关关系。     

Exercise training prevents decline in stroke volume during exercise in young healthy subjects.

Stroke volume (SV) increases above the resting level during exercise and then declines at higher intensities of exercise in sedentary subjects. The purpose of this study was to determine whether an attenuation of the decline in SV at higher exercise intensities contributes to the increase in maximal cardiac output (Qmax) that occurs in response to endurance training. We studied six men and six women, 25 +/- 1 (SE) yr old, before and after 12 wk of endurance training (3 days/wk running for 40 min, 3 days/wk interval training). Cardiac output was measured at rest and during exercise at 50 and 100% of maximal O2 uptake (Vo2max) by the C2H2-rebreathing method. VO2max was increased by 19% (from 2.7 +/- 0.2 to 3.2 +/- 0.3 l/min, P less than 0.001) in response to the training program. Qmax was increased by 12% (from 18.1 +/- 1 to 20.2 +/- 1 l/min, P less than 0.01), SV at maximal exercise was increased by 16% (from 97 +/- 6 to 113 +/- 8 ml/beat, P less than 0.001) and maximal heart rate was decreased by 3% (from 185 +/- 2 to 180 +/- 2 beats/min, P less than 0.01) after training. The calculated arteriovenous O2 content difference at maximal exercise was increased by 7% (14.4 +/- 0.4 to 15.4 +/- 0.4 ml O2/100 ml blood) after training. Before training, SV at VO2max was 9% lower than during exercise at 50% VO2max (P less than 0.05). In contrast, after training, the decline in SV between 50 and 100% VO2max was only 2% (P = NS). Furthermore, SV was significantly higher (P less than 0.01) at 50% VO2max after training than it was before. Left ventricular hypertrophy was evident, as determined by two-dimensional echocardiography at the completion of training. The results indicate that in young healthy subjects the training-induced increase in Qmax is due in part to attenuation of the decrease in SV as exercise intensity is increased.