Oxygen uptake during running as related to body mass in circumpubertal boys: a longitudinal study

Summary To investigate the effect of endurance training on physiological characteristics during circumpubertal growth, eight young runners (mean starting age 12 years) were studied every 6 months for 8 years. Four other boys served as untrained controls. Oxygen uptake ( O ₂) and blood lactate concentrations were measured during submaximal and maximal treadmill running. The data were aligned with each individual's age of peak height velocity. The maximal oxygen uptake ( O _2max; ml · kg^–1 · min^–1) decreased with growth in the untrained group but remained almost constant in the training group. The oxygen cost of running at 15 km · h^–1 ( O ₂₁₅, ml · kg^–1 · min^–1) was persistently lower in the trained group but decreased similarly with age in both groups. The development of O _2max and O ₂₁₅ (1 · min^–1) was related to each individual's increase in body mass so that power functions were obtained. The mean body mass scaling factor was 0.78 (SEM 0.07) and 1.01 (SEM 0.04) for O _2max and 0.75 (SEM 0.09) and 0.75 (SEM 0.02) for O ₂₁₅ in the untrained and trained groups, respectively. Therefore, expressed as ml · kg^–0.75 · min^–1, O ₂₁₅ was unchanged in both groups and O _2max increased only in the trained group. The running velocity corresponding to 4 mmol · 1^–1 of blood lactate ( _la4) increased only in the trained group. Blood lactate concentration at exhaustion remained constant in both groups over the years studied. In conclusion, recent and the present findings would suggest that changes in the oxygen cost of running and O _2max (ml · kg^–1 · min^–1) during growth may mainly be due to an overestimation of the body mass dependency of O ₀₂ during running. The O ₂ determined during treadmill running may be better related to kg^0.75 than to kg¹.     

Modelling height in adolescence: a comparison of methods for estimating the age at peak height velocity

Background: Controlling for maturational status and timing is crucial in lifecourse epidemiology. One popular non-invasive measure of maturity is the age at peak height velocity (PHV). There are several ways to estimate age at PHV, but it is unclear which of these to use in practice.

Aim: To find the optimal approach for estimating age at PHV.

Subjects and methods: Methods included the Preece &; Baines non-linear growth model, multi-level models with fractional polynomials, SuperImposition by Translation And Rotation (SITAR) and functional data analysis. These were compared through a simulation study and using data from a large cohort of adolescent boys from the Christ’s Hospital School.

Results: The SITAR model gave close to unbiased estimates of age at PHV, but convergence issues arose when measurement error was large. Preece &; Baines achieved close to unbiased estimates, but shares similarity with the data generation model for our simulation study and was also computationally inefficient, taking 24?hours to fit the data from Christ’s Hospital School. Functional data analysis consistently converged, but had higher mean bias than SITAR. Almost all methods demonstrated strong correlations (r?>?0.9) between true and estimated age at PHV.

Conclusions: Both SITAR or the PBGM are useful models for adolescent growth and provide unbiased estimates of age at peak height velocity. Care should be taken as substantial bias and variance can occur with large measurement error.     

Oxygen transport system during exhaustive exercise in Japanese boys

Summary The study was designed to investigate the age-related increase in maximal oxygen uptake with special reference to the other physiological parameters (ventilation, pulmonary diffusing capacity, cardiac output etc.). 77 normal boys aged 10–18 years were tested by the progressive loading method on a bicycle ergometer. O₂ max increased by approximately 55% with age from 10–18 years. The increase in O₂ max was accompanied with increase in ventilation (49%), pulmonary diffusing capacity (45%) and cardiac output (5%).     

中国人群胎儿大脑中动脉峰值流速特点的研究

目的建立应用超声多谱勒技术测量各孕周胎儿大脑中动脉峰值血流速度(middle cerebral artery peak systolic velocity,MCV-PSV)的正常值。方法对1197例次的胎儿进行各孕周大脑中动脉峰值血流速度进行测量,计算中位数,百分位数,1.5倍中位数(multiples of the median,MOM表示)。结果胎儿大脑中动脉峰值血流速度随着孕周增加而升高。结论利用这不同孕周正常值数据,算出1.5倍中位数值作为判断胎儿宫内贫血状态的指标。     

Changes in height and motor performance relative to peak height velocity: A mixed-longitudinal study of Spanish boys and girls

Longitudinal changes in stature and motor performance were studied in an adolescent sample of 36 boys and 53 girls. Peak height velocity (PHV) was determined in 28 boys and 38 girls using non-smoothed polynomials. The estimations of PHV and the age-at—PHV are, respectively, 11.4 ± 2.2 cm/yr and 13.0 ± 0.63 years (boys), and 8.7 ± 1.6 cm/yr and 12.4 ± 0.57 years (girls). Performances in explosive strength (standing long jump; medicine ball throw) and flexibility (trunk maximal flexion) exhibit peak development during the year following PHV in both sexes. Maximal mean growth velocities in an endurance run (six minutes) occur before PHV in girls and after PHV in boys. Peak velocities in agility (4 × 6 m shuttle run), running speed (40 m dash) and abdominal strength-resistance (sit-ups for 30 seconds) occur before PHV in both sexes. There also is an acceleration of performances in these three tests after PHV. The results indicate that performance in several motor tests shows an adolescent spurt of an intensity that is proportionally comparable to the adolescent height spurt in both sexes. The dynamics of changes in motor performance in relation to PHV appears similar in both sexes. The most striking difference occurs in the endurance run. Am. J. Hum. Biol. 10:647–660, 1998. © 1998 Wiley-Liss, Inc.     

The comparison of peak oxygen uptake between swim-bench exercise and arm stroke

To compare maximal cardio-respiratory stress between swim-bench exercise (SB) and arm stroke (AS), peak oxygen uptake (VO_{2 peak}) was measured in six trained swimmers. The SB was performed at stroke frequency of 50 · min^–1. Oxygen uptake (VO₂) was measured during exercise at 3-min constant exercise intensities in SB and at 4-min constant water flow rates in AS. We measured a steady-state VO₂ within 3 or 4 min after the beginning of each exercise. The exercise intensity or the water flow rate was increased by 14.7 W or by 0.05 m · s^–1, respectively, until a levelling-off of VO₂ was observed. The VO₂ was measured by the Douglas bag method. Heart rate (HR) and blood lactate concentration ([1a^–]_b) were determined at the exercise intensity and the water flow rate at which VO_{2 peak} was obtained. At submaximal levels, VO₂ increased in proportion to exercise intensity for SB and to the water flow rate for AS. A levelling-off of VO₂ was observed in all subjects for both kinds of exercise. The VO₂ during SB [2.13 (SD 0.25)1 · min^–1] was significantly lower than that during AS [2.72 (SD 0.39)1 · min^–1] and corresponded to 78.9 (SD 7.0)% of AS VO_{2 peak}. Maximal HR during SB was also significantly lower than that during AS. No significant differences between SB and AS were found for either pulmonary ventilation or [1a^–]_b. The peak exercise duration in SB [2.4 (SD 0.5) min] was significantly shorter than that in As [3.6 (SD 0.5) min]. These results would suggest that even though both kinds of exercise use the muscles of the upper body, active muscle groups involved during SB are different and/or smaller, and maximal stress on the cardio-respiratory system is lower when compared to AS.     

The relationship of saccadic peak velocity to latency: evidence for a new prosaccadic abnormality in schizophrenia

Antisaccades have not only longer latencies but also lower peak velocities than prosaccades. It is not known whether these latency and velocity differences are related. Studies of non-human primates suggest that prosaccade peak velocity declines as latency from target appearance increases. We examined whether a similar relationship between peak velocity and latency existed in human saccades, whether it accounted for the difference in peak velocity between antisaccades and prosaccades, and whether it was affected by schizophrenia, a condition that affects antisaccade performance. Sixteen control and 21 schizophrenia subjects performed prosaccade and antisaccade trials in the same test session. In both groups antisaccades had lower peak velocities than prosaccades. Latency did not influence the peak velocities of antisaccades in either subject group. At short latencies, the peak velocities of prosaccades were also similar in the two groups. However, while prosaccade peak velocities declined minimally with increasing latency in control subjects, those in the schizophrenia group declined significantly until they reached a value similar to antisaccade peak velocities. We conclude that, in normal subjects, the effect of latency on prosaccade peak velocity is minimal and cannot account for the lower velocity of antisaccades. In schizophrenia, we hypothesize that the latency-related decline in prosaccade peak velocity may reflect either an increased rate of decay of the effect of the transient visual signal at the saccadic goal, or a failure of the continuing presence of the target to sustain neural activity in the saccadic system.     

Growth patterns and secular trends over four decades in the dynamics of height growth of Indian boys and girls in Sri Aurobindo Ashram: A cohort study

Background:?Growth parameters are widely used in the assessment of health, nutrition and physical characteristics of a population; however, there still exist uncertainties regarding ethnic variation and the influence of physical activity on growth. Due to the paucity of longitudinal data, the dynamics of the adolescent growth spurt have not been satisfactorily examined in most populations.

Aim:?The main purpose of this longitudinal study is to present the secular trends in the dynamics of height growth over four decades. In the process, this paper also aims to establish current norms for some biological parameters of growth and to address issues concerning ethnic variation and the effect of childhood physical activity on growth.

Methodology:?Three hundred and one boys and 235 girls of Indian origin who had been enrolled in the Sri Aurobindo International Centre of Education (SAICE) by age 6 and remained for at least 3 uninterrupted years were divided into four birth cohort periods. Cross-sectional and longitudinal analyses were carried out to derive distance, velocity and acceleration curves.

Results:?No significant differences were found between ethnic groups in any of the growth parameters. Over the 40-year span of this study, SAICE children prove to be taller than their Indian peers. A significant positive secular trend was seen in the height attained at all velocity turning points over the first two decades. Most pre-pubertal growth parameters in these children resemble those from developed nations.

Conclusions:?Children from most parts of India have similar genetic growth potential. After a significant positive secular trend in height attained over the first 20 years, the adult height has now plateaued. The significant difference in post-pubertal stature between the current generation and those of European origin indicates a genetic difference. Regular and graded physical activities have a salutary effect on growth. The data provide norms for healthy, active Indian child growing up in a satisfactory environment.     

Thermoregulation at rest and during exercise in prepubertal boys

Summary Thermal balance was studied in 11 boys, aged 10–12 years, with various values for maximal oxygen uptake ( ), during two standardized sweating tests performed in a climatic chamber in randomized order. One of the tests consisted in a 90-min passive heat exposure [dry bulb temperature (T _db) 45° C] at rest. The second test was represented by a 60-min ergocycle exercise at 60% of individual (T _db 20° C). At rest, rectal temperature increased during heat exposure similar to observations made in adults, but the combined heat transfer coefficient reached higher values, reflecting greater radiative and convective heat gains in the children. Children also exhibited a greater increase in mean skin temperature, and a greater heat dissipation through sweating. Conversely, during the exercise sweating-test, although the increase in rectal temperature did not differ from that of adults for similar levels of exercise, evaporative heat loss was much lower in children, suggesting a greater radiative and convective heat loss due to the relatively greater body surface area. Thermophysiological reactions were not related to in children, in contrast to adults.     

Force/velocity and power/velocity relationships in squat exercise

The purpose of this study was to describe the force/velocity and power/velocity relationships obtained during squat exercise. The maximal force (F ₀) was extrapolated from the force/velocity relationship and compared to the isometric force directly measured with the aid of a force platform placed under the subject's feet. Fifteen international downhill skiers [mean (SD) age 22.4 (2.6) years, height 178 (6.34) cm and body mass 81.3 (7.70) kg] performed maximal dynamic and isometric squat exercises on a guided barbell. The dynamic squats were performed with masses ranging from 60 to 180 kg, which were placed on the shoulders. The force produced during the squat exercise was linearly related to the velocity in each subject (r ²=0.83–0.98, P < 0.05–0.0001). The extrapolated F ₀ was 23% higher than the measured isometric force (P < 0.001), and the two measurements were not correlated. This may be attributed to the position of the subject, since the isometric force was obtained at a constant angle (90° of knee flexion), whereas the dynamic forces were measured through a range of movements (from 90° to 180°). The power/velocity relationship was parabolic in shape for each subject (r ²=0.94–0.99, P < 0.01–0.0001). However, the curve obtained exhibited only an ascending part. The highest power was produced against the lightest load (i.e., 60 kg). The maximal power (W˙ _max ) and optimal velocity were never reached. The failure to observe the descending part of the power/velocity curve may be attributed to the upper limitation of the velocities studied. Nevertheless, the extrapolation of W˙ _max from the power/velocity equation showed that it would be reached for a load close to body mass, or even under unloaded conditions. Accepted: 19 September 2000     

Relationship between plasma renin activity and physical fitness in normal subjects

Summary The relationship between plasma renin activity (PRA) at rest and physical fitness was studied in 40 normal young subjects on a liberal sodium intake.Plasma renin activity was measured in arterial blood withdrawn at the end of a 30-min period of rest in recumbency, while physical fitness was expressed by the highest oxygen uptake achieved during an uninterrupted graded exercise test performed in the sitting position on an electromagnetically braked ergometer bicycle (peak ).Log PRA correlated significantly and inversely with peak adjusted for body weight (r=–0.34; P<0.05) in single regression analysis. Using multiple regression analysis with log PRA as dependent variable and adjusted peak , age, urinary sodium excretion and mean intra-arterial pressure as independent variables, no combination of two or more independent variables yielded significant partial correlation coefficients with log PRA.This correlation suggests that PRA at rest is inversely related to the subject's physical fitness.     

The effect of shuttle test protocol and the resulting lactacidaemia on maximal velocity and maximal oxygen uptake during the shuttle exercise test

Summary The purpose of this study was to investigate the influence of the shuttle test protocol (20-MST) and the resulting lactacidaemia on maximal velocity (V _max) and maximal oxygen uptake (VO_2max). Firstly, three randomly assigned tests to exhaustion were performed by 12 subjects: the treadmill test, the 20-MST, and a continuous running track test using the same prerecorded 1-min protocol as in the 20-MST (T1). One week later, subjects performed another track test, which was conducted up to the same level of effort as attained during the 20-MST (T2). For each test, V _max, VO_2max) lactate concentration at rest and during recovery, maximal heart rate, and distance covered were determined. The results indicated that the 20-MST underestimated V _max; only Tl satisfactorily assessed V _max (F=15.49, P<0.001). At the same level of effort, the peak blood lactate concentration (t=2.7, P<0.02) and VO_2max (t=11.35, P<0.001) values were higher for the shuttle than for the continuous protocol. It was concluded that V _max was limited by the running backwards and forwards in the protocol of the shuttle test. The higher values of peak blood lactate concentration and its earlier appearance obtained for the shuttle may have been one of the limiting factors of V _max. However, the higher values of VO_2max obtained for the 20-MST were most likely due to a combination of the relative hyperlactacidaemia and the biomechanical complexities required for this type of protocol.     

Aerobic high intensity one and two legs interval cycling in chronic obstructive pulmonary disease: the sum of the parts is greater than the whole

The purpose of this study was to investigate whether individual leg cycling could produce higher whole body peak oxygen uptake (VO_2peak) than two legs cycling during aerobic high intensity interval training in chronic obstructive pulmonary disease (COPD) patients. Nineteen patients trained in 24 supervised cycling sessions either by one leg training (OLT) (n = 12) or by two legs training (TLT) (n = 7) at 4 × 4 min intervals at 85–95% of peak heart rate. Whole body VO_2peak and peak work rate increased significantly by 12 and 23% in the OLT, and by 6 and 12% in the TLT from pre- to post-training, respectively, and were significantly greater in the OLT than the TLT (P < 0.05). The present study demonstrates that one leg aerobic high intensity interval cycling is superior to two legs in increasing whole body VO_2peak, indicating a muscle rather than a cardiovascular limitation to VO_2peak in these COPD patients.     

Influence of posture on arm exercise tolerance and physiologic responses in persons with spinal cord injured paraplegia

This study compared metabolic and cardiopulmonary responses to incremental supine and upright sitting arm crank ergometry (ACE) in nine men with spinal cord injured paraplegia ranging from T1–T5. Both tests consisted of continuous graded ACE from rest to volitional fatigue on a modified electronically braked cycle ergometer with the work rate increased by 8.2 W · min^–1. No significant differences (P>0.05) existed for peak ACE power output ( ), oxygen uptake, pulmonary ventilation, respiratory exchange ratio, and O₂ pulse between the two tests. Heart rate and O₂ pulse responses at six submaximal work rates representing 0–58% peak were also not significantly different between postures. These data indicate that ACE tolerance in persons with high-lesion paraplegia was not enhanced when ACE was performed in the supine posture.     

Critical velocity during continuous and intermittent exercises in children

The purpose of this study was to apply the “critical velocity” concept to short intermittent high-intensity running exercises in prepubescent girls and boys and to compare the running performances obtained either by intermittent or continuous exercise runs. Eleven 8 to 11-year-old children underwent a maximal graded field test to determine peak oxygen uptake (peakVO₂) and maximal aerobic velocity (MAV). During the six following sessions, they randomly performed three continuous runs (90, 100, and 110% of MAV) and three intermittent runs (120, 130, and 140% of MAV) until exhaustion. Intermittent exercises consisted of repeated 15 s runs each one separated by a 15 s passive recovery interval. For continuous as well as intermittent exercises, distance versus time to exhaustion (TTE) relationships were calculated to determine continuous (CVc) and intermittent (CVi) critical velocities. Values for peakVO₂ and MAV were 45.8 ± 5.3 ml·kg⁻¹·min⁻¹ and 10.5 ± 1.0 km h⁻¹, respectively. For the whole population, a significant relationship was found between the distance to exhaustion (DTE) and TTE for continuous (r ² = 0.99, P < 0.05) and intermittent exercises (r ² = 0.99, P < 0.05). Significant relationships were found between peakVO₂ and both CVc (r ² = 0.60, P < 0.01) and CVi (r ² = 0.47, P < 0.05). In conclusion, as for continuous exercises, a linear relationship was found between DTE and TTE for short high-intensity intermittent exercises. CVc was significantly related to peakVO₂, while a significant lower relationship was found between peakVO₂ and CVi.     

Physical work capacity and effect of endurance training in visually handicapped boys and young male adults

Summary The purpose of the present study was to evaluate the relationship between several physical fitness parameters and eyesight divided into 3 grades in visually handicapped boys and young male adults, and to investigate the effect of mild exercise training on physical and psychic symptoms as well as cardiorespiratory fitness. Four subjects were totally blind (TB), 6 were semi-blind (SB) and 27 had amblyopia (AM). Physical fitness tests consisted of maximal oxygen uptake (V _{O 2max}), maximal pedalling speed and power, maximal stepping rate, and isometric knee extention strength. Compared with AM and SB groups, the TB group was inferior in all physical fitness parameters. Especially,V _{O 2max} in TB (26 ml · kg^–1 · min^–1) was about 56% of that in agematched Japanese sighted subjects and was significantly low compared with the AM and SB groups. Both muscle strength and maximal pedalling power corresponded to about 50% that of the age-matched sighted group. Six SB and 4 TB students (¯x=17.7 years) were trained for 6 weeks on a bicycle ergometer at an intensity of 50%V _{O 2max}. Training was undertaken for 3 days per week and maintained for 60 min per session. After training, physical and psychic symptoms determined by the Cornell Medical Index improved significantly. These results indicate that low physical work capacity in visually handicapped boys and young male adults is due to the lack of physical activity, and that mild endurance training is effective in improving physical and psychic symptoms as well as cardiorespiratory fitness.     

Aerobic determinants of the decline in preferred walking speed in healthy, active 65- and 80-year-olds

The preferred walking speed is a common measure of mobility that declines with age and has been related to maximal oxygen uptake (O_2,max). The present study determined whether this decline is associated with a higher percentage of the ventilatory threshold in older adults walking at their preferred speed. We compared the preferred walking speed and O₂ at this speed in relation to both O_2,max and O₂ corresponding to the ventilatory threshold (T _VE) in healthy, physically active sexagenarians (G65, n=10) and octogenarians (G80, n=10) walking on a treadmill. The preferred walking speed was lower in G80 (1.16±0.09 m·s^–1) than in G65 (1.38±0.09 m·s^–1; P<0.001). Energy expenditure and the energy cost of walking at the preferred walking speed were not significantly different between the two groups. G80 subjects exhibited significantly higher fractions of O_2,max (60.8±8.0%) and T _VE (74.2±7.9%) at the preferred walking speed than G65 (42.9±5.0 and 53.2±5.7% respectively; P<0.001). Multiple regression analysis showed that the fraction of T _VE was the main determinant, with a small contribution of height, in the decline in the preferred walking speed in healthy and active elderly subjects (R ²=64%; P<0.001). These findings show that with age, walking at the preferred speed requires a higher fraction of T _VE. This increase in the relative physiological effort at preferred walking speed could explain the reduction in this gait speed in healthy older subjects.     

Effects of 20-s and 180-s double poling interval training in cross-country skiers

The purpose of this study was to investigate the effect of upper body 20-s or 180-s interval training, using a double poling ergometer, on upper body power output and selected physiological and biomechanical parameters in cross-country skiers. Twenty (12 male, 8 female) well-trained cross-country skiers took part. Two intervention groups, a 20-s interval training group (IT20; n=6) and a 180-s interval training group (IT180; n=7), underwent training three times a week for 6 weeks on a double poling ergometer. A third group served as a control (CON; n=7) and followed the same training program as the IT20 and IT180 groups without the double poling ergometer interval training. The IT20 and IT180 groups significantly (P<0.05) increased both peak and mean power in a 30-s test and mean power in a 6-min test after double poling training. There was a significant improvement in work efficiency in both IT20 and IT180 (P<0.05) and, in IT180, a significant reduction (P<0.05) in blood lactate concentration at given sub-maximal workloads. O_2peak increased significantly during double poling in IT180 (P<0.05) only. O_2max did not change significantly in either group. There were no significant changes in any of the test variables in CON. In conclusion, this study shows that 6 weeks of 20-s or 180-s double poling interval training, three times a week, significantly increases power output in both 30-s and 6-min tests, as well as in selected physiological and biomechanical parameters in well-trained cross-country skiers.     

Dissociated oxygen uptake response to an incremental intermittent repetitive lifting and lowering exercise in humans

Five subjects performed a maximal exercise test of repetitive lifting and lowering, with a discontinuous protocol of incremental exercise (3 min) and relative rest (2 min). Exercise periods consisted of repetitive lifting and repetitive lifting and lowering at increasing movement frequencies. Relative rest periods consisted of ergometer cycling at a constant, low power output. An unexpected, dissociated, response of cardiovascular and pulmonary parameters was found: during relative rest, values for oxygen uptake, carbon dioxide production, pulmonary ventilation and tidal volume were significantly higher than during the preceding exercise periods, though exercise intensity was much lower. To our knowledge, such a response has not been reported in previous studies. Since the response could not be attributed to methodological or technical factors, it is hypothesized that the type of exercise itself impeded the optimal performance of the oxygen transporting system. The function of the pulmonary system could have been influenced by a high intra-abdominal pressure, the involvement of respiratory muscles in stabilizing trunk and head, a flexed trunk posture and the entrainment of respiratory frequency with movement frequency. More likely, the function of the cardiovascular system was hindered by a high blood pressure and high intramuscular pressures. Since this response occurred at low exercise intensities, optimal functioning of the cardiovascular and pulmonary system during daily activities of repetitive lifting and lowering could similarly be impeded. The hypotheses put forward could also explain the lower peak oxygen uptake reported during repetitive lifting, compared to running and cycling.