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Purpose To challenge current conventions in paediatric sport science and use data from recent longitudinal studies to elucidate the development of aerobic and anaerobic fitness, with reference to youth athletes. Methods (1) To critically review the traditional practice of ratio scaling physiological variables with body mass and, (2) to use multiplicative allometric models of longitudinal data, founded on 1053 (550 from boys) determinations of 10–17-year-olds’ peak oxygen uptake ($$ {{\text{V}}\text{O}}_{2} $$ VO 2 ) and 763 (405 from boys) determinations of 11–17-year-olds’ peak power output (PP) and mean power output (MP), to investigate the development of aerobic and anaerobic fitness in youth. Results The statistical assumptions underpinning ratio scaling of physiological variables in youth are seldom met. Multiplicative allometric modelling of longitudinal data has demonstrated that fat free mass (FFM) acting as a surrogate for active muscle mass, is the most powerful morphological influence on PP, MP, and peak $$ {{\text{V}}\text{O}}_{2} $$ VO 2 . With FFM appropriately controlled for, age effects remain significant but additional, independent effects of maturity status on anaerobic and aerobic fitness are negated. Conclusions Ratio scaling of physiological variables with body mass is fallacious, confounds interpretation of the development of anaerobic and aerobic fitness, and misleads fitness comparisons within and across youth sports. Rigorous evaluation of the development of anaerobic and aerobic fitness in youth requires longitudinal analyses of sex-specific, concurrent changes in age- and maturation-driven morphological covariates. Age and maturation-driven changes in FFM are essential considerations when evaluating the physiological development of youth athletes.

Purpose To investigate (1) whether maximal stroke volume (SVmax) occurs at submaximal exercise intensities, (2) sex differences in SVmax once fat-free mass (FFM) has been controlled for, and, (3) the contribution of concurrent changes in FFM and SVmax to the sex-specific development of peak oxygen uptake $$ \left( {{\dot{\text{V}}\text{O}}_{2} } \right) $$V˙O2. Methods The peak $$ {\dot{\text{V}}\text{O}}_{2} $$V˙O2 s of 61 (34 boys) 11–12-year-olds were determined and their SV determined during treadmill running at 2.28 and 2.50 m s−1 using carbon dioxide rebreathing. The SVmax and peak $$ {\dot{\text{V}}\text{O}}_{2} $$V˙O2 of 51 (32 boys) students who volunteered to be tested treadmill running at 2.50 m s−1 on three annual occasions were investigated using multilevel allometric modelling. The models were founded on 111 (71 from boys) determinations of SVmax, FFM, and peak $$ {\dot{\text{V}}\text{O}}_{2} $$V˙O2. Results Progressive increases in treadmill running speed resulted in significant (p $$ {\dot{\text{V}}\text{O}}_{2} $$V˙O2, but SV levelled-off with nonsignificant (p > 0.05) changes within ~ 2–3%. In the multilevel models, SVmax increased proportionally to FFM0.72 and with FFM controlled for, there were no significant (p > 0.05) sex differences. Peak $$ {\dot{\text{V}}\text{O}}_{2} $$V˙O2 increased with FFM but after adjusting for FFM0.98, a significant (p $$ {\dot{\text{V}}\text{O}}_{2} $$V˙O2 remained. Introducing SVmax to the multilevel model revealed a significant (p $$ {\dot{\text{V}}\text{O}}_{2} $$V˙O2. Conclusions Fat-free mass explained sex differences in SVmax, but with FFM controlled for, there was still a ~ 5% sex difference in peak $$ {\dot{\text{V}}\text{O}}_{2} $$V˙O2. SVmax made a modest additional contribution to explain the development of peak $$ {\dot{\text{V}}\text{O}}_{2} , $$V˙O2, but there remained an unresolved sex difference of ~ 4%.

Purpose To investigate the development of peak power output (PP) and mean power output (MP) during two different modes of exercise in relation to sex and concurrent changes in age, body mass, fat-free mass (FFM), maturity status and, in the case of MP, peak oxygen uptake (\documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$ \dot{V}{\text{O}}_{2} $$\end{document}V˙O2). Methods PP and MP were determined cycling against a fixed braking force (Wingate anaerobic test) and running on a non-motorized treadmill. Peak \documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$ \dot{V}{\text{O}}_{2} $$\end{document}V˙O2 was determined using cycle ergometry and treadmill running. 135 (63 girls) students initially aged 11–14 years were tested over 2 days on three annual occasions. The data were analysed using multiplicative allometric modelling which enables the effects of variables to be partitioned concurrently within an allometric framework. Multiplicative models were founded on 301 (138 from girls) determinations of PP and MP on each ergometer. Results With body mass controlled for, both PP and MP increased with age but maturity status did not independently contribute to any of the multiplicative allometric models. Boys’ PP and MP were significantly (p

Purposes To investigate the development of peak oxygen uptake (\documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$\dot{{V}}{\text{O}}_{2}$$\end{document}V˙O2) assessed on both a treadmill and a cycle ergometer in relation with sex and concurrent changes in age, body mass, fat-free mass (FFM), and maturity status and to evaluate currently proposed ‘clinical red flags’ or health-related cut-points for peak \documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$\dot{{V}}{\text{O}}_{2}$$\end{document}V˙O2. Methods Multiplicative multilevel modelling, which enables the effects of variables to be partitioned concurrently within an allometric framework, was used to analyze the peak \documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$\dot{{V}}{\text{O}}_{2}$$\end{document}V˙O2s of 138 (72 boys) students initially aged 11–14 years and tested on three annual occasions. Models were founded on 640 (340 from boys) determinations of peak \documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$\dot{{V}}{\text{O}}_{2}$$\end{document}V˙O2, supported by anthropometric measures and maturity status. Results Mean peak \documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$\dot{{V}}{\text{O}}_{2}$$\end{document}V˙O2s were 11–14% higher on a treadmill. The data did not meet the statistical assumptions underpinning ratio scaling of peak \documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$\dot{{V}}{\text{O}}_{2}$$\end{document}V˙O2 with body mass. With body mass appropriately controlled for boys’ peak \documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$\dot{{V}}{\text{O}}_{2}$$\end{document}V˙O2s were higher than girls’ values and the difference increased with age. The development of peak \documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$\dot{{V}}{\text{O}}_{2}$$\end{document}V˙O2 was sex-specific, but within sex models were similar on both ergometers with FFM the dominant anthropometric factor. Conclusions Data should not be pooled for analysis but data from either ergometer can be used independently to interpret the development of peak \documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$\dot{{V}}{\text{O}}_{2}$$\end{document}V˙O2 in youth. On both ergometers and in both sexes, FFM is the most powerful morphological influence on the development of peak \documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$\dot{{V}}{\text{O}}_{2}$$\end{document}V˙O2. ‘Clinical red flags’ or health-related cut-points proposed without consideration of exercise mode and founded on peak \documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$\dot{{V}}{\text{O}}_{2}$$\end{document}V˙O2 in ratio with body mass are fallacious.

James Lasdun's memoir of being stalked, Give Me Everything You Have, has provoked considerable controversy. Whilst the quality of the writing is widely praised, some critics object to the way Lasdun documents in unsparing detail his experiences without taking any account of the stalker's apparent mental health problems. There are ethical and conceptual problems with Lasdun's approach, but side-stepping medical knowledge and relying on what we might call common sense help Lasdun to find ways to interpret his stalker's actions as meaningful and human. I suggest three interlinked implications concerning: medicalization, stigma, and the relationship between ethics and scientific knowledge.

During constant work rate exercise above the lactate threshold (LT), the initial rapid phase of pulmonary oxygen uptake ( $$\dot{V}$$ O2) kinetics is supplemented by an additional $$\dot{V}$$ O2 slow component ( $$\dot{V}$$ O2Sc) which reduces the efficiency of muscular work. The $$\dot{V}$$ O2Sc amplitude has been shown to increase with maturation but the mechanisms are poorly understood. We utilized the transverse relaxation time (T 2) of muscle protons from magnetic resonance imaging (MRI) to test the hypothesis that a lower $$\dot{V}$$ O2 slow component ( $$\dot{V}$$ O2Sc) amplitude in children would be associated with a reduced muscle recruitment compared to adults. Eight boys (mean age 11.4 ± 0.4) and eight men (mean age 25.3 ± 3.3 years) completed repeated step transitions of unloaded-to-very heavy-intensity (U → VH) exercise on a cycle ergometer. MRI scans of the thigh region were acquired at rest and after VH exercise up to the $$\dot{V}$$ O2Sc time delay (ScTD) and after 6 min. T 2 for each of eight muscles was adjusted in relation to cross-sectional area and then summed to provide the area-weighted ΣT 2 as an index of thigh recruitment. There were no child/adult differences in the relative $$\dot{V}$$ O2Sc amplitude [Boys 14 ± 7 vs. Men 18 ± 3 %, P = 0.15, effect size (ES) = 0.8] during which the change (∆) in area-weighted ΣT 2 between the ScTD and 6 min was not different between groups (Boys 1.6 ± 1.2 vs. Men 2.3 ± 1.1 ms, P = 0.27, ES = 0.6). A positive and strong correlation was found between the relative $$\dot{V}$$ O2Sc amplitude and the magnitude of the area-weighted ∆ΣT 2 in men (r = 0.92, P = 0.001) but not in boys (r = 0.09, P = 0.84). This study provides evidence to show that progressive muscle recruitment (as inferred from T 2 changes) contributes to the development of the $$\dot{V}$$ O2Sc during intense submaximal exercise independent of age.

Short stature and later maturation of youth artistic gymnasts are often attributed to the effects of intensive training from a young age. Given limitations of available data, inadequate specification of training, failure to consider other factors affecting growth and maturation, and failure to address epidemiological criteria for causality, it has not been possible thus far to establish cause–effect relationships between training and the growth and maturation of young artistic gymnasts. In response to this ongoing debate, the Scientific Commission of the International Gymnastics Federation (FIG) convened a committee to review the current literature and address four questions: (1) Is there a negative effect of training on attained adult stature? (2) Is there a negative effect of training on growth of body segments? (3) Does training attenuate pubertal growth and maturation, specifically, the rate of growth and/or the timing and tempo of maturation? (4) Does training negatively influence the endocrine system, specifically hormones related to growth and pubertal maturation? The basic information for the review was derived from the active involvement of committee members in research on normal variation and clinical aspects of growth and maturation, and on the growth and maturation of artistic gymnasts and other youth athletes. The committee was thus thoroughly familiar with the literature on growth and maturation in general and of gymnasts and young athletes. Relevant data were more available for females than males. Youth who persisted in the sport were a highly select sample, who tended to be shorter for chronological age but who had appropriate weight-for-height. Data for secondary sex characteristics, skeletal age and age at peak height velocity indicated later maturation, but the maturity status of gymnasts overlapped the normal range of variability observed in the general population. Gymnasts as a group demonstrated a pattern of growth and maturation similar to that observed among short-, normal-, late-maturing individuals who were not athletes. Evidence for endocrine changes in gymnasts was inadequate for inferences relative to potential training effects. Allowing for noted limitations, the following conclusions were deemed acceptable: (1) Adult height or near adult height of female and male artistic gymnasts is not compromised by intensive gymnastics training. (2) Gymnastics training does not appear to attenuate growth of upper (sitting height) or lower (legs) body segment lengths. (3) Gymnastics training does not appear to attenuate pubertal growth and maturation, neither rate of growth nor the timing and tempo of the growth spurt. (4) Available data are inadequate to address the issue of intensive gymnastics training and alterations within the endocrine system. Electronic supplementary material The online version of this article (doi:10.1007/s40279-013-0058-5) contains supplementary material, which is available to authorized users.

Use of the Surgical Safety Checklist (SSC) has blossomed since a landmark publication showed improved morbidity and mortality with its implementation. Parallel to increasing use of the SSC is a growing body of research investigating the effect of the SSC on the safety of care delivered. Nevertheless, at least one study shows an inconsistent degree of effect on outcomes. Others have investigated the impact of modifications of the SSC tailored to different clinical settings, as Morgan et al. show in their study, ‘‘Surgical safety checklist: implementation in an ambulatory surgical facility’’, in this issue of the Journal. The purpose of this study was ‘‘to add ambulatory carespecific items to the checklist, to assess adherence to safety checklist items, and to examine the impact of the SSC on safety attitudes and important patient outcomes’’ – all in an ambulatory surgical centre. On first thought, this is a logical concept, given that more and more procedures are being carried out on an ambulatory basis. What distinguishes this study from others that have investigated the impact of a SSC on various outcomes is the ambulatory scope and application of a modified SSC to this unique clinical environment. The primary outcome of the study consisted of two end points obtained through telephone interviews with patients on postoperative day one: (1) severity of pain (assessed on a scale of 1-10) and (2) incidence of postdischarge nausea/vomiting (PDNV). Secondary outcomes included the ‘‘incidence of perioperative antibiotic timing, use of regional anesthesia/ analgesia, length of stay, and the number of hospital admissions’’. Despite engaging a multidisciplinary team (consisting of nurses, surgeons, and anesthesiologists) to identify ambulatory-specific factors for inclusion on a modified SSC, clinically relevant differences in the primary and secondary outcomes were not achieved. Why did this occur? The authors identify several possible reasons for lack of effect with their well-intentioned ambulatory SSC: too many additions creating an unwieldy tool, issues with perceived importance of the new items by perioperative staff using the modified SSC, and low rates of overall checklist completion. Though many possible explanations exist, one must ultimately question if the SSC — with its recognized effect on mortality — can be expected to influence ambulatory outcomes like pain scores and PDNV. In their recent review of how and why checklists work, Weiser and Berry detail two main types of checklists. ‘‘Read-do’’ checklists are also known as ‘‘call-doresponse’’ or ‘‘verbal action and confirmation’’. These checklists are used by one person to identify ‘‘items to consider or tasks to accomplish’’, much like a grocery list or a ‘‘cook book’’. ‘‘Challenge-confirm’’ — also known as ‘‘verbal challenge and response’’ — checklists are generally more formalized and are used by two or more individuals, for example, a flight captain and co-pilot completing pre-takeoff checks. With this type of checklist, the reader of the checklist ‘‘challenges’’ another team member to ‘‘confirm’’ completion of each task in a communication format that is scripted to minimize confusion and maximize efficiency. Many checklists in industry and healthcare are a combination of ‘‘read-do’’ and ‘‘challenge-confirm’’, but use of a checklist (like the SSC) should be much more than simply ‘‘double checking’’, which has been described as the use of ‘‘one fallible person (to) monitor the work of another imperfect C. L. Pysyk, MD (&) Department of Anesthesiology, General Campus, The Ottawa Hospital, 501 Smyth Rd., Critical Care Wing 1401, Ottawa, ON K1H 8L6, Canada e-mail: cpysyk@toh.on.ca

The ML 450 Hybrid is the first Mercedes-Benz full hybrid vehicle, promising significant fuel consumption and emission reductions ” great efficiency both in inner city “stop and go” traffic and on fast long-distance journeys at increasing engine loads and higher speed ranges. The ML 450 Hybrid is, therefore, a central element of the Mercedes-Benz strategy for achieving sustainable mobility.

Der ML 450 Hybrid ist das erste Vollhybridfahrzeug von Mercedes-Benz und vereint erhebliche Verbrauchs- und Emissionsreduzierungen mit souveranem Fahrverhalten. Das erstmalig eingesetzte „AHS-C Two-Mode-Hybrid system“ zeichnet sich vor allem durch eine hohe Effizienz sowohl im innerstadtischen „Stop-and-go“-Verkehr als auch bei zugiger Uberlandfahrt mit steigenden Motorlasten und hoheren Geschwindigkeitsbereichen aus. Der ML 450 Hybrid ist somit ein Kernelement auf dem Weg zur nachhaltigen Mobilitat von Mercedes-Benz.

Auf dem Weg zur emissionfreien Mobilitat macht Mercedes-Benz einen weiteren Schritt nach vorne. Der ab diesem Sommer erhaltliche „S 400 Hybrid“ ist das erste Hybridfahrzeug des Premiumherstellers. Mit einem kompakten Hybridsystem und der weltweit ersten Lithium-Ionen-Batterie in einem Serienfahrzeug bietet Mercedes-Benz eine innovative Losung an, die bei erheblichen Verbrauchs- und CO2-Einsparungen den gewohnten Kundennutzen der S-Klasse aufweist.

Mercedes-Benz is taking another step towards emissionfree mobility. The “S 400 Hybrid”, available from this summer, is the premium brand’s first hybrid vehicle. With its compact hybrid system and the world’s first lithium ion battery in a production vehicle, Mercedes-Benz presents an innovative solution that offers the usual customer benefits of an S-Class while significantly improving fuel economy and CO2 emissions.

To further understand the mechanism(s) explaining the faster pulmonary oxygen uptake $$(p{\dot{V}}\hbox{O}_{2})$$ kinetics found in children compared to adults, this study examined whether the phase II $$p{\dot{V}}\hbox{O}_{2}$$ kinetics in children are mechanistically linked to the dynamics of intramuscular PCr, which is known to play a principal role in controlling mitochondrial oxidative phosphorylation during metabolic transitions. On separate days, 18 children completed repeated bouts of moderate intensity constant work-rate exercise for determination of (1) PCr changes every 6 s during prone quadriceps exercise using 31P-magnetic resonance spectroscopy, and (2) breath by breath changes in $$p{\dot{V}}\hbox{O}_{2}$$ during upright cycle ergometry. Only subjects (n = 12) with 95% confidence intervals ≤±7 s for all estimated time constants were considered for analysis. No differences were found between the PCr and phase II $$p{\dot{V}}\hbox{O}_{2}$$ time constants at the onset (PCr 23 ± 5 vs. $$p{\dot{V}}\hbox{O}_{2}\ 23 \pm 4\,\hbox{s}, P=1.000)$$ or offset (PCr 28 ± 5 vs. $$p{\dot{V}}\hbox{O}_{2}\ 29 \pm 5\,\hbox{s},\, P=1.000)$$ of exercise. The average difference between the PCr and phase II $$p{\dot{V}}\hbox{O}_{2}$$ time constants was 4 ± 4 s for the onset and offset responses. Pooling of the exercise onset and offset responses revealed a significant correlation between the PCr and $$p{\dot{V}}\hbox{O}_{2}$$ time constants (r = 0.459, P = 0.024). The close kinetic coupling between the $$p{\dot{V}}\hbox{O}_{2}$$ and PCr responses at the onset and offset of exercise in children is consistent with our current understanding of metabolic control and suggests that an age-related modulation of the putative phosphate linked controller(s) of mitochondrial oxidative phosphorylation may explain the faster $$p{\dot{V}}\hbox{O}_{2}$$ kinetics found in children compared to adults.

This study examined the reliability of (31)P-magnetic resonance spectroscopy (MRS) to measure parameters of muscle metabolic function in children. On separate days, 14 children (7 boys and 7 girls) completed three knee-extensor incremental tests to exhaustion inside a whole-body scanner (1.5 T, Phillips). The dynamic changes in the ratio of inorganic phosphate to phosphocreatine (Pi/PCr) and intracellular muscle pH were resolved every 30 s. Using plots of Pi/PCr and pH against power output (W), intracellular thresholds (ITs) for each variable were determined using both subjective and objective procedures. The IT(Pi/PCr) and IT(pH) were observed subjectively in 93 and 81% of their respective plots, whereas the objective method identified the IT(Pi/PCr) in 88% of the plots. The IT(pH) was undetectable using the objective method. End exercise (END) END(Pi/PCr), END(pH), IT(Pi/PCr) and IT(pH) were examined using typical error statistics expressed as a % coefficient of variation (CV) across all three exercise tests. The CVs for the power output at the subjectively determined IT(Pi/PCr) and IT(pH) were 10.6 and 10.3%, respectively. Objective identification of the IT(Pi/PCr) had a CV of 16.3%. CVs for END(pH) and END(Pi/PCr) were 0.9 and 50.0%, respectively. MRS provides a valuable window into metabolic changes during exercise in children. During knee-extensor exercise to exhaustion, END(pH) and the subjectively determined IT(Pi/PCr) and IT(pH) demonstrate good reliability and thus stable measures for the future study of developmental metabolism. However, the objectively determined IT(Pi/PCr) and END(Pi/PCr) displayed poor reliability.

The purpose of this study was to evaluate the reliability of a thoracic electrical bioimpedance based device (PhysioFlow) for the determination of cardiac output and stroke volume during exercise at peak oxygen uptake (peak VO(2) in children. The reliability of peak VO(2) is also reported. Eleven boys and nine girls aged 10-11 years completed a cycle ergometer test to voluntary exhaustion on three occasions each 1 week apart. Peak VO(2) was determined and cardiac output and stroke volume at peak VO(2) were measured using a thoracic bioelectrical impedance device (PhysioFlow). The reliability of peak VO(2) cardiac output and stroke volume were determined initially from pairwise comparisons and subsequently across all three trials analysed together through calculation of typical error and intraclass correlation. The pairwise comparisons revealed no consistent bias across tests for all three measures and there was no evidence of non-uniform errors (heteroscedasticity). When three trials were analysed together typical error expressed as a coefficient of variation was 4.1% for peak VO(2) 9.3% for cardiac output and 9.3% for stroke volume. Results analysed by sex revealed no consistent differences. The PhysioFlow method allows non-invasive, beat-to-beat determination of cardiac output and stroke volume which is feasible for measurements during maximal exercise in children. The reliability of the PhysioFlow falls between that demonstrated for Doppler echocardiography (5%) and CO(2) rebreathing (12%) at maximal exercise but combines the significant advantages of portability, lower expense and requires less technical expertise to obtain reliable results.

The oxygen uptake (.VO2) kinetic response to exercise assesses the integrated response of the cardiovascular system and the metabolic requirements of the exercising muscle. The response differs both qualitatively and quantitatively according to the exercise intensity domain (moderate, heavy, very heavy and severe) in which it lies. In each domain, a rapid cardiodynamic phase 1 response is followed by an exponential rise in .VO2 toward a projected steady state (for which the inverse of the rate constant is represented as the time constant [tau]). The achievement of the new steady state may be delayed and elevated due to a slow component of .VO2 in the heavy intensity domain, or above this exercise intensity, the achievement of peak .VO2 truncates the exercise period. For each of these domains, specific mathematical models have been identified and may be applied to appropriate breath-by-breath response data in order to allow quantification of the response. Much of our understanding of the .VO2 kinetic response and the methodologies required to obtain meaningful assessment are derived from adult studies. Although pioneering, early studies with young people were lacking in suitable equipment and the methodologies used may consequently have clouded the true interpretation of the kinetic response. More recently, with the advent of online breath-by-breath analysis systems, studies using mathematical modelling procedures have been hindered by the low signal-to-noise ratio which is inherent to children's response profiles. This has the effect of widening the confidence intervals for estimated parameters, and therefore questions the validity in making inter- and intra-study comparisons. In addition, the difficulty in accurately assessing domain demarcators, especially critical power, often confounds the interpretation of age and sex effects on the exercise response.This review therefore analyses the literature to date on the .VO2 kinetic response during childhood and adolescence, and specifically highlights concerns with technical rigour in its determination. Rigorously determined data indicate that the exponential rise in .VO2 is more rapid in children than adults and that at exercise intensities above the anaerobic threshold, the slow component of .VO2 may be attenuated in the young. Sex differences have not been found in the response to moderate intensity exercise, and there does not appear to be a consistent correlation between peak .VO2 and tau in children. However, sex differences in the response to exercise intensities above the anaerobic threshold are identified and discussed.

This study used multilevel modelling to examine peak oxygen uptake (VO2peak) during growth and maturation. Body mass, stature, triceps and subscapular skinfold thicknesses, blood haemoglobin concentration, and VO2peak of boys and girls, [mean (SD)] aged 11.1 (0.4) years at the onset of the study, were measured at ages 11, 12, 13 and 17 years. Sexual maturation was assessed on the first three occasions and was assumed to be Tanner stage 5 at 17 years. The analysis was founded on 388 VO2peak determinations from 132 children. The initial model revealed mass, stature and age as significant explanatory variables of VO2peak with an additional positive effect for stage of maturity. Girls' values were significantly lower than those of boys and a significant age-by-sex interaction described a progressive divergence in boys' and girls' VO2peak. The introduction of skinfold thicknesses produced a model with an improvement in fit. The stature term was negated and the mass exponent almost doubled. The sex and age-by-sex terms were reduced but remained significant. Many of the observed maturity effects were explained with stage 5 becoming non-significant. Blood haemoglobin concentration was a nonsignificant parameter estimate in both models. Fat-free mass was the dominant influence on the growth of VO2peak but the multilevel regression models demonstrated that, with body size and fatness allowed for, VO2peak increased with age and maturation in both sexes.