The Influence of Acute Hypoxia on Oxygen Uptake and Muscle Oxygenation Kinetics During Cycling Exercise in Prepubertal Boys.

PURPOSE: To examine the effect of normobaric hypoxia on pulmonary oxygen uptake (V˙O2) and muscle oxygenation kinetics during incremental and moderate-intensity exercise in children. METHODS: Eight prepubertal boys (9-11 y) performed incremental cycle tests to exhaustion in both normoxia and hypoxia (fraction of inspired O2 of 15%) followed by repeat 6-minute transitions of moderate-intensity exercise in each condition over subsequent visits. RESULTS: Maximal oxygen uptake (V˙O2max) was reduced in hypoxia compared with normoxia (1.69 [0.20] vs 1.87 [0.26] L·min-1, P = .028), although the gas exchange threshold was not altered in absolute terms (P = .33) or relative to V˙O2max (P = .78). During moderate-intensity exercise, the phase II V˙O2 time constant (τ) was increased in hypoxia (18 [9] vs 24 [8] s, P = .025), with deoxyhemoglobin τ unchanged (17 [8] vs 16 [6], P ≥ .28). CONCLUSIONS: In prepubertal boys, hypoxia reduced V˙O2max and slowed V˙O2 phase II kinetics during moderate-intensity exercise, despite unchanged deoxyhemoglobin kinetics. These data suggest an oxygen delivery dependence of V˙O2max and moderate-intensity V˙O2 kinetics under conditions of reduced oxygen availability in prepubertal boys.

Is it Still Ok to be Ok? Mental Health Labels as a Campus Technology.

This article uses ethnography and coproduced ethnography to investigate mental health labels amongst university students in the UK. We find that although labels can still be a source of stigma, they are also both necessary and useful. Students use labels as 'campus technologies' to achieve various ends. This includes interaction with academics and administrators, but labels can do more than make student distress bureaucratically legible. Mental health labels extend across the whole student social world, as a pliable means of negotiating social interaction, as a tool of self-discovery, and through the 'soft-boy' online archetype, they can be a means of promoting sexual capital and of finessing romantic encounters. Labels emerge as flexible, fluid and contextual. We thus follow Eli Clare in attending to the varying degrees of sincerity, authenticity and pragmatism in dealing with labels. Our findings give pause to two sets of enquiry that are sometimes seen as opposed. Quantitative mental health research relies on what appear to be questionable assumptions about labels embedded in questionnaires. But concerns about the dialogical power of labels to medicalise students also appears undermined.

Happenstance and regulatory culture: the evolution of innovative community mental health services in Oxfordshire in the late twentieth century.

This paper uses co-produced historical material to explore the evolution of two innovative mental healthcare institutions that emerged in Oxfordshire in the 1960s. We highlight how the trajectories of both institutions were driven by chance events occurring within social environments, rather than emerging out of evidence or policy initiatives. Both institutions found a role for spontaneity and an openness to chance in the way they worked. We argue that this kind of institutional history would be unlikely today; the paper develops and uses the concept of regulatory culture to explain why. We suggest that the role of regulatory culture has been neglected in the history of psychiatry.

The development of a creative work rehabilitation organisation.

Work as therapy has a place in mental healthcare, but there is disagreement about how and why it might be helpful, and how best to conceptualise or represent those benefits. Over the last 50 years, occupational and industrial therapy sheltered workshops have been key elements in the provision of work activities in psychiatric settings, and community-based horticultural activities and creative craft work have offered additional approaches. Using archival material, interviews, witness seminars and personal reflections, this article charts the birth and initial growth of Restore, a charity providing creative work-based services in Oxfordshire between 1977 and 1988. Although Restore might be understood as a response to national trends in mental healthcare policy and research, its trajectory reflects local contingencies.

Innovation in mental health care: Bertram Mandelbrote, the Phoenix Unit and the therapeutic community approach.

Bertram Mandelbrote was Physician Superintendent and Consultant Psychiatrist at Littlemore Hospital in Oxford from 1959 to 1988. A humane pragmatist rather than theoretician, Mandelbrote was known for his facilitating style of leadership and working across organisational boundaries. He created the Phoenix Unit, an innovative admission unit run on therapeutic community lines which became a hub for community outreach. Material drawn from oral histories and witness seminars reflects the remarkably unstructured style of working on the Phoenix Unit and the enduring influence of Mandelbrote and fellow consultant Benn Pomryn's styles of leadership. Practices initiated at Littlemore led to a number of innovative services in Oxfordshire. These innovations place Mandelbrote as a pioneer in social psychiatry and the therapeutic community approach.

The processes and context of innovation in mental healthcare: Oxfordshire as a case study.

This article introduces the four following articles and the Classic Text. They describe the development of a sequence of innovative local mental health services in Oxfordshire, and explore the processes of innovation, led by the humane pragmatism practised by Dr Bertram Mandelbrote, who was Physician Superintendent at Littlemore Hospital in Oxford from 1959 to 1988. The articles describe emerging patterns of therapeutic community practice, and trace the events leading to a set of discrete service developments outside the hospital. Together, they suggest a positive role for chance in these developments, and a focus on the then prevailing national and local regulatory culture. The Classic Text by David Millard provides an overview of the origins of the therapeutic community movement.

Influence of sex-specific concurrent changes in age, maturity status, and morphological covariates on the development of peak ventilatory variables in 10-17-year-olds.

PURPOSES: (i) To investigate the influence of concurrent changes in age, maturity status, stature, body mass, and skinfold thicknesses on the development of peak ventilatory variables in 10-17-year-olds; and, (ii) to evaluate the interpretation of paediatric norm tables of peak ventilatory variables. METHODS: Multiplicative multilevel modelling which allows both the number of observations per individual and the temporal spacing of the observations to vary was used to analyze the expired ventilation (peak [Formula: see text]) and tidal volume (peak VT) at peak oxygen uptake of 420 (217 boys) 10-17-year-olds. Models were founded on 1053 (550 from boys) determinations of peak ventilatory variables supported by anthropometric measures and maturity status. RESULTS: In sex-specific, multiplicative allometric models, concurrent changes in body mass and skinfold thicknesses (as a surrogate of FFM) and age were significant (p < 0.05) explanatory variables of the development of peak [Formula: see text], once these covariates had been controlled for stature had no additional, significant (p > 0.05) effect on peak [Formula: see text]. Concurrent changes in age, stature, body mass, and skinfold thicknesses were significant (p < 0.05) explanatory variables of the development of peak VT. Maturity status had no additional, significant (p > 0.05) effect on either peak [Formula: see text] or peak VT once age and morphological covariates had been controlled for. CONCLUSIONS: Elucidation of the sex-specific development of peak [Formula: see text] requires studies which address concurrent changes in body mass, skinfold thicknesses, and age. Stature is an additional explanatory variable in the development of peak VT, in both sexes. Paediatric norms based solely on age or stature or body mass are untenable.

Sex-related differences in accumulated O2 deficit incurred by high-intensity rowing exercise during childhood and adolescence.

PURPOSE: The aims of the present study were to determine during childhood and adolescence (i) the effect of sex on non-oxidative energy production, quantified by the accumulated oxygen deficit (AOD), and (ii) the influence of AOD on high-intensity performance. METHODS: Thirty-nine boys and 35 girls aged 10-17 years performed a 60 s all-out test on a rowing ergometer to determine AOD and mean power output (MPO). Multiplicative allometric modelling was used to assess the concurrent effects of lean body mass (LBM) and age on AOD. RESULTS: AOD significantly increased with age in both sexes (p < 0.001) with boys exhibiting significantly higher AOD than girls from the age of 14 years (10-11.9 yr: 1.9 vs 1.9 L, 12-13.9 yr: 2.4 vs 2.7 L, 14-15.9 yr: 2.8 vs 4.6 L and 16-17.9 yr: 2.9 vs 5.2 L, in girls and boys respectively, p < 0.001). However, a sex difference was no longer significant when AOD was analysed using an allometric model including age and LBM (p = 0.885). Finally, significant correlations were found between AOD and MPO in boys and girls but with lower evidence in girls (r2 = 0.41 vs. 0.89). CONCLUSION: Non-oxidative energy production increased more extensively in boys than girls from the age of 14 years. Age and LBM accounted for the sexual differentiation of AOD during childhood and adolescence. In addition, AOD was found to be a determinant factor of high-intensity performance, more particularly in boys.

Allometric Scaling of Force-velocity Test Output Among Pre-pubertal Basketball Players.

Basketball is characterized by high-intensity episodes predominantly reliant on anaerobic metabolism. The force-velocity test enables individual determination of an optimal braking force and emerged as appropriate to estimate optimal peak power. It has rarely been used in youth basketball. This study aimed to examine the contribution of body size, composition, and biological maturation to interindividual variation in force-velocity test output among pre-pubertal basketball players. The sample consisted of 64 male participants (8.4-12.3 years). Stature, sitting height, body mass and two skinfolds were measured, and leg length estimated. Fat-free mass and lower limb volume were estimated from anthropometry. Age at peak height velocity was predicted from maturity offset. Optimal peak power was correlated with all body size descriptors (correlation: 0.541-0.700). Simple allometric models explained 30-47% of inter-individual variance, with fat-free mass being the best predictor of performance. Whole-body fat-free mass (as a surrogate for active muscle mass) plus the indicator of maturation emerged as the best proportional allometric model (53% explained variance). Even at pre-pubertal ages, the interpretation of the force-velocity test requires assessing the metabolically active component of body mass.

Multilevel allometric modelling of maximum cardiac output, maximum arteriovenous oxygen difference, and peak oxygen uptake in 11-13-year-olds.

PURPOSES: To investigate longitudinally (1) the contribution of morphological covariates to explaining the development of maximum cardiac output ([Formula: see text] max) and maximum arteriovenous oxygen difference (a-vO2 diff max), (2) sex differences in [Formula: see text] max and a-vO2 diff max once age, maturity status, and morphological covariates have been controlled for, and, (3) the contribution of concurrent changes in morphological and cardiovascular covariates to explaining the sex-specific development of peak oxygen uptake ([Formula: see text]). METHODS: Fifty-one (32 boys) 11-13-year-olds had their peak [Formula: see text], maximum heart rate (HR max), [Formula: see text] max, and a-vO2 diff max determined during treadmill running on three annual occasions. The data were analysed using multilevel allometric modelling. RESULTS: There were no sex differences in HR max which was not significantly (p > 0.05) correlated with age, morphological variables, or peak [Formula: see text]. The best-fit models for [Formula: see text] max and a-vO2 diff max were with fat-free mass (FFM) as covariate with age, maturity status, and haemoglobin concentration not significant (p > 0.05). FFM was the dominant influence on the development of peak [Formula: see text]. With FFM controlled for, the introduction of either [Formula: see text] max or a-vO2 diff max to multilevel models of peak [Formula: see text] resulted in significant (p < 0.05) additional contributions to explaining the sex difference. CONCLUSIONS: (1) With FFM controlled for, there were no sex differences in [Formula: see text] max or a-vO2 diff max, (2) FFM was the dominant influence on the development of peak [Formula: see text], and (3) with FFM and either [Formula: see text] max or a-vO2 diff max controlled for, there remained an unresolved sex difference of ~ 4% in peak [Formula: see text].

Importance of dimensional changes on glycolytic metabolism during growth.

PURPOSE: The aim of the present study was to investigate (i) how glycolytic metabolism assessed by accumulated oxygen deficit (AODgly) and blood metabolic responses (lactate and pH) resulting from high-intensity exercise change during growth, and (ii) how lean body mass (LBM) influences AODgly and its relationship with blood markers. METHODS: Thirty-six 11- to 17-year olds performed a 60-s all-out test on a rowing ergometer. Allometric modelling was used to investigate the influence of LBM and LBM + maturity offset (MO) on AODgly and its relationship with the extreme post-exercise blood values of lactate ([La]max) and pH (pHmin) obtained during the recovery period. RESULTS: AODgly and [La]max increased while pHmin decreased linearly with LBM and MO (r2 = 0.46 to 0.72, p < 0.001). Moreover, AODgly was positively correlated with [La]max (r2 = 0.75, p < 0.001) and negatively correlated with pHmin (r2 = 0.77, p < 0.001). When AODgly was scaled for LBM, the coefficients of the relationships with blood markers drastically decreased by three to four times ([La]max: r2 = 0.24, p = 0.002; pHmin: r2 = 0.30, p < 0.001). Furthermore, by scaling AODgly for LBM + MO, the correlation coefficients with blood markers became even lower ([La]max: r2 = 0.12, p = 0.037; pHmin: r2 = 0.18, p = 0.009). However, MO-related additional changes accounted much less than LBM for the relationships between AODgly and blood markers. CONCLUSION: The results challenge previous reports of maturation-related differences in glycolytic energy turnover and suggest that changes in lean body mass are a more powerful influence than maturity status on glycolytic metabolism during growth.

Youth cardiorespiratory fitness: evidence, myths and misconceptions.

Rigorously determined peak oxygen uptake is internationally recognized as the criterion measure of youth cardiorespiratory fitness. The assessment and interpretation of children's and adolescents' peak oxygen uptake and the relationship of the measure with other health-related variables are well documented. There has been a recent resurgence of interest in the prediction of peak oxygen uptake from field performance tests in young people. However, coupled with ratio-scaling of data and the raising of clinical red flags, these practices risk clouding our understanding of youth cardiorespiratory fitness and its relationship with current and future health. We believe these methods have the potential to mislead clinical practice and misguide recommendations for the promotion of youth cardiovascular health. We discuss relevant scientific evidence and interpretations that have emerged from predicting youth cardiorespiratory fitness from performance test scores. We argue that children deserve to have health care founded on evidence-based science and not on myths and misconceptions.

La consommation maximale d'oxygène rigoureusement déterminée est reconnue à l'échelle internationale comme la mesure du critère de la capacité cardiorespiratoire des jeunes. On dispose de nombreuses informations sur l'évaluation et l'interprétation de la consommation maximale d'oxygène des enfants et des adolescents, ainsi que sur le lien de la mesure avec d'autres variables relatives à la santé. On a récemment constaté un regain d'intérêt à l'égard de la prédiction de la consommation maximale d'oxygène à partir de tests de performance sur le terrain chez les jeunes. Néanmoins, associées à une mise à l'échelle proportionnelle des données et à la diffusion d'alertes cliniques, ces pratiques risquent de brouiller notre compréhension de la capacité cardiorespiratoire des jeunes et de son lien avec leur santé actuelle et future. Nous pensons que ces méthodes sont susceptibles d'altérer les pratiques cliniques et les recommandations liées à la promotion de la santé cardiovasculaire des jeunes. Nous examinons les données et les interprétations scientifiques pertinentes qui ont émergé de la prédiction de la capacité cardiorespiratoire des jeunes à partir des résultats des tests de performance. Nous soutenons que les enfants méritent de bénéficier de soins de santé fondés sur des données scientifiques, et non sur des mythes et des idées fausses.

La rigurosa determinación del consumo máximo de oxígeno es reconocida internacionalmente como la medida de criterio de la condición cardiorrespiratoria de los jóvenes. La evaluación e interpretación del consumo máximo de oxígeno de niños y adolescentes y la relación de la medida con otras variables relacionadas con la salud están bien documentadas. Recientemente ha resurgido el interés por la predicción del consumo máximo de oxígeno a partir de pruebas de rendimiento en campo en personas jóvenes. Sin embargo, junto con los datos de la escala de razón y el incremento de las señales de alerta clínicas, estas prácticas corren el riesgo de nublar nuestra comprensión de la condición cardiorrespiratoria en los jóvenes y su relación con la salud actual y futura. Se considera que estos métodos pueden inducir a error a la práctica clínica y a las recomendaciones mal orientadas para la promoción de la salud cardiovascular en los jóvenes. Se analizan las evidencias científicas relevantes y las interpretaciones que han surgido de la predicción de la condición cardiorrespiratoria en los jóvenes a partir de los puntajes de las pruebas de rendimiento. Se argumenta que los niños merecen que el cuidado de la salud se base en la ciencia basada en la evidencia y no en mitos y conceptos erróneos.

Relationship between (non)linear phase II pulmonary oxygen uptake kinetics with skeletal muscle oxygenation and age in 11-15 year olds.

NEW FINDINGS: What is the central question of this study? Do the phase II parameters of pulmonary oxygen uptake ( V̇O2 ) kinetics display linear, first-order behaviour in association with alterations in skeletal muscle oxygenation during step cycling of different intensities or when exercise is initiated from an elevated work rate in youths. What is the main finding and its importance? Both linear and non-linear features of phase II V̇O2 kinetics may be determined by alterations in the dynamic balance between microvascular O2 delivery and utilization in 11-15 year olds. The recruitment of higher-order (i.e. type II) muscle fibres during 'work-to-work' cycling might be responsible for modulating V̇O2 kinetics with chronological age. ABSTRACT: This study investigated in 19 male youths (mean age: 13.6 ± 1.1 years, range: 11.7-15.7 years) the relationship between pulmonary oxygen uptake ( V̇O2 ) and muscle deoxygenation kinetics during moderate- and very heavy-intensity 'step' cycling initiated from unloaded pedalling (i.e. U â†’ M and U â†’ VH) and moderate to very heavy-intensity step cycling (i.e. M â†’ VH). Pulmonary V̇O2 was measured breath-by-breath along with the tissue oxygenation index (TOI) of the vastus lateralis using near-infrared spectroscopy. There were no significant differences in the phase II time constant ( τV̇O2p ) between U â†’ M and U â†’ VH (23 ± 6 vs. 25 ± 7 s; P = 0.36); however, the τV̇O2p was slower during M â†’ VH (42 ± 16 s) compared to other conditions (P < 0.001). Quadriceps TOI decreased with a faster (P < 0.01) mean response time (MRT; i.e. time delay + τ) during U â†’ VH (14 ± 2 s) compared to U â†’ M (22 ± 4 s) and M â†’ VH (20 ± 6 s). The difference (Δ) between the τV̇O2p and MRT-TOI was greater during U â†’ VH compared to U â†’ M (12 ± 7 vs. 2 ± 7 s, P < 0.001) and during M â†’ VH (23 ± 15 s) compared to other conditions (P < 0.02), suggesting an increased proportional speeding of fractional O2 extraction. The slowing of the τV̇O2p during M â†’ VH relative to U â†’ M and U â†’ VH correlated positively with chronological age (r = 0.68 and 0.57, respectively, P < 0.01). In youths, 'work-to-work' transitions slowed microvascular O2 delivery-to-O2 utilization with alterations in phase II V̇O2 dynamics accentuated between the ages of 11 and 15 years.

Multilevel allometric modelling of maximal stroke volume and peak oxygen uptake in 11-13-year-olds.

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 [Formula: see text]. METHODS: The peak [Formula: see text] 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 [Formula: see text] 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 [Formula: see text]. RESULTS: Progressive increases in treadmill running speed resulted in significant (p < 0.01) increases in [Formula: see text], 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 [Formula: see text] increased with FFM but after adjusting for FFM0.98, a significant (p < 0.05) sex difference in peak [Formula: see text] remained. Introducing SVmax to the multilevel model revealed a significant (p < 0.05), but small additional effect of SVmax on peak [Formula: see text]. CONCLUSIONS: Fat-free mass explained sex differences in SVmax, but with FFM controlled for, there was still a ~ 5% sex difference in peak [Formula: see text]. SVmax made a modest additional contribution to explain the development of peak [Formula: see text] but there remained an unresolved sex difference of ~ 4%.

Development of peak oxygen uptake from 11-16 years determined using both treadmill and cycle ergometry.

PURPOSES: To investigate the development of peak oxygen uptake ([Formula: see text]) 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 [Formula: see text]. METHODS: Multiplicative multilevel modelling, which enables the effects of variables to be partitioned concurrently within an allometric framework, was used to analyze the peak [Formula: see text]s 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 [Formula: see text], supported by anthropometric measures and maturity status. RESULTS: Mean peak [Formula: see text]s were 11-14% higher on a treadmill. The data did not meet the statistical assumptions underpinning ratio scaling of peak [Formula: see text] with body mass. With body mass appropriately controlled for boys' peak [Formula: see text]s were higher than girls' values and the difference increased with age. The development of peak [Formula: see text] 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 [Formula: see text] in youth. On both ergometers and in both sexes, FFM is the most powerful morphological influence on the development of peak [Formula: see text]. 'Clinical red flags' or health-related cut-points proposed without consideration of exercise mode and founded on peak [Formula: see text] in ratio with body mass are fallacious.

Development of 11- to 16-year-olds' short-term power output determined using both treadmill running and cycle ergometry.

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 ([Formula: see text]). METHODS: PP and MP were determined cycling against a fixed braking force (Wingate anaerobic test) and running on a non-motorized treadmill. Peak [Formula: see text] 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 < 0.05) higher than girls' values on both ergometers. On both ergometers in both sexes, the most powerful morphological influence on PP and MP was FFM. Ergometer-specific peak [Formula: see text] had a significant (p < 0.05), additional effect in explaining the development of MP. CONCLUSIONS: The development of short-term power output is sex specific but within sex multiplicative allometric models of running- and cycling-determined PP and MP were similar, suggesting that either mode of exercise can be used in future studies of short-term power output in youth.

Interpreting Youth Aerobic Fitness: Promoting Evidence-Based Discussion­A Response to Dotan (2019)

We welcome Raffy Dotan's Letter to the Editor (14) as it gives us another opportunity to promote evidence-based discussion of the development of youth aerobic fitness. Readers of our contributions to the 2019 Special Issue of Pediatric Exercise Science (6,27,28) will recall that we concluded with, "The authors encourage all pediatric exercise scientists to engage with this discussion, to share ideas and methods, and be willing to explore alternatives. There are many issues to resolve and constructive, collaborative debate will speed our collective aim toward a better understanding of pediatric aerobic fitness in health and disease" (27, p. 256). Not the words of authors preaching a "gospel" with "evangelistic persistence" as Dotan (14) suggests, but of scientists genuinely seeking to stimulate evidence-based discussion of the development of youth aerobic fitness and its relationship with health and well-being.

Interpreting Aerobic Fitness in Youth: The Fallacy of Ratio Scaling.

In this paper, we draw on cross-sectional, treadmill-determined, peak oxygen uptake data, collected in our laboratory over a 20-year period, to examine whether traditional per body mass (ratio) scaling appropriately controls for body size differences in youth. From an examination of the work of pioneering scientists and the earliest studies of peak oxygen uptake, we show how ratio scaling appears to have no sound scientific or statistical rationale. Using simple methods based on correlation and regression, we demonstrate that the statistical relationships, which are assumed in ratio scaling, are not met in groups of similar aged young people. We also demonstrate how sample size and composition can influence relationships between body mass and peak oxygen uptake and show that mass exponents derived from log-linear regression effectively remove the effect of body mass. Indiscriminate use of ratio scaling to interpret young people's fitness, to raise "Clinical Red Flags", and to assess clinical populations concerns us greatly, as recommendations and conclusions based upon this method are likely to be spurious. We urge those involved with investigating youth fitness to reconsider how data are routinely scaled for body size.

Sex-Specific Longitudinal Modeling of Youth Peak Oxygen Uptake.

Purpose: To investigate peak oxygen uptake ( V˙O2 ) in relation to sex, age, body mass, fat-free mass (FFM), maturity, and overweight status. Methods: Multiplicative, allometric models of 10- to 18-year-olds were founded on 1057 determinations of peak V˙O2 supported by anthropometry and estimates of maturity status. Results: Baseline models with body mass controlled for showed age to exert a positive effect on peak V˙O2 , with negative estimates for age2, sex, and a sex-by-age interaction. Sex-specific models showed maturity status to have a positive effect on peak V˙O2 in addition to the effects of age and body mass. Introducing skinfold thicknesses to provide, with body mass, a surrogate for FFM explained maturity effects and yielded a significantly (P < .05) better statistical fit in all models compared with those based on FFM estimated from youth-specific skinfold equations. With girls only, the introduction of overweight, defined by body mass index, resulted in a small but significant (P < .05) negative effect, with an age-by-overweight status interaction. Conclusions: FFM has a powerful influence on peak V˙O2 in both sexes. Interpretation of the development of youth aerobic fitness and its application to health should reflect the sex- and maturity-associated variation in FFM.

Expert's Choice: 2018's Most Exciting Research in the Field of Pediatric Exercise Science.

This commentary highlights 23 noteworthy publications from 2018, selected by leading scientists in pediatric exercise science. These publications have been deemed as significant or exciting in the field as they (a) reveal a new mechanism, (b) highlight a new measurement tool, (c) discuss a new concept or interpretation/application of an existing concept, or (d) describe a new therapeutic approach or clinical tool in youth. In some cases, findings in adults are highlighted, as they may have important implications in youth. The selected publications span the field of pediatric exercise science, specifically focusing on: aerobic exercise and training; neuromuscular physiology, exercise, and training; endocrinology and exercise; resistance training; physical activity and bone strength; growth, maturation, and exercise; physical activity and cognition; childhood obesity, physical activity, and exercise; pulmonary physiology or diseases, exercise, and training; immunology and exercise; cardiovascular physiology and disease; and physical activity, inactivity, and health.