Abstract
. 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 $${\dot{\mathrm{V}}}_{\mathrm{E}}$$
.
.
. V
. ˙
.
. E
.
. ) 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 $${\dot{\mathrm{V}}}_{\mathrm{E}}$$
.
.
. V
. ˙
.
. E
.
. once these covariates had been controlled for stature had no additional, significant (p > 0.05) effect on peak $${\dot{\mathrm{V}}}_{\mathrm{E}}$$
.
.
. V
. ˙
.
. E
.
. 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 $${\dot{\mathrm{V}}}_{\mathrm{E}}$$
.
.
. V
. ˙
.
. E
.
. or peak VT once age and morphological covariates had been controlled for.
.
. Conclusions
. Elucidation of the sex-specific development of peak $${\dot{\mathrm{V}}}_{\mathrm{E}}$$
.
.
. V
. ˙
.
. E
.
. 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.
.

Abstract
Purposes
To investigate longitudinally (1) the contribution of morphological covariates to explaining the development of maximum cardiac output ($${\dot{\text{Q}}}$$Q˙ max) and maximum arteriovenous oxygen difference (a-vO2 diff max), (2) sex differences in $${\dot{\text{Q}}}$$Q˙ 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 ($$\dot{{V}}{\mathrm{O}}_{2}$$V˙O2).

Methods
Fifty-one (32 boys) 11–13-year-olds had their peak $$\dot{{V}}{\mathrm{O}}_{2}$$V˙O2, maximum heart rate (HR max), $${\dot{\text{Q}}}$$Q˙ 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 $$\dot{{V}}{\mathrm{O}}_{2}$$V˙O2. The best-fit models for $${\dot{\text{Q}}}$$Q˙ 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 $$\dot{{V}}{\mathrm{O}}_{2}$$V˙O2. With FFM controlled for, the introduction of either $${\dot{\text{Q}}}$$Q˙ max or a-vO2 diff max to multilevel models of peak $$\dot{{V}}{\mathrm{O}}_{2}$$V˙O2 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 $${\dot{\text{Q}}}$$Q˙ max or a-vO2 diff max, (2) FFM was the dominant influence on the development of peak $$\dot{{V}}{\mathrm{O}}_{2}$$V˙O2, and (3) with FFM and either $${\dot{\text{Q}}}$$Q˙ max or a-vO2 diff max controlled for, there remained an unresolved sex difference of ~ 4% in peak $$\dot{{V}}{\mathrm{O}}_{2}. $$V˙O2.

Abstract
. 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 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 

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.

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.

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.

Abstract
.
. 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 < 0.01) increases in $$ {\dot{\text{V}}\text{O}}_{2} $$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 < 0.05) sex difference in peak $$ {\dot{\text{V}}\text{O}}_{2} $$V˙O2 remained. Introducing SVmax to the multilevel model revealed a significant (p < 0.05), but small additional effect of SVmax on peak $$ {\dot{\text{V}}\text{O}}_{2} $$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%.
.

BackgroundUK general practice faces a workforce crisis, with general practitioner (GP) shortages, organisational change, substantial pressures across the whole health-care system and an ageing population with increasingly complex health needs. GPs require lengthy training, so retaining the existing workforce is urgent and important.Objectives(1) to identify the key policies and strategies that might (i) facilitate the retention of experienced GPs in direct patient care or (ii) support the return of GPs following a career break. (2) to consider the feasibility of potentially implementing those policies and strategies.DesignThis was a comprehensive, mixed-methods study.SettingThis study took place in primary care in England.ParticipantsGeneral practitioners registered in south-west England were surveyed. Interviews were with purposively selected GPs and primary care stakeholders. A RAND/UCLA Appropriateness Method (RAM) panel comprised GP partners and GPs working in national stakeholder organisations. Stakeholder consultations included representatives from regional and national groups.Main outcome measuresSystematic review – factors affecting GPs’ decisions to quit and to take career breaks. Survey – proportion of GPs likely to quit, to take career breaks or to reduce hours spent in patient care within 5 years of being surveyed. Interviews – themes relating to GPs’ decision-making. RAM – a set of policies and strategies to support retention, assessed as ‘appropriate’ and ‘feasible’. Predictive risk modelling – predictive model to identify practices in south-west England at risk of workforce undersupply within 5 years. Stakeholder consultation – comments and key actions regarding implementing emergent policies and strategies from the research.ResultsPast research identified four job-related ‘push’ factors associated with leaving general practice: (1) workload, (2) job dissatisfaction, (3) work-related stress and (4) work–life balance. The survey, returned by 2248 out of 3370 GPs (67%) in the south-west of England, identified a high likelihood of quitting (37%), taking a career break (36%) or reducing hours (57%) within 5 years. Interviews highlighted three drivers of leaving general practice: (1) professional identity and value of the GP role, (2) fear and risk associated with service delivery and (3) career choices. The RAM panel deemed 24 out of 54 retention policies and strategies to be ‘appropriate’, with most also considered ‘feasible’, including identification of and targeted support for practices ‘at risk’ of workforce undersupply and the provision of formal career options for GPs wishing to undertake portfolio roles. Practices at highest risk of workforce undersupply within 5 years are those that have larger patient list sizes, employ more nurses, serve more deprived and younger populations, or have poor patient experience ratings. Actions for national organisations with an interest in workforce planning were identified. These included collection of data on the current scope of GPs’ portfolio roles, and the need for formal career pathways for key primary care professionals, such as practice managers.LimitationsThe survey, qualitative research and modelling were conducted in one UK region. The research took place within a rapidly changing policy environment, providing a challenge in informing emergent policy and practice.ConclusionsThis research identifies the basis for current concerns regarding UK GP workforce capacity, drawing on experiences in south-west England. Policies and strategies identified by expert stakeholders after considering these findings are likely to be of relevance in addressing GP retention in the UK. Collaborative, multidisciplinary research partnerships should investigate the effects of rolling out some of the policies and strategies described in this report.Study registrationThis study is registered as PROSPERO CRD42016033876 and UKCRN ID number 20700.FundingThe National Institute for Health Research Health Services and Delivery Research programme.

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 

ObjectivesThe 20 m shuttle run test (20mSRT) is used to estimate cardiorespiratory fitness (CRF) through the prediction of peak oxygen uptake (V˙O2), but its validity as a measure of CRF during childhood and adolescence is questionable. This study examined the validity of the 20mSRT to predict peak V˙O2. MethodsPeak V˙O2 was measured during treadmill running. Log-linear regression was used to correct peak V˙O2 for body mass and sum of skinfolds plus age. Boys completed the 20mSRT under standardised conditions. Maximum speed (km/h) was used with age to predict peak V˙O2 using the equation developed by Léger et al. Validity was examined from linear regression methods and limits of agreement (LoA). Relationships between 20mSRT performance and allometrically adjusted peak V˙O2, and predicted per cent fat were examined.ResultsThe sample comprised 76 boys aged 11–14 years. Predicted and measured mass-related peak V˙O2 (mL/kg/min) shared common variance of 32%. LoA revealed that measured peak V˙O2 ranged from 15% below to 25% above predicted peak V˙O2. There were no significant relationships (p>0.05) between predicted peak V˙O2 and measured peak V˙O2 adjusted for mass, age and skinfold thicknesses. Adjusted for body mass and age, peak V˙O2 was not significantly related (p>0.05) to 20mSRT final speed but a weak, statistically significant (r=0.24, p<0.05) relationship was found with peak V˙O2 adjusted for mass and fatness. Predicted per cent fat was negatively correlated with 20mSRT speed (r=−0.61, p<0.001).ConclusionsThe 20mSRT reflects fatness rather than CRF and has poor validity grounded in its flawed estimation and interpretation of peak V˙O2 in mL/kg/min.

Objective to identify factors influencing general practitioners’ (GPs’) decisions about whether or not to remain in direct patient care in general practice and what might help to retain them in that role. Design Qualitative, in-depth, individual interviews exploring factors related to GPs leaving, remaining in and returning to direct patient care. Setting South West England, UK. Participants 41 GPs: 7 retired; 8 intending to take early retirement; 11 who were on or intending to take a career break; 9 aged under 50 years who had left or were intending to leave direct patient care and 6 who were not intending to leave or to take a career break. Plus 19 stakeholders from a range of primary care-related professional organisations and roles. Results Reasons for leaving direct patient care were complex and based on a range of job-related and individual factors. Three key themes underpinned the interviewed GPs’ thinking and rationale: issues relating to their personal and professional identity and the perceived value of general practice-based care within the healthcare system; concerns regarding fear and risk, for example, in respect of medical litigation and managing administrative challenges within the context of increasingly complex care pathways and environments; and issues around choice and volition in respect of personal social, financial, domestic and professional considerations. These themes provide increased understanding of the lived experiences of working in today’s National Health Service for this group of GPs. Conclusion Future policies and strategies aimed at retaining GPs in direct patient care should clarify the role and expectations of general practice and align with GPs’ perception of their own roles and identity; demonstrate to GPs that they are valued and listened to in planning delivery of the UK healthcare; target GPs’ concerns regarding fear and risk, seeking to reduce these to manageable levels and give GPs viable options to support them to remain in direct patient care.

BACKGROUND: There is a growing literature on evaluating aspects of patient and public involvement (PPI). We have suggested that at the core of successful PPI is the dynamic interaction of different forms of knowledge, notably lay and professional. We have developed a four-dimensional theoretical framework for understanding these interactions. AIM: We explore the practical utility of the theoretical framework as a tool for mapping and evaluating the experience of PPI in health services research. METHODS: We conducted three workshops with different PPI groups in which participants were invited to map their PPI experiences on wall charts representing the four dimensions of our framework. The language used to describe the four dimensions was modified to make it more accessible to lay audiences. Participants were given sticky notes to indicate their own positions on the different dimensions and to write explanatory comments if they wished. Participants' responses were then discussed and analysed as a group. RESULTS: the three groups were distinctive in their mapped responses suggesting different experiences in relation to having a strong or weak voice in their organization, having few or many ways of getting involved, addressing organizational or public concerns and believing that the organization was willing to change or not. DISCUSSION: the framework has practical utility for mapping and evaluating PPI interactions and is sensitive to differences in PPI experiences within and between different organizations. The workshops enabled participants to reflect collaboratively on their experiences with a view to improving PPI experiences and planning for the future.

UNLABELLED: Significant increased hip fracture incidence has been reported in the year following total knee replacement. This study demonstrates that bone and muscle loss is a post-surgical consequence of total knee replacement, alongside poor outcomes in function and activity potentially contributing to reduced quality of life and increased hip fracture risk. INTRODUCTION: a significant increase in hip fracture incidence in the year following total knee replacement (TKR) surgery has been reported. This study investigated function and activity following TKR and the effects of limited mobility on bone and muscle loss and their potential contribution to hip fracture risk. METHODS: Changes in dual-energy X-ray absorptiometry (DXA) (GE Lunar Prodigy, Bedford MA), bone mineral density (BMD) at the neck of femur (NOF), total hip region (TH) and lumbar spine were measured alongside leg lean tissue mass (LLTM) in post-menopausal Caucasian females following TKR (N = 19) compared to controls (N = 43). Lumbar spine trabecular bone scores (TBSs) were calculated. Ipsilateral/contralateral weight bearing, lower limb function, 3-day pedometer readings, pain levels and falls were also recorded. Measurements were obtained at pre-surgery baseline and at 6 weeks, 6 months and 12 months post-surgery. RESULTS: No statistically significant differences were demonstrated between groups at baseline bilaterally in LLTM or BMD at the NOF and TH. Losses in ipsilateral NOF and TH BMD and contralateral LLTM were significantly higher in the TKR group at 6 months. Impairment in function and weight bearing persisted in the TKR group 12 months post-operatively alongside deficits in bilateral muscle mass and ipsilateral NOF and TH BMD. Falls incidence was not significantly higher in the TKR group. CONCLUSIONS: Bone loss at the hip with associated muscle loss is a consequence of TKR that, in addition to poor patient outcomes in function and activity, potentially contributes to increased hip fracture risk in the year following surgery.

Background
Depression is associated with physical inactivity, which may mediate the relationship between depression and a range of chronic physical health conditions. However, few interventions have combined a psychological intervention for depression with behaviour change techniques, such as behavioural activation (BA), to promote increased physical activity.

Methods
To determine procedural and clinical uncertainties to inform a definitive randomised controlled trial (RCT), a pilot parallel-group RCT was undertaken within two Improving Access to Psychological Therapies (IAPT) services in South West England. We aimed to recruit 80 adults with depression and randomise them to a supported, written self-help programme based on either BA or BA plus physical activity promotion (BAcPAc). Data were collected at baseline and 4 months post-randomisation to evaluate trial retention, intervention uptake and variance in outcomes to inform a sample size calculation. Qualitative data were collected from participants and psychological wellbeing practitioners (PWPs) to assess the acceptability and feasibility of the trial methods and the intervention. Routine data were collected to evaluate resource use and cost.

Results
Sixty people with depression were recruited, and a 73 % follow-up rate was achieved. Accelerometer physical activity data were collected for 64 % of those followed. Twenty participants (33 %) attended at least one treatment appointment. Interview data were analysed for 15 participants and 9 study PWPs. The study highlighted the challenges of conducting an RCT within existing IAPT services with high staff turnover and absences, participant scheduling issues, PWP and participant preferences for cognitive focussed treatment, and deviations from BA delivery protocols. The BAcPAc intervention was generally acceptable to patients and PWPs.

Conclusions
Although recruitment procedures and data collection were challenging, participants generally engaged with the BAcPAc self-help booklets and reported willingness to increase their physical activity. A number of feasibility issues were identified, in particular the under-use of BA as a treatment for depression, the difficulty that PWPs had in adapting their existing procedures for study purposes and the instability of the IAPT PWP workforce. These problems would need to be better understood and resolved before proceeding to a full-scale RCT.

Total body (TB) dual-energy X-ray absorptiometry (DXA) is increasingly being used to measure body composition in research and clinical settings. This study investigated the effect of body mass index (BMI) and body fat on precision errors for total and regional TB DXA measurements of bone mineral density, fat tissue, and lean tissue using the GE Lunar Prodigy (GE Healthcare, Bedford, UK). One hundred forty-four women with BMI's ranging from 18.5 to 45.9kg/m2 were recruited. Participants had duplicate DXA scans of the TB with repositioning between examinations. Participants were divided into 3 groups based on their BMI, and the root mean square standard deviation and the percentage coefficient of variation were calculated for each group. The root mean square standard deviation (percentage coefficient of variation) for the normal (30kg/m2; n=32) BMI groups, respectively, were total BMD (g/cm2): 0.009 (0.77%), 0.009 (0.69%), 0.011 (0.91%); total fat (g): 545 (2.98%), 486 (1.72%), 677 (1.55%); total lean (g): 551 (1.42%), 540 (1.34%), and 781 (1.68%). These results suggest that serial measurements in obese subjects should be treated with caution because the least significant change may be larger than anticipated.

BACKGROUND: Challenges remain to find ways to support patients with depression who have low levels of physical activity (PA) to overcome perceived barriers and enhance the perceived value of PA for preventing future relapse. There is an evidence-base for behavioural activation (BA) for depression, which focuses on supporting patients to restore activities that have been avoided, but practitioners have no specific training in promoting PA. We aimed to design and evaluate an integrated BA and PA (BAcPAc) practitioner-led, written, self-help intervention to enhance both physical and mental health. METHODS/DESIGN: This study is informed by the Medical Research Council Complex Intervention Framework and describes a protocol for a pilot phase II randomised controlled trial (RCT) to test the feasibility and acceptability of the trial methods to inform a definitive phase III RCT. Following development of the augmented written self-help intervention (BAcPAc) incorporating behavioural activation with physical activity promotion, depressed adults are randomised to receive up to 12 sessions over a maximum of 4 months of either BAcPAc or behavioural activation alone within a written self-help format, which represents treatment as usual. The study is located within two 'Improving Access to Psychological Therapies' services in South West England, with both written self-help interventions supported by mental health paraprofessionals. Measures assessed at 4, 9, and 12 month follow-up include the following: CIS-R, PHQ-9, accelerometer recorded (4 months only) and self-reported PA, body mass index, blood pressure, Insomnia Severity Index, quality of life, and health and social care service use. Process evaluation will include analysis of recorded support sessions and patient and practitioner interviews. At the time of writing the study has recruited 60 patients. DISCUSSION: the feasibility outcomes will inform a definitive RCT to assess the clinical and cost-effectiveness of the augmented BAcPAc written self-help intervention to reduce depression and depressive relapse, and bring about improvements across a range of physical health outcomes. TRIAL REGISTRATION: Current Controlled Trials ISRCTN74390532, 26.03.2013.

OBJECTIVE: to investigate: the accuracy of measuring relative left/right weight-bearing using two identically calibrated weighing scales; the short-term weight-bearing tendencies in a general population of 9 participants and long-term in 42 females; the effect weight-bearing inequalities on hip bone mineral density and leg lean tissue mass. METHOD: Participants were measured standing astride two scales. Short-term volunteers were measured 10 times on one visit, with repositioning between measurements and the long-term group were measured on three visits at 6 month intervals. Baseline bilateral hip and total body Dual X-ray Absorptiometry scans were performed on the long-term group. RESULTS: the short-term Coefficient of Variation is 5.41% and long-term 7.01%. No significant correlations were found between hip bone density differences and weight-bearing inequalities, although a weak correlation of r = 0.31 (p = 0.047) was found for differences in leg lean tissue mass. CONCLUSION: Left/right weight-bearing measured using two scales is a consistent method for evaluating weight distribution through the legs. The short- and long-term weight-bearing tendencies showed a similar degree of variation. Weight-bearing inequalities were not associated with any significant left/right differences in bone mineral density at the hip, but were weakly associated with left-right differences in leg muscle mass.

A previous modelling study predicted that the forces applied by the extensor muscles to stabilise the lumbar spine would be greater in spines that have a larger sagittal curvature (lordosis). Because the force-generating capacity of a muscle is related to its size, it was hypothesised that the size of the extensor muscles in a subject would be related to the size of their lumbar lordosis. Magnetic resonance imaging (MRI) data were obtained, together with age, height, body mass and back pain status, from 42 female subjects. The volume of the extensor muscles (multifidus and erector spinae) caudal to the mid-lumbar level was estimated from cross-sectional area measurements in axial T1-weighted MRIs spanning the lumbar spine. Lower lumbar curvature was determined from sagittal T1-weighted images. A stepwise linear regression model was used to determine the best predictors of muscle volume. The mean lower lumbar extensor muscle volume was 281cm3 (SD=49cm3). The mean lower lumbar curvature was 30° (SD=7°). Five subjects reported current back pain and were excluded from the regression analysis. Nearly half the variation in muscle volume was accounted for by the variables age (standardised coefficient, B=-3.2, P=0.03) and lower lumbar curvature (B=0.47, P=0.002). The results support the hypothesis that extensor muscle volume in the lower lumbar spine is related to the magnitude of the sagittal curvature; this has implications for assessing muscle size as an indicator of muscle strength. © 2013 Anatomical Society.

The influence of training status on pulmonary VO(2) recovery kinetics, and its interaction with maturity, has not been investigated in young girls. Sixteen prepubertal (Pre: trained (T, 11.4 ± 0.7 years), 8 untrained (UT, 11.5 ± 0.6 years)) and 8 pubertal (Pub: 8T, 14.2 ± 0.7 years; 8 UT, 14.5 ± 1.3 years) girls completed repeat transitions from heavy intensity exercise to a baseline of unloaded exercise, on both an upper and lower body ergometer. The VO2 recovery time constant was significantly shorter in the trained prepubertal and pubertal girls during both cycle (Pre: T, 26 ± 4 vs. UT, 32 ± 6; Pub: T, 28 ± 2 vs. UT, 35 ± 7 s; both p <. 05) and upper body exercise (Pre: T, 26 ± 4 vs. UT, 35 ± 6; Pub: T, 30 ± 4 vs. UT, 42 ± 3 s; both p <. 05). No interaction was evident between training status and maturity. These results demonstrate the sensitivity of VO(2) recovery kinetics to training in young girls and challenge the notion of a "maturational threshold" in the influence of training status on the physiological responses to exercise and recovery.

The precision errors of dual-energy X-ray absorptiometry (DXA) measurements are important for monitoring osteoporosis. This study investigated the effect of body mass index (BMI) on precision errors for lumbar spine (LS), femoral neck (NOF), total hip (TH), and total body (TB) bone mineral density using the GE Lunar Prodigy. One hundred two women with BMIs ranging from 18.5 to 45.9kg/m 2 were recruited. Participants had duplicate DXA scans of the LS, left hip, and TB with repositioning between scans. Participants were divided into 3 groups based on their BMI and the percentage coefficient of variation (%CV) calculated for each group. The %CVs for the normal (30kg/m 2) (n=28) BMI groups, respectively, were LS BMD: 0.99%, 1.30%, and 1.68%; NOF BMD: 1.32%, 1.37%, and 2.00%; TH BMD: 0.85%, 0.88%, and 1.06%; TB BMD: 0.66%, 0.73%, and 0.91%. Statistically significant differences in precision error between the normal and obese groups were found for LS (p=0.0006), NOF (p=0.005), and TB BMD (p=0.025). These results suggest that serial measurements in obese subjects should be treated with caution because the least significant change may be larger than anticipated. © 2012 the International Society for Clinical Densitometry.

The precision errors of dual-energy X-ray absorptiometry (DXA) measurements are important for monitoring osteoporosis. This study investigated the effect of body mass index (BMI) on precision errors for lumbar spine (LS), femoral neck (NOF), total hip (TH), and total body (TB) bone mineral density using the GE Lunar Prodigy. One hundred two women with BMIs ranging from 18.5 to 45.9 kg/m(2) were recruited. Participants had duplicate DXA scans of the LS, left hip, and TB with repositioning between scans. Participants were divided into 3 groups based on their BMI and the percentage coefficient of variation (%CV) calculated for each group. The %CVs for the normal (30 kg/m(2)) (n=28) BMI groups, respectively, were LS BMD: 0.99%, 1.30%, and 1.68%; NOF BMD: 1.32%, 1.37%, and 2.00%; TH BMD: 0.85%, 0.88%, and 1.06%; TB BMD: 0.66%, 0.73%, and 0.91%. Statistically significant differences in precision error between the normal and obese groups were found for LS (p=0.0006), NOF (p=0.005), and TB BMD (p=0.025). These results suggest that serial measurements in obese subjects should be treated with caution because the least significant change may be larger than anticipated.

It has been suggested that the potential for training to alter the physiological responses to exercise in children is related to a "maturational threshold". To address this, we investigated the interaction of swim-training status and maturity on cardiovascular and metabolic responses to lower and upper body exercise. Twenty-one prepubertal [Pre: 11 trained (T), 10 untrained (UT)], 30 pubertal (Pub: 14 T, 16 UT), and 18 postpubertal (Post: 8 T, 10 UT) girls completed ramp incremental exercise on a cycle and an upper body ergometer. In addition to pulmonary gas exchange measurements, stroke volume and cardiac output were estimated by thoracic bioelectrical impedance, and muscle oxygenation status was assessed using near-infrared spectroscopy. All T girls had a higher peak O(2) uptake during cycle (Pre: T 49 ± 5 vs. UT 40 ± 4; Pub: T 46 ± 5 vs. UT 36 ± 4; Post: T 48 ± 5 vs. UT 39 ± 8 ml·kg(-1)·min(-1); all P < 0.05) and upper body exercise (Pre: T 37 ± 6 vs. UT 32 ± 5; Pub: T 36 ± 5 vs. UT 28 ± 5; Post: T 39 ± 3 vs. UT 28 ± 7 ml·kg(-1)·min(-1); all P < 0.05). T girls also had a higher peak cardiac output during both modalities, and this reached significance in Pub (cycle: T 21 ± 3 vs. UT 18 ± 3; upper body: T 20 ± 4 vs. UT 15 ± 4 l/min; all P < 0.05) and Post girls (cycle: T 21 ± 4 vs. UT 17 ± 2; upper body: T 22 ± 3 vs. UT 18 ± 2 l/min; all P < 0.05). None of the measured pulmonary, cardiovascular, or metabolic parameters interacted with maturity, and the magnitude of the difference between T and UT girls was similar, irrespective of maturity stage. These results challenge the notion that differences in training status in young people are only evident once a maturational threshold has been exceeded.

The influence of training status on the oxygen uptake (VO2) response to heavy intensity exercise in pubertal girls has not previously been investigated. We hypothesised that whilst training status-related adaptations would be evident in the VO2, heart rate (HR) and deoxyhaemoglobin ([HHb]) kinetics of pubertal swimmers during both lower and upper body exercise, they would be more pronounced during upper body exercise. Eight swim-trained (T; 14.2 ± 0.7 years) and eight untrained (UT; 14.5 ± 1.3 years) girls completed a number of constant-work-rate transitions on cycle and upper body ergometers at 40% of the difference between the gas exchange threshold and peak VO2. The phase II VO2 time constant (τ) was significantly shorter in the trained girls during both cycle (T: 21 ± 6 vs. UT: 35 ± 11 s; P < 0.01) and upper body exercise (T: 29 ± 8 vs. UT: 44 ± 8 s; P < 0.01). The VO2 slow component was not influenced by training status. The [HHb] τ was significantly shorter in the trained girls during both cycle (T: 12 ± 2 vs. UT: 20 ± 6 s; P < 0.01) and upper body exercise (T: 13 ± 3 vs. UT: 21 ± 7 s; P < 0.01), as was the HR τ (cycle, T: 36 ± 5 vs. UT: 53 ± 9 s; upper body, T: 32 ± 3 vs. UT: 43 ± 2; P < 0.01). This study suggests that both central and peripheral factors contribute to the faster VO2 kinetics in the trained girls and that differences are evident in both lower and upper body exercise.

A maturational threshold has been suggested to be present in young peoples' responses to exercise, with significant influences of training status evidenced only above this threshold. The presence of such a threshold has not been investigated for short-term, high-intensity exercise. To address this, we investigated the relationship between swim-training status and maturity on the power output, pulmonary gas exchange, and metabolic responses to an upper- and lower-body Wingate anaerobic test (WAnT). Girls at 3 stages of maturity participated:, prepubertal (Pre: 8 trained (T), 10 untrained (UT)), pubertal (Pub: 9 T, 15 UT), and postpubertal (Post: 8 T, 10 UT). At all maturity stages, T exhibited higher peak power (PP) and mean power (MP) during upper-body exercise (PP: Pre, T, 163 ± 20 vs. UT, 124 ± 29; Pub, T, 230 ± 42 vs. UT, 173 ± 41; Post, T, 245 ± 41 vs. UT, 190 ± 40 W; MP: Pre, T, 130 ± 23 vs. UT, 85 ± 26; Pub, T, 184 ± 37 vs. UT, 123 ± 38; Post, T, 200 ± 30 vs. UT, 150 ± 15 W; all p < 0.05) but not lower-body exercise, whilst the fatigue index was significantly lower in T for both exercise modalities. Irrespective of maturity, the oxidative contribution, calculated by the area under the oxygen uptake response profile, was not influenced by training status. No interaction was evident between training status and maturity, with similar magnitudes of difference between T and UT at all 3 maturity stages. These results suggest that there is no maturational threshold which must be surpassed for significant influences of training status to be manifest in the "anaerobic" exercise performance of young girls.

The limited available evidence suggests that endurance training does not influence the pulmonary oxygen uptake (V(O)(2)) kinetics of pre-pubertal children. We hypothesised that, in young trained swimmers, training status-related adaptations in the V(O)(2) and heart rate (HR) kinetics would be more evident during upper body (arm cranking) than during leg cycling exercise. Eight swim-trained (T; 11.4 +/- 0.7 years) and eight untrained (UT; 11.5 +/- 0.6 years) girls completed repeated bouts of constant work rate cycling and upper body exercise at 40% of the difference between the gas exchange threshold and peak V(O)(2). The phase II V(O)(2) time constant was significantly shorter in the trained girls during upper body exercise (T: 25 +/- 3 vs. UT: 37 +/- 6 s; P < 0.01), but no training status effect was evident in the cycle response (T: 25 +/- 5 vs. UT: 25 +/- 7 s). The V(O)(2) slow component amplitude was not affected by training status or exercise modality. The time constant of the HR response was significantly faster in trained girls during both cycle (T: 31 +/- 11 vs. UT: 47 +/- 9 s; P < 0.01) and upper body (T: 33 +/- 8 vs. UT: 43 +/- 4 s; P < 0.01) exercise. The time constants of the phase II V(O)(2)and HR response were not correlated regardless of training status or exercise modality. This study demonstrates for the first time that swim-training status influences upper body V(O)(2) kinetics in pre-pubertal children, but that cycle ergometry responses are insensitive to such differences.

Disuse osteopenia is a complication of immobilisation, with reversal generally noted upon remobilisation. This case report focuses on a patient who was seen 18 years following a road traffic collision when multiple fractures were sustained. The patient had an external fixator fitted for a tibia and fibula fracture, which remained in situ for a period of 4 years. Following removal, the patient was mobilised but, still required a single crutch to aid walking. Fourteen years post removal of the fixator, the patient had a DXA scan which, demonstrated a T-score 2.5 SD lower on the affected hip. This places the patient at an increased risk of hip fracture on this side, which requires monitoring. There appear to be no current studies investigating prolonged disuse-osteopenia in patients following removal of long-term external fixators. Further research is required to quantify unilateral long-term effects to bone health and fracture risk in this population.

PURPOSE: This study tested the hypothesis that the muscle metabolic responses of 9- to 12-yr-old children and young adults during incremental quadriceps exercise are dependent on age and sex. METHODS: Fifteen boys, 18 girls, 8 men, and 8 women completed a quadriceps step-incremental test to exhaustion inside a magnetic resonance scanner for determination of the muscle metabolic responses using P-magnetic resonance spectroscopy. Quadriceps muscle mass was determined using magnetic resonance imaging scans enabling comparison of metabolic data at a normalized power output. RESULTS: the power output and the energetic state at the Pi/PCr and pH intracellular thresholds (IT) were independent of age and sex. The rate of change in Pi/PCr against power output after the ITPi/PCr (S2) was lower in boys (0.158 +/- 0.089) and girls (0.257 +/- 0.110) compared with men (0.401 +/- 0.114, P < 0.001) and women (0.391 +/- 0.133, P = 0.014), respectively, with sex differences present for children only (P = 0.003). Above the ITpH, S2 was more rapid in the men (-0.041 +/- 0.022, P = 0.003) and girls (-0.030 +/- 0.013, P = 0.011) compared with boys (-0.019 +/- 0.007), with no differences between the girls and the women (-0.035 +/- 0.015, P = 0.479). The increase in Pi/PCr at exhaustion was lower in boys (0.85 +/- 0.38) than that in men (1.86 +/- 0.65, P < 0.001) and in girls (1.78 +/- 1.25) than that in women (4.97 +/- 3.52, P = 0.003), with sex differences in both the child (P = 0.005) and the adult groups (P = 0.019). CONCLUSIONS: During moderate-intensity exercise, muscle metabolism appears adult-like in 9- to 12-yr-old children, although both age- and sex-related differences in the "anaerobic" energy turnover are present during high-intensity exercise.

Twelve 11-year-old girls (six lean, six overweight) were given meals in the laboratory and at school for 5 days, with exercise imposed for 2 days and sedentary activities on another 2 days in counterbalanced sequences. During a preliminary visit, the FLEX heart rate method was used to predict individual exercise durations eliciting 1.5 MJ energy expenditure. Morning and afternoon cycling exercise was subsequently imposed in the laboratory on 2 consecutive days as part of the 5-day intervention. Energy intake was measured via observation with meals being standardised between conditions, prepared and weighed by the research team. Hunger, fullness and desire to eat were rated by subjects immediately before and after meals and exercise. Energy expenditure was significantly elevated in the exercise condition, compared to sedentary. No exercise-induced differences in total daily or 5-day total energy intake were observed between groups or treatments. Overweight girls, however, rated their appetite immediately after exercise as being stronger than they rated it before exercise. In response to exercise-induced energy expenditure, 11-year old overweight and lean girls did not elevate their energy intake over a 5-day period.

To further understand the mechanism(s) explaining the faster pulmonary oxygen uptake (p(VO)(2)) kinetics found in children compared to adults, this study examined whether the phase II p(VO)(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 (31)P-magnetic resonance spectroscopy, and (2) breath by breath changes in p(VO)(2) during upright cycle ergometry. Only subjects (n = 12) with 95% confidence intervals

The splitting of muscle phosphocreatine (PCr) plays an integral role in the regulation of muscle O2 utilization during a "step" change in metabolic rate. This study tested the hypothesis that the kinetics of muscle PCr would be faster in children compared with adults both at the onset and offset of moderate-intensity exercise, in concert with the previous demonstration of faster phase II pulmonary O2 uptake kinetics in children. Eighteen peri-pubertal children (8 boys, 10 girls) and 16 adults (8 men, 8 women) completed repeated constant work-rate exercise transitions corresponding to 80% of the Pi/PCr intracellular threshold. The changes in quadriceps [PCr], [Pi], [ADP], and pH were determined every 6 s using 31P-magnetic resonance spectroscopy. No significant (P>0.05) age- or sex-related differences were found in the PCr kinetic time constant at the onset (boys, 21+/-4 s; girls, 24+/-5 s; men, 26+/-9 s; women, 24+/-7 s) or offset (boys, 26+/-5 s; girls, 29+/-7 s; men, 23+/-9 s; women 29+/-7 s) of exercise. Likewise, the estimated theoretical maximal rate of oxidative phosphorylation (Qmax) was independent of age and sex (boys, 1.39+/-0.20 mM/s; girls, 1.32+/-0.32 mM/s; men, 2.36+/-1.18 mM/s; women, 1.51+/-0.53 mM/s). These results are consistent with the notion that the putative phosphate-linked regulation of muscle O2 utilization is fully mature in peri-pubertal children, which may be attributable to a comparable capacity for mitochondrial oxidative phosphorylation in child and adult muscle.

Aerobic fitness depends upon the components of oxygen delivery and the oxidative mechanisms of the exercising muscle. Peak oxygen uptake is recognised as the best single criterion of aerobic fitness but it is strongly correlated with body size. Methods of controlling for body size are discussed and it is demonstrated how inappropriate use of ratio scaling has clouded our understanding of aerobic fitness during growth and maturation and across time. Changes in aerobic fitness over time are reviewed but no published study of peak oxygen uptake, appropriately adjusted for body mass and maturation, has investigated secular changes in aerobic fitness. Data expressed in direct ratio with body mass provide limited insights into secular changes in aerobic fitness but aerobic performance appears to be decreasing in accord with the secular increase in body mass. Cross-sectional and longitudinal peak oxygen uptake data are analysed in relation to age, maturation and sex. Muscle lactate production and blood lactate accumulation are outlined and young people's blood lactate responses to submaximal and maximal exercise are examined. However, exercise of the intensity and duration required to monitor conventional laboratory measures of aerobic fitness are rarely experienced in young people's lives. In many situations it is the oxygen uptake kinetics of the non-steady state which best assess the integrated responses of the oxygen delivery system and the metabolic requirements of the exercising muscle. The chapter therefore concludes with a discussion of insights into aerobic fitness provided by the emerging database on young people's oxygen uptake kinetics responses to exercise of different intensities.

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.

This article reviews the habitual physical activity of children and adolescents from member countries of the European Union in relation to methods of assessing and interpreting physical activity. Data are available from all European Union countries except Luxembourg and the trends are very similar. European boys of all ages participate in more physical activity than European girls and the gender difference is more marked when vigorous activity is considered. The physical activity levels of both genders are higher during childhood and decline as young people move through their teen years. Physical activity patterns are sporadic and sustained periods of moderate or vigorous physical activity are seldom achieved by many European children and adolescents. Expert committees have produced guidelines for health-related physical activity for youth but they are evidence-informed rather than evidence-based and where there is evidence of a relationship between physical activity during youth and health status there is little evidence of a particular shape of that relationship. The number of children who experience physical activity of the duration, frequency and intensity recommended by expert committees decreases with age but accurate estimates of how many girls and boys are inactive are clouded by methodological problems. If additional insights into the promotion of health through habitual physical activity during youth are to be made, methods of assessment need to be further refined and recommended guidelines re-visited in relation to the existing evidence base.

AIM: to investigate whether aerobic fitness is associated with skin microvascular function in healthy adults with an increased risk of developing Type 2 diabetes. METHODS: Twenty-seven healthy normal glucose-tolerant humans with either a previous diagnosis of gestational diabetes or having two parents with Type 2 diabetes and 27 healthy adults who had no history of diabetes were recruited. Maximal oxygen uptake was assessed using an incremental exercise test to exhaustion. Skin microvascular function was assessed using laser Doppler techniques as the maximum skin hyperaemic response to a thermal stimulus (maximum hyperaemia) and the forearm skin blood flow response to the iontophoretic application of acetylcholine (ACh) and sodium nitroprusside. RESULTS: Maximal oxygen uptake was not significantly different in the 'at-risk' group compared with healthy controls. Maximum hyperaemia was reduced in those 'at risk' (1.29 +/- 0.30 vs. 1.46 +/- 0.33 V, P = 0.047); however, the peak response to acetylcholine or sodium nitroprusside did not differ in the two groups. A significant positive correlation was demonstrated between maximal oxygen uptake and maximum hyperaemia (r = 0.52, P = 0.006 l/min and r = 0.60, P = 0.001 ml/kg/min) and peak ACh response (r = 0.40, P = 0.04 l/min and r = 0.47, P = 0.013 ml/kg/min) in the 'at-risk' group when expressed in absolute (l/min) or body mass-related (ml/kg/min) terms. No significant correlations were found in the control group. CONCLUSIONS: in this 'at-risk' group with skin microvascular dysfunction maximal oxygen uptake was not reduced compared with healthy controls. However, in the 'at-risk' group alone, individuals with higher levels of aerobic fitness also had better microvascular and endothelial responsiveness.

Short-term effects of different intensities of exercise-induced energy expenditure on energy intake and hunger were compared in 19 girls (10.0 +/- 0.6 years) in three conditions: sedentary, low-intensity exercise and high-intensity exercise. The exercise conditions involved cycling at 50 and 75% of peak oxygen uptake, respectively, but were designed to evoke approximately 1.50 MJ of total expenditure, as estimated from continuously monitored heart rate. A maintenance breakfast of controlled energy intake was provided and ad libitum energy intake was measured at lunch and dinner. Differences in energy intake relative to expenditure, between 09:30 and 17:00, were calculated by subtracting energy expenditure from energy intake (energy difference). Hunger, fullness and prospective consumption were rated before and after meals and exercise sessions. Lunch energy intake was significantly less after low-intensity exercise than after high-intensity exercise. Energy expenditure was greater in the exercise conditions than when sedentary and the energy difference was more positive in the sedentary condition than in each of the exercise conditions. At mid-afternoon, rated prospective consumption was less after the high-intensity exercise. The imposition of energy expenditure through exercise of either low or high intensity resulted in no detectable increase in energy intake in the short term.

These studies used multilevel modelling to examine optimised peak power (PPopt) from a force velocity test over the age range 12-14 years. In the first study, body mass, stature, triceps and subscapular skinfold thicknesses of boys and girls, aged 12.3 ± 0.3 y at the onset of the study, were measured on four occasions at 6 monthly intervals. The analysis was founded on 146 PPopt determinations (79 from boys and 67 from girls). Body mass and stature were significant explanatory variables with sum of two skinfolds exerting an additional effect. No gender differences were evident but PPopt increased with age. In the second study, thigh muscle volume (TMV) was estimated using magnetic resonance imaging at test occasions two and four. The analysis, founded on a subsample of 67 PPopt determinations (39 from boys and 28 from girls), demonstrated TMV to be a significant additional explanatory variable along-side body mass and stature with neither age nor gender making a significant contribution to PP opt. Together the studies demonstrate the influence of body size and TMV on young people's PPopt.

Age- and sex-related differences in optimal peak power (PPopt) and associated measures determined using a force-velocity (F-V) cycling test were examined in pre teenage, teenage and adult males and females. Absolute PPopt increased significantly with age in both males and females. With body mass controlled for using allometric scaling significant age related increases remained, an effect masked in the females when PPopt was expressed as W · kg-1. Sex differences in PPopt were minimal in the preteens but males demonstrated higher PPopt than females in both teenage and adult groups. These patterns of change with age and sex broadly reflect those obtained for Wingate Anaerobic Test determined PP but the use of a single non-optimized braking force underestimates the magnitude of any differences observed.

The purpose of this study was to assess the reliability of the ventilatory threshold using visual analysis (TVent) and a computerised v-slope method (TV - slope) with children. Twenty-two children completed 2 ramp incremental cycling tests to voluntary exhaustion. Oxygen uptake (V̇O2) at TVent was derived independently by two observers using plots of V̇E/V̇CO2, V̇E/V̇O2, PETO2 and PETCO2, V̇E and RER as a function of time. V̇O2 at TV - slope was determined by both observers using linear regression analysis of the plot of V̇CO2 against V̇O2. A TV - slope, was determined for each test, although a TVent could not be found by one of the observers in 7 of the 44 tests. Inter-observer reliability was slightly better for TV - slope, and both methods had similar test-retest coefficients of repeatability (0.19 and 0.22 L · min-1, TVent and TV - slope, respectively). Although TV - slope may be the method of choice, investigators should consider the 95% limits of agreement when interpreting their data.

In this study, we used multi-level regression modelling to assess the influence of age, sex, body size, skinfold thicknesses, maturity, thigh muscle volume and isokinetic leg strength on the development of load- and inertia-adjusted peak (1 s) and mean power (30 s) determined using the Wingate anaerobic test. Fifteen males and 19 females were measured twice, first aged 10.0 +/- 0.3 years and then aged 11.8 +/- 0.3 years. Initial models identified body mass and height as significant explanatory variables (P < 0.05) for peak power and mean power, with an additional age effect for the former. No significant differences between the sexes or maturity effects were observed for either peak or mean power (P > 0.05). The introduction of sum of skinfolds improved the fit of the model and rendered the height term non-significant for both peak and mean power (P> 0.05). An age effect became apparent for mean power. When isokinetic leg strength and thigh muscle volume were entered into the model, the latter exerted a significant effect on both peak and mean power (P< 0.05), whereas isokinetic leg strength was not a significant explanatory variable for either (P> 0.05). In conclusion, thigh muscle volume exerts a positive influence on young people's short-term power output, which is additional to the effects of body mass, sum of skinfolds and age.

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.

OBJECTIVE: to examine short term power output during growth and maturation using a multilevel modelling approach. METHODS: Body mass, stature, and triceps and subscapular skinfold thicknesses of boys and girls, aged 12.2 (0.4) years (mean (SD)) at the onset of the study, were measured at age 12, 13, and 17 years. Sexual maturation, classified according to Tanner's stage of pubic hair development, was assessed on the first two occasions and assumed to be stage 5 at 17 years. Peak power (PP) and mean power (MP) were assessed on each occasion using the Wingate anaerobic test. RESULTS: Initial models, founded on 417 determinations of short term power output, identified body mass, stature, and age as significant explanatory variables of both PP and MP. The values for girls were significantly lower than those for boys, and a significant age by sex interaction described a progressive divergence in the MP of boys and girls. The introduction of sum of two skinfold thicknesses produced a model with an improvement in fit as indicated by a significant change in log likelihood. The stature term was negated and the body mass term increased. The age and sex terms were reduced but remained significant. The age by sex interaction term remained a significant explanatory variable for MP. Maturity effects were non-significant additional explanatory variables in all models of power output. CONCLUSION: the values of PP and MP for boys are higher than those for girls, and, for MP, sex differences increase with age. Body mass and skinfold thicknesses are significant influences on both PP and MP, but age exerts a positive but non-linear effect on power output independent of body size and fatness.

UNLABELLED: the aim of this study was to investigate the effects of exercise training on the peak oxygen uptake (peak VO2) and blood lipid profile of 13 to 14-y-old postmenarcheal girls. Treadmill determined peak VO2, total cholesterol, high density lipoprotein cholesterol, low density cholesterol, and triglycerides were the outcome measures assessed at baseline and following exercise training. Twenty girls completed a 20-wk programme of exercise training which involved maintaining the heart rate at 75-85% maximum for 20 min, three times per week. Heart rate was rigorously monitored using telemetry throughout each training session. Eighteen girls acted as the control group. There were no significant (p > 0.05) changes in the outcome measures following the training programme. CONCLUSIONS: These findings suggest that exercise training of this frequency, intensity and duration for a period of 20 wk has no significant effect on either the peak VO2 or blood lipid and lipoprotein profile of normolipidaemic, postmenarcheal girls.

UNLABELLED: the influence of age, sex, maturity, body mass and body fatness on the physical activity (PA) of 11-13-y-olds was examined longitudinally. Body mass, triceps and subscapular skinfold thickness and pubic hair were recorded and 3-d continuous heart rate (HR) monitoring was used to estimate PA on each annual measurement occasion. At the onset, subjects were 11.0 (0.4)-y-old and data were available on 202, 143 and 160 subjects in years 1 to 3, respectively with an almost equal sex distribution. Multilevel regression modelling examined age-, sex- and maturity-related changes in time spent with HR above 139 (moderate activity) and 159 (vigorous activity) bpm. Sustained (10 or 20 min) periods of moderate or vigorous activity were not characteristic of PA patterns. Both PA measures declined with age, with a consistent sex difference reflecting the lower PA levels of girls. Body mass and fatness were not significant explanatory variables, but an additional decrement in activity was evident in late maturity. CONCLUSION: Few children experience extended bouts of PA, and from 11-13 y, PA decreases, with more girls than boys becoming inactive. The data emphasize the importance of promoting active lifestyles during youth.

The aim of this study was to monitor longitudinal changes in young people's submaximal oxygen uptake (VO2) responses during horizontal treadmill running at 8 km x h(-1). The 236 participants (118 boys, 118 girls) were aged 11.2+/-0.4 years (mean +/- s) at the onset of the study. Submaximal VO2, peak VO2 and anthropometry were recorded annually for three consecutive years. The data were analysed using multi-level regression modelling within a multiplicative, allometric framework. The initial model examined sex, age and maturity-related changes in submaximal VO2 relative to body mass as the sole anthropometric covariate. Our results demonstrate that the conventional ratio standard ml x kg(-1) x min(-1) does not adequately describe the true relationship between body mass and submaximal VO2 during this period of growth. The effects of maturity and age were non-significant, but girls consumed significantly less VO2 than boys running at 8 km x h(-1). In subsequent models, stature was shown to be a significant explanatory variable, but this effect became non-significant when the sum of two skinfolds was added. Thus, within this population, submaximal VO2 responses were explained predominantly by changes in body mass and skinfold thicknesses, with no additional maturity-related increments. When differences in body mass and skinfolds were controlled for, there was still a difference between the sexes in submaximal VO2, with girls becoming increasingly more economical with age.

PURPOSE: the influences of age, body size, skin-fold thickness, gender, and maturation on the short-term power output of young people were examined using multilevel modelling. METHODS: Subjects were 97 boys and 100 girls, aged 12.2 +/- 0.4 yr at the onset of the study. Sexual maturity was classified according to Tanner's indices of pubic hair. Peak power (PP) and mean power (MP) were determined on two occasions 1 yr apart using the Wingate Anaerobic Test (WAnT). The data were analyzed using multilevel regression modelling. RESULTS: Initial models identified body mass and stature as significant explanatory variables with an additional positive effect of age, which was smaller for girls' MP. A significant gender difference was apparent for both power indices with girls achieving lower values than boys. A significant incremental effect of later maturity (stages 4 and 5 for pubic hair development) was identified for MP only. Subsequent incorporation of sum of two skin-fold thicknesses into the model yielded significant negative parameter estimates for PP and MP and negated both the stature effects and the maturation influence upon MP. CONCLUSION: There are gender differences in the longitudinal growth of performance on the WanT. Regardless of gender differences, body mass and skin-fold thicknesses appear to be the best anthropometric predictors of WAnT determined PP and MP in young people.

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.

The aim of this study was to examine the maturation responses of young people to submaximal treadmill exercise. Body mass was controlled using both the conventional ratio standard and allometric modelling. Ninety-seven boys and 97 girls with a mean age of 12.2 years completed a discontinuous, incremental exercise test to voluntary exhaustion. We measured peak oxygen uptake (VO2peak) and VO2 when running at 8, 9 and 10 km x h(-1). Sexual maturation was assessed visually using Tanner's indices of pubic hair. Peak VO2 was significantly higher in boys (P0.05); however, values of VO2, expressed both in ratio with body mass and adjusted for body mass using allometry, were significantly greater in boys than in girls (P

The influences of gender and sexual maturation on the peak VO2 of 12-yr olds were examined. Subjects were 106 boys and 106 girls, ages 12.2 +/- 0.4 yr. The sexual maturity of 93 boys and 83 girls was classified according to Tanner's indices of pubic hair. No significant gender differences (P > 0.05) were detected in age, stature, or hemoglobin concentration. Peak VO2 was determined on a treadmill and boys' peak VO2 was significantly higher (P < 0.01) than girls' whether expressed in L x min(-1) (2.10 +/- 0.34 vs 1.92 +/- 0.28) or mL x kg(-1) x min(-1) (52 +/- 6 vs 44 +/- 5). With body mass controlled for using log-linear ANCOVA, the gender difference decreased from 18.2 to 17.1% but remained significant (P < 0.01). For peak VO2 (L x min[-1]) ANOVA revealed no significant interaction (P > 0.05) but significant (P < 0.01) main effects for both gender and maturation. For peak VO2 in ratio with body mass (mL x kg(-1) x min[-1]), ANOVA detected no significant interaction (P > 0.05) or significant main effect (P > 0.05) for maturation although the main effect for gender was significant (P < 0.01). Analysis of peak VO2 with body mass controlled for using log-linear ANCOVA revealed no significant interaction (P > 0.05) but main effects (P < 0.01) for both gender and maturation. Thus, gender differences, which are not simply explained by differences in body size or hemoglobin concentration, have been demonstrated in the peak VO2 of 12-yr olds. A log-linear scaling model has identified in both boys and girls a significant influence of maturation on peak VO2 independent of body mass. This effect may have been masked in previous studies by the inappropriate use of peak VO2 in ratio with body mass.

This study examined the relationships between thigh muscle volume (TMV) and aerobic and anaerobic performance in children. A total of 32 children, 16 boys and 16 girls, aged 9.9 (0.3) years completed a treadmill running test to exhaustion for the determination of peak oxygen uptake (peak VO2) and a Wingate Anaerobic Test (WAnT) for the determination of peak power (PP) and mean power (MP). The volume of the right thigh muscle was determined using magnetic resonance imaging. TMV was not significantly different in boys and girls [2.39 (0.29) l vs 2.18 (0.38) l, P > 0.05]. Peak VO2 and MP were significantly higher in boys than girls (P < 0.01) whether expressed in absolute, mass-related or allometrically scaled terms. Absolute PP was not significantly different in boys and girls but mass-related and allometrically scaled values were higher in boys (P < 0.01). TMV was correlated with absolute peak VO2, PP and MP in both sexes (r = 0.52-0.89, P < 0.01). In boys, mass-related PP was correlated with TMV (r = 0.53, P < 0.01), and in girls mass-related peak VO2 was correlated with TMV (r = -0.61, P < 0.01). However, in neither sex were allometrically scaled peak VO2, PP or MP correlated with TMV (P > 0.05). There were no significant differences between boys and girls in terms of peak VO2, PP or MP when expressed in a ratio to TMV or allometrically scaled TMV. In conclusion, this study has demonstrated that, when body size is appropriately accounted for using allometric scaling, TMV is unrelated to indices of aerobic and anaerobic power in 10-year-old children. Furthermore, there appear to be no qualitative differences in the muscle function of boys and girls in respect of aerobic and anaerobic function.

The influence of sexual maturation on the Wingate anaerobic test performance of 100 boys and 100 girls, ages 12.2 ± 0.4 years, was examined using Tanner's indices of pubic hair and, in boys, salivary testosterone as measures of maturation. No sex differences (p >. 05) in either peak power (PP) or mean power (MP) were revealed. Significant main effects (p <. 01) for maturation were detected for both PP and MP expressed in W, W·kg-1, or with body mass controlled using allometric principles. Testosterone did not increase the variance in PP or MP explained by body mass alone (p >. 05). No sex or maturational effects were observed for postexercise blood lactate (p >. 05). Testosterone was not (p >. 05) correlated with blood lactate. Thus, sexual maturation exerts an influence on PP and MP independent of body mass, but maturational effects on postexercise blood lactate remain to be proven in this age group. © 1997 Human Kinetics Publishers, Inc.

STUDY OBJECTIVES: to examine the ventilatory responses of prepubescent children to submaximal and peak exercise using appropriate allometric modeling to control for differences in body size. DESIGN: Cross-sectional study of a representative sample of children. SETTING: Middle schools (8 to 11 years) in Exeter, UK. PARTICIPANTS: We studied 101 boys and 76 girls aged 11.1 (0.4) years and classified Tanner stage 1 for pubic hair (no true pubic hair). MEASUREMENTS: at rest: stature, mass, sum of skinfolds, hemoglobin concentration, FVC, and FEV1. During treadmill exercise at 7, 8, 9, and 10 km/h, and at peak exercise: oxygen uptake (VO2), minute ventilation (VE), tidal volume (VT), and respiratory frequency (Rf). RESULTS: at peak exercise, boys' VO2, VE, and VT were significantly (p

OBJECTIVES: to investigate the physiological effects of two different three times a week, eight week training programmes on the aerobic fitness of nine to ten year old girls. METHODS: Treadmill determined peak VO2, submaximal heart rates, and submaximal blood lactate were the criterion measures. Seventeen girls completed a programme of "aerobics" training where sessions lasted 20-25 minutes. Eighteen girls followed a cycle ergometer training programme which involved pedalling continuously for 20 minutes with the heart rate maintained between 160 and 170 beats/minute. A control group of 16 girls completed the criterion tests but did not train. In the cycle ergometer group and eight control subjects plasma total cholesterol and high density lipoprotein cholesterol were determined before and after training. RESULTS: Peak VO2 did not change significantly with training in either training group, neither were there any significant changes in submaximal heart rates. Blood lactate declined significantly at the two lowest submaximal exercise intensities in the cycle ergometer training group (from 2.3 (1.1) to 1.4 (0.06) mmol/l at stage 1 and from 2.1 (1.2) to 1.6 (0.06) mmol/l at stage 2; means (SD); P < 0.01). Total cholesterol and high density lipoprotein cholesterol remained unchanged with training. CONCLUSIONS: These findings suggest that an eight week structured exercise programme produces minimal changes in either the aerobic fitness or blood lipids of young girls. It may be more beneficial for long term health to promote enjoyment in activity and positive attitudes to exercise rather than attempting to enhance aerobic fitness through strenuous exercise programmes.

This paper examined the influence of different statistical modeling techniques on the interpretation of peak VO2 data in groups of prepubertal, circumpubertal, and adult males (group 1M, N = 29; group 2M, N = 26; group 3M, N = 8) and females (group 1F, N = 33; group 2F, N = 34; group 3F, N = 16). Conventional comparisons of the simple per-body-mass ratio (ml.kg-1.min-1) revealed no significant differences between the three male groups (P < 0.05). In females, a decline in VO2 between group 2F and 3F was observed (P < 0.05). Both linear and log-linear (allometric) models revealed significant increases across all three male groups for peak VO2 adjusted for body mass (P < 0.05). In females these scaling models identified a significantly lower peak VO2 in group 1F versus groups 2F and 3F (P < 0.05). Based upon the common mass exponent identified (b = 0.80, SE = 0.04), power function ratios (y.mass0.80) were generated and the logarithms of these compared. Again, results indicated a progressive increase in peak VO2 across groups 1M to 3M (P < 0.05) and an increase between groups 1F and 2F (P < 0.05). Incorporating stature into the allometric equation reduced the mass exponent to 0.71 (SE = 0.06) with the contribution of the stature exponent shown to be 0.44 (SE = 0.20). These results indicate that conventional ratio standards do not adequately account for body size differences when investigating functional changes in peak VO2.

This study was designed to enhance understanding of the assessment and interpretation of the aerobic fitness of prepubertal children. Written informed consent to participate was obtained from 70% of the children in year six of the 15 state schools in the city of Exeter. Twenty-five per cent of the eligible children in each school were randomly selected from those who volunteered. The data reported here are those obtained from the 111 boys (11.1 SD 0.4 years) and 53 girls (10.9 SD 0.3 years) classified as Tanner stage 1 in both pubic hair rating and either genitalia rating (boys) or breast rating (girls). Peak oxygen uptake (peak VO2) was determined using a discontinuous, incremental protocol on a treadmill. Only a minority of children demonstrated a levelling-off or plateau in VO2 despite an increase in exercise intensity. There was no evidence to suggest that the children who demonstrated a VO2 plateau had significantly (p < 0.05) higher peak VO2, peak heart rate, peak respiratory exchange ratio or peak blood lactate than those children who did not demonstrate a plateau in VO2. These findings indicate that a VO2 plateau should not be used as a requirement for defining a maximal exercise test with prepubertal children. Boys had a significantly (p < 0.01) higher peak VO2 than girls, whether expressed in 1.min-1 (1.78 vs 1.46) or in relation to body mass (51 vs 45 ml.kg-1.min-1). The results compare favourably with those of similarly aged children from other countries, but why prepubescent boys have significantly higher (13.3%) mass-related peak VO2 than prepubescent girls is not readily apparent. Although conventional, the expression of peak VO2 as per body mass ratio may not adequately partition out body-size differences. The influence of body mass was therefore removed using a linear adjustment scaling model and a log-linear model, but the boys' peak VO2 remained significantly (p < 0.01) higher than the girls' peak VO2 with the difference now being 16.0% and 16.2%, respectively.

Our understanding of the development of children and adolescents' aerobic fitness is limited by ethical considerations and methodological constraints. Protocols, apparatus, and criteria of maximal effort used with adults are often unsuitable for use with children. In normal children and adolescents, peak VO2 increases with growth and maturation, although there are indications that girls' peak VO2 may level off around 14 years of age. Males exhibit higher values of peak VO2 than females, and the sex difference increases as they progress through adolescence. The difference between males and females has been attributed to the boys' greater muscle mass and hemoglobin concentration. It appears that boys experience an adolescent growth spurt in peak VO2, which reaches a maximum gain near the time of PHV, but data are insufficient to offer any generalization for girls. Peak VO2 has usually been expressed in relation to body mass, and with this convention it appears that boys' values are consistent throughout the developmental period, whereas girls' values decrease as they get older. This type of analysis may, however, have clouded our understanding of growth and maturational changes in peak VO2, and scaling for differences in body size may provide further clarification. If differences are shown where none were previously thought to exist, then physiological explanations must be sought. Methodological issues have also hindered the understanding of how children's blood lactate responses to exercise develop. The actual lactate level recorded during an exercise test is influenced by the site of sampling and the blood handling and assay techniques. Valid interstudy comparisons can only be made where similar procedures have been employed. In general, children demonstrate lower blood lactate levels at peak VO2 than adults, although individual variation is wide. Therefore the use of blood lactate measures to confirm the attainment of peak VO2 cannot be supported. Exercise at the same relative submaximal intensity elicits a lower blood lactate in children than in adults, but interpretation and identification of developmental and maturational patterns of response are limited by the use of different testing conditions and reference points (e.g. lactate threshold and fixed level reference points). There is growing evidence that the 2.5 mM reference level should be used in preference to the 4.0 mM level, as the adult criterion occurs close to maximal exercise in many children and adolescents. Explanations for child-adult differences in blood lactate responses to exercise are difficult to elucidate.(ABSTRACT TRUNCATED AT 400 WORDS)

This study examined the relationship between daily physical activity and aerobic fitness in 11-16-year-olds. Habitual physical activity was assessed in 28 boys (mean(s.d.) age 13.6(1.3) years) and 45 girls (mean(s.d) age 13.7(1.3) years) from minute-by-minute heart rate monitoring during 3 school days. Aerobic fitness was assessed by determining the percentage peak VO2 at blood lactate reference values of 2.5 and 4.0 mmol l-1 during incremental treadmill running. The 4.0 mmol l-1 level occurred at a mean(s.d.) value of 89(7)% peak VO2 in both boys and girls and mean(s.d.) values at the 2.5 mmol l-1 level were 82(9)% peak VO2 in girls. Mean(s.d.) percentage time with heart rates at or above 140 beats min-1 was 6(3)% in boys and 5(3)% in girls. Corresponding values for percentage time at or above 160 beats min-1 were 3(2) for boys and 2(1) for girls. The number of 10- and 20-min periods of activity with the heart rate sustained above the 140 and 160 beats min-1 thresholds were also totalled over the 3 days. No significant relationships were identified between percentage peak VO2 at the 2.5 or 4.0 mmol l-1 blood lactate reference levels and either percentage time or number of 10- or 20-min periods above 140 or 160 beats min-1 (P > 0.05). These results support the hypothesis that daily physical activity levels in 11-16-year-old children do not stress aerobic metabolism sufficiently to influence aerobic fitness.