Neil Armstrong

What proportion of youth are physically active? Measurement issues, levels and recent time trends

Aim The aim of this review is to summarise issues surrounding the measurement of physical activity (PA) by self-report and accelerometry in youth (2–18 years old). Current levels and temporal trends in PA and sport participation and the effect of assessment method on data interpretation will be summarised. Methods Relevant papers were extracted from a computerised literature search of MEDLINE and personal databases. Additional papers were extracted from reference lists of recently published reviews. Results The criterion validity (direct comparison with an objective method) of self-reported instruments is low to moderate, with correlation coefficients generally between 0.3 and 0.4. Self-report instruments overestimate the intensity and duration of PA and sport participation. The interpretation of PA data from accelerometry is a challenge, and specific issues include the definition of intensity thresholds and the influence of age on intensity thresholds. Recent data on self-reported PA in youth suggest that between 30% and 40% are sufficiently active. Prevalence values for sufficiently active youth measured by accelerometry range between 1% and 100%, depending on the intensity thresholds used. Sport participation is likely to contribute to higher levels of PA. The available evidence does not support the notion that PA levels and sport participation in youth have declined in recent decades. Conclusion The number of youth meeting current PA guidelines varies by assessment method and the intensity thresholds used when PA is measured by accelerometry. The available evidence does not firmly support the notion that PA in young people has declined during the last decades. It is unlikely that any self-report method is sufficiently accurate for examining cross-cultural differences and temporal trends in young peoples PA and sport participation over time. Surveillance systems therefore need to strive for an international standardisation using objective measurements of PA to complement existing self-report instruments.

The Physical Activity Patterns of European Youth with Reference to Methods of Assessment

AbstractThis 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.

Young people and physical activity

Growth and maturation physiological responses to physical activity exercise training physical activity and health intensive participation in youth sport sport, health and physical activity.

Patterns of physical activity among 11 to 16 year old British children.

OBJECTIVE--To examine the patterns of physical activity among British schoolchildren aged 11 to 16 and to assess whether the children experience the intensity and duration of physical activity that are believed to stress the cardiopulmonary system appropriately. DESIGN--Cross sectional study of a sample of children drawn from a larger survey of coronary risk factors in children. Continuous monitoring of heart rate for 12 hour periods on three school days and one Saturday. SETTING--Two communities in Devon. SUBJECTS--266 Children (163 girls, 103 boys) aged 11 to 16 randomly selected from a sample of 707 children. MAIN OUTCOME MEASURES--Percentage of time and number of sustained periods in which heart rate was greater than 139 beats/min. Anthropometric measures and external assessment of sexual maturity with Tanners indices. RESULTS--The boys had heart rates greater than 139 beats/min for a significantly higher percentage of time than the girls (p less than 0.01) during the weekday (6.2% v 4.3%) and the Saturday (5.6% v 2.6%). The boys had significantly more five and 10 minute periods with heart rates greater than 139 beats/min than the girls during the Saturday and weekdays and more 20 minute periods during the weekdays. 84 Girls and 37 boys had no 10 minute period with a heart rate greater than 139 beats/min during the three weekdays and 112 girls and 65 boys had no such 10 minute period during the Saturday. No significant relation was detected in either sex between the amount or habitual physical activity (heart rate) and skinfold thickness or maturity group. CONCLUSIONS--British children have surprisingly low levels of habitual physical activity, and many children seldom undertake the volume of physical activity believed to benefit the cardiopulmonary system. Boys are more active than girls. The pubertal stage of development or body fatness, or both, do not seem to be sensitive indicators of physical activity in either girls or boys.

International Olympic Committee consensus statement on youth athletic development

The health, fitness and other advantages of youth sports participation are well recognised. However, there are considerable challenges for all stakeholders involved—especially youth athletes—in trying to maintain inclusive, sustainable and enjoyable participation and success for all levels of individual athletic achievement. In an effort to advance a more unified, evidence-informed approach to youth athlete development, the IOC critically evaluated the current state of science and practice of youth athlete development and presented recommendations for developing healthy, resilient and capable youth athletes, while providing opportunities for all levels of sport participation and success. The IOC further challenges all youth and other sport governing bodies to embrace and implement these recommended guiding principles.

Assessment and interpretation of isokinetic muscle strength during growth and maturation.

The majority of strength studies examining changes during growth and maturation have investigated isometric actions, which tell us little about the muscle under dynamic conditions. There are numerous methodological issues in the isokinetic testing of paediatric populations that require further investigation. However, several studies have indicated that children can be reliably assessed isokinetically using both concentric and eccentric actions. Most paediatric studies have examined the knee joint and more data are needed to elucidate the reliability of upper body isokinetic strength testing. The age- and sex-associated development of isokinetic strength is less well understood. Studies have indicated that isokinetic strength increases with age but the mechanisms associated with this increase require further investigation. Current data are also conflicting regarding the age at which sex differences become apparent in isokinetic strength. More work is needed to examine the influence of maturation on isokinetic strength development, but available data suggest that maturation is a non-significant contributory factor once stature and body mass are accounted for. Most studies have demonstrated a significant relationship between stature, body mass and isokinetic strength during growth and maturation. The importance that changes in body composition during growth have on isokinetic strength has been investigated using fat-free mass and muscle cross-sectional area. Data have shown that although fat-free mass and muscle cross-sectional area are important contributors to isokinetic strength, other unexplained factors also influence isokinetic strength development. Additional work needs to investigate possible qualitative changes in muscle during growth and maturation. More work is also needed to examine changes in eccentric strength with age and to investigate sex differences in upper body isokinetic strength. Future studies should preferably be longitudinal in nature and examine known covariates simultaneously using appropriate statistical techniques.

Short term power output in relation to growth and maturation

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 Tanners 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.

Establishing maximal oxygen uptake in young people during a ramp cycle test to exhaustion

Objectives This study tested the hypotheses that (1) secondary criteria (respiratory exchange ratio (RER), heart rate, blood [lactate]) traditionally used to verify the determination of maximum oxygen uptake (V̇O2max) in children can result in the acceptance of a ‘submaximal’ V̇O2max or falsely reject a ‘true’ V̇O2max and (2) the V̇O2peak recorded during a ramp test in children is comparable to the V̇O2peak achieved during supramaximal testing. Methods Thirteen children (9–10 years) completed a ramp cycle test to exhaustion to determine their V̇O2peak. After 15 min of recovery, the participants performed a supramaximal cycle test to exhaustion at 105% of their ramp test peak power. Results Compared with the V̇O2peak during the ramp test, a significantly lower V̇O2 was recorded at a RER of 1.00 (1.293 litre/min (SD 0.265) vs 1.681 litre/min (SD 0.295), p<0.001, n=12), at a heart rate of 195 beats/min (1.556 litre/min (SD 0.265) vs 1.721 litre/min (SD 0.318), p<0.001, n=10) and at 85% of age-predicted maximum (1.345 litre/min (SD 0.228) vs 1.690 litre/min (SD 0.284), p<0.001, n=13). Supramaximal testing yielded a V̇O2peak that was not significantly different from the ramp test (1.615 litre/min (SD 0.307) vs 1.690 litre/min (SD 0.284), p=0.090, respectively). Conclusions The use of secondary criteria to verify a maximal effort in young people during ramp cycling exercise may result in the acceptance of a submaximal V̇O2max. As supramaximal testing elicits a V̇O2peak similar to the ramp protocol, thus satisfying the plateau criterion, the use of such tests is recommended as the appropriate method of confirming a ‘true’ V̇O2max with children. Keywords Children, Aerobic Fitness, Fitness Testing, Supramaximal Exercise.

International olympic committee consensus statement on the health and fitness of young people through physical activity and sport

The International Olympic Committee (IOC) recognises the health and fitness benefits of physical activity (PA) and sport as stated in recommendation #51 from the Olympic Movement in Society Congress held in Copenhagen, 2009: Everyone involved in the Olympic Movement must become more aware of the fundamental importance of Physical Activity and sport for a healthy lifestyle, not least in the growing battle against obesity, and must reach out to parents and schools as part of a strategy to counter the rising inactivity of young people.1 The IOC assembled an expert group (January 2011) to discuss the role of PA and sport on the health and fitness of young people and to critically evaluate the scientific evidence as a basis for decision making. Specifically, the purpose of this consensus paper is to identify potential solutions through collaboration between sport and existing programmes and to review the research gaps in this field. The ultimate aim of the paper is to provide recommendations for young peoples sport and PA stakeholders. After an introduction to the scope of the problem, issues addressed include how best to define the current state of …

Oxygen uptake kinetics in children and adults after the onset of moderate-intensity exercise

The literature suggests that the oxygen uptake ( V O 2 ) response to the onset of moderate-intensity exercise may be both mature from childhood and independent of sex. Yet the cardiorespiratory response to exercise and the metabolic profile of the muscle appear to change with growth and deve . lopment and to differ between the sexes. The aim of this study was to investigate further changes in the V O2 kinetic response with age and sex. Participants completed a series of no less than four step change transitions, from unloaded pedalling to a constant work rate corresponding to 80% of their previously determined ventilatory threshold. Each participants breath-by-breath responses were interpolated to 1 s intervals, time aligned and then averaged. A single exponential model that included a time delay was used to analyse the averaged response following phase 1 (15 s). Participants with parameter confidence intervals more than - 5 s were removed from the sample; the results for the remaining 13 men and 12 women (age 19-26 years), 12 boys and 11 girls (age 11-12 years) were used for statistical analysis. Children had a significantly shorter time constant than adults, both for males (19.0 - 2.0 and 27.9 - 8.6 s respectively; P ≪ 0.01) and females (21.0 - 5.5 and 26.0 - 4.5 s respectively; P ≪ 0.05). There were no significant differences in the time constant between the sexes for either adults or children ( P > 0.05). A significant relationship between the time constant and peak V O 2 was found only in adult males ( P ≪ 0.05). A shorter time constant in children may reflect an enhanced potential for oxidative metabolism.