Samantha G. Fawkner

Oxygen uptake kinetic response to exercise in children

The oxygen uptake (V̇O2) kinetic response to exercise assesses the integrated response of the cardiovascular system and the metabolic requirements of the exercising muscle. The response differs both qualitatively and quantitatively according to the exercise intensity domain (moderate, heavy, very heavy and severe) in which it lies. In each domain, a rapid cardiodynamic phase 1 response is followed by an exponential rise in V̇O2 toward a projected steady state (for which the inverse of the rate constant is represented as the time constant [τ]). The achievement of the new steady state may be delayed and elevated due to a slow component of V̇O2 in the heavy intensity domain, or above this exercise intensity, the achievement of peak V̇O2 truncates the exercise period. For each of these domains, specific mathematical models have been identified and may be applied to appropriate breath-by-breath response data in order to allow quantification of the response.Much of our understanding of the V̇O2 kinetic response and the methodologies required to obtain meaningful assessment are derived from adult studies. Although pioneering, early studies with young people were lacking in suitable equipment and the methodologies used may consequently have clouded the true interpretation of the kinetic response. More recently, with the advent of online breath-by-breath analysis systems, studies using mathematical modelling procedures have been hindered by the low signal-to-noise ratio which is inherent to children’s response profiles. This has the effect of widening the confidence intervals for estimated parameters, and therefore questions the validity in making inter- and intra-study comparisons. In addition, the difficulty in accurately assessing domain demarcators, especially critical power, often confounds the interpretation of age and sex effects on the exercise response.This review therefore analyses the literature to date on the V̇O2 kinetic response during childhood and adolescence, and specifically highlights concerns with technical rigour in its determination. Rigorously determined data indicate that the exponential rise in V̇O2 is more rapid in children than adults and that at exercise intensities above the anaerobic threshold, the slow component of V̇O2 may be attenuated in the young. Sex differences have not been found in the response to moderate intensity exercise, and there does not appear to be a consistent correlation between peak V̇O2 and τ in children. However, sex differences in the response to exercise intensities above the anaerobic threshold are identified and discussed.

A longitudinal examination of the influence of maturation on physical self-perceptions and the relationship with physical activity in early adolescent girls

This longitudinal study investigated the influence of maturation on physical self-perceptions and the relationship with physical activity in early adolescent girls (N=150; mean age=12.79+/-0.31). Physical characteristics were measured and participants completed the Physical Activity Questionnaire for Children, the Children and Youth Physical Self-Perception Profile and the Pubertal Development Scale on two occasions 12 months apart. The results demonstrated a decrease in overall physical activity levels over 12 months which was not influenced by maturational status or physical characteristics. Additional analysis indicated that physical self-perceptions partially accounted for the explained variance in physical activity change, with physical condition being an important individual predictor of physical activity. Further analysis indicated that body mass was an important individual predictor of changes in perceptions of body attractiveness and physical self-worth. At this age maturation has a limited influence on the physical activity behaviours of early adolescent girls and although the variance in physical activity was partly accounted for by physical self-perceptions, this was a relatively small contribution and other factors related to this drop in physical activity need to be considered longitudinally.

Sex differences in the oxygen uptake kinetic response to heavy-intensity exercise in prepubertal children

It has been demonstrated that there are no sex differences in the oxygen uptake (V̇O2) kinetic response to moderate intensity exercise. However, sex differences in the response to maximal exercise are readily apparent even in the prepubertal years. The purpose of this study was therefore to investigate if sex differences exist in the V̇O2 kinetic response to heavy-intensity exercise. Forty-eight prepubertal children (25 male, 23 female) completed four transitions from baseline to 40% of the difference between their previously determined TV-slope (ventilatory threshold determined by the V-slope method) and peak V̇O2 on an electronically braked cycle ergometer. Each subject’s breath-by-breath responses were interpolated to 1xa0s intervals, time aligned and averaged. The data following phasexa01 were fit with: (1) a double exponential model and (2) a single exponential model within a fitting window that was previously identified to exclude the slow component. There were no significant differences in the parameters of the primary component between each model. Subsequent analysis was carried out using modelxa02. The primary time constant (τ1) was significantly (P<0.05) faster in boys [17.6 (5.8)xa0s] than girls [21.9 (8.2)xa0s], and the slow component contribution to the total change in amplitude after 9xa0min was significantly greater in girls [11.8 (5.5)%] than boys [8.9 (3.7)%]. Sex differences in the kinetic response to heavy-intensity exercise were identified and suggest that during the prepubertal years, sex differences exist in the ability to deliver and/or utilise oxygen in children.

Social physique anxiety and physical activity in early adolescent girls: The influence of maturation and physical activity motives

Abstract In this study, we examined the influence of maturation on social physique anxiety, the relationship between social physique anxiety and current and future physical activity levels, and the influence of motives for physical activity on this relationship in early adolescent girls (n = 162; mean age = 11.8 ± 0.3 years). Participants completed the Pubertal Development Scale, the modified Social Physique Anxiety Scale, and the Motives for Physical Activity Scale at baseline and the Physical Activity Questionnaire for Older Children at baseline and 6 months later. The girls became less active across the 6 months and girls in the early stages of maturation had significantly lower social physique anxiety than the girls in the middle and late stages of maturation. Social physique anxiety was not related to current or future physical activity in the sample as a whole. Cluster analysis identified four groups with different motive profiles and the High Appearance and Fitness group demonstrated a moderate negative relationship between social physique anxiety and physical activity at phase 1, whereas the other groups did not. These findings indicate that social physique anxiety may increase with maturation and the relationship between social physique anxiety and physical activity is dependent on reasons for being active. For girls who are motivated to be active primarily by body-related reasons, social physique anxiety is likely to lead to lower levels of physical activity.

Adolescent girls' energy expenditure during dance simulation active computer gaming

Abstract The objective of this study was to determine the energy expended and intensity of physical activity achieved by adolescent girls while playing on a dance simulation game. Twenty adolescent girls were recruited from a local secondary school. Resting oxygen uptake ([Vdot]O2) and heart rate were analysed while sitting quietly and subsequently during ∼30 min of game play, with 10 min at each of three increasing levels of difficulty. Energy expenditure was predicted from [Vdot]O2 at rest and during game play at three levels of play, from which the metabolic equivalents (METS) of game playing were derived. Mean ± standard deviation energy expenditure for levels 1, 2, and 3 was 3.63 ± 0.58, 3.65 ± 0.54, and 4.14 ± 0.71 kcal · min−1 respectively, while mean activity for each level of play was at least of moderate intensity (>3 METS). Dance simulation active computer games provide an opportunity for most adolescent girls to exercise at moderate intensity. Therefore, regular playing might contribute to daily physical activity recommendations for good health in this at-risk population.

Modelling the VO2 kinetic response to heavy intensity exercise in children.

The purpose of this study was to apply a series of mathematical models in order to investigate the nature of the kinetic response to heavy intensity exercise with children and identify a suitable model with which to estimate parameters of the response. Sixty two children (35 male, 27 female aged 10u200a–u200a15 years) completed four transitions from baseline pedalling to 40% of the difference between their previously determined anaerobic threshold and peak [Vdot]O2 on an electronically braked cycle ergometer. Initially three models were fitted to the averaged response profiles following the end of phase 1, and their residuals compared; 1, a single exponential with a delay term; 2, an exponential and linear term with independent delays; and 3, a double exponential with independent delays. Up to 95% of the response profiles were better fitted by either model 2 or 3 (pu200a<u200a0.05), and model 3 was a statistically better fit (pu200a<u200a0.05) than model 2 in 77% of cases. Residual inspection confirmed the superior fit by model 3. A fourth model which consisted of a single exponential with a delay term was fitted within the phase 2 fitting window. Estimated parameters (A1 and τ1), using model 4 were not significantly different from model 3, and model 4 was identified as the model of choice due to the wide confidence intervals in τ2 and A2 using model 3. It was concluded that the nature of the response to heavy intensity exercise in children is similar to that previously reported with adults and that the response should be modelled accordingly.

Longitudinal changes in the oxygen uptake kinetic response to heavy-intensity exercise in 14- to 16-year-old boys.

This study examined longitudinal changes in the pulmonary oxygen uptake (pVO(2)) kinetic response to heavy-intensity exercise in 14-16 yr old boys. Fourteen healthy boys (age 14.1 +/- 0.2 yr) completed exercise testing on two occasions with a 2-yr interval. Each participant completed a minimum of three step exercise transitions, from unloaded pedalling to a constant work rate corresponding to 40% of the difference between the pVO(2) at the gas exchange threshold and peak pVO(2) (40% Delta). Over the 2-yr period a significant increase in the phase II time constant (25 +/- 5 vs. 30 +/- 5 s; p = .002, omega(2) = 0.34), the relative amplitude of the pVO(2) slow component (9 +/- 5 vs. 13 +/- 4%; p = .036, omega(2) = 0.14) and the pVO(2) gain at end-exercise (11.6 +/- 0.6 vs. 12.4 +/- 0.7 mL x min(-1) x W(-1); p < .001, omega(2) = 0.42) were observed. These data indicate that the control of oxidative phosphorylation in response to heavy-intensity cycling exercise is age-dependent in teenage boys.

Non-invasive methods in paediatric exercise physiology.

Oded Bar-Ors hypothesis that children may be metabolic non-specialists, even when engaging in specialized sports, has stimulated the study of paediatric exercise metabolism since the publication of his classic text Pediatric sports medicine for the practitioner in 1983. Evidence drawn from several methodologies indicates an interplay of anaerobic and aerobic exercise metabolism in which children have a relatively higher metabolic contribution from oxidative energy pathways than adolescents or adults, whereas there is a progressive increase in glycolytic support of exercise with age, at least into adolescence and possibly into young adulthood. The picture is generally consistent but incomplete, as research with young people has been limited by both ethical and methodological constraints. The recent rigorous introduction of non-invasive techniques such as breath-by-breath respiratory gas analysis and magnetic resonance spectroscopy into paediatric exercise physiology promises to open up new avenues of research and generate unique insights into the metabolism of the exercising muscle during growth and maturation. It therefore appears that we might have available the tools necessary to answer some of the elegant questions raised by Professor Bar-Or over 25 years ago.