Joanne R. Welsman

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.

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.

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.

Short-term appetite and energy intake following imposed exercise in 9 to 10-year old girls

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.

Aerobic Fitness: What Are We Measuring?

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 peoples 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 peoples 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 peoples oxygen uptake kinetics responses to exercise of different intensities.

Exercise performance and magnetic resonance imaging-determined thigh muscle volume in children

Abstract 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 V˙O2) 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 V˙O2 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 V˙O2, 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 V˙O2 was correlated with TMV (r = −0.61, P < 0.01). However, in neither sex were allometrically scaled peak V˙O2, PP or MP correlated with TMV (P > 0.05). There were no significant differences between boys and girls in terms of peak V˙O2, 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.

Obesity Increases Precision Errors in Dual-Energy X-Ray Absorptiometry Measurements

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 (<25 kg/m(2)) (n=48), overweight (25-30 kg/m(2)) (n=26), and obese (>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.

Energy intake and appetite following exercise in lean and overweight girls.

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.

Daily physical activity and blood lactate indices of aerobic fitness in children.

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.