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An important consideration in pediatric exercise sciences is how researchers can identify the effects of risk factors (e.g., physical inactivity, dietary composition, social class, and ethnic origin) on health-related fitness variables (e.g., peak VO₂, lung function, grip strength, leg power, and arterial blood pressure) in the presence of confounding effects (e.g., differences in age, body size, and maturation). Allometric scaling provides an elegant method of identifying such risk factors while adjusting for the confounding effects of body size, age, and maturation while at the same time overcoming the undesirable distributional characteristics of such data (i.e., skewness [nonnormal] with heteroscedastic error variances). In contrast, the simple ratio standard (e.g., peak oxygen uptake [ml · kg^-1 · min^-1], and peak and mean power [W · kg^-1]), although not a truly scaled ratio or index, is still able to provide the best prediction of weight-bearing athletic (e.g., running) performance.

We adopted allometric models to identify the most appropriate body size/shape characteristics associated with physical performance activities of Greek school children. Children underwent assessments for aerobic and anaerobic fitness, flexibility and hand-grip strength. Results suggest that the inverse Ponderal index and not BMI is the most appropriate body-shape indicator associated with running and jumping activities. Height was negatively associated with flexibility, but both height and weight were positively associated with hand-grip strength. In conclusion, allometric models provide a valuable insight into the most appropriate body size and shape characteristics associated with children’s physical performances and at the same time ensure valid inference when investigating group/population differences (e.g., between gender and maturation status).

Purpose: To assess the effects of a 7-wk low-volume, high-intensity training (HIT) intervention on performance parameters in national-level youth swimmers. Methods: Sixteen swimmers (age 15.8 [1.0] y, age at peak height velocity 12.9 [0.6] y, 100-m freestyle 61.4 [4.1] s) were randomly assigned to an HIT group or a low-intensity, high-volume training (HVT) group that acted as a control. The HIT group reduced their weekly training volume of zone 1 (low-intensity) training by 50% but increased zone 3 (high-intensity) training by 200%. The HVT group performed training as normal. Pretest to posttest measures of physiological performance (velocity at 2.5- and 4-mM blood lactate [velocity_2.5mM and velocity_4mM] and peak blood lactate), biomechanical performance (stroke rate, stroke length [SL], and stroke index [SI] over a 50- and 400-m freestyle), and swimming performance (50-, 200-, and 400-m freestyle) were assessed. Results: There were no significant 3-way interactions between time, group, and sex for all performance parameters (P > .05). There was a significant 2-way interaction between time and group for velocity_4mM (P = .02, ${\eta }_{\mathrm{p}}^2=.40$ ), SL₅₀ (P = .03, ${\eta }_{\mathrm{p}}^2=.37$ ), and SI₅₀ (P = .03, ${\eta }_{\mathrm{p}}^2=.39$ ). Velocity_4mM decreased in the HIT group but increased in the HVT group while SL₅₀ and SI₅₀ decreased in the HVT group. Conclusions: A 7-wk HIT intervention was neither beneficial nor detrimental to performance parameters; however, the HIT group completed 6 h (17.0 km) of swimming per week compared with 12 h (33.4 km) per week for the HVT group.

Purpose: Insufficient recovery can lead to a decrease in performance and increase the risk of injury and illness. The aim of this study was to evaluate salivary cortisol as a marker of recovery in elite rugby union players. Method: Over a 10-wk preseason training period, 19 male elite rugby union players provided saliva swabs biweekly (Monday and Friday mornings). Subjective markers of recovery were collected every morning of each training day. Session rating of perceived exertion (sRPE) was taken after every training session, and training load was calculated (sRPE × session duration). Results: Multilevel analysis found no significant association between salivary cortisol and training load or subjective markers of recovery (all P > .05) over the training period. Compared with baseline (wk 1), Monday salivary cortisol significantly increased in wk 4 (14.94 [7.73] ng/mL; P = .04), wk 8 (16.39 [9.53] ng/mL; P = .01), and wk 9 (15.41 [9.82] ng/mL; P = .02), and Friday salivary cortisol significantly increased in wk 5 (14.81 [8.74] ng/mL; P = .04) and wk 10 (15.36 [11.30] ng/mL; P = .03). Conclusions: The significant increase in salivary cortisol on certain Mondays may indicate that players did not physically recover from the previous week of training or match at the weekend. The increased Friday cortisol levels and subjective marker of perceived fatigue indicated increased physiological stress from that week’s training. Regular monitoring of salivary cortisol combined with appropriate planning of training load may allow sufficient recovery to optimize training performance.

The purpose of this study was to compare physical activity levels between white and South Asian children in the UK. The data were obtained from 606, 11–14 year old schoolchildren (397 white; 209 Asian). Physical activity was assessed using the ‘four by one day’ recall questionnaire from which the time spent in moderate and vigorous physical activity was calculated. Boys were significantly more active than girls (p = .0001), and white children reported significantly greater physical activity than south Asian children (p = .001). Mean ± SD of time spent in moderate and vigorous activity was 90.2 ± 65.4 mins and 68.2 ± 49.3 mins for white and south Asian children and 103.5 ± 63.4 mins and 65.6 ± 53.5 mins for boys and girls respectively. These findings indicate that south Asian children are significantly less active than their white peers and there may be a need for specific interventions to target South Asian children particularly.

The present study examines the relationship of sex, ethnicity, and socio-economic status to physical activity levels of young people. Participants were 301 males and females (12.9 – 0.81 years). Physical activity was measured using the four by one-day physical activity recall questionnaire. ANOVA revealed that high socio-economic status children reported greater average daily energy expenditure levels than low socio-economic status children (p < .01). The daily energy expenditure of white-Caucasian children was significantly higher than black or Asian children. White boys were significantly more active than white girls, but no such sex differences were observed among black and Asian children. Although activity was always greater at weekends, a decline in activity by school year was observed on Saturdays and Sundays but with no such decline observed on weekdays.