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Exercise metabolism in children has traditionally been assessed using the respiratory exchange ratio (RER) to determine the contributions of fat and carbohydrate to the exercise energy demands. Although easily measured, RER measurements have limitations. Other methods to assess metabolism such as the obtainment of a muscle biopsy and the use of nuclear magnetic resonance spectroscopy carry ethical and feasibility concerns, respectively, which limit their use in studies involving children. Stable isotopes, used routinely in studies involving adults, can also be applied in studies involving children in an ethical and feasible manner. Two common stable isotopes used in metabolic studies involving children include carbon-13 (¹³C) and nitrogen-15 (¹⁵N). ¹³C-glucose can be used to study carbohydrate metabolism and ¹⁵N-glycine can be used to assess protein metabolism. This article reviews the use of ¹³C-glucose and ¹⁵N-glycine to study exercise metabolism in children, considers some of the associated ethical aspects, explains the general methodology involved in administering these isotopes and the resources required, and describes studies involving children utilizing these methods. Finally, suggestions for future research are provided to encourage further use of these techniques.

This study was undertaken to examine the stability of adolescents’ physical self-perceptions across short (4 days) and longer (6 and 12 months) periods of time. Boys and girls (n = 195) from 12 to 13 years of age completed the Children’s Physical Self-Perception Profile for 4 consecutive days; follow-up measurements were performed 6 and 12 months later. Results for the short term revealed relatively high stability of physical self-perceptions for the group, although most individuals showed fluctuations in self-perceptions over the 4 days. As expected, adolescents’ self-perceptions were less stable when follow-up measurements were administered.

Secular changes in anaerobic fitness test performance in healthy 6- to 17-year-old Australasians were examined by meta-analysis of 232,564 power- and speed-test performances between 1960 and 2002. Overall, power-test performance improved at a rate of +0.05% [95% confidence interval (CI) = +0.01% to +0.09%] per annum, and speed at +0.04% (CI = +0.02% to +0.06%) per annum. Results indicate that anaerobic-fitness-test performances have remained relatively stable in Australasian children and adolescents in recent decades.

In adults, maximum oxygen uptake (VO₂max) serves as a useful indicator of cardiopulmonary reserve as well as performance in endurance exercise events. Whether VO₂max can be interpreted in the same manner in children is less certain, since maximal oxygen uptake per kg body weight remains essentially stable during the growing years while endurance performance improves dramatically. Gains in ability in endurance events may be achieved through improved submaximal exercise economy, qualitative changes in oxygen delivery not indicated by VO₂max, or the development of nonaerobic factors (speed, strength). Maximal oxygen uptake in children may therefore be a less valid indicator of cardiopulmonary function, endurance capacity, and response to training than in adult subjects.

Past studies have shown the patterning of affective responses during a graded exercise test (GXT) in adult and male adolescent populations, but none have explored the patterns in adolescent girls or younger children. This study explored the patterning of affective responses during a GXT in adolescents and younger children. Forty-nine children (21 male and 28 female) aged between 8–14 years (10.8 ± 1.8 years) completed a GXT. Ventilatory threshold (VT) was identified. At the end of each incremental step, participants reported affective valence. Results revealed that affective valence assessed by the Feeling Scale (FS) significantly declined from the onset of exercise until the point of VT in the younger children, but remained relatively stable in the adolescents. Exercise above the VT brought about significant declines in affective valence regardless of age or sex, but the decrease was significantly greater in adolescents. Results suggest it may be preferable to prescribe lower exercise intensities (below VT) for children, compared with adolescents, to ensure a positive affective response.

This article looks retrospectively at lessons learned from the Trois-Rivières physical education study. A brief review of the experimental design shows 546 students assigned by class cohort to either an additional 5 hours of quality physical education per week in grades 1 through 6, or a control treatment (minimal physical education by the homeroom teacher). Strengths of the study include a quasi-experimental design, a prolonged and well-defined intervention, assessment of compensation for the program, continuation of observations into middle age, collection of data in urban and rural environments, consistency of teaching staff and technical personnel, documentation of changes in academic achievement, assessment of bone maturation, a carefully constructed database, and control for cross-contamination. Limitations include some secular change, limited information on pubertal stages, difficulty in generalizing findings to an English-speaking environment, and some rigidity in the statistical design. The study demonstrates that cardiorespiratory function, muscle strength, and field performance can all be enhanced in primary school with no negative impact on academic work. Further, attitudes, behavior, and function are favorably influenced in adults. Future studies should seek out stable populations, define interventions closely, contract with participants for a long-term follow-up, and assess the immediate and long-term impact on health and function. Above all, there is a need for a dedicated principal investigator who will devote his or her entire career to the longitudinal study.

Ten males and 10 females in each of four grade/age groups threw styrofoam balls of six different diameters as hard as possible at a wall 6.7 m away. Each ball size was thrown four times. The first hypothesis, that the levels of the five components of the one-hand overhand throw would be quite stable for individuals for throws of a particular ball size, was supported. Ball sizes at which the component levels were unstable marked the beginning of a transition to a new component level 70.6% of the time. The second hypothesis, that five components would change from higher to lower levels for most of the subjects as ball size was scaled up, was supported only for the backswing and forearm components. These components were more likely to be affected by increasing ball size because the higher level components required a firm, one-hand grip on the ball, which became more difficult as ball diameters exceeded the subjects’ hand widths. The results indicate that practitioners need to recognize that different ball sizes may elicit different throwing patterns, and specifically that a critical ball diameter may be reached when it is equal to hand width.