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Neil Armstrong and Alan R. Barker

The pulmonary oxygen uptake (pVO2) kinetic response at the onset of exercise provides a noninvasive window into the metabolic activity of the muscle and a valuable means of increasing our understanding of developmental muscle metabolism. However, to date only limited research has been devoted to investigating the pVO2 kinetic response during exercise in children and adolescents. From the rigorous studies that have been conducted, both age- and sex-related differences have been identified. Specifically, children display a faster exponential rise in the phase II pVO2 kinetics, which are purported to reflect the rise in muscle O2 consumption, during moderate, heavy and very heavy intensity exercise compared with adults. Furthermore, for heavy and very heavy exercise, the O2 cost of exercise is higher for the exponential phase and the magnitude of the pVO2 slow component is smaller in young children. Sex-related differences have been identified during heavy, but not moderate exercise, with prepubertal boys displaying a faster exponential phase II pVO2 kinetic response and a smaller pVO2 slow component compared with prepubertal girls. The mechanisms underlying these differences are currently poorly understood, and form the basis for future research in this area. However, it is hypothesized that an age-related modulation of the muscle phosphate feedback controllers to signal an increased rate of oxidative phosphorylation and/or altered muscle fiber type recruitment strategies have the potential to play an important role. Overall, the data support the view that at the onset of exercise children have an enhanced potential for oxidative metabolism in the myocyte compared with adults.

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Alan R. Barker and Neil Armstrong

31phosphorous-magnetic resonance spectroscopy (31P-MRS) has become an extremely valuable technique to investigate changes in muscle metabolism noninvasively and in vivo. The purpose of this article is to critically review how 31P-MRS has contributed to current understanding of muscle metabolic function in healthy children and adolescents. In addition, an overview of the basic principles of 31P-MRS and its application to the study of muscle metabolism is provided and discussed in relation to child-specific methodological concerns when using this technique.

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Shilo J. Dormehl, Samuel J. Robertson, Alan R. Barker and Craig A. Williams

Purpose:

To evaluate the efficacy of existing performance models to assess the progression of male and female adolescent swimmers through a quantitative and qualitative mixed-methods approach.

Methods:

Fourteen published models were tested using retrospective data from an independent sample of Dutch junior national-level swimmers from when they were 12–18 y of age (n = 13). The degree of association by Pearson correlations was compared between the calculated differences from the models and quadratic functions derived from the Dutch junior national qualifying times. Swimmers were grouped based on their differences from the models and compared with their swimming histories that were extracted from questionnaires and follow-up interviews.

Results:

Correlations of the deviations from both the models and quadratic functions derived from the Dutch qualifying times were all significant except for the 100-m breaststroke and butterfly and the 200-m freestyle for females (P < .05). In addition, the 100-m freestyle and backstroke for males and 200-m freestyle for males and females were almost directly proportional. In general, deviations from the models were accounted for by the swimmers’ training histories. Higher levels of retrospective motivation appeared to be synonymous with higher-level career performance.

Conclusion:

This mixed-methods approach helped confirm the validity of the models that were found to be applicable to adolescent swimmers at all levels, allowing coaches to track performance and set goals. The value of the models in being able to account for the expected performance gains during adolescence enables quantification of peripheral factors that could affect performance.

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Robert H. Mann, Craig A. Williams, Bryan C. Clift and Alan R. Barker

Purpose: To investigate the effect of measurement timing and concurrent validity of session and differential ratings of perceived exertion (sRPE and dRPE, respectively) as measures of internal training load in adolescent distance runners. Methods: A total of 15 adolescent distance runners (15.2 [1.6] y) performed a 2-part incremental treadmill test for the assessment of maximal oxygen uptake, heart rate (HR), and blood lactate responses. Participants were familiarized with RPE and dRPE during the treadmill test using the Foster modified CR-10 Borg scale. Subsequently, each participant completed a regular 2-wk mesocycle of training. Participants wore an HR monitor for each exercise session and recorded their training in a logbook, including sRPE, dRPE leg exertion (dRPE-L), and breathlessness (dRPE-B) following session completion (0 min), 15 min postsession, and 30 min postsession. Results: sRPE, dRPE-L, and dRPE-B scores were all most likely lower when reported 30 min postsession compared with scores 0 min postsession (%change, ±90% confidence limits; sRPE −26.5%, ±5.5%; dRPE-L −20.5%, ±5.6%; dRPE-B −38.9%, ±7.4%). sRPE, dRPE-L, and dRPE-B all maintained their largest correlations (r = .74–.89) when reported at session completion (0 min) in comparison with each of the HR-based criteria measures. Conclusion: sRPE, whether reported 0, 15, or 30 min postsession, provides a valid measure of internal training load in adolescent distance runners. In addition, dRPE-L and dRPE-B can be used in conjunction with sRPE across all time points (0, 15, and 30 min) to discriminate between central and peripheral exertion.

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Brynmor C. Breese, Craig A. Williams, Alan R. Barker, Joanne R. Welsman, Samantha G. Fawkner and Neil Armstrong

This study examined longitudinal changes in the pulmonary oxygen uptake (pV̇O2) 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 pV̇O2 at the gas exchange threshold and peak pV̇O2 (Δ). Over the 2-yr period a significant increase in the phase II time constant (25 ± 5 vs. 30 ± 5 s; p = .002, ω2 = 0.34), the relative amplitude of the pV̇O2 slow component (9 ± 5 vs. 13 ± 4%; p = .036, ω2 = 0.14) and the pV̇O2 gain at end-exercise (11.6 ± 0.6 vs. 12.4 ± 0.7 mL·min−1·W−1; p < .001, ω2 = 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.

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Brynmor C. Breese, Craig A. Williams, Alan R. Barker, Joanne R. Welsman, Samantha G. Fawkner and Neil Armstrong

This study examined longitudinal changes in the pulmonary oxygen uptake (pV̇O 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 pV̇O 2 at the gas exchange threshold and peak pV̇O 2 (40% Δ). Over the 2-yr period a significant increase in the phase II time constant (25 ± 5 vs. 30 ± 5 s; p = .002, ω2 = 0.34), the relative amplitude of the pV̇O 2 slow component (9 ± 5 vs. 13 ± 4%; p = .036, ω2 = 0.14) and the pV̇O 2 gain at end-exercise (11.6 ± 0.6 vs. 12.4 ± 0.7 mL·min−1·W−1; p < .001, ω2 = 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.

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Kate M. Sansum, Max E. Weston, Bert Bond, Emma J. Cockcroft, Amy O’Connor, Owen W. Tomlinson, Craig A. Williams and Alan R. Barker

Purpose: This study had 2 objectives: (1) to examine whether the validity of the supramaximal verification test for maximal oxygen uptake (V˙O2max) differs in children and adolescents when stratified for sex, body mass, and cardiorespiratory fitness and (2) to assess sensitivity and specificity of primary and secondary objective criteria from the incremental test to verify V˙O2max. Methods: In total, 128 children and adolescents (76 male and 52 females; age: 9.3–17.4 y) performed a ramp-incremental test to exhaustion on a cycle ergometer followed by a supramaximal test to verify V˙O2max. Results: Supramaximal tests verified V˙O2max in 88% of participants. Group incremental test peak V˙O2 was greater than the supramaximal test (2.27 [0.65] L·min−1 and 2.17 [0.63] L·min−1; P < .001), although both were correlated (r = .94; P < .001). No differences were found in V˙O2 plateau attainment or supramaximal test verification between sex, body mass, or cardiorespiratory fitness groups (all Ps > .18). Supramaximal test time to exhaustion predicted supramaximal test V˙O2max verification (P = .04). Primary and secondary objective criteria had insufficient sensitivity (7.1%–24.1%) and specificity (50%–100%) to verify V˙O2max. Conclusion: The utility of supramaximal testing to verify V˙O2max is not affected by sex, body mass, or cardiorespiratory fitness status. Supramaximal testing should replace secondary objective criteria to verify V˙O2max.

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Asunción Ferri-Morales, Marcus Vinicius Nascimento-Ferreira, Dimitris Vlachopoulos, Esther Ubago-Guisado, Ana Torres-Costoso, Augusto Cesar F. De Moraes, Alan R. Barker, Luis A. Moreno, Vicente Martínez-Vizcaino and Luis Gracia-Marco

Purpose: To examine the intermethods agreement of dual-energy X-ray absorptiometry (DXA) and foot-to-foot bioelectrical impedance analysis (BIA) to assess the percentage of body fat (%BF) in young male athletes using air-displacement plethysmography (ADP) as the reference method. Methods: Standard measurement protocols were carried out in 104 athletes (40 swimmers, 37 footballers, and 27 cyclists, aged 12–14 y). Results: Age-adjusted %BF ADP and %BF BIA were significantly higher in swimmers than footballers. ADP correlates better with DXA than with BIA (r = .84 vs r = .60, P < .001). %BF was lower when measured by DXA and BIA than ADP (P < .001), and the bias was higher when comparing ADP versus BIA than ADP versus DXA. The intraclass correlation coefficients between DXA and ADP showed a good to excellent agreement (r = .67–.79), though it was poor when BIA was compared with ADP (r = .26–.49). The ranges of agreement were wider when comparing BIA with ADP than DXA with ADP. Conclusion: DXA and BIA seem to underestimate %BF in young male athletes compared with ADP. Furthermore, the bias significantly increases with %BF in the BIA measurements. At the individual level, BIA and DXA do not seem to predict %BF precisely compared with ADP in young athletic populations.