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Traditionally, sports participation has been based on the chronological age of the individual with year of birth determining participation grouping. However, grouping by chronological age can result in individuals who are nearly a full year different in age competing within the same age group. Moreover, during the pubertal years, age grouping may provide physical (size) advantage to early maturers and disadvantage to late maturers. These advantages/disadvantages could impact talent selection, psychosocial aspects of sport participation, technical and tactical skill development, competitiveness, and injury risk. Biobanding is an alternative method for determining sport participation categorization and uses factors of growth and/or maturation, rather than traditional chronological age, for grouping athletes. Implementation of biobanding in sports may be advantageous to both early and late-maturing athlete development. more...

Purpose: This study examined the relationship between parent physical activity (PA) support and children's motor skill development and PA during early childhood and explored the potential moderating effect of child PA and motor skills on these relationships., Methods: Participants (N = 589, 250 girls, meanage = 4.93 [0.59] y) were part of a larger, longitudinal cohort study. Motor skills were assessed using the Movement Assessment Battery for Children-Second Edition. Moderate to vigorous PA (MVPA) was measured using ActiGraph accelerometers. Five items were used to measure parent support frequency (1 = none, 3 = 3-4 times, 5 = daily). Moderation analyses were conducted to examine the moderating effect of MVPA and motor skills on the relationship between parent support and motor skills and MVPA, respectively., Results: Parent support was significantly related to motor skills (B = 14.45, P = .007), and child MVPA significantly moderated this relationship (B = -0.17, P = .021). The relationship between parent support and child MVPA did not reach significance (B = 2.89, P = .051); however, motor skills had a significant moderating effect (B = -0.08, P = .022)., Conclusions: These novel findings suggest parent PA support is related to child motor skills and PA during early childhood, but this relationship is context dependent. Child-level characteristics should be considered in future parent PA support research. more...

Clear definition, identification, and reporting of adverse event (AE) monitoring during training interventions are essential for decision making regarding the safety of training and testing in youths., Purpose: To document the extent to which AEs, resulting from intervention studies targeting muscle strengthening training (MST) in youth, are reported by researchers., Methods: Electronic databases (CINAHL, PubMed, SPORTDiscus, and Web of Science) were searched for English peer-reviewed articles published before April 2018. Inclusion criteria were: (1) average age <16 years, (2) use of MST, (3) statement(s) linked to the presence/absence of AEs, and (4) randomized controlled trials or quasi-experimental designs. Risk of reporting bias for AEs followed recommendations by the Cochrane Collaboration group., Results: One hundred and ninety-one full-text articles were screened. One hundred and thirty met all MST criteria, out of which only 44 (33.8%; n = 1278, age = 12.1 [1.1] y) included a statement as to the presence/absence of adverse events. The 86 other studies (66.2%) included no such statement. Of the reporting 44 studies, 18 (40.1%) indicated one or more adverse events. Of the 93 reported adverse events, 55 (59.1%) were linked to training or testing., Conclusions: Most MST studies in youth do not report presence/absence of adverse events, and when reported, adverse events are not well defined. more...

This study examined differences in resting concentrations of markers of bone formation and resorption, and osteokines between female adolescent (12-16 y) swimmers, soccer players, and nonathletic controls. Resting, morning blood samples were obtained after an overnight fast from 20 swimmers, 20 soccer players, and 20 nonathletic controls, matched for age. carboxyl-terminal cross-linking telopeptide of type I collagen (CTX), amino-terminal propeptide of type I collagen (P1NP), total osteocalcin (OC), sclerostin, osteoprotegerin (OPG), and receptor activator of nuclear factor kappa B ligand (RANKL) were analyzed in serum. After controlling for percent body fat, there were no significant differences between swimmers and nonathletic controls in any of the measured markers. In contrast, soccer players had significantly higher P1NP (89.5 [25.6] ng·mL-1), OC (57.6 [22.9] ng·mL-1), and OPG (1052.5 [612.6] pg·mL-1) compared with both swimmers (P1NP: 66.5 [20.9] ng·mL-1; OC: 24.9 [12.5] ng·mL-1; OPG: 275.2 [83.8] pg·mL-1) and controls (P1NP: 58.5 [16.2] ng·mL-1; OC: 23.2 [11.9] ng·mL-1; OPG: 265.4 [97.6] pg·mL-1), with no differences in CTX, sclerostin, and RANKL. These results suggest that bone formation is higher in adolescent females engaged in high-impact sports like soccer compared with swimmers and controls. more...

Purpose: To determine sex-related differences in the skin blood flow (SkBF) response to exercise, local heating, and acetylcholine (ACh) in children, and to assess nitric oxide contribution to the SkBF response., Methods: Forearm SkBF during local heating (44°C), ACh iontophoresis, and exercise (30-min cycling and 60% of maximum oxygen consumption) was assessed, using laser Doppler fluxmetry, in 12 boys and 12 girls (7-13 y old), with and without nitric oxide synthase inhibition, using Nω-nitro-L-arginine methyl ester iontophoresis., Results: Local-heating-induced and ACh-induced SkBF increase were not different between boys and girls (local heating: 1445% [900%] and 1432% [582%] of baseline, P = .57; ACh: 673% [434%] and 558% [405%] of baseline, respectively, P = .18). Exercise-induced increase in SkBF was greater in boys than girls (528% [290%] and 374% [192%] of baseline, respectively, P = .03). Nω-nitro-L-arginine methyl ester blunted the SkBF response to ACh and during exercise (P < .001), with no difference between sexes., Conclusion: SkBF responses to ACh and local heat stimuli were similar in boys and girls, while the increase in SkBF during exercise was greater in boys. The apparent role of nitric oxide was not different between boys and girls. It is suggested that the greater SkBF response in boys during exercise was related to greater relative heat production and dissipation needs at this exercise intensity. The response to body size-related workload should be further examined. more...

This study compared salivary and serum concentrations of testosterone and cortisol at rest and in response to intense multitask exercise in boys and men. Early morning saliva and venous blood samples were obtained before and 15 minutes after exercise from 30 competitive swimmers (15 boys, age 14.3 [1.9] y; 15 men, age 21.7 [3.1] y). Exercise included a swim-bench maximal strength task and an all-out 200-m swim, followed by a high-intensity interval swimming protocol (5 × 100 m, 5 × 50 m, and 5 × 25 m). At baseline, fasting testosterone (but not cortisol) concentration was higher in men than boys in serum and saliva (P < .05). Salivary and serum cortisol increased postexercise, with a greater increase in men compared with boys (men: 226% and 242%; boys: 78% and 64%, respectively; group by time interaction, P < .05). Testosterone was reduced postexercise in serum but not in saliva (men: -14.7% and 0.1%; boys: -33.9% and -4.5%, respectively, fluid by time interaction, P < .01). Serum and salivary cortisol (but not testosterone), preexercise and postexercise values were strongly correlated in both men and boys (r = .79 and .82, respectively; P < .01). In summary, early morning high-intensity exercise results in a decrease in testosterone in serum, but not saliva, and an increase in cortisol irrespective of the fluid used, in both boys and men. When examining immediate postexercise changes, the lack of correlation in testosterone between saliva and serum suggests that saliva may not be an appropriate fluid to examine changes in testosterone. The high correlation observed between serum and saliva for cortisol indicates that, in both boys and men, saliva may be used to monitor the immediate cortisol response to exercise. more...

The assessment of maximal aerobic power ( V ˙ O 2 max ) in both children and adults is an invaluable tool for the evaluation of exercise performance capacity and general physical fitness in clinical, athletic, public health, and research applications. The complexity of means and considerations, as well as varying specific aims of V ˙ O 2 max testing, has prevented the formulation of a universally applicable, standard testing protocol, in general, and for children in particular. Numerous tester-controllable factors, such as exercise modality, metabolic measurement system, testing protocol, or data reduction strategies, can affect both the measurement and interpretation of V ˙ O 2 max data. Although the general guiding principles are similar, children differ from adults in several aspects. One notable difference is the frequent absence of a discernible V ˙ O 2 plateau in children. Thus, the proper choice of equipment and procedures may be different for children than for adults. It is therefore the aim of this article to highlight the general and pediatric-specific considerations that may affect V ˙ O 2 max measurement and interpretation of results. more...

This commentary highlights 23 noteworthy publications from 2018, selected by leading scientists in pediatric exercise science. These publications have been deemed as significant or exciting in the field as they (a) reveal a new mechanism, (b) highlight a new measurement tool, (c) discuss a new concept or interpretation/application of an existing concept, or (d) describe a new therapeutic approach or clinical tool in youth. In some cases, findings in adults are highlighted, as they may have important implications in youth. The selected publications span the field of pediatric exercise science, specifically focusing on: aerobic exercise and training; neuromuscular physiology, exercise, and training; endocrinology and exercise; resistance training; physical activity and bone strength; growth, maturation, and exercise; physical activity and cognition; childhood obesity, physical activity, and exercise; pulmonary physiology or diseases, exercise, and training; immunology and exercise; cardiovascular physiology and disease; and physical activity, inactivity, and health. more...

Purpose: This study examined osteokines related to Wnt signaling at rest and in response to plyometric exercise in 12 boys [10.2 (0.4) y] and 12 girls [10.5 (0.4) y]., Methods: One resting (preexercise) and 3 postexercise (5 min, 1 h, and 24 h) blood samples were analyzed for sclerostin, dickkopf-related protein 1 (DKK-1), osteoprotegerin (OPG), and receptor activator of nuclear factor kappa-β ligand (RANKL)., Results: Girls had higher resting sclerostin than boys [187.1 (40.1) vs 150.4 (36.4) pg·mL -1 , respectively; P = .02]. However, boys had higher DKK-1 [427.7 (142.3) vs 292.8 (48.0) pg·mL -1 , respectively; P = .02] and RANKL [3.9 (3.8) vs 1.0 (0.4) pg·mL -1 , respectively; P < .01] than girls. In girls, sclerostin significantly decreased 5-minute and 1-hour postexercise (χ 2  = 12.7, P = .01), and RANKL significantly decreased 5-minute postexercise (χ 2  = 19.1, P < .01) and continued to decrease up to 24-hour postexercise, with large effect sizes. In boys, DKK-1 significantly decreased 1-hour postexercise and remained lower than preexercise 24-hour postexercise (χ 2  = 13.0, P = .01). OPG increased in both boys (χ 2  = 13.7, P < .01) and girls (χ 2  = 11.4, P = .01), with boys having significantly higher OPG at 5-minute and 1-hour postexercise, whereas in girls, this increase was only seen 24-hour postexercise., Conclusion: Plyometric exercise induces an overall anabolic osteokine response favoring osteoblastogenesis over osteoclastogenesis in both boys and girls although the timeline and mechanism(s) may be different. more...

This study examined resting levels of catabolic and anabolic osteokines related to Wnt signaling and their responses to a single bout of plyometric exercise in child and adolescent females. Fourteen premenarcheal girls [10.5 (1.8) y old] and 12 postmenarcheal adolescent girls [15.0 (1.0) y old] performed a plyometric exercise trial. One resting and 3 postexercise blood samples (5 min, 1 h, and 24 h postexercise) were analyzed for sclerostin, dickkopf-1 (DKK-1), osteoprotegerin (OPG), receptor activator of nuclear factor kappa-β ligand (RANKL), and transforming growth factors (TGF-β1, TGF-β2, and TGF-β3). Premenarcheal girls had significantly higher resting sclerostin, TGF-β1, TGF-β2, and TGF-β3 than the postmenarcheal girls, with no significant time effect or group-by-time interaction. DKK-1 was higher in premenarcheal compared with postmenarcheal girls. There was an overall significant DKK-1 decrease from baseline to 1 h postexercise, which remained lower than baseline 24 h postexercise in both groups. There was neither a significant group effect nor group-by-time interaction in OPG, RANKL, and their ratio. RANKL decreased 5 min postexercise compared with baseline and remained significantly lower from baseline 24 h following the exercise. No changes were observed in OPG. OPG/RANKL ratio was significantly elevated compared with resting values 1 h postexercise. In young females, high-impact exercise induces an overall osteogenic effect through a transitory suppression of catabolic osteokines up to 24 h following exercise. more...

Background: The electromyographic threshold (EMG Th ) is thought to reflect increased high-threshold/type-II motor-unit (MU) recruitment and was shown higher in boys than in men. Women differ from men in muscular function., Purpose: Establish whether females' EMG Th and girls-women differences are different than males'., Methods: Nineteen women (22.9 ± 3.3yrs) and 20 girls (10.3 ± 1.1yrs) had surface EMG recorded from the right and left vastus lateralis muscles during ramped cycle-ergometry to exhaustion. EMG root-mean-squares were averaged per pedal revolution. EMG Th was determined as the least residual sum of squares for any two regression-line data divisions, if the trace rose ≥ 3SD above its regression line. EMG Th was expressed as % final power-output (%Pmax) and %VO 2 pk power (%P VO2pk )., Results: EMG Th was detected in 13 (68%) of women, but only 9 (45%) of girls (p < .005) and tended to be higher in the girls (%Pmax= 88.6 ± 7.0 vs. 83.0 ± 6.9%, p = .080; %P VO2pk = (101.6 ± 17.6 vs. 90.6 ± 7.8%, p = .063). When EMG Th was undetected it was assumed to occur at 100%Pmax or beyond. Consequently, EMG Th values turned significantly higher in girls than in women (94.8 ± 7.4 vs. 88.4 ± 9.9%Pmax, p = .026; and 103.2 ± 11.7 vs. 95.2 ± 9.9%P VO2pk , p = .028)., Conclusions: During progressive exercise, girls appear to rely less on higher-threshold/type-II MUs than do women, suggesting differential muscle activation strategy. more...

Exercise has long been reputed to have beneficial effects on cognitive processes and emotional stability, with obvious applications to lifespan developmental issues in mental health. Over the last 20 years, animal studies have provided potential mechanisms for this link in neurophysiological terms. Only a very small number of studies have applied this model to well-controlled child and adolescent studies of psychological development, with such studies necessarily requiring collaboration across the fields of exercise science and developmental psychology. In this paper, I outline why the field is now well positioned to increase this effort. Core to this argument is an outline of historical reasons for a (somewhat still active) resistance to this integrative perspective within developmental psychology and a brief synopsis of the countering evidence, followed by a summary of how advances in electrophysiology now make such studies highly accessible and reasonable in terms of cost and convenience. more...

The current understanding of child-adult differences in muscular and neuromotor function will be reviewed while highlighting the gaps in our knowledge and raising research questions that could be addressed in the immediate or near future. Topics include muscle activation, muscle composition, strength attributes, strength- and aerobic-training, neuromotor development, where neuromuscular differences originate from, and the possible interrelationships between motor and cognitive function. The various differences will be discussed on their specific merits, but also as possible manifestations of a common underlying factor which, if true, could provide a more holistic view of child-adult functional differences. more...

Although osteoporosis is considered a geriatric disease, factors affecting bone strength are most influential during child growth and development. This article reviews what is known and still unclear in terms of bone growth, development and adaptation relative to physical activity before and during puberty. Bone is responsive to certain exercise protocols early in puberty and less so in postpubertal years, where bone strength, rather than bone mass, being the outcome of interest. Mechanical loading and high impact exercise promote bone strength. Intense training before and during puberty, however, may negatively affect bone development. Future research should focus on increasing our mechanistic understanding of the manner by which diverse physical stressors alter the integrity of bone. Longitudinal studies that examine the extent to which muscle and bone are comodulated by growth in children are also recommended. more...

Children differ from adults in many muscular performance attributes such as size-normalized strength and power, endurance, fatigability and the recovery from exhaustive exercise, to name just a few. Metabolic attributes, such as glycolytic capacity, substrate utilization, and VO2 kinetics also differ markedly between children and adults. Various factors, such as dimensionality, intramuscular synchronization, agonist-antagonist coactivation, level of volitional activation, or muscle composition, can explain some, but not all of the observed differences. It is hypothesized that, compared with adults, children are substantially less capable of recruiting or fully employing their higher-threshold, type-II motor units. The review presents and evaluates the wealth of information and possible alternative factors in explaining the observations. Although conclusive evidence is still lacking, only this hypothesis of differential motor-unit activation in children and adults, appears capable of accounting for all observed child-adult differences, whether on its own or in conjunction with other factors. more...

Bone properties, reflected by speed of sound (SOS), and physical activity levels were examined in overweight (OW) girls (n = 19) and adolescents (n = 22), in comparison with normal-weight (NW) girls (n = 21) and adolescents (n = 13). Moderate-to-vigorous physical activity (MVPA) was higher in NW than in OW in both age groups. Tibial SOS was lower in OW compared with NW in both age groups. MVPA correlated with tibial SOS, once age was partialed out. The results suggest that overweight girls and adolescents are characterized by low tibial SOS, which may be partially attributed to lower physical activity levels. more...

This pilot study compared bone speed of sound (SOS), bone turnover and insulin-like growth factor 1 (IGF-1) between 20 Caucasian, postmenarcheal, adolescent synchronized swimmers (SS) and 20 aged- and maturity-matched nonswimmers (NS). Daily dietary intake and physical activity levels were also assessed. Bone SOS was measured by quantitative ultrasound. Blood samples were analyzed for osteocalcin, cross-linked N-teleopeptide of type I collagen (NTx), IGF-I and 25-OH vitamin D. Although no differences in bone SOS or turnover markers were observed between groups, the lower IGF-1 and vitamin D intake found in synchronized swimmers, in combination with their higher strenuous activity levels, should be further explored. more...

Ten prepubertal girls and 15 young women were tested for maximal torque, peak rate of torque development, electro-mechanical delay (EMD), and time to peak rate of torque development during isometric elbow flexion. Absolute peak torque (17.0 +/- 7.7 vs. 40.5 +/- 8.3 Nm) and peak rate of torque development (105.9 +/- 58.6 vs. 297.2 +/- 113.0 Nm s(-1)) were lower in the girls (p < .05). Normalized to muscle cross sectional area, torque was similar (8.27 +/- 2.74 vs. 8.44 +/- 1.65 Nm cm(-2)), as was peak rate of torque development, normalized to peak torque (6.21 +/- 1.94 vs. 7.30 +/- 2.26 Nm s(-1)/ Nm). Both, time to peak rate of torque development (123.8 +/- 36.0 vs. 110.5 +/- 52.6 ms) and EMD (73.2 +/- 28.6 vs. 51.9 +/- 25.6 ms), were longer in the girls, although EMD's difference only approached statistical significance (p = .06). Age-related isometric strength differences in females appear to be mainly muscle-size dependent. However, the time to peak torque and EMD findings suggest differential motor-unit activation which may functionally manifest itself in fast dynamic contractions. more...

The objective of this study was to assess bone strength using quantitative ultrasound (QUS, Sunlight Omnisense) in pre- and early-pubertal normal weight (NW, % body fat < or = 20, n = 28), and overweight (OW, % body fat < or = 25, n = 15) boys. Groups were similar in chronological and skeletal age, sexual maturity, sports participation, and calcium intake. Leisure-time physical activity was lower in OW boys. Radial speed of sound (SOS) was similar in the two groups. Tibial SOS, however, was significantly lower in OW compared with NW (3,554 +/- 109 vs. 3,646 +/- 71 m.s-1, respectively). Among pre- and early- pubertal boys, higher adiposity appears to be associated with lower bone SOS in the lower extremities. more...