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Purpose: To assess the correlates of sedentary time among children and adolescents in Ethiopia. Methods: The study was conducted in representative samples of children and adolescents in the capital city of Ethiopia, Addis Ababa. Multivariable logistic regression models were used to determine associations of sedentary time and predictor variables. Results: The mean sedentary time was 4.61 (95% confidence interval [CI], 4.35–4.86) hours per day. Overall, the prevalence of high sedentary time (>3 h/d) was 68.2% (95% CI, 64.2–72.2). Results of multivariable logistic regression analyses showed a statistically significant association between high sedentary time and female household head (adjusted odds ratio [AOR] = 0.50; 95% CI, 0.32–0.80), literate mothers (AOR = 1.98; 95% CI, 1.26–3.11), child attending public school (AOR = 1.79; 95% CI, 1.12–2.85), children who belonged to the poor and rich household wealth tertiles compared with medium wealth tertile (AOR = 2.30; 95% CI, 1.42–3.72 and AOR = 2.04; 95% CI, 1.14–3.65, respectively), and those families that did not have adequate indoor play space for children (AOR = 0.45; 95% CI, 0.29–0.72). Conclusion: The study found that time spent sedentary was high in the study area as compared with other studies of similar settings. Several modifiable factors were identified that can be targeted in interventions to reduce sedentary time in the study setting.

Purpose: Symptom scores commonly measured following concussion were compared between male and female adolescents with (Hx+) and without (Hx−) a history of concussion, pre and post physical exertion testing. Methods: Eighty (males [n = 60; Hx+ = 19], female [n = 20; Hx+ = 5]) high school students (ages 15–17 y) completed the Buffalo Concussion Treadmill Test once and the modified shuttle run test twice. Symptom scores were collected using the 22-point Symptom Evaluation Scale on the Sport Concussion Assessment Tool (version 5) immediately pre and post physical exertion testing. Results: The symptoms most reported during preexertional testing were fatigue/low energy, feeling slowed down, and nervous/anxious, whereas feeling slowed down, fatigue/low energy, “pressure in head” (males only), and headache (females only) were most frequently reported during postexertion testing. Conclusion: An understanding of the common exertion-related symptoms at baseline in a laboratory or field-based setting in adolescents may be advantageous for clinicians as they manage individual recovery postconcussion. This is particularly important during an adolescent’s recovery and return to play when exertional testing may be implemented, especially since symptoms were reported pre and post exertional testing in both males and females regardless of concussion history.

Purpose: Regular physical activity (PA) is a cornerstone therapy for many childhood chronic health conditions, and questionnaires offer a simple method for monitoring PA and identifying children who do not meet clinical practice guidelines. The purpose of this systematic review is to determine which questionnaires are most efficacious for assessing PA in children with chronic health conditions. Methods: Systematic literature searches were conducted through ProQuest, MEDLINE, Scopus, and SPORTDiscus from January 2010 to August 2020 to identify studies that measured PA with a validated questionnaire in children and adolescents aged 3–18 years old with chronic health conditions. In eligible studies, the validity and reliability of questionnaires were identified, and the modified COnsensus-based Standards for the selection of health status Measurement INstruments checklist and Grading of Recommendations, Assessment, Development, and Evaluations were used to assess the quality and strength of evidence and risk of bias. Results: Four thousand four hundred and seventy-eight references were extracted, and 10 articles were included for review. From 10 eligible studies, 6 questionnaires were identified, none of which adequately measure PA in clinical pediatric populations. Conclusion: Questionnaires to adequately measure PA in children with chronic conditions are lacking. This compromises the identification of those who do not meet PA guidelines, limiting the opportunity to identify and address factors contributing to low PA levels.

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.

Purpose: Muscle power is a component of muscular fitness and is proportional to its volume. Reduced muscular fitness in children is linked to negative health outcomes. Associations between muscle volume (MV) and power have not been examined in young children and could reveal important insights into early neuromuscular development. Method: Forty-four children (2–8 y) completed 3 tests of short-term muscular power: repeated anaerobic sprint test, vertical jump, and horizontal jump. MV was assessed using 3D ultrasound for 3 lower limb muscles (rectus femoris, medial gastrocnemius, and tibialis anterior) and summed for across legs. Associations between muscular power and summed MV were assessed using Pearson correlation (r). Sex-based differences in muscular power and MV were assessed using 1-way analysis of covariance. Results: Moderate–strong associations (r = .57 − .87) were found between muscular power and summed MV. No differences were found between boys and girls for height, weight, MV, or muscular power. Conclusions: Young children who have larger lower limb muscles perform better at tasks dependent on short-term muscular power, such as running and jumping, compared with children with smaller muscles. Sex-based differences in short-term muscular power do not exist in young children and reflect similar anthropometry, including lower limb MV.

Purpose: This study analyzed day-to-day estimates of bidirectional associations between sleep parameters and intensity-specific physical activity and assessed whether the timing of physical activity influences these relationships. Methods: The sample was comprised of 651 high school students (51.2% female, 16.33 [1.0] y old) from southern Brazil. Physical activity and sleep were measured using accelerometers. Multilevel models were applied to test associations of nocturnal total sleep time, onset, and efficiency with moderate to vigorous and light (LPA) physical activity. Results: Higher engagement in moderate to vigorous physical activity and LPA was associated with increased total sleep time, and this effect was greater when physical activity was performed in the morning. Morning and evening LPA were associated with increased sleep efficiency and reduced total sleep time, respectively. Practice of LPA in the morning leads to early sleep onset, whereas evening LPA was associated with later onset. Higher total sleep time and later sleep onset were associated with lower moderate to vigorous physical activity and LPA on the following day. However, higher sleep efficiency was associated with increased LPA. Conclusion: The relationship between sleep parameters and physical activity is bidirectional and dependent on physical activity intensity and timing.

This study aimed to develop the optimal allometric body size/shape and a biological maturity model that predicted the change of direction (CoD) mean speed performance in youth male soccer players. One-hundred and fifteen youth soccer players (age: 12.4 [1.3] y) participated in this study. The 505 test was used to assess CoD mean speed performance. Anthropometric measurements comprised body height (cm), sitting height (cm), body mass (kg), fat mass (kg), lower limb length (cm), thigh length (cm), leg length (cm), foot length (cm), thigh girth (cm), and calf girth (cm). The maturity status was determined based on the maturity offset method. To identify size/shape and maturity characteristics associated with CoD speed performance, we computed a multiplicative allometric log-linear regression model, which was refined using backward elimination. The multiplicative allometric model exploring the association between 505 CoD mean speed performance and the different anthropometric characteristics in youth soccer players estimated that fat mass (P < .001), sitting height (P = .02), and maturity offset (P = .004) are the key predictors. More specifically, youths who are more mature and have a lower fat mass and a shorter trunk length, are likely to achieve a better CoD mean speed performance. These findings highlight the relevance of considering anthropometric and maturity characteristics in youth soccer players to support talent identification.

Purpose: To determine sex-related differences in oxygen consumption ( $\dot{\mathrm{V}}{\mathrm{O}}_2$ ) recovery after high-intensity exercise during childhood and adolescence. Methods: Forty-two boys and 35 girls (10–17 y) performed a 60-second all-out test on a rowing ergometer. Postexercise $\dot{\mathrm{V}}{\mathrm{O}}_2$ recovery was analyzed from (1) the $\dot{\mathrm{V}}{\mathrm{O}}_2$ recovery time constant obtained from a biexponential model (τ1 $\dot{\mathrm{V}}{\mathrm{O}}_2$ ) and (2) excess postexercise oxygen consumption calculated over a period of 8 minutes (EPOC₈) and until τ ₁ $\dot{\mathrm{V}}{\mathrm{O}}_2$ was reached (EPOCτ ₁). Multiplicative allometric modeling was used to assess the concurrent effects of body mass or lean body mass, and age on EPOC₈ and EPOCτ ₁. Results: EPOC₈ increased significantly more in boys from the age of 14 years. However, the sex difference was no longer significant when EPOC₈ was analyzed using an allometric model including body mass + age or lean body mass + age. In addition, despite a greater increase in EPOCτ ₁ in boys from the age of 14 years, τ ₁ $\dot{\mathrm{V}}{\mathrm{O}}_2$ was not significantly different between sexes whatever age. Conclusion: While age and lean body mass accounted for the sex-related differences of EPOC during childhood and adolescence, no significant effect of age and sex was observed on the $\dot{\mathrm{V}}{\mathrm{O}}_2$ recovery time constant after high-intensity exercise.