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Yvonne G. Ellis, Dylan P. Cliff, Steven J. Howard and Anthony D. Okely

Purpose: To examine the acute effects of a reduced sitting day on executive function (EF) and musculoskeletal health in preschoolers. Methods: A sample of 29 children (54% boys; 4–5 y) participated in a randomized cross-over trial. Each child completed 2 protocols, which simulate a day at childcare in random order for 2.5 hours; a typical preschool day (50% sitting) and a reduced preschool day (25% sitting) where most sitting activities were replaced with standing activities. Sitting, standing, and stepping time were objectively assessed using an activPAL accelerometer. EF was evaluated using tablet-based EF assessments (inhibition, working memory, and task shifting). Musculoskeletal health was assessed using a handheld dynamometer and goniometer. Results: Compared with the typical preschool day, the reduced sitting day showed no significant differences for EF scores. Effect sizes for inhibition (d = 0.04), working memory (d = 0.02), and shifting (d = 0.11) were all small. For musculoskeletal health, no significant differences were reported after the reduced preschool day. The effect sizes for the hip extension force, hamstring flexibility, gastrocnemius length, and balancing on 1 leg were all small (d = 0.21, d = 0.25, d = 0.28, and d = 0.28). Conclusions: This study suggests that reducing sitting time is unlikely to result in acute changes in EF and musculoskeletal health among preschoolers.

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Emma Weston, Matthew Nagy, Tiwaloluwa A. Ajibewa, Molly O’Sullivan, Shannon Block and Rebecca E. Hasson

Purpose: To compare the acute effects of intermittent physical activity (PA) across 4 different intensities on blood pressure. Methods: Thirty children (12 males and 18 females; aged 7–11 y; 33% overweight/obese; 53% nonwhite) completed 4 experimental conditions in random order: 8 hours sitting interrupted with 20, 2-minute low-, moderate-, high-intensity PA breaks, or sedentary screen-time breaks. PA intensity corresponded with 25%, 50%, and 75% of heart rate reserve. Blood pressure was measured during each condition in the morning (0800 h), noon (1200 h), and afternoon (1600 h). Results: There were no significant differences across conditions for systolic blood pressure (SBP; all Ps > .05). There was a significant effect of time with SBP decreasing throughout the day for all conditions (average morning SBP: 106 [1] mm Hg, average noon SBP: 101 [2] mm Hg, average afternoon SBP: 103 [1] mm Hg; P = .01). There were no significant effects of condition or time on diastolic blood pressure (all Ps > .05). Conclusion: While sedentary behavior is known to be associated with hypertension in both adults and children, a single bout of prolonged sitting may be insufficient to produce hypertensive effects in otherwise healthy children. Future research should examine the appropriate dose of intermittent PA to accrue hypotensive responses in preadolescent children.

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Sandro Venier, Jozo Grgic and Pavle Mikulic

Purpose: To explore the acute effects of caffeinated chewing gum on vertical-jump performance, isokinetic knee-extension/flexion strength and power, barbell velocity in resistance exercise, and whole-body power. Methods: Nineteen resistance-trained men consumed, in randomized counterbalanced order, either caffeinated chewing gum (300 mg of caffeine) or placebo and completed exercise testing that included squat jump; countermovement jump; isokinetic knee extension and knee flexion at angular velocities of 60 and 180°·s−1; bench-press exercise with loads corresponding to 50%, 75%, and 90% of 1-repetition maximum (1RM); and an “all-out” rowing-ergometer test. Results: Compared with placebo, caffeinated chewing gum enhanced (all Ps < .05) (1) vertical-jump height in the squat jump (effect size [ES] = 0.21; +3.7%) and countermovement jump (ES = 0.27; +4.6%); (2) knee-extension peak torque (ES = 0.21; +3.6%) and average power (ES = 0.25; +4.5%) at 60°·s−1 and knee-extension average power (ES = 0.30; +5.2%) at 180°·s−1, and knee-flexion peak torque at 60°·s−1 (ES = 0.22; +4.1%) and 180°·s−1 (ES = 0.31; +5.9%); (3) barbell velocity at 50% of 1RM (ES = 0.30; +3.2%), 75% of 1RM (ES = 0.44; +5.7%), and 90% of 1RM (ES = 0.43; +9.1%); and (4) whole-body peak power on the rowing-ergometer test (ES = 0.41; +5.0%). Average power of the knee flexors did not change at either angular velocity with caffeine consumption. Conclusions: Caffeinated chewing gum with a dose of caffeine of 300 mg consumed 10 min preexercise may acutely enhance vertical-jump height, isokinetic strength and power of the lower-body musculature, barbell velocity in the bench-press exercise with moderate to high loads, and whole-body power.

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Katie Weatherson, Lira Yun, Kelly Wunderlich, Eli Puterman and Guy Faulkner

Background: Ecological momentary assessment (EMA) is a method of collecting behavioral data in real time. The purpose of this study was to examine EMA compliance, identify factors predicting compliance, assess criterion validity of, and reactivity to, using EMA in a workplace intervention study. Methods: Forty-five adults (91.1% female, 39.7 [9.6] y) were recruited for a workplace standing desk intervention. Participants received 5 surveys each day for 5 workdays via smartphone application. EMA items assessed current position (sitting/standing/stepping). EMA responses were time matched to objectively measured time in each position before and after each prompt. Multilevel logistic regression models estimated factors influencing EMA response. Cohen kappa measured interrater agreement between EMA-reported and device-measured position. Reactivity was assessed by comparing objectively measured sitting/standing/stepping in the 15 minutes before and after each EMA prompt using multilevel repeated-measures models. Results: Participants answered 81.4% of EMA prompts. Differences in compliance differed by position. There was substantial agreement between EMA-reported and device-measured position (κ = .713; P < .001). Following the EMA prompt, participants sat 0.87 minutes more than before the prompt (P < .01). Conclusion: The use of EMA is a valid assessment of position when used in an intervention to reduce occupational sitting and did not appear to disrupt sitting in favor of the targeted outcome.

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Taylor K. Dinyer, M. Travis Byrd, Ashley N. Vesotsky, Pasquale J. Succi and Haley C. Bergstrom

Purpose: To determine if the mathematical model used to derive critical power could be used to identify the critical resistance (CR) for the deadlift; compare predicted and actual repetitions to failure at 50%, 60%, 70%, and 80% 1-repetition maximum (1RM); and compare the CR with the estimated sustainable resistance for 30 repetitions (ESR30). Methods: Twelve subjects completed 1RM testing for the deadlift followed by 4 visits to determine the number of repetitions to failure at 50%, 60%, 70%, and 80% 1RM. The CR was calculated as the slope of the line of the total work completed (repetitions × weight [in kilograms] × distance [in meters]) vs the total distance (in meters) the barbell traveled. The actual and predicted repetitions to failure were determined from the CR model and compared using paired-samples t tests and simple linear regression. The ESR30 was determined from the power-curve analysis and compared with the CR using paired-samples t tests and simple linear regression. Results: The weight and repetitions completed at CR were 56 (11) kg and 49 (14) repetitions. The actual repetitions to failure were less than predicted at 50% 1RM (P < .001) and 80% 1RM (P < .001) and greater at 60% 1RM (P = .004), but there was no difference at 70% 1RM (P = .084). The ESR30 (75 [14] kg) was greater (P < .001) than the CR. Conclusions: The total work-vs-distance relationship can be used to identify the CR for the deadlift, which reflected a sustainable resistance that may be useful in the design of resistance-based exercise programs.

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Rheanna Bulten, Sara King-Dowling and John Cairney

Purpose: To determine the validity of standing long jump (SLJ) for predicting muscle power in children with and without developmental coordination disorder (DCD). Methods: A total of 589 children were recruited as part of the Coordination and Activity Tracking in CHildren study (251 girls and 338 boys; mean age 59.2 mo). Children were classified as typically developing (>16th percentile), at risk for DCD (sixth to 16th percentile), or probable DCD (<sixth percentile) based on Movement Assessment Battery for Children—Second Edition scores. SLJ was measured from the back of the heel. Peak power and mean power over 10 seconds and 30 seconds were measured using the Wingate test. Results: SLJ was moderately correlated with peak and mean powers in all groups (R = .51–.55). Regression analysis showed that when combined with weight and age, SLJ performance could predict peak power and mean power over 10 seconds and 30 seconds in typically developing children (adjusted R 2 = .68, .61, and .58, P < .001, respectively) and in children with risk for DCD (adjusted R 2 = .74, .65, and .60, respectively) and probable DCD (adjusted R 2 = .68, .61, and .59, respectively). Conclusions: SLJ, in combination with weight and age, may be used to measure muscle power in typically developing children, and in children with risk for DCD and probable DCD. This measure can be used as an inexpensive estimate of musculoskeletal fitness in children regardless of motor abilities.

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Andrzej Gawrecki, Aleksandra Araszkiewicz, Agnieszka Szadkowska, Grzegorz Biegański, Jan Konarski, Katarzyna Domaszewska, Arkadiusz Michalak, Bogda Skowrońska, Anna Adamska, Dariusz Naskręt, Przemysława Jarosz-Chobot, Agnieszka Szypowska, Tomasz Klupa and Dorota Zozulińska-Ziółkiewicz

Purpose: To assess glycemic control and safety of children and adolescents with type 1 diabetes participating in a 2-day football tournament. Methods: In total, 189 children with type 1 diabetes from 11 diabetes care centers, in Poland, participated in a football tournament in 3 age categories: 7–9 (21.2%), 10–13 (42.9%), and 14–17 (36%) years. Participants were qualified and organized in 23 football teams, played 4 to 6 matches of 30 minutes, and were supervised by a medical team. Data on insulin dose and glycemia were downloaded from personal pumps, glucose meters, continuous glucose monitoring, and flash glucose monitoring systems. Results: The median level of blood glucose before the matches was 6.78 (4.89–9.39) mmol/L, and after the matches, it was 7.39 (5.5–9.87) mmol/L (P = .001). There were no episodes of severe hypoglycemia or ketoacidosis. The number of episodes of low glucose value (blood glucose ≤3.9 mmol/L) was higher during the tournament versus 30 days before: 1.2 (0–1.5) versus 0.7 (0.3–1.1) event/person/day, P < .001. Lactate levels increased during the matches (2.2 [1.6–4.0] mmol/L to 4.4 [2.6–8.5] mmol/L after the matches, P < .001). Conclusions: Large football tournaments can be organized safely for children with type 1 diabetes. For the majority of children, moderate mixed aerobic–anaerobic effort did not adversely affect glycemic results and metabolic safety.

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Leanna M. Ross, Jacob L. Barber, Alexander C. McLain, R. Glenn Weaver, Xuemei Sui, Steven N. Blair and Mark A. Sarzynski

Background: This study examined the cross-sectional and longitudinal associations of cardiorespiratory fitness (CRF) and ideal cardiovascular health (CVH). Methods: CRF and the 7 CVH components were measured in 11,590 (8865 males; 2725 females) adults at baseline and in 2532 (2160 males; 372 females) adults with at least one follow-up examination from the Aerobics Center Longitudinal Study. Ideal CVH score was calculated as a composite of 7 measures, each scored 0 to 2. CVH groups were based on participant point score: ≤7 (poor), 8 to 11 (intermediate), and 12 to 14 (ideal). Analyses included general linear, logistic regression, and linear mixed models. Results: At baseline, participants in the high CRF category had 21% and 45% higher mean CVH scores than those in the moderate and poor CRF categories (P < .001). The adjusted odds (95% confidence interval) of being in the poor CVH group at baseline were 4.9 (4.4–5.4) and 16.9 (14.3–19.9) times greater for individuals with moderate and low CRF, respectively, compared with those with high CRF (P < .001). Longitudinal analysis found that for every 1-minute increase in treadmill time, CVH score increased by 0.23 units (P < .001) independent of age, sex, exam number, and exam year. Conclusions: Higher CRF is associated with better CVH profiles, and improving CRF over time is independently associated with greater improvements in CVH.

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Zhiguang Zhang, Eduarda Sousa-Sá, João R. Pereira, Anthony D. Okely, Xiaoqi Feng and Rute Santos

Background: This study examined the associations between environmental characteristics of early childhood education and care (ECEC) centers and 1-year change in toddlers’ physical activity and sedentary behavior while at the centers. Methods: Data from 292 toddlers from the GET-UP! study were analyzed. Environmental characteristics of ECEC centers were rated using the Infant/Toddler Environment Rating Scale-revised edition at baseline. Children’s physical activity and sedentary behavior in the centers were assessed using activPAL devices, at baseline and at 1-year follow-up. Linear mixed models were performed to examine the associations between the environmental characteristics and change in the proportion of time spent in physical activity and sedentary behavior. Results: Compared with baseline, children spent a higher proportion of time in sedentary behavior (sitting) but a lower proportion of time in standing and physical activity (stepping) while at ECEC centers, at 1-year follow-up. The environmental characteristics “interaction” (B = −1.39; P = .01) and “program structure” (B = −1.15; P = .04) were negatively associated with change in the proportion of time spent in physical activity. Conclusion: Better “interaction” and “program structure” may preclude children’s physical activity from declining over time and may be considered important features to target in future interventions in ECEC centers aiming at promoting active lifestyles.

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Mauricio Castro-Sepulveda, Jorge Cancino, Rodrigo Fernández-Verdejo, Cristian Pérez-Luco, Sebastian Jannas-Vela, Rodrigo Ramirez-Campillo, Juan Del Coso and Hermann Zbinden-Foncea

During exercise, the human body maintains optimal body temperature through thermoregulatory sweating, which implies the loss of water, sodium (Na+), and other electrolytes. Sweat rate and sweat Na+ concentration show high interindividual variability, even in individuals exercising under similar conditions. Testosterone and cortisol may regulate sweat Na+ loss by modifying the expression/activity of the cystic fibrosis transmembrane conductance regulator. This has not been tested. As a first approximation, the authors aimed to determine whether basal serum concentrations of testosterone or cortisol, or the testosterone/cortisol ratio relate to sweat Na+ loss during exercise. A total of 22 male elite soccer players participated in the study. Testosterone and cortisol were measured in blood samples before exercise (basal). Sweat samples were collected during a training session, and sweat Na+ concentration was determined. The basal serum concentrations of testosterone and cortisol and their ratio were (mean [SD]) 13.6 (3.3) pg/ml, 228.9 (41.4) ng/ml, and 0.06 (0.02), respectively. During exercise, the rate of Na+ loss was related to cortisol (r = .43; p < .05) and to the testosterone/cortisol ratio (r = −.46; p < .01), independently of the sweating rate. The results suggest that cortisol and the testosterone/cortisol ratio may influence Na+ loss during exercise. It is unknown whether this regulation depends on the cystic fibrosis transmembrane conductance regulator.