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Purpose: The aim of this study was to examine the concurrent validity of force–velocity (FV) variables assessed across 5 Keiser leg press devices. Methods: A linear encoder and 2 independent force plates (MuscleLab devices) were mounted on each of the 5 leg press devices. A total of 997 leg press executions, covering a wide range of forces and velocities, were performed by 14 participants (29 [7] y, 181 [5] cm, 82 [8] kg) across the 5 devices. Average and peak force, velocity, and power values were collected simultaneously from the Keiser and MuscleLab devices for each repetition. Individual FV profiles were fitted to each participant from peak and average force and velocity measurements. Theoretical maximal force, velocity, and power were deduced from the FV relationship. Results: Average and peak force and velocity had a coefficient of variation of 1.5% to 8.6%, near-perfect correlations (.994–.999), and a systematic bias of 0.7% to 7.1% when compared with reference measurements. Average and peak power showed larger coefficient of variations (11.6% and 17.2%), despite excellent correlations (.977 and .952), and trivial to small biases (3.9% and 8.4%). Extrapolated FV variables showed near-perfect correlations (.983–.997) with trivial to small biases (1.4%–11.2%) and a coefficient of variation of 1.4% to 5.9%. Conclusions: The Keiser leg press device can obtain valid measurements over a wide range of forces and velocities across different devices. To accurately measure power, theoretical maximal power calculated from the FV profile is recommended over average and peak power values from single repetitions, due to the lower random error observed for theoretical maximal power.

Background: The purposes of this study were to examine the proportions of youth receiving special education services in the United States who individually and jointly met physical activity, screen time, and sleep duration guidelines, and to examine the impact of meeting none, one, two, and three of the guidelines on overweight and obesity. Methods: This cross-sectional analysis utilized data from the 2016 to 2017 National Survey for Children’s Health data set on 3582 youth aged 10–17 years who received special education services. The frequency of the participants’ compliance with the 24-hour movement guidelines and body weight status (based on the age- and sex-specific percentile cutoffs) were estimated. Meeting guidelines was defined as: 9–11 hours/night (5–13 y) or 8–10 hours/night (14–17 y) of sleep, ≤120 minutes per day of screen time, and ≥60 minutes per day of moderate to vigorous physical activity. A multinomial logistic regression analysis was conducted to estimate the impact of meeting none, one, two, or three guidelines on body weight status, adjusted for potential confounders. Results: Overall, 8.1% of youth met all three guidelines, 42.0% met two guidelines, 38.0% met one guideline, and 11.9% did not meet any guideline. Meeting all three guidelines was associated with an approximately 50% decreased likelihood of overweight than meeting no guideline, or sleep or screen time guidelines independently. Conclusions: This study extends the 24-hour movement framework to children receiving special education services and should prompt the continued study of its utility for understanding health disparities experienced by this population.

Background: Social emotional development is imperative to young children’s long-term psychological and physical health. Physical activity (PA) may be important for young children’s social emotional development. The association between preschooler PA duration and intensity and social emotional development was investigated. Methods: Data from six hundred and fifty-one 2- to 4-year-olds in the Play Spaces and Environments for Children’s Physical Activity (PLAYCE) study were analyzed. PA was measured using ActiGraph-GT3X accelerometers worn over 7 days. Social emotional development was measured using the parent-completed Strengths and Difficulties Questionnaire. Multilevel linear regression models examined the association between PA duration and intensity and Strengths and Difficulties Questionnaire subscales. Results: Preschoolers did 158.2 (SD = 40.2) minutes per day of PA with 27% meeting the Australian Physical Activity Guidelines for the Early Years. There was a 1.74 point decrease in the total Strengths and Difficulties Questionnaire score for each additional hour of moderate-intensity PA per day (P < .05). Similar significant associations were found across all domains of social emotional development except hyperactivity, and were consistent across different intensities of light, moderate, and vigorous PA. Conclusions: These findings highlight the potential importance of PA, especially moderate-intensity play-based PA, for different aspects of preschool children’s social emotional development. Longitudinal and intervention research is required to confirm whether promoting PA in the early years provides developmental benefit.

Background: To examine the associations between motor competence (MC), moderate to vigorous physical activity (MVPA), and body mass index (BMI) changes over 1 year in preschoolers. Methods: Fifty-four preschoolers (24 girls; 42.4%) aged 4–5 years old from the metropolitan area of Porto, Portugal comprised the sample. Height, body mass, and BMI were calculated. MC was assessed according to the Movement Assessment Battery for Children-2. MVPA was measured by accelerometry. For each participant, changes in MVPA, MC, and BMI over a year were computed. Different levels of MC were calculated; and then data were analyzed. Results: The MVPA increased over time in all levels of MC in the follow-up. The BMI decreased over time for all levels in follow-up (P = .001). The preschoolers classified as at a high level of MC were more likely to spend more time in MVPA (in minutes) than their counterparts with low MC in follow-up. Multiple linear regression analyses, adjusted by sex and age, were fit to predict Δ% MC by Δ% MVPA and Δ% BMI. The Δ% MC was positively associated with Δ% MVPA. Conclusion: Increases in MC were positively associated with MVPA. Higher performance in MC increases due to time spent in MVPA. Improvement of MC in young children has potentially relevant policy implications related to MVPA and public health.

Purpose: To compare resistance training using a velocity loss threshold with training to repetition failure on upper-body strength parameters in professional Australian footballers. Methods: A total of 26 professional Australian footballers (23.9 [4.2] y, 189.9 [7.8] cm, 88.2 [8.8] kg) tested 1-repetition-maximum strength (FP_max) and mean barbell velocity at 85% of 1-repetition maximum on floor press (FP_vel). They were then assigned to 2 training groups: 20% velocity loss threshold training (VL; n = 12, maximum-effort lift velocity) or training to repetition failure (TF; n = 14, self-selected lift velocity). Subjects trained twice per week for 3 weeks before being reassessed on FP_max and FP_vel. Training volume (total repetitions) was recorded for all training sessions. No differences were present between groups on any pretraining measure. Results: The TF group significantly improved FP_max (105.2–110.9 kg, +5.4%), while the VL group did not (107.5–109.2 kg, +1.6%) (P > .05). Both groups significantly increased FP_vel (0.38–0.46 m·s⁻¹, +19.1% and 0.37–0.42 m·s⁻¹, +16.7%, respectively) with no between-groups differences evident (P > .05). The TF group performed significantly more training volume (12.2 vs 6.8 repetitions per session, P > .05). Conclusions: Training to repetition failure improved FP_max, while training using a velocity loss threshold of 20% did not. Both groups demonstrated similar improvements in FP_vel despite the VL group completing 45% less total training volume than the TF group. The reduction in training volume associated with implementing a 20% velocity loss threshold may negatively impact the development of upper-body maximum strength while still enhancing submaximal movement velocity.

Along with digestion and absorption of nutrients, the gastrointestinal epithelium acts as a primary intestinal defense layer, preventing luminal pathogens from entering the circulation. During exercise in the heat, epithelial integrity can become compromised, allowing bacteria and bacterial endotoxins to translocate into circulation, triggering a systemic inflammatory response and exacerbating gastrointestinal damage. While this relationship seems clear in the general population in endurance/ultraendurance exercise, the aim of this systematic review was to evaluate the effect of exercise in the heat on blood markers of gastrointestinal epithelial disturbance in well-trained individuals. Following the 2009 Preferred Reporting Items for Systematic Reviewed and Meta-Analyses guidelines, five electronic databases were searched for appropriate research, and 1,885 studies were identified. Five studies met the inclusion criteria and were subject to full methodological appraisal by two reviewers. Critical appraisal of the studies was conducted using the McMasters Critical Review Form. The studies investigated changes in markers of gastrointestinal damage (intestinal fatty acid–binding protein, endotoxin, and/or lipopolysaccharide-binding protein) following acute exercise in warm to hot conditions (≥ 30 °C) and included trained or well-trained participants with direct comparisons to a control temperate condition (≤ 22 °C). The studies found that prolonged submaximal and strenuous exercise in hot environmental conditions can acutely increase epithelial disturbance compared with exercise in cooler conditions, with disturbances not being clinically relevant. However, trained and well-trained populations appear to tolerate exercise-induced gastrointestinal disturbance in the heat. Whether this is an acquired tolerance related to regular training remains to be investigated.

Background: There is an alarming and constant worldwide progression of physical inactivity and sedentary behaviors in children and adolescents. The present paper summarizes findings from France’s 2020 Report Card on physical activity for children and youth, comparing its results to its 2 previous editions (2016 and 2018). Methods: France’s 2020 Report Card follows the standardized methodology established by the Active Healthy Kids Global Matrix, grading 10 common physical activity indicators using the best available evidence. The grades were informed by national surveys, peer-reviewed literature, government and nongovernment reports, and online information. Results: The expert panel awarded the following grades: Overall Physical Activity: D; Organized Sport Participation and Physical Activity: C−; Active Play: INC; Active Transportation: C−; Sedentary Behaviors: D−; Family and Peers: D−; Physical Fitness: D; School: B−; Community and the Built Environment: F; Government: C. Conclusions: This 2020 edition of France’s Report Card again highlights the alarming levels of physical activity and sedentary behaviors among French children and adolescents, calling for the development of effective national action. It also draws attention to the particular deleterious effects of the COVID-19 confinement on youth’s movement behaviors, which significantly worsened the situation.

Background: A walking school bus (WSB) consists of students and adults walking to and from school and promotes active commuting to school. Self-efficacy (SE) and outcome expectations (OE) are behavioral constructs associated with active commuting to school. The authors sought to assess the impact of a WSB program on child SE, and parent SE, and OE. Methods: The authors conducted a cluster randomized controlled trial of a WSB intervention from 2012 to 2016 among 22 elementary schools serving racially diverse, low-income populations in Houston, TX and Seattle, WA. Surveys collected data from third- to fifth-grade students and their parents, (n = 418) child-parent dyads, before school randomization and at the school year’s end. Child surveys included 16 SE items, while parent surveys included 15 SE items and 14 OE items. Scores were averaged from responses ranging from 1 to 3. The authors compared changes in SE and OE between groups over time and accounted for clustering using linear mixed-effects models. Results: The intervention group had increases in child SE of 0.12 points (P = .03), parent SE of 0.11 points (P = .048), and parent OE of 0.09 points (P = .02) compared to controls over time. Conclusions: As hypothesized, the WSB improved child SE, parent SE, and parent OE related to active commuting to school.

Background: Regular physical activity is crucial for healthy aging, but older adults are the least active age group. This study explored the feasibility, acceptability, and efficacy of a multilevel mHealth intervention for increasing physical activity of older adults living in a retirement community. Methods: Participants included 54 older adults (mean age = 81.2 y, 77.8% female, 98.1% white) living in a retirement community. Participants received a Fitbit Zip and access to a multilevel mHealth physical activity intervention (MapTrek Residential) for 8 weeks. Physical activity (in steps per day) and intervention compliance (days worn) were measured objectively with the Fitbit for 12 weeks (8-wk intervention plus 4-wk follow-up). Psychosocial outcomes (social support, self-efficacy, and outcome expectations) were assessed at baseline and 8 weeks. Acceptability outcomes were assessed with an open-ended process evaluation survey and focus groups. Descriptive statistics and linear mixed models were used to examine intervention effects. Results: Participants increased daily steps from 5438 steps per day at baseline (95% CI, 4620 to 6256) to 6201 steps per day (95% CI, 5359 to 7042) at week 8 (P < .0001) but this was not maintained at 12 weeks (P = .92). Conclusions: Our multilevel mHealth physical activity intervention was effective for increasing physical activity older adults over 8 weeks. Additional research focused on maintaining physical activity gains with this approach is warranted.

Purpose: To track cardiac-autonomic functioning, indexed by heart-rate variability, in American college football players throughout a competitive period. Methods: Resting heart rate (RHR) and the natural logarithm root mean square of successive differences (LnRMSSD) were obtained throughout preseason and ∼3 times weekly leading up to the national championship among 8 linemen and 12 nonlinemen. Seated 1-minute recordings were performed via mobile device and standardized for time of day and proximity to training. Results: Relative to preseason, linemen exhibited suppressed LnRMSSD during camp-style preparation for the playoffs (P = .041, effect size [ES] = −1.01), the week of the national semifinal (P < .001, ES = −1.27), and the week of the national championship (P = .005, ES = −1.16). As a combined group, increases in RHR (P < .001) were observed at the same time points (nonlinemen ES = 0.48–0.59, linemen ES = 1.03–1.10). For all linemen, RHR trended upward (positive slopes, R ² = .02–.77) while LnRMSSD trended downward (negative slopes, R ² = .02–.62) throughout the season. Preseason to postseason changes in RHR (r = .50, P = .025) and LnRMSSD (r = −.68, P < .001) were associated with body mass. Conclusions: Heart-rate variability tracking revealed progressive autonomic imbalance in the lineman position group, with individual players showing suppressed values by midseason. Attenuated parasympathetic activation is a hallmark of impaired recovery and may contribute to cardiovascular maladaptations reported to occur in linemen following a competitive season. Thus, a descending pattern may serve as an easily identifiable red flag requiring attention from performance and medical staff.