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Charlotte Skau Pawlowski, Henriette Bondo Andersen and Jasper Schipperijn

Background: It remains unclear if schoolyard interventions “just” provide more opportunities for those children who are already active. The authors wanted to investigate schoolyard use and physical activity (PA) among the least-active children during recess following schoolyard renewals. Methods: An intervention study design with preresults and postresults comparison was used. Accelerometer and global positioning system data were collected at 6 Danish schools from 553 children at baseline and 439 after renewals (grades 4–9). Based on mean minutes of recess moderate to vigorous PA per child per school, the least-active children were defined as all children in the lowest activity quartile at baseline and follow-up, respectively. Results: One hundred and thirty-five children (70% girls) at baseline and 108 (76% girls) at follow-up were categorized as the least-active children. At follow-up they accumulated more time (12.1 min/d) and PA (4.4 min/d) in the schoolyard during recess compared with baseline. The difference in schoolyard PA found for the least-active children was relatively small compared with the difference for all children. Conclusions: Solely improving the physical schoolyard environment seemed to have limited impact on the least-active children’s PA. Future studies should investigate the complex interrelations between the least-active children and the entire schoolyard environment.

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Sanne L.C. Veldman, Rachel A. Jones, Rebecca M. Stanley, Dylan P. Cliff, Stewart A. Vella, Steven J. Howard, Anne-Maree Parrish and Anthony D. Okely

Background: The aim of this study was to examine the efficacy of an embedded after-school intervention, on promoting physical activity and academic achievement in primary-school-aged children. Methods: This 6-month, 2-arm cluster randomized controlled trial involved 4 after-school centers. Two centers were randomly assigned to the intervention, which involved training the center staff on and implementing structured physical activity (team sports and physical activity sessions for 75 min) and academic enrichment activities (45 min). The activities were implemented 3 afternoons per week for 2.5 hours. The control centers continued their usual after-school care practice. After-school physical activity (accelerometry) and executive functions (working memory, inhibition, and cognitive flexibility) were assessed pre- and postintervention. Results: A total of 60 children were assessed (7.7 [1.8] y; 50% girls) preintervention and postintervention (77% retention rate). Children in the intervention centers spent significantly more time in moderate to vigorous physical activity (adjusted difference = 2.4%; 95% confidence interval, 0.6 to 4.2; P = .026) and scored higher on cognitive flexibility (adjusted difference = 1.9 units; 95% confidence interval, 0.9 to 3.0; P = .009). About 92% of the intervention sessions were implemented. The participation rates varied between 51% and 94%. Conclusion: This after-school intervention was successful at increasing moderate to vigorous physical activity and enhancing cognitive flexibility in children. As the intervention was implemented by the center staff and local university students, further testing for effectiveness and scalability in a larger trial is required.

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Tatiana Plekhanova, Alex V. Rowlands, Tom Yates, Andrew Hall, Emer M. Brady, Melanie Davies, Kamlesh Khunti and Charlotte L. Edwardson

Introduction: This study examined the equivalency of sleep estimates from Axivity, GENEActiv, and ActiGraph accelerometers worn on the nondominant and dominant wrists and with and without using a sleep log to guide the algorithm. Methods: 47 young adults wore an Axivity, GENEActiv, and ActiGraph accelerometer continuously on both wrists for 4–7 days. Sleep time, sleep window, sleep efficiency, sleep onset, and wake time were produced using the open-source software (GGIR). For each outcome, agreement between accelerometer brands, dominant and nondominant wrists, and with and without use of a sleep log, was examined using pairwise 95% equivalence tests (±10% equivalence zone) and intraclass correlation coefficients (ICCs), with 95% confidence intervals and limits of agreement. Results: All sleep outcomes were within a 10% equivalence zone irrespective of brand, wrist, or use of a sleep log. ICCs were poor to good for sleep time (ICCs ≥ .66) and sleep window (ICCs ≥ .56). Most ICCs were good to excellent for sleep efficiency (ICCs ≥ .73), sleep onset (ICCs ≥ .88), and wake time (ICCs ≥ .87). There were low levels of mean bias; however, there were wide 95% limits of agreement for sleep time, sleep window, sleep onset, and wake time outcomes. Sleep time (up to 25 min) and sleep window (up to 29 min) outcomes were higher when use of the sleep log was not used. Conclusion: The present findings suggest that sleep outcomes from the Axivity, GENEActiv, and ActiGraph, when analyzed identically, are comparable across studies with different accelerometer brands and wear protocols at a group level. However, caution is advised when comparing studies that differ on sleep log availability.

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David C. Kingston and Stacey M. Acker

A musculoskeletal model of the right lower limb was developed to estimate 3D tibial contact forces in high knee flexion postures. This model determined the effect of intersegmental contact between thigh–calf and heel–gluteal structures on tibial contact forces. This model includes direct tracking and 3D orientation of intersegmental contact force, femoral translations from in vivo studies, wrapping of knee extensor musculature, and a novel optimization constraint for multielement muscle groups. Model verification consisted of calculating the error between estimated tibial compressive forces and direct measurements from the Grand Knee Challenge during movements to ∼120° of knee flexion as no high knee flexion data are available. Tibial compression estimates strongly fit implant data during walking (R 2 = .83) and squatting (R 2 = .93) with a root mean squared difference of .47 and .16 body weight, respectively. Incorporating intersegmental contact significantly reduced model estimates of peak tibial anterior–posterior shear and increased peak medial–lateral shear during the static phase of high knee flexion movements by an average of .33 and .07 body weight, respectively. This model supports prior work in that intersegmental contact is a critical parameter when estimating tibial contact forces in high knee flexion movements across a range of culturally and occupationally relevant postures.

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Seong-won Han, Andrew Sawatsky, Azim Jinha and Walter Herzog

Vastus medialis (VM) weakness is thought to alter patellar tracking, thereby changing the loading of the patellofemoral joint (PFJ), resulting in patellofemoral pain. However, it is challenging to measure VM force and weakness in human studies, nor is it possible to measure the associated mechanical changes in the PFJ. To obtain fundamental insight into VM weakness and its effects on PFJ mechanics, the authors determined PFJ loading in the presence of experimentally simulated VM weakness. Skeletally mature New Zealand White rabbits were used (n = 6), and the vastus lateralis, VM, and rectus femoris were stimulated individually through 3 custom-built nerve cuff electrodes. Muscle torque and PFJ pressure distribution were measured while activating all muscles simultaneously, or when the vastus lateralis and rectus femoris were activated, while VM was not, to simulate a quadriceps muscle strength imbalance. For a given muscular joint torque, peak pressures were greater and joint contact areas were smaller when simulating VM weakness compared with the condition where all muscles were activated simultaneously. The results in the rabbit model support that VM weakness results in altered PFJ loading, which may cause patellofemoral pain, often associated with a strength imbalance of the knee extensor muscle group.

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Jeffrey Sallen, Christian Andrä, Sebastian Ludyga, Manuel Mücke and Christian Herrmann

Background: The relationship between engagement in physical activity and the development of motor competence (MC) is considered to be reciprocal and dynamic throughout childhood and adolescence. The 10-month follow-up study aimed to explore this reciprocal relationship and investigated whether the relationship is mediated by the corresponding self-perception of MC (PMC). Methods: A total of 51 children aged between 10 and 11 years (M = 10.27 [0.45]) participated in the study (52.9% boys, 47.1% girls). As an indicator for physical activity, the average vigorous physical activity (VPA) per day was measured by ActiGraph accelerometers. Two aspects of MC and PMC were recorded: self-movement and object movement. Saturated pathway models in a cross-lagged panel design with 2 measurement points were analyzed. Results: Reciprocal and direct relationships between VPA and MC object movement respectively MC self-movement were not found in longitudinal analyses with PMC as a mediator. Indirect effects of MC at t1 on VPA at t2 via PMC were identified (self-movement: β = 0.13, 95% confidence interval, 0.04 to 0.26; object movement: β = 0.14, 95% confidence interval, 0.01 to 0.49). Conclusion: The results highlight the importance of MC and PMC in promoting children’s VPA. However, VPA does not drive the development of MC.

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Samuel R. Nyman

Despite interest as to the benefits of Tai Chi, there remains a controversy over its effectiveness as an exercise intervention for preventing falls among older adults. This review synthesizes the evidence base with a focus on meta-analyses and randomized controlled trials with community-dwelling older adults. It provides a critical lens on the evidence and quality of the trials. High-quality evidence suggests that Tai Chi is an effective intervention for preventing falls in community settings; however, there is unclear evidence for long-term care facilities and an absence of evidence for hospital settings. When compared directly with other exercise interventions, Tai Chi may offer a superior strategy for reducing falls through its benefits on cognitive functioning. Using data from the current Cochrane review, a new synthesis is presented suggesting that 71–81% of community-dwelling older adults are adherent to class-based Tai Chi interventions. The practical opportunities and challenges for practitioners are discussed.