This study aimed to verify the effects of 12 weeks of swimming lessons implemented in age school Brazilian children’s aquatic skills and motor coordination. Fifty children aged 6 to 10 years old (mean ± SD: 8.34 ± 1.10 years), participated in one swimming lesson per week provided by the school curriculum. Each child was evaluated for their aquatic skills (17 skills checklist) and motor coordination (Körperkoordinationstest Für Kinder test–KTK) before and after the swimming program. This study showed significant improvements in the sum of scores obtained in swimming skills evaluation (31.40 ± 12.89 vs. 46.90 ± 10.73 points, p < .01, d = 3.38). Large effects were found in water orientation and adjustment at the vertical position, breath control, horizontal buoyancy, body position at ventral, dorsal gliding and at longitudinal rotation, front and back somersaults, leg kicking with breath control, feet-first/head-first entries, autonomy in a deep pool and vertical buoyancy and immersion at deep water. The sum of scores in motor coordination assessment increased from 140.64 ± 41.94 to 175.20 ± 41.39 points (p < .01, d = 1.56). These results showed that 12 weeks of swimming practices, even conditioned by state school context (i.e., once a week), allowed Brazilian children aged 6-10 years old to increase aquatic skills and motor coordination.  Resumen. Este estudio tuvo como objetivo verificar los efectos de las clases de natación durante un período de 12 semanas en las habilidades acuáticas y la coordinación motora en niños brasileños. Cincuenta niños entre los 6 y los 10 años de edad (media ± DE: 8.34 ± 1.10 años) participaron una vez por semana en una clase de natación ofrecida por el plan de estudios escolar. Cada niño fue evaluado en cuanto a sus habilidades acuáticas (lista de verificación de 17 habilidades) y coordinación motora (Körperkoordinationstest Für Kinder test - KTK) antes y después del programa de natación. Los resultados del estudio mostraron mejoras significativas en la suma de las puntuaciones obtenidas en la evaluación de las habilidades de natación (31.40 ± 12.89 frente a 46.90 ± 10.73 puntos, p < .01, d = 3.38). Se observaran efectos importantes en la orientación y el ajuste del agua en la posición vertical, en el control de la respiración, en la flotabilidad horizontal, en la posición del cuerpo en la posición ventral, en el deslizamiento dorsal y la rotación longitudinal, en los saltos mortales hacia adelante y hacia atrás, en los empujes con las piernas con control de la respiración, pies primero / cabeza primero entradas, en la autonomía en piscina profunda y flotabilidad vertical y inmersión en aguas profundas. La suma de las puntuaciones en la evaluación de la coordinación motora aumentó de 140.64 ± 41.94 a 175.20 ± 41.39 puntos (p < .01, d = 1.56). Estos resultados mostraron que 12 semanas de prácticas de natación, incluso condicionadas por el contexto de la escuela estatal (es decir, una vez por semana), permitieron a los niños brasileños de 6 a 10 años aumentar de forma significativa la preparación acuática y la coordinación motora.

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Introduction: In swimming, it is necessary to understand and identify the main factors that are important to reduce active drag and, consequently, improve the performance of swimmers. However, there is no up-to-date review in the literature clarifying this topic. Thus, a systematic narrative review was performed to update the body of knowledge on active drag in swimming through numerical and experimental methods.Methods: To determine and identify the most relevant studies for this review, the Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) approach was used.Results: 75 studies related to active drag in swimming and the methodologies applied to study them were analyzed and kept for synthesis. The included studies showed a high-quality score by the Delphi scale (mean score was 5.85 ± 0.38). Active drag was included in seven studies through numerical methods and 68 through experimental methods. In both methods used by the authors to determine the drag, it can be concluded that the frontal surface area plays a fundamental role. Additionally, the technique seems to be a determining factor in reducing the drag force and increasing the propulsive force. Drag tends to increase with speed and frontal surface area, being greater in adults than in children due to body density factors and high levels of speed. However, the coefficient of drag decreases as the technical efficiency of swimming increases (i.e., the best swimmers (the fastest or most efficient) are those with the best drag and swimming hydrodynamics efficiency).Conclusion: Active drag was studied through numerical and experimental methods. There are significantly fewer numerical studies than experimental ones. This is because active drag, as a dynamical phenomenon, is too complex to be studied numerically. Drag is greater in adults than in children and greater in men than in women across all age groups. The study of drag is increasingly essential to collaborate with coaches in the process of understanding the fundamental patterns of movement biomechanics to achieve the best performance in swimming. Although most agree with these findings, there is disagreement in some studies, especially when it is difficult to define competitive level and age. The disagreement concerns three main aspects: 1) period of the studies and improvement of methodologies; 2) discrimination of methodologies between factors observed in numerical vs. experimental methods; 3) evidence that drag tends to be non-linear and depends on personal, technical, and stylistic factors. Based on the complexity of active drag, the study of this phenomenon must continue to improve swimming performance.

Evidence on the role of propulsion compared to drag in swimming, based on experimental settings, is still lacking. However, higher levels of propulsion seem to lead to faster swimming velocities. The aim of this study was to understand the variation in a set of kinematic and kinetic variables between two swimming sections and their relationship to swimming velocity. The sample consisted of 15 young adult recreational swimmers (8 males: 20.84 ± 2.03 years; 7 females: 20.13 ± 1.90 years). Maximum swimming velocity and a set of kinematic and kinetic variables were measured during two consecutive sections of the swimming pool. Differences between sections were measured and the determinants of swimming velocity were analyzed. Swimming velocity, propulsive force, and the other kinematic and kinetic variables did not change significantly (p < 0.05) between sections (only the intra-cyclic fluctuation of swimming velocity decreased significantly, p = 0.005). The modeling identified the propulsive force, stroke length, and active drag coefficient as the determinants of swimming velocity. Swimming velocity was determined by the interaction of kinematic and kinetic variables, specifically propulsive force and active drag coefficient.

Water management in transboundary situations is a multidisciplinary subject. The main objective of this article is to provide a reflection on the impact of centralized versus decentralized wastewater systems, regarding the potential of water reuse within a transboundary context. The Occupied Palestinian Territories are the presented scenario. The existent wastewater treatment plants are not enough to guarantee good environmental and public health conditions and there are serious operational and maintenance problems. Due to the geopolitical situation in the Occupied Palestinian Territories, decentralized systems have been extensively used throughout the whole West Bank but most of the systems are not functioning correctly. Two case studies are analyzed: Ras ‘Atiya is an example of a possible transboundary wastewater management system where the wastewater treatment is proposed to be at an Israeli wastewater treatment plant and Atouf is based on a decentralized on‐site system at household level. In transboundary situations water reuse becomes a sensitive issue. Whenever there is centralized transboundary wastewater treatment, there is a risk that one of the parties involved may lose rights of its treated water.