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The aims of this study were to compare surface electromyographic (EMG) activity and kinematic variables among open, somersault, bucket and crossover backstroke-to-breaststroke turning techniques, and identify relationships between the integrated electromyography (iEMG) and kinematics profile focusing on the rotation and push-off efficacy. Following a four-week of systematically increasing contextual interference intervention program, eight 12.38 ± 0.55 years old male swimmers randomly performed twelve repetitions (three in each technique) turns in and out of the wall at maximum speed until the 7.5 m reference mark. Surface EMG values of the right vastus lateralis, biceps femoris, tibialis anterior, gastrocnemius medialis, rectus abdominis, external oblique, erector spinae and latissimus dorsi were recorded and processed using the integrated electromyography (iEMG) and the total integrated electromyography (TiEMG) that was expressed as a percentage of iEMGmax to normalize per unit of time for each rotation and push-off phase. Complementarily, 2D sagittal views from an underwater video camera were digitized to determine rotation and push-off efficacy. The crossover turn presented the highest rotation and push-off iEMG values. Erector spinae and gastrocnemius medialis had the highest activity in the rotation and push-off phases (89 ± 10 and 98 ± 69%, respectively). TiEMG depicted a very high activity of lower limb muscles during push-off activity (222 ± 17 to 247 ± 16%). However, there were no relation between TiEMG and rotation and push-off time, tuck index and final push-off velocity during the rotation and the push-off phases across all the studied turning techniques. The rotation efficacy in age-group swimmers were dependent on rotation time (p = 0.04). The different turning techniques were not distinguishable regarding iEMG activity as a possible determinant of rotation and push-off efficacy. Our study has direct implications for selecting appropriate exercises and designing training programs for optimizing the rotation and push-off phases of backstroke-to-breaststroke turning at young ages.

The purpose of the present study was to identify the performance determinant factors predicting 15-m backstroke-to-breaststroke turning performance using and comparing linear and tree-based machine-learning models. The temporal, kinematic, kinetic and hydrodynamic variables were collected from 18 age-group swimmers (12.08 ± 0.17 yrs) using 23 Qualisys cameras, two tri-axial underwater force plates and inverse dynamics approach. The best models were obtained: (i) with Lasso linear model of the leave-one-out cross-validation in open turn (MSE = 0.011; R

Compreender a aquisição de experiência em habilidades de viragens na perspetiva de um jovem nadador em desenvolvimento, geralmente requer o desenvolvimento de uma relação e interação entre as características do movimento efetivo e o processo de ensino-aprendizagem. No entanto, poucas análises biomecânicas de viragens em nadadores de grupos de idade foram conduzidas para facilitar o diagnóstico biomecânico e a intervenção científica em técnicas de viragem nado costas para bruços. Os objetivos desta Tese foram: (1) identificar as características biomecânicas determinantes em cada uma das quatro diferentes técnicas de viragens de nado costas para bruços e (ii) investigar o efeito de 16 treinos de interferência contextuais sistemáticos de 40 minutos cada (quatro semanas), seguido de prática bloqueada, em série e aleatória sobre como facilitar e aprender as técnicas de viragem de nado de costas para nado bruços. Uma abordagem multidisciplinar, incluindo um sistema de captura de movimento, uma plataforma de força tri-axial subaquática personalizada, eletromiografia de superfície (EMG) e uma abordagem dinâmica inversa utilizando variáveis hidrodinâmicas, foi usada para atingir esse objetivo. Começamos (no primeiro estudo) identificando as principais características biomecânicas e determinantes das viragens open, somersault, bucket e crossover. O comportamento eletromiográfico (EMG) e as variáveis cinemáticas selecionadas das quatro técnicas de viragem foram comparadas no segundo estudo, com ênfase particular na eficácia de rotação e no empurrada da parede. O terceiro estudo comparou as características hidrodinâmicas e a estratégia de arrancamento relacionadas à eficácia fase de saída da viragem. O quarto estudo empregou os modelos de aprendizado de máquina linear e baseado em árvore para identificar os modelos altamente realistas de desempenho das viragens com base em variáveis temporais, cinemáticas e cinéticas abrangentes (incluindo hidrodinâmicas). Finalmente, vimos como um programa de intervenção de quatro semanas que ofereceu aumentos sistemáticos na interferência contextual permite que nadadores de grupos de idade melhorem as técnicas de viragens de nado de costas para nado bruços. Os resultados apontaram que um programa de intervenção de quatro semanas melhorou as técnicas de giro de nado de costas para peito de nadadores de grupos de idade. De acordo com os modelos lineares e não lineares previstos, o desempenho de torneamento otimizado foi alcançado por um compromisso e continuidade entre as fases de entrada e saída das viragens. A eficácia de virada foi diretamente influenciada pelas contribuições da velocidade de aproximação à parede e habilidades de rotação na melhoria da velocidade de rolamento e força de empurrão. A atividade eletromiográfica integrada de oito músculos foi semelhante em quatro variantes de rotação, o eretor da espinha e o gastrocnémio medial foram os mais ativados, com viragem crossover tendo os maiores valores de Iemg na rotação e empurre. Uma comparação de medidas cinéticas revela que a viragem bucket tem um pico de força mais alto, enquanto um impulso horizontal mais alto leva a uma velocidade de empurre mais alta na viragem crossover. A viragem somersault apresentou um deslizamento ligeiramente mais profundo, enquanto as características hidrodinâmicas e a estratégia de saída, como determinantes da eficácia da saída na viragem, não diferiram significativamente entre as quatro técnicas de viragem. PALAVRAS-CHAVE: NATACAO, FAIXAS ETARIA, BIOMECHANICA, VIRAGENS Understanding the acquisition of expertise in turning skills from the perspective of a developing young swimmer generally requires the development of a relationship and interaction between characteristics of effective movement and the teaching-learning process. However, few turning biomechanical analyses on age-group swimmers have been conducted to facilitate biomechanical diagnosis and scientific intervention in backstroke to breaststroke turning techniques. The objective of this Thesis were twofold: (i) to identify the biomechanical features that have the greatest influence in each of the four different backstroke to breaststroke turning techniques and (ii) to investigate the effect of four weeks and 16 systematically contextual interference training sessions of 40 minutes each, followed by blocked, serial, and random practice on facilitating learning of the backstroke to breaststroke turning techniques. A multidisciplinary approach, including a motion capture system, a customized underwater tri-axial force plate, surface electromyography (EMG) and an inverse dynamic approach utilizing hydrodynamic variables, was used to accomplish this goal. We began (in the first study) by identifying the key biomechanical features and determinants of open, somersault, bucket, and crossover turning performance. The electromyographic (EMG) behavior and selected kinematic variables of the four backstroke to breaststroke turning techniques were compared in the second study, with a particular emphasis on rotation and push-off efficacy. The third analysis compared the hydrodynamic characteristics and pull-out strategy related to turn out efficacy. The fourth study employed the linear and tree-based machine learning models to identify the highly realistic models of backstroke to breaststroke turn performance based on comprehensive temporal, kinematic, kinetic (including hydrodynamic) variables. Finally, we looked at how a four-week intervention program that offered systematic increases in contextual interference allows age-group swimmers to improve backstroke to breaststroke turning techniques. Results pointed out that a four-week intervention program improved age-group swimmers' backstroke to breaststroke turning techniques. According to the linear and nonlinear predicted models, optimized turning performance was achieved by a compromise and continuity between the turn-in and turn-out phases. Turn-in efficacy was directly influenced by the contributions of approaching velocity to the wall and rotating abilities in improving rolling velocity and pushing-off force. The integrated electromyographic activity of eight muscles was similar across four turning techniques. The erector spinae and gastrocnemius medialis were the most activated muscles, with the crossover turn having the highest rotation and push-off iEMG values. A comparison of kinetic measures reveals that the bucket turn has a higher peak force, while a higher horizontal impulse leads to higher push-off velocity in the crossover turn. The somersault has a slightly deeper gliding depth, while hydrodynamic characteristics and pull-out strategy, as determinants of turn-out efficacy, did not differ between turning techniques.

We compared the hydrodynamic characteristics and pull-out strategies of four backstroke-to-breaststroke turning techniques in young swimmers. Eighteen 11 and 12-year-old swimmers participated in a 4 week intervention program including 16 contextual interference sessions. The hydrodynamic variables were assessed through inverse dynamics, and the pull-out strategy kinematics were assessed with tracking markers followed by 12 land cameras and 11 underwater cameras. Swimmers randomly completed sixteen 30 m maximal backstroke-to breaststroke-open, somersault, bucket and crossover turns (four in each technique) with a 3 min rest. The data showed higher drag force, cross-sectional area and drag coefficient values for the first (compared with the second) gliding position. The crossover turn revealed the highest push-off velocity (2.17 ± 0.05 m.s−1), and the somersault turn demonstrated the lowest foot plant index (0.68 ± 0.03, 68%), which could have affected the first gliding, transition and second gliding depths (0.73 ± 0.13, 0.86 ± 0.17 and 0.76 ± 0.17 m). The data revealed the consistency of the time spent (4.86 ± 0.98 s) and breakout distance (6.04 ± 0.94 m) among the four turning techniques, and no differences were observed between them regarding time and average velocity up to 7.5 m. The hydrodynamic characteristics and pull-out strategy of the backstroke-to-breaststroke turns performed by the age group swimmers were independent of the selected technique.

Zacca, R, Azevedo, R, Chainok, P, Vilas-Boas, JP, Castro, FAdS, Pyne, DB, and Fernandes, RJ. Monitoring age-group swimmers over a training macrocycle: energetics, technique, and anthropometrics. J Strength Cond Res 34(3): 818-827, 2020-The aim of this study was to quantify changes and contributions of energetic, technique, and anthropometric profiles across the first training macrocycle (16-week) in a traditional 3-peak swimming season. Twenty-four age-group swimmers (10 boys and 14 girls age 14.4 ± 0.9 years) of equal maturational stage were monitored through a 400-m test in front crawl (T400). Energetic, technique, and anthropometric characteristics were compared before (experimental testing 1, E1) and after the preparatory (E2), specific (E3), and competitive (E4) training periods. Sex interaction was not significant for any variable. Multiple linear regressions and principal component analysis were used to identify the most influential variables and the relative contribution of each domain (energetics, technique, and anthropometrics) to changes in swimming performance of T400. The relative contributions for performance of T400 at E1, E2, E3, and E4 were 15, 12, 6, and 13% for energetics, 78, 85, 75, and 70% for technique, and 7, 3, 19 and 17% for anthropometrics, respectively. Technique played the main role during the first 16-week macrocycle in a competitive season, regardless of small fluctuations in the influence of energetics and anthropometrics. Changes and influence of energetics, technique, and anthropometric on age-group swimmers' performance could be described by the T400 swimming test, providing a comprehensive biophysical overview of the main contributors to swimming performance.

Foot and hand set-up position effects were analysed on backstroke start performance. Ten swimmers randomly completed 27 starts grouped in trials (n = 3) of each variation, changing foot (totally immersed, partially and totally emerged) and hand (lowest, highest horizontal and vertical) positioning. Fifteen cameras recorded kinematics, and four force plates collected hands and feet kinetics. Standardised mean difference and 95% confidence intervals were used. Variations with feet immersed have shown lower vertical centre of mass (CM) set-up position (0.16 m), vertical impulse exerted at the hands, horizontal and vertical impulse exerted at the feet (0.28, 0.41, 0.16 N/BW.s, respectively) than feet emerged with hands horizontal and vertically positioned. Most variations with feet partially emerged exhibited higher and lesser vertical impulse exerted at hands than feet immersed and emerged (e.g. vertical handgrip, 0.13, 0.15 N/BW.s, respectively). Variation with feet emerged and hands on the lowest horizontal handgrip depicted shorter horizontal (0.23, 0.26 m) and vertical CM positioning at flight (0.16, 0.15 m) than the highest horizontal and vertical handgrip, respectively. Start variations have not affected 15-m time. Variations with feet partially or totally emerged depicted advantages, but focusing on the entry and underwater biomechanics is relevant for a shorter start time.