Neuromuscular Activity of Upper and Lower Limbs during two Backstroke Swimming Start Variants.

A proficient start is decisive in sprint competitive swimming events and requires swimmers' to exert maximal forces in a short period to complete the task successfully. The aim of this study was to compare the electromyographic (EMG) activity in-between the backstroke start with feet positioned parallel and partially emerged performed with the hands on the highest horizontal and on the vertical handgrip at hands-off, take-off, flight and entry start phases. EMG comparisons between starting variants were supported by upper and lower limb joint angles at starting position and 15 m start time data. Following a four-week start training to familiarize participants with each start variant, 10 male competitive backstroke swimmers performed randomly six 15 m maximal trials, being three of each start variant. Surface EMG of Biceps Brachii, Triceps Brachii, Rectus Femoris, Biceps Femoris, Gastrocnemius Medialis and Tibialis Anterior was recorded and processed using the time integral EMG (iEMG). Eight video cameras (four surface and four underwater) were used to determine backstroke start phases and joint angles at starting position. EMG, joint angles and temporal parameters have not evidenced changes due to the different handgrips. Nevertheless, clear differences were observed in both variants for upper and lower limb muscles activity among starting phases (e.g. Biceps Brachii at take-off vs. flight phase, 15.17% ± 2.76% and 22.38% ± 4.25%; 14.24% ± 7.11% and 25.90% ± 8.65%, for variant with hands horizontal and vertically positioned, respectively). It was concluded that different handgrips did not affect EMG, kinematics and temporal profile in backstroke start. Despite coaches might plan similar strength training for both start variants, further attention should be given on the selection of proper exercises to maximize the contribution of relevant muscles at different starting phases. Key pointsAn effective swim start component (from the starting signal until the swimmers' vertex reaches the 15 m mark) is decisive in short distance events.In 2008, FINA approved the Omega OSB11 starting block (Swiss Timing Ltd., Switzerland) with two horizontal and one vertical backstroke start handgrip and currently swimmers can adopt different starting variants.The start performance is related to the exertion of maximal force in the shortest time, as other high-velocity movements; thus, the study of the current variants in-between them from a neuromuscular standpoint is indispensable for training support.The use of different handgrips did not affect upper and lower limb electromyographic activity; angular kinematics and overall 15 m backstroke start profile.Independent of the start variant selected, the role played by each upper and lower limb muscles at different starting phases should be considered in specific resistance training program to optimize backstroke start performance.

Are there differences in the kinetic parameters of the vertical jump performed by beach volleyball players on different types of sand?

Beach volleyball (BV) is an intermittent sport characterised by short-duration and highly demanding activities with low intensity periods. Establishing if players' jump ability is influenced by sand granulometry is a useful information for sport scientists, coaches and players. This study aimed to assess the possible differences in the kinetics parameters of the vertical jump on different types of sand performed by BV players. Twelve elite female players performed six countermovement jumps (CMJs) in three different surface conditions (fine sand, reference, coarse sand) in a random counterbalanced order (216 jumps). A generalised mixed model approach detected differences for CMJ model in total duration (p: 0.016), eccentric phase duration (p: 0.007), concentric phase duration (p: 0.011), time to peak power (p: < 0.001), time to peak force (p: 0.014), maximum rate force development concentric phase (p: 0.004), maximum velocity (p: 0.028) and peak power eccentric (p: 0.018). Coarse sand decreases the time spent jumping compared to fine sand, without a penalty to jump height. Coaches and athletes should take this information into account to enhance their understanding of practice strategies and game conditions. One might anticipate a faster pace in games played on coarse sand and a slower pace on fine sand.

Acute Effects of Different Set Configurations on Neuromuscular, Metabolic, and Perceptual Responses in Young Women.

We compared neuromuscular, metabolic, and perceptual responses between different resistance training configurations in young women. In a counterbalanced randomized order, 13 young women performed the following protocols in separate sessions (sets x repetitions): traditional (TRAD): 5x10, 90-s of rest interval between sets; more frequent and shorter total rest (FSR): 10x5, 30-s of rest interval between sets. The sessions were composed of leg press exercise with the same intensity. Force (maximum voluntary isometric contraction [MVIC]) and metabolic (lactate concentration) responses were measured pre- and post-resistance training sessions. The rating of perceived exertion (RPE) was measured after each set. The internal training load was calculated using the session-RPE method. There was a significant reduction in the MVIC only after TRAD configuration (Effect size [ES] = 0.36). The lactate concentration increased in both conditions but was higher after TRAD (ES = 2.81) than FSR (ES = 1.23). The RPE has progressively increased in both configurations. On the other hand, the internal training load was lower in the FSR configuration. From our findings, we suggest that more frequent and shorter total rest is an effective strategy for maintaining the ability to produce force, generating less metabolic stress and lower perceived internal load in young women.

Modelling and Predicting Backstroke Start Performance Using Non-Linear and Linear Models.

Our aim was to compare non-linear and linear mathematical model responses for backstroke start performance prediction. Ten swimmers randomly completed eight 15 m backstroke starts with feet over the wedge, four with hands on the highest horizontal and four on the vertical handgrip. Swimmers were videotaped using a dual media camera set-up, with the starts being performed over an instrumented block with four force plates. Artificial neural networks were applied to predict 5 m start time using kinematic and kinetic variables and to determine the accuracy of the mean absolute percentage error. Artificial neural networks predicted start time more robustly than the linear model with respect to changing training to the validation dataset for the vertical handgrip (3.95 ± 1.67 vs. 5.92 ± 3.27%). Artificial neural networks obtained a smaller mean absolute percentage error than the linear model in the horizontal (0.43 ± 0.19 vs. 0.98 ± 0.19%) and vertical handgrip (0.45 ± 0.19 vs. 1.38 ± 0.30%) using all input data. The best artificial neural network validation revealed a smaller mean absolute error than the linear model for the horizontal (0.007 vs. 0.04 s) and vertical handgrip (0.01 vs. 0.03 s). Artificial neural networks should be used for backstroke 5 m start time prediction due to the quite small differences among the elite level performances.

The effect of different foot and hand set-up positions on backstroke start 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.

Existe associação entre nível de atividade física e composição corporal em adolescentes? / Is there an association between level physical activity and body composition of adolescents?

Os objetivos do presente estudo foram (i) testar se existe associação e (ii) diferença entre o nível de atividade física (NAF) e composição corporal de adolescentes de escolas públicas e p riv adas. Participaram do presente estudo 84 adolescentes (feminino: n = 52; 61,9% e masculino: n = 3 2 ; 3 8 ,1 %) com idade média de 16,4 ± 0,8 anos (feminino = 16,5±0,8 anos e masculino 16,4 ± 0,8 anos) regularmente matriculados em uma escola pública e uma privada do município de Fortaleza/CE. O NAF foi quantificado por meio da aplicação do o questionário de atividade física para adolescentes. Posteriormente foram obtidos dados (massa corporal e estatura) para cálculo do índice de massa corporal (IMC). O percentual de gordura (%G) foi estimado de acordo com o sexo. O teste de correlação de Pea rso n foi utilizado para verificar associação entre as variáveis. Para comparação entre estudantes de escolas públicas e privadas, utilizamos as diferenças de médias estandardizadas, intervalo de co n fiança (90 %), tamanho do efeito e probabilidades de haver diferenças. Não encontramos associações significantes en tre o NAF e IMC (r = 0,033 à 0,214; p > 0,05) e NAF e %G (r = - 0,199 à 0,310; p > 0,05). Não h ouv eram diferenças substanciais entre estudantes de escolas pública e privada para NAF e variáveis de composição corporal. A falta de associação forte entre NAF e composição corporal aponta para o caráter multifatorial que perpassa a relação entre essas duas variáveis na população jovem. Adicionalmente, estudar em escola pública ou privada parece não afetar o NAF e a composição corporal de adolescentes...(AU)

The objectives of present study were (i) to test if there is an association and (ii) differen ce between the level of physical activity (LPA) and body composition of adolescents from public and private schools. A total of 84 adolescents (female: n = 52, 61.9% and males: n = 32, 38.1%), with a mean age o f .4 ± 0.8 years (female = 16.5 ± 0, 8 years and male 16.4 ± 0.8 years) regularly enrolled in a public an d private school in the municipality of Fortaleza/CE. NAF was quantified through the ap p lication o f t he physical activity questionnaire for adolescents. Subsequently data were obtained (body mass and height) to calculate the body mass index (BMI). The percentage of body fat (% BF) was estimated according to sex . The Pearson correlation test was used to verify association between the variables. For comparison between public and private school students, we used the differences of standardized means, co nfiden ce in terv al (90%), effect size and probability of differences. We did not find significant associations bet ween LPA and BMI (r = 0.033 to 0.214; p> 0.05) and LPA and % BF (r = - 0.19 to 0.310; p> 0.05). There were n o substantial differences between public and private school students for LPA and body co mpo sition. The lack of strong association between NAF and body composition points to the multifactorial character t hat per passes the relationship between these two variables in the young population. Additionally, studying in a public or private school does not seem to affect LPA and the body composition of adolescents...(AU)

Body fat percentage and lower limbs temperature in recreational cyclists during an incremental test / Porcentagem de gordura e temperatura dos membros inferiores em ciclistas recreativos durante teste incremental

This study aimed to evaluate temperature variations on the thighs in an incremental cycling test in healthy recreational cyclists with two different fat percentages. Thirty-two male recreational cyclists were measured in height, body mass, thigh skinfold and body fat percentage, and from the body fat percentage were divided into two groups, Group 1: 16 cyclists who presented body fat percentage < 24% and Group 2: 16 cyclists who presented body fat percentage > 24%. Three thermographic photos were taken, before (Pre), just after (Post) and after 10 min (Post10) of the incremental cycling test to determine mean temperature of right and left Vastus Lateralis, Rectus Femoris and Biceps Femoris. Temperature variations were defined as the difference among the three moments: (i) var1 = Post-Pre, (ii) var2 = Post10- Pre and (iii) var3 = Post10-Post. Differences between groups and moments were calculated using magnitude-based inferences. Group 1 evidenced a very likely large increase in the cycling peak power output. Group 2 showed a likely and most likely moderate, large and very large increase in age, body mass and fat. Group 1 depicted a very likely to likely moderate temperature increase in the right and left Vastus Lateralis, Rectus Femoris and Biceps Femoris on Post10 compared to Post effort moment. Both groups depicted a very likely and most likely moderate and large temperature decrease of right and left Biceps Femoris on Pre compared to Post effort. Percentage of fat seems to discreetly influence skin temperature response, finding that might not be observed when we evaluate trained cyclists exhibiting different percentages of fat....(AU)

Este estudo objetivou a avaliar as variações de temperatura das coxas em um teste incremental de ciclismo em ciclistas recreacionais saudáveis com dois diferentes percentuais de gordura. Trinta e dois ciclistas recreacionais do sexo masculino foram avaliados em estatura, massa corporal, dobras cutâneas da coxa e percentual de gordura corporal, e, a partir do percentual de gordura corporal, foram divididos em dois grupos, Grupo 1: 16 ciclistas que apresentaram percentual de gordura corporal < 24% e Grupo 2: 16 ciclistas que apresentaram percentual de gordura corporal > 24%. Foram tiradas três fotos termográficas, antes (Pré), logo após (Pós) e após 10 min (Pós10) do teste de ciclismo para determinar a temperatura média do Vasto Lateral, Reto Femoral e Bíceps Femoral direito e esquerdo. As variações de temperatura foram definidas como a diferença entre os três momentos: (i) var1 = Pós-Pré, (ii) var2= Pós10-Pré e (iii) var3= Pós10-Pós. Diferenças entre grupos e momentos foram calculadas usando inferências baseadas em magnitude. Grupo 1 apresentou um provável a muito provável aumento moderado da temperatura para os Vastos Laterais direito e esquerdo, o Reto Femoral e o Bíceps Femoral no Pós10 em comparação com o momento pós-esforço. Grupo 2 mostrou aumentos provável e muito provável moderado, grande e muito grande na idade, massa corporal e gordura. Ambos os grupos descreveram uma muito provável e mais provável moderada e grande queda de temperatura do Bíceps Femoral direito e esquerdo no Pré comparado ao Pós-esforço. Percentagem de gordura parece influenciar discretamente a resposta da temperatura da pele, resultado que poderá não ser observado quando avaliados ciclistas treinados que apresentam diferentes percentagens de gordura....(AU)

Análise do comportamento das variáveis antropométricas e respostas hemodinâmicas em crianças / Analysis the behavior of anthropometric variables and hemodynamic responses in children

O objetivo do estudo foi analisar o comportamento das variáveis antropométricas e respostas hemodinâmicas em crianças, relacionado à comorbidades cardiovasculares e estado nutricional. A amostra foi composta por 93 crianças (sexo masculino), com idades entre 6 a 12 anos (8,8±1,6 anos). Foram coletadas as seguintes variáveis: massa corporal, estatura, índice de massa corporal (IMC), porcentagem de gordura, circunferência da cintura, relação cintura/estatura e pressão arterial (sistólica e diastólica). As crianças com presença de comorbidades cardiovasculares foram aquelas que apresentaram uma ou mais das variáveis fora dos parâmetros de saúde. Para a classificação do estado nutricional das crianças, utilizou-se o indicativo de peso normal, excesso de peso e obesidade. Os dados foram analisados através de estatística descritiva, diferenças de médias estandardizadas e os respectivos intervalos de confiança. As diferenças entre os momentos foram analisadas através de diferenças de médias estandardizadas e os respectivos intervalos de confiança. Adicionalmente foi calculado o tamanho do efeito seguido a seguinte escala: 0 - 0.2 trivial, > 0,2 - 0.6 pequeno, > 0.6 - 1.2 moderado, > 1.2 - 2.0 grande, e > 2.0 muito grande. Os resultados mostraram que as crianças com presença de comorbidades cardiovasculares apresentaram valores substancialmente mais elevados (tamanho do efeito grande) nas variáveis antropométricas (IMC, percentual de gordura, circunferência da cintura e relação cintura/estatura) quando comparadas com as crianças ausentes de comorbidades cardiovasculares. Além disso, as crianças com excesso de peso e obesidade apresentaram valores substancialmente mais elevados (tamanho do efeito muito grande e grande) no IMC, no percentual de gordura, na circunferência da cintura e na relação cintura/estatura quando comparada com as que possuem peso normal. Conclui-se que as crianças classificadas com a presença de comorbidades cardiovasculares possuem valores substancialmente mais elevados nas variáveis antropométricas, assim como as crianças com excesso de peso e obesidade....(AU)

The aim of the study was to analyze the behavior of anthropometric variables and hemodynamic responses in children relate to cardiovascular comorbidities and nutritional status. Crosssectional study with 93 children (male), aged 6-12 years (8.8 ± 1.6 years). The following variables were collected: body weight, height, body mass index (BMI), body composition, waist circumference, waist-toheight ratio and blood pressure (systolic and diastolic). Children, with one or more variables outside the health parameters, were considered with the presence of cardiovascular comorbidities. For the classification of children nutritional status, it was used the indicative of normal weight, overweight and obesity. Data were analysed using descriptive statistics, magnitude-based inferences and interval confidence. In addition, the effect size was calculated following scale: 0 - 0.2 trivial,> 0.2 - 0.6 small,> 0.6 - 1.2 moderate,> 1.2 - 2.0 large, and> 2.0 very large. The results showed that children with cardiovascular comorbidities had substantially higher values (large effect size) in the anthropometric variables (BMI, fat percentage, waist circumference and waist-to-height ratio) when compared to children without cardiovascular comorbidities. In addition, overweight and obese children had substantially higher (very large and large effect size) values on BMI, in fat percentage, waist circumference and waist/height when compared to those with normal weight. It is concluded that children classified with the presence of cardiovascular comorbidities have substantially higher values in the anthropometric variables, as well as children with overweight and obesity....(AU)