Applying Unsupervised Machine Learning Models to Identify Serve Performance Related Indicators in Women's Volleyball.

In volleyball, the effect of different factors on serve performance has usually been analyzed with traditional statistical techniques such as logistic regression or discriminant analysis. Purpose: In this study, two of the main models used in unsupervised machine learning (cluster and principal component analysis) were applied to achieve these objectives: (a) to create groups of players considering their serve coefficient, age, height, and team ranking, and (b) to identify which variables related to the serve (type and performance), the players (role, age, and height), and the teams (ranking, match location, and quality of opposition) most explained the total variance of the data during an entire women's volleyball season. Method: A total of 20,936 serves were analyzed during the 132 matches played in the 2017-2018 season in the Liga Iberdrola (women Spanish first division). The variables were related to the serving action (type of serve and performance), the players' traits (player role, age, and height), and the teams' characteristics (final ranking, match location, quality of opposition, and tournament). Results: Cluster analysis showed five groups of players differing in age, serve coefficient, team ranking, and height. Principal component analysis showed how the first five components explained 72.12% of the total variance. From these components, serve coefficient, team ranking, match location, quality of opposition, and player role each contributed more than 10%. Conclusions: These findings can help coaches to improve talent selection and players' development according to competition demands.

Comparison of Rally Length between Women and Men in High-Level Spanish Volleyball.

The aim of this study was to evaluate whether the rally length in high-level Spanish volleyball was longer in women than in men. A total of 1,786 rallies were observed: 792 for women and 994 for men. The recorded variables were match (quarter-final 1, quarter-final 2, semi-final 1, semi-final 2, final), gender (men, women), rally length (seconds), pseudo-rally (no, yes), and terminal event (ball out of sight, ball in/out, fault). Different non-parametric statistical techniques were used to compare the rally length between groups or subsets of data, i.e., the Kruskal-Wallis H test, the Mann-Whitney U test, quantile regression, and survival analysis. The mean and median rally length was significantly and slightly longer in women than in men. The rally length difference between genders was barely 1 s in quantile 0.5 or median, while in quantile 0.95, it was just over 4 s. In women, the probability of ending the rally at 3.9, 5.1, 10.2, and 43.9 s (at 4.4, 6.3, 11.6, and 43.9 s without pseudo-rallies) was 25%, 50%, 75%, and 100%, respectively. In men, the probability of ending the rally at 3.2, 4.3, 7.9, and 29.1 s (at 3.9, 4.8, 8.8, and 29.1 s without pseudo-rallies) was 25%, 50%, 75%, and 100%, respectively. These temporal thresholds can help volleyball coaches to train their players in a coherent manner.

Análisis de Datos Antropométricos y Madurativos para la Selección de Talentos en Voleibol / Analysis of Anthropometric and Maturational Data for Talents Selection in Volleyball

El proceso madurativo tiene una gran influencia sobre los factores antropométricos y las capacidades físicas del atleta, y por tanto, sobre el proceso de selección de talentos deportivos. El objetivo de este trabajo fue analizar el estado madurativo y las características antropométricas junto con la comparación de estos datos por sexo en una muestra de 39 jugadores jóvenes de voleibol dentro de un proceso de selección de talentos (19 damas de 14,88±1,05 años y 13 varones de 15,1 años). Se obtuvieron datos de edad cronológica, altura, peso, altura sentado, altura de la madre y padre, la edad pico de crecimiento, el "timing" o periodo de tiempo por encima o por debajo de la edad pico, altura al final del proceso madurativo, el porcentaje actual de altura máxima, los centímetros restantes y el estado madurativo (pre-púber, púber o pos-púber). Los jugadores mostraron una mayor altura en el momento de las mediciones (179,92±6,87 vs 171,05±4,80; p<0,001), así como una mayor altura final calculada (189,46±3,73 vs 178,52±5,17; p<0,001), en comparación a las jugadoras. El pico en la velocidad de crecimiento también fue superior en los jugadores (14,56±0,44 vs 12,60±0,57; p<0,001), aunque su timing era inferior al de las jugadoras (0,531±1,19 vs 2,27±0,64; p<0,001). Esto se debió a un mayor porcentaje de jugadores masculinos en estados puberales, incluyendo un jugador en estadio pre-puberal, mientras que fue abundante la presencia de jugadoras en estado pospuberal. Estos datos reflejan la gran cantidad de jugadores que tienden a estar en periodos avanzados de maduración en procesos de selección de talentos. Por tanto, entrenadores y seleccionadores deben contemplar estas variables para evitar sesgos en el proceso de identificación del talento deportivo.

SUMMARY: The maturation process has a great influence on the anthropometric factors and physical capabilities of the athlete, and therefore, on the selection process of sporting talents. The objective of this work was to analyze the maturational state and anthropometric characteristics together with the comparison of these data by sex in a sample of 39 young volleyball players within a talent selection process (19 ladies of 14.88±1. 05 years old and 13 males aged 15.1 years). Data were obtained on chronological age, height, weight, sitting height, height of the mother and father, peak age of growth, timing or period of time above or below the peak age, height at the end of the process. maturation, the current percentage of maximum height, the remaining centimeters and the maturation status (pre-pubertal, pubertal or post-pubertal). The players showed a greater height at the time of the measurements (179.92±6.87 vs. 171.05±4.80; p<0.001), as well as a greater final calculated height (189.46±3.73 vs. 178.52±5.17; p<0.001), compared to the female players. The peak in growth speed was also higher in male players (14.56±0.44 vs 12.60±0.57; p<0.001), although their timing was lower than that of female players (0.531±1.19 vs 2.27±0.64; p<0.001). This was due to a higher percentage of male players in pubertal states, including one player in a pre-pubertal stage, while the presence of female players in a post-pubertal stage was abundant. These data reflect the large number of players who tend to be in advanced periods of maturation in talent selection processes. Therefore, coaches and selectors must consider these variables to avoid biases in the process of identifying sporting talent.

Assessing the Maximal Mechanical Capacities Through the Load-Velocity Relationship in Elite Versus Junior Male Volleyball Players.

BACKGROUND: Physical testing is crucial for athlete monitoring, talent identification, optimizing training, and tailoring programs to enhance game-performance in elite competitions. HYPOTHESIS: Load-velocity (L-V) relationship variables discriminate between elite and junior volleyball players, correlate with volleyball-specific performance, and are generalizable across lower- and upper-body exercises. STUDY DESIGN: Cross-sectional study. LEVEL OF EVIDENCE: Level 3. METHODS: A total of 9 elite and 11 junior volleyball players were assessed for the L-V relationship (load-axis intercept [L0], velocity-axis intercept [v0], and area under the L-V relationship line [Aline]) during the countermovement jump (CMJ) and bench press throw (BPT) exercises. Block and spike jump height, as well as standing and jumping spike speed were assessed 24 hours later. RESULTS: Elite players presented greater magnitude in the L-V variables (P ≤ 0.03; effect size [ES] ≥ 1.06) and higher volleyball-specific performance (P ≤ 0.03; ES ≥ 1.09) than juniors (except for CMJ v0 and Aline). The L-V relationship variables were significantly associated with the block and spike jump height and jumping spike speed only in elite players (r ≥ 0.703 and P ≤ 0.04 in 11 out of 18 correlations). No significant associations were observed between CMJ and BPT for any L-V relationship variable (r ≤ 581; P ≥ 0.08, except for Aline in junior players). CONCLUSION: The L-V relationship is a practical procedure to assess volleyball players' maximal mechanical capacities, which are associated with volleyball-specific performance in elite players. However, these data should not be used interchangeably between playing standards or exercises. CLINICAL RELEVANCE: This information might help strength and conditioning coaches to prescribe more effective training programs that focus on developing the specific physical capacities necessary for players to potentially advance to elite status.

Physical-Performance Changes Over the Season: Are They Related to Game-Performance Indicators in Elite Men Volleyball Players?

BACKGROUND: The development and influence of physical capabilities and game action performance over the course of the season are a big challenge for coaches and players. PURPOSE: The aims of the present study were to examine (1) the seasonal changes in the physical capabilities (mechanical and kinematic) and game-performance indicators in top-level men volleyball players and (2) the relationship between these physical capabilities and game-performance indicators in official matches. METHODS: Eleven top-level players participated. Players were physically tested 3 times during the season. Before each test, players' match performance (11 sets) was analyzed according to the level of opposition and match location. The percentage of change, statistical differences over the season (Friedman and Wilcoxon tests), and associations between variables (Spearman r) were calculated (P < .05) among mechanical (force-velocity profile during vertical jump and bench press), kinematic (jump height and spike ball speed), and game action performance features (coefficient, efficacy, and percentage of errors in serve, attack, and block). RESULTS: The theoretical maximal force and velocity during vertical jump and bench press, respectively; the peak spike ball speed; and the serve efficacy significantly increased over the season. Moreover, there was a significant reduction in serve errors as the jump height increased (r = -.44; P = .026), as well as a significant increase in serve errors as the peak spike ball speed increased (r = -.62; P = .001). CONCLUSION: These findings reveal how the physical and game action performance variables evolve and interact during the season. This may help coaches and trainers to monitor and analyze the most relevant volleyball performance factors.

Concurrent Validity and Reliability of Devices to Measure Jump Height in Men's Handball Players.

Although there is a wide range of validated devices to measure vertical jump height, the degree of interchangeability among them is currently unknown. AIMS: The purpose of this study was to examine the concurrent validity and reliability of multiple devices to measure jump height in men's handball players. METHODS: Sixteen players (age = 24.0 ± 3.7 years old) performed three types of jumps (n= 144-squat jump (SJ), countermovement jump (CMJ) and Abalakov jump (ABK)) on a contact platform (CHRONOJUMP®) while simultaneously being measured with two inertial devices (WIMU® and VERT®) and recorded with a high-speed camera. Vertical jump height was analyzed according to each type of jump. RESULTS: The t-test showed statistically significant differences (p = 0.001) between the contact platform (reference standard) and the rest of the tools that tended to overestimate jump height in all jumps. SJ and CMJ proved to be the jump tests with the most stable reliability values in all devices (ICC: 0.92-0.98), except in the comparison with VERT®. CONCLUSIONS: Although all the analyzed devices proved to be valid and reliable in previous studies, they are not interchangeable. Therefore, it is suggested to always use the same type of device to evaluate vertical height jump.

The influence of removing home advantage on the Chinese Football Super League.

BACKGROUND: Due to the COVID-19 pandemic, the 2020 season Chinese Super League (CSL) was held in neutral venues, this study aims to analyse the impact of removing home advantage (HA) in CSL. METHOD: 240 games of the CSL 2019 season (home and away double round-robin system) and 160 games of the 2020 season (in neutral venues) were analysed. 27 technical and tactical performance indicators were involved as dependent variables. A multiple linear regression model was established to analyse the influence of removing HA on the performance indicators. RESULTS: After moving from home stadium to neutral venue in 2020 season, goal, shot, shot on target, shot from outside box, shot from inside box, shot on target from inside box, corner kick, key pass, cross, breakthrough, tackle decreased significantly (p < 0.05), while yellow card and foul increased steeply (p < 0.05). Comparing with playing away match, in neutral venue, free kicks and pass accuracy enhanced radically (p < 0.05), while tackle, clearance and block shot dropped noticeably (p < 0.05). CONCLUSION: When removing HA and playing in the neutral venue, teams' performance dropped significantly. This study confirmed the positive impact of HA on the teams' performance and may help elite football teams make proper playing strategies regarding different match locations.

Influence of oral contraceptive phase on cardiorespiratory response to exercise in endurance-trained athletes.

OBJECTIVE: The aim of the study was to analyse the cardiorespiratory response to exercise during an oral contraceptive (OC) cycle in endurance-trained women. METHODS: Sixteen low-dose monophasic OC pill (OCP) users performed an interval-running protocol. The protocol consisted of eight 3 min bouts at 85% of participants' maximal aerobic speed (vV̇o2peak) with a 90s recovery at 30% vV̇o2peak in two OC phases: a withdrawal phase (WP) and an active pill phase (APP). The non-parametric Wilcoxon test was applied to analyse differences (p < 0.05) in performance variables between OC cycle phases. RESULTS: Throughout the high-intensity intervals, higher ventilation (WP 80.90 ± 11.49 L/min, APP 83.10 ± 13.33 L/min; p < 0.001) and relative perceived exertion (WP 14.51 ± 2.58, APP 15.11 ± 3.11; p = 0.001) during the APP were found, whereas carbon dioxide production (WP 2040.92 ± 262.93 mL/min, APP 2010.25 ± 305.68 mL/min; p = 0.003) was higher in the WP. During the active recovery intervals, ventilation (WP 65.78 ± 9.90 L/min, APP 67.88 ± 12.66 L/min; p < 0.001) was higher in the APP, while heart rate (WP 159.93 ± 10.26 bpm, APP 159.74 ± 12.83 bpm; p = 0.029) was higher in the WP. CONCLUSION: An increase in ventilation occurs during the APP, which is accompanied by higher perceived exertion. Therefore, coaches and athletes should be aware of these variations, especially perceived exertion, in regard to women's training programmes, in order to improve their performance, wellness and adherence to physical activity.

Impact of Possession and Player Position on Physical and Technical-Tactical Performance Indicators in the Chinese Football Super League.

The purpose of this study was to investigate the impact of high (HPBPT) and low percentage ball possession teams (LPBPT) on physical and technical-tactical performance indicators in the Chinese Football Super League (CSL). Eight physical performance indicators and 26 technical-tactical performance indicators from all 240 matches from season 2018 were analyzed, as well as three contextual variables (team strength, quality of opposition, and match location). Players were divided according to five positions: fullbacks, central defenders, wide midfielders, central midfielders, and attackers. A k-means cluster analysis was conducted to classify all match observations into two groups: HPBPT (n = 229) and LPBPT (n = 251). A mixed linear model was fitted with contextual variables as covariates. When significant interactions or main effects were detected, a post hoc comparison was used to compare physical and technical/tactical differences between HPBPT and LPBPT. Results showed that central defenders and fullbacks covered more high-intensity and sprint running distance in the high possession teams, while wide midfielders and forward covered more high-intensity and sprint running distance in the low possession teams. Meanwhile, players from high ball possession teams were strong in technical indicators, especially in attacking organization. These results may help coaches to understand current football development trends and develop suitable training plans and tests for elite football players.

Personal and Social Responsibility Development in a Volleyball Hybrid Positive Youth Development Program: A Mixed Methods Approach.

Positive Youth Development (PYD) programs are being used to foster holistic growth in children and adolescents. The hybridized application of two or more programs of this type has acquired special relevance in recent years. Although their application is common in the school context, there are few research studies that attempt their implementation in an extracurricular context. This study analyzed the effects of an intervention based on a hybrid PYD program on personal responsibility (PR) and social responsibility (SR) in youth volleyball players in an extracurricular context. A hybrid program was applied during the competitive season, with a total of 37 sessions with 30 girl students (15 experimental and 15 control) aged between 8 and 10 years (M = 8.87, SD = 0.82). A convergent mixed methods design was applied to integrate the following: (a) semi-structured interviews and field notes and (b) personal and social responsibility questionnaires. The results indicated that the implementation of the hybrid program appeared to yield a positive perception of learning in both the participants and the coach. Although there were no statistically significant intergroup or intragroup differences, the findings suggest that the hybrid program seems to be effective in fostering PR and SR in youth girl volleyball players.

Impact of Scoring First on Match Outcome in the Chinese Football Super League.

The aim of this study was to explore the effect of scoring first on match outcomes in the Chinese Football Super League (CSL). A total of 1,116 matches in which at least one goal was scored from the 2014 to 2018 seasons were collected. Match outcomes, absolute goal differences, the minute of the first goal, match locations, and teams' budgets were analyzed. A team's budget was measured in terms of a team's value at the beginning of the season, and teams were clustered into two groups (high and low budget with means of 50.77 and 13.77 million dollars, respectively). A descriptive analysis was conducted, and two generalized linear models (a multinomial logit model and a Poisson model; p < 0.05) were applied. The results showed a favorable outcome for the team that scored first both in match outcome and goal difference. Regarding the teams that scored first, 66.31% won their matches, 20.70% achieved a draw, and 12.99% lost. Specifically, home teams were more likely to win (13.42%) and less likely to lose (9.52%) or draw (3.90%) than away teams. Home teams also had a higher likelihood of obtaining a larger goal difference. Higher budget teams were more likely to win (14.90%) and less likely to lose (9.75%) or draw (5.14%) than low-budget teams. Additionally, for each minute, the team scores closer to the end of the match, and the average probability of winning increased by 0.0028. These findings can guide the strategies of coaches in different match scenarios according to the match location and the opponent's quality.

The force-velocity profile as determinant of spike and serve ball speed in top-level male volleyball players.

Understanding the relationship between mechanical variables derived from actions such as jumping, sprinting, or ballistic bench press throwing and sport-specific performance moves is of scientific and practical interest for strength and conditioning coaches for improving training programs. We examined the association between mechanical variables derived from the force-velocity (FV) profiles of the aforementioned actions and spike and serve ball speeds in elite volleyball players. Twenty-two male elite volleyball players (age: 24.3 ± 4.5 years; height: 1.89 ± 0.06 m; body mass: 86.3 ± 8.6 kg) were tested in two sessions. Squatting, sprinting, and bench press throwing FV profiles were determined in the first session, while spike and serve ball speeds were assessed in the second session. The theoretical maximal force (F0) of vertical jumping, the theoretical maximal velocity of sprinting, and the F0 of bench press throwing in ascending order, were strongly associated (rs range 0.53-0.84; p<0.05) with spike and serve ball speeds. These mechanical variables explained 20%-36% of the variability in spike and serve ball speeds, with a greater influence on the serve speed. These results suggest that assessing jumping, sprinting, and bench press throwing force-velocity profiles might help provide player-specific training programs and optimize performance in these technical-tactical actions in male elite volleyball players.

Effects of Plyometric Jump Training on Physical Fitness in Amateur and Professional Volleyball: A Meta-Analysis.

We aimed to examine the effects of plyometric jump training (PJT) on measures of physical fitness in amateur and professional volleyball players. A systematic electronic literature search was carried out in the databases PubMed, MEDLINE, Web of Science, and SCOPUS. Controlled studies including pre-to-post intervention tests of physical fitness and involving healthy volleyball players regardless of age and sex were considered. A random-effects model was used to calculate effect sizes (ES) between intervention and control groups. Moderator analyses considered programme duration, training frequency, total number of training sessions and jumps, participants' sex, age, and expertise level. The Physiotherapy Evidence Database scale was used to assess the methodological quality of the included studies. Eighteen moderate-to-high quality (median of 5 PEDro points) studies were eligible, comprising a total of 746 athletes. None of the included studies reported injuries related to the PJT intervention. The main findings showed small-to-moderate effects (p < 0.05) of PJT on linear sprint speed (ES = 0.70), squat jump (ES = 0.56), countermovement jump (CMJ) (ES = 0.80), CMJ with arm swing (ES = 0.63), drop jump (ES = 0.81), and spike jump height (ES = 0.84). Sub-analyses of moderator factors included 48 data sets. Only age had a significant effect on CMJ performance. Participants aged ≥16 years achieved greater improvements in CMJ performance compared to <16 years old (ES = 1.28 and 0.38, respectively; p = 0.022). No significant differences (p = 0.422) were identified between amateur (ES = 0.62) and professional volleyball players (ES = 1.01). In conclusion, PJT seems safe and is effective in improving measures of physical fitness in amateur and professional volleyball players, considering studies performed in both male and female.

Methodological Approach of the Iron and Muscular Damage: Female Metabolism and Menstrual Cycle during Exercise Project (IronFEMME Study).

Background: The increase in exercise levels in the last few years among professional and recreational female athletes has led to an increased scientific interest about sports health and performance in the female athlete population. The purpose of the IronFEMME Study described in this protocol article is to determine the influence of different hormonal profiles on iron metabolism in response to endurance exercise, and the main markers of muscle damage in response to resistance exercise; both in eumenorrheic, oral contraceptive (OC) users and postmenopausal well-trained women. Methods: This project is an observational controlled randomized counterbalanced study. One hundered and four (104) active and healthy women were selected to participate in the IronFEMME Study, 57 of which were eumenorrheic, 31 OC users and 16 postmenopausal. The project consisted of two sections carried out at the same time: iron metabolism (study I) and muscle damage (study II). For the study I, the exercise protocol consisted of an interval running test (eight bouts of 3 min at 85% of the maximal aerobic speed), whereas the study II protocol was an eccentric-based resistance exercise protocol (10 sets of 10 repetitions of plate-loaded barbell parallel back squats at 60% of their one repetition maximum (1RM) with 2 min of recovery between sets). In both studies, eumenorrheic participants were evaluated at three specific moments of the menstrual cycle: early-follicular phase, late-follicular phase and mid-luteal phase; OC users performed the trial at two moments: withdrawal phase and active pill phase. Lastly, postmenopausal women were only tested once, since their hormonal status does not fluctuate. The three-step method was used to verify the menstrual cycle phase: calendar counting, blood test confirmation, and urine-based ovulation kits. Blood samples were obtained to measure sex hormones, iron metabolism parameters, and muscle damage related markers. Discussion: IronFEMME Study has been designed to increase the knowledge regarding the influence of sex hormones on some aspects of the exercise-related female physiology. Iron metabolism and exercise-induced muscle damage will be studied considering the different reproductive status present throughout well-trained females' lifespan.

Effects of Resistance Training on Arterial Stiffness in Healthy People: A Systematic Review.

The influence of aerobic training on cardiovascular disorders has already been demonstrated. However, the effect of resistance training is less well known. Arterial stiffness is an increasingly important measure in cardiovascular health. Therefore, this review attempted to study the results of resistance training-based interventions on arterial stiffness in healthy people, for both acute and chronic interventions. A literature search was conducted for randomized controlled trials on the acute and chronic effects of strength training. Studies published in PubMed and SportDiscus databases between 1999 and April 2019 were analyzed. In chronic strength training effects, the majority of groups showed large (d = -1.49 to -1.20) and moderate (d = -1.07) decreases, and small and trivial changes in arterial stiffness. In acute effects interventions, a very large decrease (d = -3.92) was observed, while large (d = 1.24-1.48) and very large (d = 3.88) increases were also found. A resistance training-based intervention of more than four weeks' duration with a frequency of two days per week seems not to compromise cardiovascular health, due to decreases in arterial stiffness. However, there is a general trend towards both increasing and maintaining arterial stiffness after isolated strength training sessions.

The Sequencing of Game Complexes in Women's Volleyball.

In volleyball, each team must use no more than three hits to return the ball to the opponent's court. This unique aspect of volleyball means that playing actions can be grouped into different complexes, mainly based on the initial defensive action. The purpose of this study was to find out which game complexes are most common in women's volleyball and how those phases are sequenced. The study analyzed 4,252 complexes from 1,176 rallies or points (seven matches, with 27 sets in total) in the 2015 and 2016 Copa de la Reina. The variables analyzed were the game complex, complex efficacy, and number of complexes per point. Two Markov chains were defined to visualize how the complexes are sequenced. The first chain looked only at categories of the game complex variable, taking seven states and 24 transitions into consideration. The second chain combined the game complex and complex efficacy variables, taking 26 states and 125 transitions into consideration. These chains provide practical information regarding which sequences of complexes occur most frequently in the competition analyzed, and therefore which ones should be the main focus in training sessions. The most frequent sequence was Complex 0 (the serve), followed by Complex I with in-system attack, followed by Complex II without continuity.

Analysis of jump load during a volleyball season in terms of player role.

OBJECTIVES: The aim of this study was to analyze the jump load performed by top-level volleyball players during an entire training season in terms of the player role, training period, type of daily training, and quality of opposition in the subsequent match. DESIGN: Longitudinal panel observational study. METHODS: The total number of jumps performed by players was recorded through 174 training days distributed in 32 weeks during the 2016/2017 season (pre-season, 5 weeks; in-season, 27 weeks). The players role were classified as middle-blocker, outside-hitter, opposite and setter (the libero was omitted). A generalized mixed linear model was performed (with Bonferroni post hoc test at p<0.05) to assess the effect of training variables and the repeated-measures data of players' jumps along various training days. Additionally, the effect sizes at 95% confidence intervals were calculated to compare the jump load between players' role and training variables. RESULTS: The results showed a significant and moderate higher amount of jumps performed by middle-blockers regardless the type of macro- or micro-cycle, the micro-cycle phase, the type of training and the quality of match opposition. Contrarily, the setter performs the least jump load in all variables analyzed. Only the players' role, macro-cycle and micro-cycle phase had significant effects on the player's jump load variation along the season. CONCLUSIONS: This information could be useful to guide the monitoring and preparation process for coaches and physical trainers. These values allow differentiating between players' role and could be used as references values in order to avoid injuries whereas performance increase along the season.

Subcutaneous Adipose Tissue in Female Volleyball Players: Is It Related with Performance Indices?

The aim of the present study was to examine subcutaneous adipose tissue distribution in female volleyball players with regards to (a) variation by anatomical site, (b) differences among age groups and playing positions, and (c) physiological characteristics associated with performance. Participants were adolescent (n = 89, age 15.6 ± 0.9 years, mean ± standard deviation) and adult female volleyball players (n = 78, 24.8 ± 5.3 years), who performed a series of anthropometric and performance tests including skinfold thickness in 10 sites, Abalakov jump (AJ) and handgrip test (HG). Chin had the smallest thickness, and iliac crest and abdomen the largest. The largest correlations of skinfold thickness were shown with regards to AJ ad HG. Coefficient of variations in skinfold thickness correlated with performance indices with small magnitude. Triceps and chin were the most frequent predictors of performance indices. The anatomical site of skinfold was near the active muscle groups related to performance in HG. In conclusion, performance indices such AJ and HG were related with thickness of specific skinfolds and with the variation of thickness by anatomical site (i.e., the less the variation, the better the performance). Considering the relevance of specific skinfolds (e.g., triceps and chin) for performance, their further use would be recommended for purposes of training monitoring, volleyball players' selection and talent identification.

Efficacy and manner of execution of the serve in top-level womens beach volleyball players / Eficácia e maneira de execução do serviço em jogadoras de voleibol de praia de alto nível

ABSTRACT The study of the manner of execution (technique, and spatial aspects) can provide useful information to understand the game dynamics in beach volleyball and to obtain references values for the analysis of the game and the establishment of training goals. The aim of the study was to determine the influence of the manner of execution on serve and rally performance in elite women's beach volleyball players. A total of 3,009 serves from 44 women's players were analyzed. The variables studied were: serve technique, serve zone, serve destination, serve performance, and rally performance. An observational punctual, nomothetic, multidimensional, and intragroup design was used. A descriptive and inferential analysis of the data (Chi-Square Test) was done using SPSS v.21.0 software. The level of significance was set at p < .05. The manner of execution influences the serve performance. The jump float serve was the most used. The most effective destination was the zone between players, probability due to the players' displacement and interference between them. An absence of association between serve technique and rally performance was found. These findings showed possible connections between the way of executing the serve with the following actions done by the players and the players' strategies to control their physical load. These values may be useful to guide to players training, or to evaluate players in competition.

RESUMO O estudo da forma de execução (técnica e aspectos espaciais) pode fornecer informações úteis para compreender a dinâmica do jogo no vôlei de praia e obter valores de referência para a análise do jogo e o estabelecimento de metas de treinamento. O objetivo do estudo foi determinar a influência da forma de execução no desempenho de saque e rali em jogadores de vôlei de praia de alto nível. Um total de 3.009 saques de 44 jogadoras de alto nível foram analisados. As variáveis ​​estudadas foram: técnica de saque, zona de saque, destino do saque, desempenho de saque e desempenho de rali. Um desenho observacional pontual, nomotético, multidimensional e intragrupo foi utilizado. Foi realizada uma análise descritiva e inferencial dos dados (Teste Qui-Quadrado) utilizando o software SPSS v.21.0. O nível de significância foi estabelecido em p <0,05. A maneira de execução influencia o desempenho do saque. O saque flutuante de salto foi o mais usado. O destino mais efetivo foi a zona entre jogadoras, provavelmente devido ao deslocamento das jogadoras e a interferência entre elas. Não foi encontrada associação entre a técnica de saque e o desempenho de rally. Esses achados mostraram possíveis associações entre a maneira de executar o saque com as ações seguintes realizadas pelas jogadoras e as estratégias das jogadoras para controlar sua carga física. Esses valores podem ser úteis para orientar o treinamento de jogadoras ou avaliar jogadoras em competição de vôlei de praia.

Influence of Contextual Variables on Performance of The Libero Player in Top-Level Women's Volleyball.

Sports performance changes dynamically according to multiple variables during a match. Contextual variables play an important role in complex situations and influence player's performance depending on the player's role. The aim of this study was to analyze performance of the libero player in terms of contextual variables in top-level women's volleyball. The sample comprised 1,597 actions performed by libero players in 49 sets (13 matches) played in the Spanish Queen's Cups from 2015 to 2017. The variables analyzed were: the game phase, the match period, the set period, match status, the type of the match, and action performance. The results revealed higher participation in the reception and digging, and top performance in reception and setting. The participation of the libero player decreased at the end of the match and the set as well as in advantage score situations, while performance got worse at the end of the set (especially in digs, p < .05) and improved in score advantage situations (especially in receptions, p < .05). Performance remained stable regardless of the type of the match (p > .05). These results may be useful to coaches in order to plan and design specific tasks coherent with libero competition demands and performance values.