Validity and Reliability of the Acceleration-Speed Profile for Assessing Running Kinematics' Variables Derived From the Force-Velocity Profile in Professional Soccer Players.

ABSTRACT: Alonso-Callejo, A, García-Unanue, J, Guitart-Trench, M, Majano, C, Gallardo, L, and Felipe, J. Validity and reliability of the acceleration-speed profile for assessing running kinematics' variables derived from the force-velocity profile in professional soccer players. J Strength Cond Res 38(3): 563-570, 2024-The aim of this research is to assess the validity and reliability of the acceleration-speed profile (ASP) for measuring the mechanical variables of running kinematics when compared with the force-velocity profile (FVP) obtained by reference systems. The ASP and FVP of 14 male players of an elite football club were assessed during a competitive microcycle. Three ASPs were tested according to the number and type of sessions included in its plotting (ASP1: 5 training sessions and competitive match; ASP2: 5 training sessions; ASP3: competitive match). Force-velocity profile was tested 4 days before match (MD-4) with a 30-m linear sprint using 3 previously validated devices (encoder, mobile App, and global positioning system). Level of significance was p < 0.05. Acceptable reliability (intraclass correlation coefficient > 0.5) was found between the ASP1 and the encoder for all variables (F 0 -A 0 , V 0 -S 0 , and V max ). The more reliable ASP method was the ASP1 showing a lower bias than the ASP2 and ASP3 methods for almost all variables and reference systems. For ASP1, lower mean absolute error (MAE: 0.3-0.5) and higher correlation (P-M corr: 0.57-0.92) were found on variables related to the velocity in comparison with variables related to the early acceleration phase (F 0 -A 0 ; MAE: 0.49-0.63; P-M corr: 0.13-0.41). Acceleration-speed profile, when computed with data from a complete competitive week, is a reliable method for analyzing variables derived from velocity and acceleration kinematics. From these results, practitioners could implement ASP and the applications of the FVP previously studied, such as resistance training prescription, performance assessment, and return-to-play management.

Relationships of BMI, muscle-to-fat ratio, and handgrip strength-to-BMI ratio to physical fitness in Spanish children and adolescents.

This study aimed to determine the relationship of body mass index (BMI), muscle-to-fat ratio (MFR), and handgrip strength-to-BMI ratio to physical fitness parameters in an active young population according to sex across four different time points. A total of 2256 Spanish children and adolescents (aged 5-18) from rural areas participating in an extracurricular sport in different municipal sports schools participated in this study. Participants were divided into children (5-10 years) and adolescents (11-18 years), boys and girls, and across four different time points (2018, 2019, 2020, 2021). Data on anthropometric measures (BMI, MFR, appendicular skeletal muscle mass) and physical fitness (handgrip strength, cardiorespiratory fitness, and vertical jump) were collected. Boys who were overweight, but especially boys with obesity, had higher absolute handgrip strength in children and adolescents than their normal weight counterparts in 2020 and 2021. Boys and girls with normal weight presented higher cardiorespiratory fitness and vertical jump than their overweight and obese peers over the years. The MFR was directly correlated with the cardiorespiratory fitness and vertical jump variables, but not with handgrip strength, in boys and girls. The handgrip strength-to-BMI ratio in both sexes was positively correlated to the different physical fitness parameters.  Conclusion: BMI, MFR, and handgrip strength-to-BMI can be used as health and physical fitness indicators in this population. What is Known: • BMI is the main indicator commonly used as a proxy for obesity for many years. Nevertheless, it cannot differentiate between fat mass and fat-free mass. • There are other indicators such as MFR and handgrip strength-to-BMI that might be more accurate and can serve to monitor the health and fitness of children and adolescents. What is New: • MFR showed a positive and significant correlation with cardiorespiratory fitness and vertical jump in both sexes. On the other hand, the handgrip strength-to-BMI presented a positive correlation with cardiorespiratory fitness, vertical jump, and handgrip strength. • The use of these indicators obtained through different parameters of body composition and physical fitness can serve as a tool to identify the relationships of the paediatric population with physical fitness.

Relationship between Repeated Sprint Ability, Countermovement Jump and Thermography in Elite Football Players.

Football is a very demanding sport which requires players to exert maximum effort, producing fatigue and eventually injuries. Thermography can be used to detect fatigue and prevent its consequences through thermal asymmetries in the bilateral body areas; however, its adequacy for elite footballers has not been widely studied. Therefore, the objective of the present investigation was to determine the suitability of thermography to detect fatigue in male football players. For this reason, twenty participants were gathered into a pair of subgroups (low [<0.2 °C] vs. high thermal asymmetry [≥0.2 °C]) based on a thermography session of the lower limbs (thighs, calves, and hamstrings). After the thermography session, players performed CMJs before and after an RSA test (6 × 30 m/20″). A mixed two-way analysis of variance and Bonferroni post hoc pairwise comparisons were undertaken to analyse the results. No significant differences (p > 0.05) were found in any of the RSA test variables between low and high thermal asymmetry groups for thighs and calves. On the other hand, the low thermal asymmetry hamstring group reported a smaller percentage difference in sprints for the first sprint (%Diff) and a larger percentage difference in sprints two and three with respect to the best sprint (%Best). For CMJs, the low thermal asymmetry hamstring group reported significantly higher values post-RSA test, indicating better performance. Accordingly, thermography can provide information about performance in CMJ and RSA tests through hamstring asymmetries over 0.2 °C. Meanwhile, larger asymmetries than 0.2 °C in calves and thighs do not seem to be related to performance in these tests; therefore, coaches should consider if it is optimal to align players with high hamstring asymmetries.

Physical Demands in the Worst-Case Scenarios of Elite Futsal Referees Using a Local Positioning System.

The aim of this study is to analyze the worst-case scenarios of professional futsal referees during the first and second half of official matches in the Spanish Futsal Cup using a Local Positioning System (LPS) for monitoring their movement patterns. Eight professional futsal referees (40 ± 3.43 years; 1.80 ± 0.03 m; 72.84 ± 4.01 kg) participated in the study. The external load (total distance, high-speed running distance and efforts, sprint distance and efforts, and accelerations and decelerations distances) of the referees was monitored and collected using an LPS. The results revealed significant differences in the worst-case scenarios of the futsal referees during the match according to the time window analyzed (p < 0.05). The longest time windows (120 s, 180 s, and 300 s) showed lower relative total distances in the worst-case scenarios (p < 0.05). The high-speed running distances were significatively higher in the first half for the 120 s (+2.65 m·min-1; ES: 1.25), 180 s (+1.55 m·min-1; ES: 1.28), and 300 s (+0.95 m·min-1; ES: 1.14) time windows (p < 0.05). No differences were found between the first and second half for the high-intensity deceleration distance (p > 0.05). These results will serve to prepare the referees in the best conditions for the competition and adapt the training plans to the worst-case scenarios.

Modeling Dynamical Positional Physical Data on Field Zones Occupied by Playing Positions in Elite-Level Futsal: A Comparison Between Running Velocities, Accelerations, and Decelerations.

ABSTRACT: Serrano, C, Felipe, JL, García-Unanue, J, Vicente Gimenez, J, Jiménez-Linares, L, Ibáñez, E, Hernando, E, Gallardo, L, and Sánchez-Sánchez, J. Modeling dynamical positional physical data on field zones occupied by playing positions in elite-level futsal: a comparison between running velocities, acceleration, and deceleration. J Strength Cond Res 37(1): 200-206, 2023-The aim of this study was to analyze the influence of playing positions on the physical demands and the specific court zones occupied during official futsal games. The total number of observations were 188, corresponding to 8 matches from the first division of the Spanish Futsal League during the 2019-2020 season. All dynamic motion representations were recorded using an 18 Hz device with ultra-wideband technology and local positioning system installed on the futsal pitch for each position. Python Data Analysis Library, Matplotlib, and Python programming language were applied as computational tools to generate visual analysis of figures to represent every physical demand analyzed. An analysis of variance test showed differences between playing positions, specifically, for winger position (p < 0.05). Based on eta-square coefficients, all variables showed large effects, except acceleration distance zone 1 (1-2 m·s-2). Accordingly, the visual representation of positional dynamic motion data showed differences in the physical demands and the court zone occupied by the different playing positions. This innovative visual analysis allows fitness coaches to associate the physical demands with court zones occupied by different playing positions, and it aids in the design of training drills associated with futsal competition requirements.

Differences in body composition and physical fitness parameters among prepubertal and pubertal children engaged in extracurricular sports: the active health study.

BACKGROUND: This study aimed to analyze the associations of maturity status, chronological age and sex with physical fitness and body composition among active children. METHODS: A total of 1682 children (72% boys; age = 11.22 ± 2.64 years; height = 147.57 ± 15.87 cm; weight = 44.55 ± 15.29 kg) from rural areas participating in extracurricular sports were divided into four groups according to their sex and maturity status (prepubertal and pubertal according to stages described by Tanner). Body composition (body mass index, muscle mass and fat mass) and physical fitness (20-m shuttle-run test, handgrip strength and vertical jump) were assessed using standardized procedures. A two-way ANOVA and product-moment correlations were performed. RESULTS: Prepubertal boys had more fat mass (%) than pubertal boys [P<0.001; effect size (ES): 0.45], while prepubertal girls had more muscle mass (%) than pubertal girls (P<0.001; ES: 0.47). The pubertal group displayed higher fitness outcomes (absolute values) regardless of sex (P<0.05). However, the prepubertal group had higher percentile values in the 20-m shuttle-run test and vertical jumps than the pubertal group regardless of sex (P < 0.001; ES: 0.29-0.48). All the measures of physical fitness were positively associated with chronological age and muscle mass (%). CONCLUSIONS: Although absolute values of body composition and physical fitness appear to increase among pubertal children participating in extracurricular sports, the percentiles indicate that puberty is accompanied with a loss of a physical fitness levels. Thus, extracurricular sports might not be enough to enhance fitness among adolescents.

Physical Demands during the Game and Compensatory Training Session (MD + 1) in Elite Football Players Using Global Positioning System Device.

The aims of this study were to analyze the differences of physical demands of non-starter players regarding the playing time during the competition and to evaluate the physical demands of the compensatory training (MD + 1C) for substitute players in elite football. The match statistics and MD + 1C of substitute players from a professional Spanish LaLiga football club were analyzed using a 10-Hz global positioning system (GPS) Apex GPS system device, which has been validated as a reliable and valid method to analyze performance in team sports, during all games of the 2016/2017, 2017/2018 and 2018/2019 seasons. The starting players showed both lower total distances covered and high-intensity actions compared to the substitutes. Regarding the minutes played by the substitutes, greater physical performance was found for the players with fewer minutes (5−15 min). Furthermore, no differences were found between first and second divisions regarding physical performance of substitutes (p > 0.05). This study highlights the importance of individualizing the workload of training sessions for substitutes and starters. Furthermore, the complementary session should be individualized according to the minutes played by the substitutes. These players are potentially under-loaded compared to starters, especially in terms of high-intensity actions, therefore additional session-specific training for each substitute would be useful to reach the optimal training load according to the minutes played during the game.

Tracking Systems Used to Monitor the Performance and Activity Profile in Elite Team Sports.

Technology has become established in elite sport in recent years and is used on a regular basis, especially in team sports [...].

Characterisation of Goal Scoring Patterns during Open Play Related to Zone Pitch Division and Number of Players Involved in the 2018 FIFA World Cup.

The aim of this study was to characterise all the goal scoring patterns during open play (elaborate attacks versus counterattacks) related to zone pitch division and the number of players involved in the 2018 FIFA World Cup in Russia. An Iterative Dichotomiser 3 (ID3) decision tree algorithm was used to classify all the goal scoring patterns (94 goals in 64 matches). The results did not show statistical differences between the type of scoring goal during the 2018 FIFA World Cup (p > 0.05; ES = Moderate). According to the result of the patterns of how the goals were achieved, an ID3 algorithm decision tree with seven classification decision nodes was calculated. Consequently, this study may aid national team coaches for the next World Cup to establish notational analyses and spatial-temporal relations to understand how scoring patterns during open play are related to zone pitch division and the number of players involved.

Global Positioning System Analysis of Physical Demands in Elite Women's Beach Handball Players in an Official Spanish Championship.

This cross-sectional study aims to analyze the physical demands of elite beach handball players during an official competition. Nine elite female (mean age: 24.6 ± 4.0 years; body weight: 62.4 ± 4.6 kg; body height: 1.68 ± 0.059 m; training experience: 5 years; training: 6 h/week) beach handball players of the Spanish National Team were recruited for this study. A Global Positioning System was incorporated on each player's back to analyze their movement patterns. Speed and distance were recorded at a sampling frequency of 15 Hz, whereas acceleration was recorded at 100 Hz by means of a built-in triaxial accelerometer. The main finding of the study is that 53% of the distance travelled is done at speeds between 1.5 and 5 km/h and 30% of the distance is between 9 and 13 km/h (83% of the total distance covered), which shows the intermittent efforts that beach handball involves at high intensity, as reflected in the analysis of the internal load with 62.82 ± 14.73% of the game time above 80% of the maximum heart rate. These data help to orientate training objectives to the physical demands required by the competition in order to optimize the players' performance.

Local Positioning System Analysis of Physical Demands during Official Matches in the Spanish Futsal League.

The aim of this study was to analyze the influence of the match half and the playing position on physical requirements in the Spanish Professional Futsal League players during official games. The external load from distance, speed, acceleration and deceleration variables were obtained from fourteen elite futsal players during 10 official matches of the 2019-2020 season using a Local Positioning System with ultra-wideband technology installed on the futsal pitch. The results revealed similar results from physical requirements between first and second half (p > 0.05). Wingers demonstrated greater high-speed running distance (+4.04 m·min-1; CI95%: 0.35 to 7.72; ES: 0.87) than pivots (p > 0.05). There were a high number of accelerations (7.42-9.41 n·min-1) and decelerations (7.37-9.12 n·min-1) per minute in all player positions. The principal finding of the current manuscript did not evidence differences in the physical performance of players between the first and second half. The physical requirements varied among pivots and wingers regarding high-intensity actions. These outcomes add new contributions to the understanding of futsal physical demands.

Mechanical Properties of Treadmill Surfaces Compared to Other Overground Sport Surfaces.

The mechanical properties of the surfaces used for exercising can affect sports performance and injury risk. However, the mechanical properties of treadmill surfaces remain largely unknown. The aim of this study was, therefore, to assess the shock absorption (SA), vertical deformation (VD) and energy restitution (ER) of different treadmill models and to compare them with those of other sport surfaces. A total of 77 treadmills, 30 artificial turf pitches and 30 athletics tracks were assessed using an advanced artificial athlete device. Differences in the mechanical properties between the surfaces and treadmill models were evaluated using a repeated-measures ANOVA. The treadmills were found to exhibit the highest SA of all the surfaces (64.2 ± 2; p < 0.01; effect size (ES) = 0.96), while their VD (7.6 ± 1.3; p < 0.01; ES = 0.87) and ER (45 ± 11; p < 0.01; ES = 0.51) were between the VDs of the artificial turf and track. The SA (p < 0.01; ES = 0.69), VD (p < 0.01; ES = 0.90) and ER (p < 0.01; ES = 0.89) were also shown to differ between treadmill models. The differences between the treadmills commonly used in fitness centers were much lower than differences between the treadmills and track surfaces, but they were sometimes larger than the differences with artificial turf. The treadmills used in clinical practice and research were shown to exhibit widely varying mechanical properties. The results of this study demonstrate that the mechanical properties (SA, VD and ER) of treadmill surfaces differ significantly from those of overground sport surfaces such as artificial turf and athletics track surfaces but also asphalt or concrete. These different mechanical properties of treadmills may affect treadmill running performance, injury risk and the generalizability of research performed on treadmills to overground locomotion.

Physical Demands of U10 Players in a 7-a-Side Soccer Tournament Depending on the Playing Position and Level of Opponents in Consecutive Matches Using Global Positioning Systems (GPS).

The aim of this study was to analyse the physical demands of U10 players in a 7-a-side-soccer tournament based on the playing positions in 6 consecutive matches by global positioning systems (GPS). Variables of total distance, relative distance in different speed zones, maximum speed, time interval between accelerations, maximum speed acceleration, maximum acceleration, acceleration distance and the number of high-intensity accelerations were analysed. Differences between playing positions were found in the total distance covered by the midfielders. They covered higher total distances than the defenders (+1167 m; 95% CI: 411 to 1922 m; effect size (ES) = 1.41; p < 0.05) and forwards (+1388 m; CI 95%: 712 a 2063 m; TE = 0.85; p < 0.05). The total covered distance increased in the final rounds with respect to the group stage (p < 0.05; ES: 0.44 to 1.62), and high-intensity actions, such as the number of accelerations, were greater in the final rounds compared to the group stage (p < 0.05; ES: 0.44 to 1.62). The physical performance of young football players in a tournament with consecutive matches on a 40 × 62 m football field on the same day is influenced by the playing position and dependent on the level difference between opponents.

A Proposed Method to Assess the Mechanical Properties of Treadmill Surfaces.

The aim of this study was to define a reliable and sensitive test method for assessing Shock Absorption (SA), Vertical Deformation (VD), and Energy Restitution (ER) in treadmill surfaces. A total of 42 treadmills belonging to four different models were included in the study: (a) Technogym Jog700 Excite (n = 10), (b) Technogym Artis Run (n = 12), (c) LifeFitness Integrity Series 97T (n = 11), and (d) LifeFitness Integrity Series DX (n = 9). An advanced artificial athlete (AAA) device was used to assess SA, VD, and ER at three different locations along the longitudinal axis of each treadmill and in the support area of the athletes' feet. For each location, our results show that the error assumed when performing one impact with the AAA instead of three (SA ≤ |0.1|%, VD ≤ |0.0| mm, and ER ≤ |0.2|%) is lower than the smallest changes that can be detected by the measuring device (SA = 0.4%, VD = 0.2 mm, and ER = 0.9%). Also, our results show the ability of the test method to detect meaningful differences between locations once the one-impact criterium is adopted, since absolute minimum differences between zones (SA: |0.6|%, VD: |0.3| mm, and ER: |1.2|%) were above the uncertainty of the measuring device. Therefore, performing a single impact with the AAA in each of the three locations described in this study can be considered a representative and reliable method for assessing SA, VD, and ER in treadmill surfaces.

Novel Methodology for Football Rebound Test Method.

Assessing and keeping control of the mechanical properties of sport surfaces is a relevant task in sports since it enables athletes to train and compete safely and under equal conditions. Currently, different tests are used for assessing athlete- and ball-surface interactions in artificial turf pitches. In order to make these evaluations more agile and accessible for every facility, it is important to develop new apparatus that enable to perform the tests in an easier and quicker way. The existing equipment for determining the vertical ball behavior requires a complex and non-easily transportable device in which the ball must be fixed to the upper part of the frame in a very precise position by means of a magnet. The rebound height is determined by capturing the acoustic signal produced when the ball bounces on the turf. When extended tests are conducted, the time required to evaluate a single field is too high due to the non-valid trials. This work proposes a novel methodology which allows to notoriously decrease the time of testing fields maintaining the repeatability and accuracy of the test method together with a compact device for improving its mobility and transport. Simulations and experiments demonstrates the repeatability and accuracy of the results obtained by the proposed device, which decreases the non-valid trials and notoriously reduces the time for field evaluation.

Effect of the Fatigue on the Physical Performance in Different Small-Sided Games in Elite Football Players.

Calderón Pellegrino, G, Paredes-Hernández, V, Sánchez-Sánchez, J, García-Unanue, J, and Gallardo, L. Effect of the fatigue on the physical performance in different small-sided games in elite football players. J Strength Cond Res 34(8): 2338-2346, 2020-Football players need to be able to perform high-intensity efforts of short duration with brief recovery periods. The aim of this study was to analyze the influence of the pitch dimension on high-intensity actions and the effect of a repeated sprint ability (RSA) test on the physical performance in different 4-against-4 (4v4) small-sided games (SSG) dimensions. Sixteen U-18 elite football players performed an RSA test between two 4v4 SSGs (pre and post) to induce fatigue and compare physical data. Speed, sprint number, accelerations, sprint distance, total distance covered, and total distance covered of the players at different intensities were evaluated in 3 different SSGs (125, 150, 250, and 300 m). Results revealed a significant detriment of physical performance in the 125-m SSG after RSA, mostly in number of sprints (-6.56; confidence interval [CI] 95%: -10.13 to -3.00; effect size [ES]: 1.13 p < 0.001), accelerations (-2.69; CI 95%: -5.13 to -0.24; ES: 0.68; p = 0.032), and sprint distance (-65.44 m; CI 95%: -103.73 to -27.16; ES: 1.20; p = 0.001). In bigger SSGs (250 and 300 m), higher distance at high intensity was covered and Vmax, Vmean, and sprint distance were greater. In summary, accelerations, sprint number, and fatigue were higher in smaller pitches, and higher velocities were reached in bigger SSGs. Football players should be aware that changes in pitch size can modify the physical performance on high-intensity actions in SSGs.

Validation of a Video-Based Performance Analysis System (Mediacoach®) to Analyze the Physical Demands during Matches in LaLiga.

The aim of the present study was to assess the accuracy of a multi-camera tracking system (Mediacoach®) to track elite football players' movements in real time. A total of 207 observations of 38 official matches from Liga 1, 2, 3™ (2nd Spanish Division, season 2017/18) were included in the study (88 defenders, 84 midfielders, and 35 attackers of the same team). Total distance (TD, m) distance in zone 4 (DZ4) at a speed of 14-21 km/h, distance in zone 5 (DZ5) at a speed of 21-24 km/h (DZ5), distance in zone 6 (DZ6) at a speed of ≥24 km/h, maximum speed (km/h), and number of sprints (actions above 24 km/h) were registered with the Apex® GPS system (STATSports™, Newry, N. Ireland) and Mediacoach® semi-automatic tracking system (LaLiga™, Madrid, Spain). The level of agreement between variables estimated by the two systems was analyzed. Bias was also calculated by deducting the GPS estimated value from the video estimated value, and then dividing the difference score by the GPS estimated value. All variables showed high ICC values (>0.75) and very large correlations (r > 0.70). However the video-based performance analysis system overestimated the results obtained in the different speed zones (DZ5: +16.59 ± 62.29 m; LOA95%: -105.49 to 138.68; DZ6: +93.26 ± 67.76 m; LOA95%: -39.55 to 226.07), the number of sprints (+2.27 ± 2.94; LOA95%: -3.49 to 8.02), and the maximum speed (+0.32 ± 1.25 km/h; LOA95%: -2.13 to 2.77). The maximum bias was found in DZ6 (47%). This demonstrates that Mediacoach® is as accurate as a GPS system to obtain objective data in real time, adapted to physical and movement demands of elite football, especially for total distance and distances traveled at medium speeds.

Pitch Size and Game Surface in Different Small-Sided Games. Global Indicators, Activity Profile, and Acceleration of Female Soccer Players.

López-Fernández, J, Gallardo, L, Fernández-Luna, Á, Villacañas, V, García-Unanue, J, and Sánchez-Sánchez, J. Pitch size and game surface in different small-sided games. Global indicators, activity profile, and acceleration of female soccer players. J Strength Cond Res 33(3): 831-838, 2019-The aim of this research was to evaluate the influence of game surface and pitch size on the movement profile in female soccer players during small-sided games (SSGs) of 4 v 4. Sixteen women played 3 different 4-a-side (400, 600, and 800 m) on 3 surfaces (ground [GR], artificial turf [AT], and natural grass [NG]). Time-motion variables were assessed through GPS devices (Spi Pro X, GPSports, Australia). Ground had the worst outputs on most variables. NG achieved higher results than AT in terms of total distance (SSG 400 [+37.000 m; p = 0.006]; SSG 600 [+59.989 m; p < 0.001]; and SSG 800 [+42.284 m; p = 0.001]). However, the smaller SSG (400) had the lowest values on most variables. However, although the middle SSG (600) presented higher output than the bigger one (800) for body load (NG [+7.745 a.u.; p < 0.001]; AT [+8.207 a.u.; p < 0.001]; and GR [+5.879 a.u.; p < 0.001]), it had lower results for high-intensity distance (NG [-13.15 m; p = 0.025] and AT [-13.59 m; p = 0.026]). Despite women's performance being higher on AT than GR, the NG surface still showed the highest outcomes in the most intense SSG. Moreover, although the performance increases in bigger pitches, if the size is too large the outputs could be reduced.

The team's influence on physical and technical demands of elite goalkeepers in LaLiga: a longitudinal study in professional soccer.

This study examined physical and technical demands and the influence of the team's level on elite goalkeepers' performance during six consecutive seasons in Spanish Professional Soccer League. The goalkeepers' performance data were obtained by analyzing a total of 3,874 matches using a multiple-camera computerized tracking system. The physical and technical match variables registered were: distance traveled; distance Sprinted and the number of sprints; total number of passes; successful passes; pass percentage; recovered balls; lost balls; ratio lost balls: recovered balls, and number of saves. The results showed that the number of saves made has shown a significant reduction (p < 0.001). When comparing between the teams' level, the goalkeepers of the worst classified teams showed a greater distance traveled by sprint (+3.72 m, IC95%: 1.00-6.44, ES: 0.41, p = 0.008). In conclusion, the results the influence of the team's level on the technical and physical parameters of the goalkeepers during the last six seasons.

Association of different types of playing surfaces with bone mass in growing girls.

The aim of this cross-sectional study was to compare bone mass in young female athletes playing ball games on different types of playing surfaces. About 120 girls, 9-13 years of age (10.6 ± 1.5 years old Tanner I-III) were recruited and divided into prepubertal and pubertal groups. The sample represented 3 groups of athletes: soccer (N = 40), basketball (N = 40), and handball (N = 40); and 6 different playing surfaces (soccer - ground, soccer - artificial turf, basketball - synthetic, basketball - parquet, handball - synthetic, and handball - smooth concrete). Total and regional body composition (bone mass, fat mass, and lean mass) were measured by dual-energy X-ray absorptiometry (DXA). The mechanical properties of the surfaces (force reduction, vertical deformation, and energy return) were measured with the Advanced Artificial Athlete (Triple A) method. The degree of sexual development was determined using Tanner test. The pubertal group showed that soccer players on the ground, basketball players on synthetic, and handball players on smooth concrete had higher values of bone mineral content (BMC) and bone mineral density (BMD) (P < 0.05) than the soccer players on the artificial turf, basketball players on parquet, and handball players on synthetic. In conclusion, a hard playing surface, with less vertical deformation and force reduction, and greater energy return, is associated with higher levels of BMD and BMC in growing girls, regardless of the sport they practice.