Under-18 Players Research Articles

Creativity in sports: The crucial role of motor skills

What enables athletes to perform creative actions in their sports? In the last two decades, sports studies have predominantly assumed that divergent thinking (DT) is the key ingredient and have developed sport-specific DT tests to assess players’ creativity. However, a fundamental question remains: Do players who score high on sport-specific DT tests perform more creative actions on the field? The DT approach in sports has recently been challenged by the hypothesis that creative actions are primarily enabled (or limited) by players’ motor skill repertoires. Here, predictions based on the DT and motor skill approach are tested in the domain of soccer. Studies 1a and b tested male under-12 players, and Study 2 tested female under-19 players of a professional soccer club. All three studies indicated no correlation between the creativity of actions performed on the field (rated with the Consensual Assessment Technique) and players’ soccer-specific DT. In contrast, moderate to high correlations between on-field creativity and motor skills were found. These results challenge the DT approach in sports and the validity of sport-specific DT tests, highlighting the crucial role of sensorimotor skills in performing creative actions in sports or other domains in which creative performance is embodied through motor actions.

The Impact of a Congested Competition Schedule on Load, Recovery, and Well-Being in Under-16 Female Soccer Players: A Comparison between Starters and Non-Starters during a Development Tournament

Monitoring training load, recovery, and wellness in maturation ages is even more relevant than in adulthood, especially during congested schedules. The objective of this study was to quantify and describe the differences in external and internal load, recovery, and perceived wellness in elite under-16 female players during a period of three competitions in seven days based on their participation during matches. An observational design was used to quantify the external load (total distance, high-speed distance, and PlayerLoad) and internal load (differential sRPE), as well as the recovery and wellness of 18 international under-16 players during a development tournament. The external load pattern of the starting players was undulating, with matches showing the highest internal load values compared to training sessions and non-starters. Non-starter players (whether training or matches) showed similar external load and differential sRPE values throughout the tournament (p > 0.05). Starting players experienced higher internal load than non-starters during matches (p < 0.037), without differences between training sessions (p > 0.05). No changes were seen in wellness or recovery (all p-values > 0.05), except for non-starters in Session 3 compared to Session 7 (p = 0.024). Starting players had more weekly total minutes (p = 0.018), differential sRPE (breath: p = 0.002; leg: p = 0.002; cognitive: p = 0.003), total distance (p = 0.003), and PlayerLoad (p = 0.008) than non-starters. Our results indicate differing load patterns between starters and non-starters, which do not affect wellness and recovery differently. Starters accumulate more weekly total load. Coaches can use these findings to guide decisions and load compensations in high competition contexts for young female soccer players.

Training loads and microcycle periodisation in Italian Serie A youth soccer players

ABSTRACT Microcycles are fundamental structures for training prescription and load management, helping to optimise training effects and performance. This study quantified external and internal loads of Italian Serie A youth soccer players across competitive weeks and their periodisation within microcycles. Data were collected from 90 players belonging to four age groups (under-19, -17, -16, -15) across a season. Methods of monitoring external [duration and global navigation satellite systems (GNSS)] and internal load [heart rate (HR) and rating of perceived exertion (RPE)] were employed. Linear mixed models determined differences in training loads across age groups, training days and player positions. Under-19 and under-17 players trained five times per week, while younger players trained four times. Late-stage academy players (under-19 and -17) demonstrated higher weekly accumulated external and sRPE training load compared to their younger counterparts (p < 0.05 between groups). Weekly accumulated HR internal loads were higher in under-15 players (p < 0.05 between groups). Marked fluctuations of daily load were observed across microcycles in under-19 and under-17 groups (p < 0.05 between days). These findings highlight progressive increases in training load throughout the development pathway, with late-stage academy players training with higher frequency, volume and marked periodisation compared to younger players.

Frequency and intensity of maximal and submaximal demanding scenarios in U19 professional soccer players

ABSTRACT This study examined the frequency of the most demanding scenarios (MDS) during official soccer matches using rolling averages over 1, 5, and 10 min. Forty-two Under-19 players from different positions (central defenders, full-backs, central midfielders, wide midfielders, offensive midfielders, and forwards) were monitored across 27 matches using GPS to track distance covered, high-speed running, sprint distance, accelerations, and decelerations. Intensity thresholds were established based on percentiles (0–25, 25–50, 50–75, 75–100, and ≥100). The main findings suggest that: (i) Peak Demands occur in less than 1% of all time windows and variables for all positions; (ii) Most efforts occur below peak demands, with around 95% for high-speed running and sprint distance, and 85% for accelerations, decelerations, and total distance; (iii) Significant differences in intensity distributions were found between positions, particularly at medium-low and high intensities. Regarding training prescription, relying solely on MDS may be limited, highlighting the need to supplement MDS with other metrics for a comprehensive understanding of match demands. This approach ensures better-informed training programs for soccer players.

Research Trends in Football Training for Young Players in the Last 15 Years: Bibliographic Analysis

The objective of this paper is to evaluate the research trends in football training for young players under 18 years old in the last 15 years. Materials and methods. This was a bibliometric analysis and systematic review study. Articles published since 2008 were searched for by the keywords “Football Training” and “Football Exercise” using a comprehensive strategy on SCOPUS research journal databases. There were 1,053 articles with 4802 citations mined on October 17th, 2023. Thereafter, 217 articles were selected for further analysis by using VOS Viewer computer software. Results. The United Kingdom (67), The United States (60), and Spain (41) were the three countries that had the most publications in football training. There were 6 keyword clusters that reflected various research focuses on football training for younger players. Based on the top 10 most cited references in football training for younger players, there were several major themes that covered various aspects of the research trend and development in the last 15 years, i.e. (1) Factors in the Development of Young Football Players, (2) Tactical Analysis and Collective Behavior in Small-Sided Games, (3) Game Intensity and Activity Profile in Young Football Players, (4) Plyometric Training and Its Effects on Preadolescent Players, and (5) Injury Prevention and Neuromuscular Training in Adolescent Football Players. Conclusions. Football research for under-18 players has grown rapidly. This research trend shows that football requires not only physical and technical skills, but also social and mental aspects. Further research can be directed toward understanding and integrating holistic aspects of football coaching, including the development of non-physical skills, such as leadership, teamwork, and conflict resolution. Further investigation into the use of technology in football coaching, such as video analysis, sensor-based performance measurement, and artificial intelligence applications to provide deeper insight into player progress.

Effects of Two Different Low-Volume Resistance Training Programs Applied During the Off-Season Period on the Speed-Power Performance of Elite Youth Soccer Players.

Loturco, I, Nunes, RFH, Lampert, RR, Silva, RLP, Hespanhol, JE, Novack, LF, Conde, JHS, Pereira, LA, and McGuigan, MR. Effects of two different low-volume resistance training programs applied during the off-season period on the speed-power performance of elite youth soccer players. . J Strength Cond Res 38(3): 571-576, 2024-The aim of this study was to analyze the changes in the speed-power performance of elite youth soccer players submitted to 2 different low-volume resistance training programs during the off-season period. Twenty under-17 players were randomly allocated to "traditional nonballistic" or "ballistic training" groups. Countermovement jump (CMJ), 20-m sprinting speed, and half-squat (HS) power tests were performed after the final match of the season (pretesting session) and at the beginning of the subsequent season (post-testing session), after 4 weeks of detraining. Between-group differences were assessed using a 2-way ANOVA with repeated measures followed by the Tukey's post hoc test. Performance variations were individually analyzed with the use of the "true changes" calculation. At post-tests, CMJ height and HS power remained unchanged ( p > 0.05) but similar and significant improvements in sprint speed were observed in both groups ( p < 0.05). However, notably, a larger number of players in the ballistic group exhibited "true changes" in HS power (i.e., 55 vs. 33%, compared with the traditional group, respectively). In conclusion, either low-volume ballistic or traditional resistance training schemes were able to increase sprint speed and maintain power output during a short interseason break in youth soccer players. Despite this apparent similarity, at the individual level, ballistic movements were more efficient at improving lower-body power. Practitioners can use the strategies described here to improve the sprint and power performance of soccer players during short periods of soccer-specific training cessation.

Visual Information in Basketball Jump-Shots: Differences between Youth and Adult Athletes.

Basketball shooting is a complex skill that requires visual routines and trained players typically evidence a specific oculomotor pattern. This study aimed to examine visual patterns in male novice youth and professional adult players while performing a jump shot. The sample included 20 basketball players grouped as under-16 youth (n = 10) and professional adult (n = 10) players. Each participant completed 50 shots at two distances (long range: 6.80 m; middle range: 4.23 m). Eye tracking glasses were used to obtain quiet eye (QE), the number of fixations, total fixation duration, duration of first and last fixation. An independent t-test was used to assess differences between groups. Shooting accuracy given by % of efficacy indicated that under-16 players attained poorer scores at both distances: long (t = -4.75, p < 0.01) and middle (t = -2.80, p < 0.012) distance. The groups also differed in QE time (long: 600 ms vs. 551 ms; middle: 572 ms vs. 504 ms) and total duration of the fixations (long: 663 ms vs. 606 ms; middle: 663 ms vs. 564 ms) in both long and middle distance shots. Significant differences also occurred in the last fixation (long distance: t = -4.301, p < 0.01; middle distance: t = -3.656, p < 0.01) with professional adult players presenting the value of, on average, 454-458 ms, while youth shooters 363-372 ms. In summary, visual strategy differed between under-16 youth and professional adult basketball players. To support their long-term sport development, it is recommended that youth basketball players focus their attention with longer final fixation before releasing the ball to improve their shot.

The discriminative, criterion, and longitudinal validity of small-sided games to assess physical fitness in female basketball players

ABSTRACT The validity of small-sided games (SSG) for assessing physical fitness was evaluated in 21 female basketball players from senior (n = 8), under-18 years (n = 6), and under-16 years (n = 7) age categories. Players underwent fitness testing (countermovement jump [CMJ], agility T-test, repeated-sprint ability (RSA) test, and Yo-Yo Intermittent Recovery Test [YYIRT1]) and 3vs3-SSG before and after a 6-week preseason. Player demands were monitored during SSG using local positioning system and heart rate technology. Regarding discriminative validity, senior players produced better CMJ, agility T-test, and YYIRT1 performance (p < 0.05, effect size [ES] = 1.72–2.25), and more distance and PlayerLoad (p < 0.05, ES = 1.53–2.47) during SSG than under-18 players following the preseason. For criterion validity, total distance and distance completing high-intensity decelerations during SSG were significantly (p < 0.05) correlated with CMJ (r = 0.44–0.66), YYIRT1 (r = 0.43–0.63), agility T-test (total distance only, r=-0.51), and RSA test performance (r=-0.49 to −0.52) among all players combined following the preseason. Regarding longitudinal validity, significantly better agility T-test and YYIRT1 performance (p ≤ 0.001, ES = 0.88–0.93) alongside lower heart rate during SSG (p = 0.001, ES = 0.88) were evident for all players combined following the preseason. These results partially support the validity of 3vs3-SSG to assess physical fitness in female basketball players.

Testing the peak running speed in analytical and contextual-based scenarios: Applied research in young adult soccer players

ABSTRACT The primary aim was to compare the peak running speed (PRS) attained in the 40-m linear sprint test, in an analytical-based soccer drill, in the 5-0-5 test, and a training match scenario. The secondary aim of the study was to evaluate the differences between the three assessment sessions and identify how the tests can vary from session to session. Additionally, we aimed to investigate the within-test variability to understand how consistent the performance is within each test format across the different sessions. Forty male under-19 players competing at the national level participated in this study. A training session was observed for each of the three study weeks in which the following tests/scenarios were monitored using a GPS. The 40-m linear sprint test and the analytical-based soccer drill presented the smallest within-subject coefficients of variation between the sessions. A large correlation (r = 0.742) was found between the PRS during the 40-m linear sprint test and the analytical-based soccer drill. The 40-m linear sprint test was the best method of those examined for measuring PRS. The analytical drill provides a reliable method for measuring PRS, although it differs from the 40-metre linear sprint test.

Why privilege the Europeans? A discussion of FIFA’s rules for international transfers for under-18 players

ABSTRACT Many professional football clubs in Europe have youth academies. The business model of such academies is that a club invests resources in training a player and then, when the player is old enough to sign an adult contract, either sells the player or offers him an adult contract. According to Fédération Internationale De Football Association (FIFA), international transfers of players are only permitted if the player is over the age of 18. There are five exceptions to this rule. One of them is that if the player is between 16 and 18 and the transfer takes place within the territory of the European Economic Area (EEA), then an international transfer is allowed. This article is a discussion of the FIFA rules that mandate non-uniform age limits for when players can first transfer to clubs within the EEA area. The conclusion of the article is that FIFA is morally unjustified in setting a higher minimum age for transfer to EEA clubs for non-EEA players than for EEA players. The article first develops an argument for its conclusion. It then discusses, and rejects, the five best objections to this argument.

Recovery of kicking kinematics and performance following repeated high-intensity running bouts in the heat: Can a rapid local cooling intervention help young soccer players?

ABSTRACT The effects of a cooling strategy following repeated high-intensity running (RHIR) on soccer kicking performance in a hot environment (>30ºC) were investigated in youth soccer players. Fifteen academy under-17 players participated. In Experiment 1, players completed an all-out RHIR protocol (10×30 m, with 30s intervals). In Experiment 2 (cross-over design), participants performed this running protocol under two conditions: (1) following RHIR 5 minutes of cooling where ice packs were applied to the quadriceps/hamstrings, (2) a control condition involving passive resting. Perceptual measures [ratings of perceived exertion (RPE), pain and recovery], thigh temperature and kick-derived video three-dimensional kinematics (lower limb) and performance (ball speed and two-dimensional placement indices) were collected at baseline, post-exercise and intervention. In Experiment 1, RHIR led to small-to-large impairments (p < 0.03;d = −0.42–-1.83) across perceptual, kinematic and performance measures. In experiment 2, RPE (p < 0.01; Kendall’s W = 0.30) and mean radial error (p = 0.057; η2 = 0.234) increased only post-control. Significant small declines in ball speed were also observed post-control (p < 0.05; d = 0.35). Post-intervention foot centre-of-mass velocity was moderately faster in the cooling compared to control condition (p = 0.04; d = 0.60). In youth soccer players, a short cooling period was beneficial in counteracting declines in kicking performance, in particular ball placement, following intense running activity in the heat.

The Association between External Training Load, Perceived Exertion and Total Quality Recovery in Sub-Elite Youth Football

Background: Moderate to very large correlation between internal training load, external training load, and recovery status have been reported in elite youth football. However, little is known about subelite youth football training environments. Objective: The purpose of this study was to assess the association between training load and recovery status in young subelite football players. Methods: Twenty under-15, twenty under-17, and twenty under-19 players were monitored over a 6-week period during the first month of the 2019-2020 competitive season. The global positioning system technology (GPS) was used to collect external training load variables. The internal training load variables were monitored using the rating of perceived exertion (RPE) scale and session RPE (sRPE). The recovery status was assessed by the total quality recovery (TQR). A total of 18 training sessions and 324 observation cases were collected. Results: Small to moderate correlation between internal and external load was observed (r = -0.316 to 0.136, p &lt; 0.05). Correlations between recovery status and external load were moderate for U15 (r = -0.326 to -0.240, p &lt; 0.05), U17 (r = -0.316 to 0.136, p &lt; 0.05) and U19 (r = -0.301 to 0.282, p &lt; 0.05). The association between perceived exertion and external training load is only significant for U19 subelite football players. Conclusion: Current research suggested that subelite youth football players were more likely to have lower capacity to judge training exertion. Additionally, recovery status was positively correlated with acceleration and deceleration movements. This study provides a new overview about training load and recovery in subelite youth training environment. Future researche should examine the between- and within-individual nonlinearity across training load and recovery variations.

Clustering ball possession duration according to players' role in football small-sided games.

This study aimed to explore which offensive variables best discriminate the ball possession duration according to players specific role (defenders, midfielders, attackers) during a Gk+3vs3+Gk football small-sided games. Fifteen under-15 players (age 13.2±1.0 years, playing experience 4.2±1.0 years) were grouped according to their positions (team of defenders, n = 5; team of midfielders, n = 7; team of attackers, n = 3). On each testing day (n = 3), each team performed one bout of 5-min against each team in a random order, accounting for a total of nine bouts in the following scenarios: i) defenders vs midfielders; ii) defenders vs attackers; iii) midfielders vs attackers. Based on video, a notational analysis process allowed to capture individual and collective actions. According to each playing position group, discriminant analysis was used to identify relevant variables that discriminate different ball possession sequences (short, medium, and long). The analysis revealed the existence of three clusters according to ball possession duration, classified as short sequence (~4 seconds), medium sequence (~10 seconds) and long sequence (~18 seconds). The number of touches per possession was the variable that discriminates the ball possession duration from all playing positions while passing actions were related to midfielders and attackers. In addition, different ball possessions sequences in the attackers were also discriminated by the number of players involved per possession. Accordingly, to increase the duration of the offensive phase during small-sided games, coaches should foster the players’ ability to stay on the ball, as it may amplify their opportunities to maintain the ball possession. In addition, coaches may also include reward rules to encourage midfielders and attackers’ passing actions and the number of attackers involved during the attack to promote longer ball possessions durations.

Visual occlusion effects on youth football players' performance during small-sided games.

This study aimed to explore how youth players’ physical, technical and positional performance may be affected by visual occlusion when playing under different SSG pitch sizes. Under-15 players performed two experimental scenarios: a) normal situation, without visual occlusion; b) visual occlusion, by using an eye patch in the eye corresponding to the dominant foot. These scenarios were tested in a small (40x30m) and a larger pitch (50x35m). Players’ positional data was used to compute tactical and time-motion variables. In addition, technical analysis was comprised using video footage. Playing with visual occlusion in the larger pitch size induced higher distance covered while walking but lower running distance (p < .05). Although no statistically significant effects were identified between the normal and visual occlusion conditions for the tactical behaviour and technical performance a lower number of successful passes (small to moderate effect sizes) and higher regularity in the distance to the opponent’s team centroid (moderate effect size) were found with visual occlusion. Players covered more distance and achieved higher maximum speed in the larger compared to the small pitch (moderate to large effect size, p < .05), while also increasing their distance to both team’s centroid and increasing the regularity to these distances (moderate to large effect size, p < .05). Overall, despite similar effects for tactical and technical variables, some important practical information can be depicted. Accordingly, coaches may use the visual occlusion to promote more stable and regular behaviors while decreasing the physical demands. Larger pitches may be used to increase the distance between players’ and teams, as well as to induce higher physical load in both the normal and visual occlusion conditions. From the technical perspective, coaches may design smaller pitches to emphasize the use of the non-dominant foot during the occlusion scenario and promote the pass during the normal scenario.

Peripheral muscle function during repeated changes of direction in professional soccer players.

To evaluate peripheral muscle function of the knee extensors during repeated changes of direction in professional soccer players by examining differences between competitive levels, periods of the season and playing positions, and to investigate the relationships between peripheral muscle function and physical activities during matches. Knee extensor peripheral muscle function (twitch peak torque, PT) of 593 male soccer players from 13 European professional clubs competing at 3 different levels was evaluated 4 times during the season. The main outcomes were PTmax (maximal PT, muscle contractility), MPmax (maximal metabolic power exercise intensity) and PTdec (PT decline, muscle fatigability) obtained during intermittent runs of increasing intensity with multiple changes of direction interspersed with electrically evoked contractions. Relative total and sprint distances covered during a whole match and during short intervals were quantified from a sub-sample. PTmax and MPmax were higher for first than for second division (p < 0.047; d = 0.15-0.23) and Under-19 players (p < 0.007; d = 0.17-0.25). MPmax was lower (p < 0.016; d = 0.23-0.32) and PTdec was higher (p < 0.004; d = 0.26-0.39) in the pre-season compared to all the other time points. MPmax was higher for fullbacks than attackers and defenders (p < 0.041; d = 0.20-0.22). PTdec was higher for defenders than fullbacks, midfielders and wings (p < 0.029; d = 0.21-0.28). PTmax was associated with whole-match relative total distance (p = 0.004; d = 0.26). PTdec was associated with whole-match relative total distance and relative short-interval sprint distance (p < 0.050; d = 0.18-0.22). The ability to sustain repeated change of direction efforts at high intensities while preserving peripheral muscle function should be considered an important determinant of soccer physical performance.

Specific Game-Based Performance in Elite Male Adolescent Team Handball Players.

In elite team handball, talent identification and selection of the best young players is a fundamental process in several national federations and clubs; however, literature addressing the specific game-based performance in team handball is almost nonexistent. Consequently, the aim of the study was to assess and compare the team-handball-specific game-based performance of elite male team handball players of different ages. Twelve under-23, 10 under-19, 10 under-17, and 10 under-15 elite male players performed the team-handball game-based performance test. During testing, oxygen uptake, heart rate, sprinting time in defense, offense, fast breaks, and fast retreats, as well as ball velocity and jump height in the jump shot, were measured. Significant differences (P < .05) between under-23, under-19, under-17, and under-15 players were found for absolute peak oxygen uptake, defense, offense and fast break time, ball velocity, and jump height in the game-based performance test, as well as in body weight and height. The results revealed that with increasing age, elite male team handball players are heavier and taller (body weight and height); faster (team-handball offense, defense, and fast break); jump higher and throw faster (in the team-handball jump shot); and perform better aerobically (absolute peak oxygen uptake). The better performance in the under-23 and under-19 players compared with male adult players competing in a lower National Federation league (not on top-elite level) demonstrates that highly specific game-based physical performance determines the potential for developing young male team handball players for competition at the top level.

Physical Fitness and Upper Limb Asymmetry in Young Padel Players: Differences between Genders and Categories.

This study aimed to assess the physical fitness and upper body asymmetries of young padel players aged between 13 and 16 years and to determine the possible differences between genders and categories. A total of 60 padel players were divided into four groups: under-14 male (n = 15; age: 13.75 ± 0.45 years; height: 1.64 ± 0.07 m; weight: 54.7 ± 8.3 kg), under-14 female (n = 15; age: 13.75 ± 0.44 years; height: 1.60 ± 0.05 m; weight: 51.5 ± 6.0 kg), under-16 male (n = 15; age: 15.44 ± 0.51 years; height:1.71 ± 0.04 m; weight: 63.88 ± 6.2 kg) and under-16 female (n = 15; age:15.46 ± 0.52 years; height:1.63 ± 0.05 m; weight: 55.08 ± 3.6 kg). Handgrip strength, ischiosural flexibility, gestural speed of the dominant arm, vertical jump, cardiorespiratory capacity, lateral movement, lateral acceleration and reaction time were measured. Male players showed better results in manual grip strength, vertical jump power, cardiorespiratory capacity and lateral movement (p < 0.05). Moreover, males presented a higher percentage of asymmetry in upper limb strength. Female players showed better reaction time and greater flexibility (p < 0.05). Regarding the differences between categories, the under-16 players showed greater flexibility, gestural speed, vertical jump power, cardiorespiratory capacity and lateral movement compared to the under-14 players. These results can be used as reference values for coaches/physical trainers of younger categories to improve health control and physical performance planning.

Exploring interactions between maturity status and playing time with fluctuations in physical fitness and hormonal markers in youth soccer players

The purpose of this study was to determine the differences in functional capacities and hormonal indices according to biological maturity and seasonal playing time status in young soccer players. Twenty-three male under-15 players (14.6 ± 0.2 years) were divided into two groups, based on their maturity status and seasonal playing time. They were measured for anthropometrics, Yo-Yo intermittent recovery level 1 (YYIR1), seven repeated sprint test (7RST), countermovement jump (CMJ), skeletal age, growth hormone, and insulin-like growth factor-1 (IGF-1) level. Age at peak height velocity (APHV) was determined to estimate the maturity timing. The results revealed that players who advanced in maturation were significantly heavier (p = 0.029) and had higher values in skeletal age (p < 0.001), sitting height (p = 0.005), CMJ (p = 0.038), and IGF-1 (p = 0.013). Players given greater playing time exhibited significantly lower fatigue index (p = 0.012), but higher CMJ (p = 0.003) and IGF-1 (p = 0.001) values. The overall results highlighted that early-maturing players and players with greater playing time obtained higher values in both CMJ and IGF-1. The findings may provide an insight on the coaches’ evaluation of players and on the possible factors that may affect the future playing status of young male soccer players.

Automatic Markerless Motion Detector Method against Traditional Digitisation for 3-Dimensional Movement Kinematic Analysis of Ball Kicking in Soccer Field Context.

Kicking is a fundamental skill in soccer that often contributes to match outcomes. Lower limb movement features (e.g., joint position and velocity) are determinants of kick performance. However, obtaining kicking kinematics under field conditions generally requires time-consuming manual tracking. The current study aimed to compare a contemporary markerless automatic motion estimation algorithm (OpenPose) with manual digitisation (DVIDEOW software) in obtaining on-field kicking kinematic parameters. An experimental dataset of under-17 players from all outfield positions was used. Kick attempts were performed in an official pitch against a goalkeeper. Four digital video cameras were used to record full-body motion during support and ball contact phases of each kick. Three-dimensional positions of hip, knee, ankle, toe and foot centre-of-mass (CMfoot) generally showed no significant differences when computed by automatic as compared to manual tracking (whole kicking movement cycle), while only z-coordinates of knee and calcaneus markers at specific points differed between methods. The resulting time-series matrices of positions (r2 = 0.94) and velocity signals (r2 = 0.68) were largely associated (all p < 0.01). The mean absolute error of OpenPose motion tracking was 3.49 cm for determining positions (ranging from 2.78 cm (CMfoot) to 4.13 cm (dominant hip)) and 1.29 m/s for calculating joint velocity (0.95 m/s (knee) to 1.50 m/s (non-dominant hip)) as compared to reference measures by manual digitisation. Angular range-of-motion showed significant correlations between methods for the ankle (r = 0.59, p < 0.01, large) and knee joint displacements (r = 0.84, p < 0.001, very large) but not in the hip (r = 0.04, p = 0.85, unclear). Markerless motion tracking (OpenPose) can help to successfully obtain some lower limb position, velocity, and joint angular outputs during kicks performed in a naturally occurring environment.

The effect of bio-banding on the anthropometric, physical fitness and functional movement characteristics of academy soccer players.

The study examined if maturity status bio-banding reduces within-group variance in anthropometric, physical fitness and functional movement characteristics of 319, under-14 and under-15 players from 19 UK professional soccer academies. Bio-banding reduced the within-bio-banded group variance for anthropometric values, when compared to an aggregated chronological banded group (chronological: 5.1–16.7%CV; bio-banded: 3.0–17.3%CV). Differences between these bio-banded groups ranged from moderate to very large (ES = 0.97 to 2.88). Physical performance variance (chronological: 4.8–24.9%CV; bio-banded: 3.8–26.5%CV) was also reduced with bio-banding compared to chronological aged grouping. However, not to the same extent as anthropometric values with only 68.3% of values reduced across banding methods compared to 92.6% for anthropometric data. Differences between the bio-banded groups physical qualities ranged from trivial to very large (ES = 0.00 to 3.00). The number of functional movement metrics and %CV reduced by bio-banding was lowest within the ‘circa-PHV’ groups (11.1–44.4%). The proportion of players achieving the threshold value score of ≥ 14 for the FMS™ was highest within the ‘post-PHV’ group (50.0–53.7%). The use of maturity status bio-banding can create more homogenous groups which may encourage greater competitive equity. However, findings here support a bio-banding maturity effect hypothesis, whereby maturity status bio-banding has a heightened effect on controlling for characteristics which have a stronger association to biological growth.