ABSTRACT Objectives This study aimed to examine the importance assigned to assessing and considering biological maturation in thematic areas of player development and provide an overview of current practices in German football academies regarding its consideration in training and competition. Methods An online survey was sent to 56 elite German football academies. A total of 46 responded to the questionnaire (82% response rate). Six participants provided incomplete information resulting in a total of 40 completed surveys in the period from March to May 2022. Results Only 20 of participants regularly carried out maturation assessments, despite 95% recognizing its importance for load management, 90% for player development, and 85% for injury prevention. There was no consistent approach to modifying training and competition formats based on maturity status, with a primary focus on gym-based sessions for load management. Conclusion The survey results highlight limited implementation of maturation assessment and training modification based on maturity status in German elite youth football academies. Despite recognizing the importance of load monitoring, reporting to parents, and long-term player development in considering biological maturation, practices are not widespread. The predominant use of the maturity offset method suggests an opportunity to improve accuracy by exploring alternative measurement methods and increasing assessment frequency. Moreover, a lack of established procedures for incorporating maturity status into training and competition exists, hindering comprehensive consideration of biological maturation and injury risk prevention. Further research is needed to understand the reasons for inconsistent approaches in maturation assessment and load modification during training and competition.

ABSTRACT Objectives To investigate the incidence, type and location of growth-related sports injuries (GRSI) in youth professional football in the Netherlands. Secondary, to gain more knowledge on the injury severity and burden of GRSI. Methods In this prospective, longitudinal cohort study, 813 players aged 10–18 are included. Data collection is performed by instructing the medical staff of six professional football club academies to register GRSI by means of standardized forms. Training and match exposure are registered individually on a weekly basis. Injury incidence was calculated as number of GRSI per 1000 hours, injury severity as the median number of days lost in categories and injury burden as the number of days lost per 1000 hours. Results A total of 62 GRSI were documented in the football season 2021–2022. The total incidence of GRSI was 0.62/1000 hours football exposure. Morbus Osgood Schlatter and Morbus Sever were most common types of GRSI, both with incidence rates of 0.22/1000 hours exposure. About 58.3% of the documented GRSI were classified as major (>28 days lost). Within this group, the mean severity was 55 days time-loss to football. Conclusions GRSI are relatively common in youth professional football. The most common types are Morbus Sever and Morbus Osgood Schlatter. Morbus Osgood Schlatter has the highest injury severity and burden compared to other types of GRSI.

ABSTRACT There is concern that exposure to soccer headers may be associated with neurological sequelae. Training proper heading technique represents a coachable intervention that may reduce head acceleration exposure. The objective was to assess relationships between heading technique and head kinematics in female youth soccer players. Fourteen players (mean age = 14.4 years) wore instrumented mouthpieces during practices and games. Headers were reviewed by three raters to assign a technique score. Mixed models and LASSO regression evaluated associations of technique with peak linear acceleration (PLA), rotational acceleration (PRA), rotational velocity (PRV), and head impact power ratio (HIP Ratio) while adjusting for session type and ball delivery. Two hundred eighty-nine headers (n = 212 standing, n = 77 jumping) were analyzed. Technique score (p = 0.043) and the technique score – session type interaction (p = 0.004) were associated with PRA of standing headers, whereby each ten-unit increase in technique score was associated with an 8.6% decrease in PRA during games but a 5.1% increase in PRA during practices. Technique was not significantly associated with any other kinematic metrics; however, peak kinematics tended to decrease as technique score increased. LASSO regression identified back extension and shoulder/hip alignment as important predictors of peak kinematics. Additional research on heading technique and head acceleration is recommended.

ABSTRACT Introduction The sport of rugby union, henceforth rugby, is associated with a risk of spinal cord injury (SCI). Perceived risks can impact participation. Understanding community perspectives on rugby-related SCI may provide insight for addressing concerns around risk. The aim of this study was to explore community perspectives through social media discussion about SCI in rugby union. Methods Posts about SCI in rugby union were identified using the advanced search function on Twitter. Data (content as original post, retweet, quote tweet and comments) were included if focused on Rugby Union and written in English. Inclusion dates (July 2018 to June 2019) were chosen to capture a period when several SCI (n = 4) occurred in community rugby in Australia. Data were analysed using a thematic approach. Results Four themes were derived from the collected data. The ‘pendulum swing’ relates to the disparate views of rugby, from being overly cautious to too dangerous to play. The ‘role of rugby culture’ described engrained behaviours and attitudes on and off-field toward safety. ‘Media influence’ describes the emotive narrative used when reporting rugby-related SCI. ‘After the injury’ looks at expressions of sympathy and inspiration. These findings showed how individuals’ views of SCI were influenced through rugby culture, trust in governing bodies and the news media. Conclusion By ‘listening in’ to community views, their most pertinent safety concerns can be addressed. Both facts and fears on rugby-related SCI were evident, and these extreme views can be balanced with evidence-based education and sensible risk management.

ABSTRACT The purpose of this study was to compare the activity profile of elite Gaelic football referees (GFR) between the National Football League (NFL) and the All-Ireland Championship (AIC), and across the four divisions of the NFL and three phases of the AIC. Match activity data was collected during 125 NFL and 201 AIC games using 10-Hz global positioning system technology from 41 elite GFR. Game duration, total distance, very low-speed movement (<0.70 m·s−1), walking (≥0.70–1.65 m·s−1), low-speed running (≥1.66–3.27 m·s−1), moderate-speed running (≥3.28–4.86 m·s−1), high-speed running (≥4.87–6.48 m·s−1), very high-speed running (≥6.49 m·s−1) distance, and peak running speed were compared between competitions. Games in the AIC were longer than in the NFL (ES = 0.59) but the total distance was similar between the NFL (119.6 ± 9.5 m·min−1) and AIC (122.6 ± 8.4 m·min−1, ES = 0.11). No other differences were found between the NFL and AIC or across the four divisions of the NFL and three phases of the AIC, except for a higher peak running speed during the All-Ireland Series (6.93 ± 0.52 m·s−1) than the All-Ireland Qualifiers (6.65 ± 0.46 m·s−1, ES = 0.35). This information can be used to design specific conditioning programmes to ensure optimal physical development of GFR at all competitive levels.

ABSTRACT Walking Football (WF) is one type of recreational football increasing in popularity, targeting older adults. Further knowledge on the intensity and physical workload of WF, characteristics of the players, the social context, and reasons for playing WF is needed. Thus, the aim of the study was to characterize the individuals that regularly play WF and their experience of WF, and the physiological characteristics of the sport. Sixty-three players from three clubs taking part in organised WF in Sweden were included. The players participated in up to four WF-games and underwent performance tests and answered a questionnaire. The participants mean age was 70.9 years, ranging from 63 to 85 years with 71% (n = 27) of the men and 68% (n = 13) of the women having a BMI > 25. Fifty-one percent (n = 27) of the players had hypertension, and 73% (n = 39) regularly used prescription drugs due to illness. During WF, the players covered on average 2,409 m (2,509 m for men and 2,205 m for women, p = .001). Expressed in percentage of their age-estimated maximal heart rate, mean heart rate represented 80 ± 9 and 80 ± 8% of max for men, and 78 ± 9 and 79 ± 9% of max for women in the first and second halves, respectively, hence WF can be considered a moderate intensity activity for older adults. The main reason for WF participation was to socialize. WF includes a considerable number of accelerations and decelerations, making it more energetically and mechanically demanding than walking.

ABSTRACT This study investigates variations in skinfold thickness in a European professional football team within and across multiple seasons, including before and after COVID-19 restrictions. Skinfold thickness was measured in 49 male players on 32 occasions across three seasons (2018/19, 2019/20 and 2020/21). Intra- and inter-seasonal trends were examined by comparing values for the sum of eight skinfolds (sum8) at key time points using linear mixed models. In each season, the largest differences in sum8 occurred after the preseason period. These differences ranged from a mean difference (Mdiff) of −11.0 mm (p < 0.001) in 2018/19 to −4.8 mm (p < 0.001) in 2020/21. Increases in sum8 occurred after each off-season; however, the increase after the off-season before the 2020/21 season (which included the COVID-19 lockdown period) was the lowest in magnitude and was not statistically significant (Mdiff = 2.9 mm, p = 0.06). Changes occurring in sum8 between the start and end of the competitive season did not follow a consistent pattern and were generally smaller in magnitude than the changes between other seasonal time points. Despite the notable heterogeneity in sum8 between players, changes within players generally followed a similar pattern between the different seasonal timepoints. In summary, changes in skinfold thickness were predominantly related to off-season and ‘preparation for competition’ periods. Increases in skinfold thickness can be mitigated during extended remote training periods with appropriate training and nutritional strategies.

ABSTRACT The interest in sports performance analysis is rising and tracking data holds high potential for game analysis in team sports due to its accuracy and informative content. Together with machine learning approaches one can obtain deeper and more objective insights into the performance structure. In soccer, the analysis of the defense was neglected in comparison to the offense. Therefore, the aim of this study is to predict ball gains in defense using tracking data to identify tactical variables that drive defensive success. We evaluated tracking data of 153 games of German Bundesliga season 2020/21. With it, we derived player (defensive pressure, distance to the ball, & velocity) and team metrics (inter-line distances, numerical superiority, surface area, & spread) each containing a tactical idea. Afterwards, we trained supervised machine learning classifiers (logistic regression, XGBoost, & Random Forest Classifier) to predict successful (ball gain) vs. unsuccessful defensive plays (no ball gain). The expert-reduction-model (Random Forest Classifier with 16 features) showed the best and satisfying prediction performance (F1-Score (test) = 0.57). Analyzing the most important input features of this model, we are able to identify tactical principles of defensive play that appear to be related to gaining the ball: press the ball leading player, create numerical superiority in areas close to the ball (press short pass options), compact organization of defending team. Those principles are highly interesting for practitioners to gain valuable insights in the tactical behavior of soccer players that may be related to the success of defensive play.

ABSTRACT We investigated the associations between Finnish top tier footballers’ self-assessed leadership roles (task, motivational, social, external) and player-assessed head coach leadership behavior (supportiveness/emotional composure, negative activation) and leadership role in both practices and games. We also explored the player age- and gender-related differences. Online survey data were anonymously collected from 53 male and 91 female footballers. One player did not identify as male or female, and one chose not to answer the question. Spearman rank-order correlations revealed that players’ self-assessed leadership roles correlated positively with their evaluation of their head coach’s supportiveness/emotional composure and negatively with negative activation during practices and games. Independent samples T-tests showed that male footballers rated their head coaches lower on negative activation during games and practices and themselves higher on external leadership than female players. The youngest age group, aged 17–20, rated themselves also lower on external leadership than the three older groups.

ABSTRACT The concurrent validity and between-unit reliability of a foot-mounted inertial measurement unit (F-IMU) was investigated during linear and change of direction running drills. Sixteen individuals performed four repetitions of two drills (maximal acceleration and flying 10 m sprint) and five repetitions of a multi-directional movement protocol. Participants wore two F-IMUs (Playermaker) and 10 retro-reflective markers to allow for comparisons to the criterion system (Qualisys). Validity of the F-IMU derived velocity was assessed via root-mean-square error (RMSE), 95% limits of agreement (LoA) and mean difference with 95% confidence interval (CI). Between-unit reliability was assessed via intraclass correlation (ICC) with 90% CI and 95% LoA. The mean difference for instantaneous velocity for all participants and drills combined was −0.048 ± 0.581 m ∙ s−1, the LoA were from −1.09 to −1.186 m ∙ s−1 and RMSE was 0.583 m ∙ s−1. The ICC ranged from 0.84 to 1, with LoA from −7.412 to 2.924 m ∙ s−1. Differences were dependent on the reference speed, with the greatest absolute difference (−0.66 m ∙ s−1) found at velocities above 7 m ∙ s−1. Between-unit reliability of the F-IMU ranges from good to excellent for all locomotor characteristics. Playermaker has good agreement with 3D motion capture for velocity and good to excellent between-unit reliability.