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Purpose: To map anthropometric and physical performance profiles in Norwegian premier league female football players. Methods: During preseason, the physical qualities of 107 players were tested on Keiser leg press, countermovement jump, 40-meter sprint, and agility. Descriptive statistics were presented as mean (SD) and median [interquartile range]. Pearson correlations analyses were made for all performance tests, and results presented as R value with 95% CIs. Results: The female players were 22 (4) years of age, stature 169.0 (6.2) cm, body weight 65.3 (6.7) kg; force 2122 (312) N, power 1090 (140) W, sprint 40 m 5.75 (0.21) seconds, agility dominant 10.18 (0.32) seconds, nondominant 10.27 (0.31) seconds, and countermovement jump 32.6 (4.1) cm. Outfield players were faster and more agile than goalkeepers, a difference of 40 m, agility of dominant, and nondominant leg, respectively: 0.20 [0.09–0.32], 0.37 [0.21–0.54], and 0.28 [0.12–45]; P P ranging from Conclusions: Our study presents anthropometric and physical performance profiles of Norwegian premier league female football players. We found no difference for the physical qualities strength, power, sprint, agility, and countermovement jump between any outfield playing positions in female premier league players. There was a difference between outfield players and goalkeepers for sprint and agility.

Several sports have published consensus statements on methods and reporting of epidemiological studies concerning injuries and illnesses with football (soccer) producing one of the first guidelines. This football-specific consensus statement was published in 2006 and required an update to align with scientific developments in the field. The International Olympic Committee (IOC) recently released a sports-generic consensus statement outlining methods for recording and reporting epidemiological data on injury and illness in sport and encouraged the development of sport-specific extensions.The Fédération Internationale de Football Association Medical Scientific Advisory Board established a panel of 16 football medicine and/or science experts, two players and one coach. With a foundation in the IOC consensus statement, the panel performed literature reviews on each included subtopic and performed two rounds of voting prior to and during a 2-day consensus meeting. The panel agreed on 40 of 75 pre-meeting and 21 of 44 meeting voting statements, respectively. The methodology and definitions presented in this comprehensive football-specific extension should ensure more consistent study designs, data collection procedures and use of nomenclature in future epidemiological studies of football injuries and illnesses regardless of setting. It should facilitate comparisons across studies and pooling of data.

BkgroundNo studies have tested the validity of the Copenhagen Hip and Groin Outcome Score (HAGOS) using modern test theory, across different cultures and languages.ObjectiveTo validate the Danish, English and Norwegian versions of HAGOS and its six subscales (Symptoms (S, Item 1–7), Pain (P, Item 1–10), activities of daily living (Item 1–5), Sport and recreation (Sport/rec, Item 1–8), Participation in physical activity (item 1–2) and quality of life (item 1–5)) by evaluating differential item functioning (DIF) and measurement invariance across the three language versions in male multidirectional team athletes with groin pain. Second, to modify subscales depending on goodness-of-fit to the item response theory models and calculate conversion tables if language DIF was observed.MethodsWe included individual responses to the Danish (n=157), English (n=146) and Norwegian (n=149) language versions of HAGOS from 452 athletes (median age 24 years old, range 20–28) with groin pain. Overall fit, model fit, individual item fit, local response dependence and measurement invariance was examined using confirmatory factor analysis and graphical Rasch models.ResultsThe removal of seven misfitting items (S2, P1, P2, A4, SP1, SP5, Q3) resulted in 6 HAGOS subscales with acceptable psychometric properties. For the Symptoms, Pain and Sports subscales evidence of DIF was disclosed between the three different language-versions of HAGOS and conversion tables were created.ConclusionsA revised HAGOS derived using modern test theory provides valid measurements for male multidirectional athletes with groin pain across different cultures and languages. Conversion tables must be applied to compare HAGOS scores from Danish, Norwegian and English language versions.

To map the current practice of handling missing data in the field of training load and injury risk and to determine how missing data in training load should be handled.A systematic review of the training load and injury risk literature was performed to determine how missing data are reported and handled. We ran simulations to compare the accuracy of modelling a predetermined relationship between training load and injury risk following handling missing data with different methods. The simulations were based on a Norwegian Premier League men's football dataset (n = 39). Internal training load was measured with the session Rating of Perceived Exertion (sRPE). External training load was the total distance covered measured by a global positioning systems (GPS) device.Only 37 (34%) of 108 studies reported whether training load had any missing observations. Multiple Imputation using Predicted Mean Matching was the best method of handling missing data across multiple scenarios.Studies of training load and injury risk should report the extent of missing data, and how they are handled. Multiple Imputation with Predicted Mean Matching should be used when imputing sRPE and GPS variables.

IntroductionPrevious studies showed that the Nordic hamstring exercise (NHE) effectively prevents primary hamstring injury. However, no study investigated the secondary preventing effect of the NHE on hamstring reinjury. The primary purpose of this study is to investigate the effectiveness of the NHE for preventing hamstring reinjury after return to play (RTP) following a hamstring injury in football players. The secondary purpose is to determine the effect of the NHE on sprint and jump performance.Methods and analysisThis is an international multicentre, prospective, parallel-group randomised controlled trial study. Subjects include male or female football players aged 18–40 years and within 1 week of RTP following a hamstring injury will be randomised into Nordics or a control group. Subjects in both groups continue their regular football training, but the Nordics group will perform an additional NHE programme. An online questionnaire will be sent to the subjects in both groups once per week within the first 10 weeks, then continued at months 6, 9 and 12. In a (performance) substudy, we will evaluate the effect of the NHE on sprint and vertical jump performance at three time points (at the beginning of the study, after 10 weeks and 12 months of follow-up).The primary outcomes are the incidence of hamstring reinjury within 2 and 12 months. The secondary outcomes are sprint and jump performance, adherence to the programme, duration of reinjury and reinjury burden.Ethics and disseminationThis study is approved by the medical ethics committee of Amsterdam University Medical Center (UMC) in the Netherlands (METC 2021_117), Faculty of Medicine Universitas Gadjah Mada in Indonesia (KE/FK/1248/EC/2021), Norwegian School of Sport Sciences in Norway (number 216–2 70 122) and Denmark (ethical submission in process). The study’s findings will be disseminated in scientific peer-reviewed journals and presented at international conferences.Trial registration numberNL9711.

To investigate whether the relationship between the acute-chronic workload ratio (ACWR) and health problems varies when different methodological approaches are used to quantify it.Prospective cohort study.An online questionnaire was used to collect daily health and training information from 86 elite youth footballers for 105 days. The relationship between players' training load and health was analyzed using a range of different definitions of ACWR and health problems. We used 21-day and 28-day chronic periods, coupled and uncoupled calculations, and the exponentially weighted moving average and rolling average. Acute-chronic workload ratio data were categorized as low, medium, or high, using predefined categories andWe recorded 6250 athlete-days and 196 health problems. Of the 108 analyses performed, 23 (21%) identified a statistically significant (The relationship between the ACWR and health problems was dependent on methodological approach.

Non-contact lower limb injuries are common in academy football. Yet, the impact these injuries have on strength development in academy footballers remains unclear. This study aimed to investigate the impact of non-contact lower limb injury on hip, groin, and knee flexor strength development in male academy youth footballers. Furthermore, this study: reports normative strength data of emerging field-based tests that can be easily deployed in football academies; explores the effect of age on injury occurrence; and highlights the number of days lost from injury in male youth footballers. Assessments of hip adductor, abductor, and eccentric knee flexor strength were obtained from 195 academy football players during pre-season and at the end of season. In-season injuries were recorded by medical staff. Those footballers who sustained non-contact lower limb injury were compared with those who did not sustain a non-contact lower limb injury. No between-group differences were observed for any strength assessments when controlled for pre-season measures. Stronger footballers at pre-season experienced strength loses, while those weaker players gained strength across the season. Hip strength development was impaired in older age group footballers. Sustaining a non-contact lower limb injury had minimal impact on strength development. In the absence of in-season lower limb strength monitoring, development in academy youth footballers may not progress as expected, and in particular, stronger and older youth athletes may benefit from individualized strength training.

Purpose: To investigate within-player effect, between-player effect, and individual response of external training load from player tracking devices on session rating of perceived exertion training load (sRPE-TL) in elite football players. Methods: The authors collected sRPE-TL from 18 outfield players in 21 training sessions. Total distance, high-speed running distance (>14.4 m/s), very high-speed running distance (>19.8 m/s), PlayerLoad™, PlayerLoad2D™, and high-intensity events (HIE > 1.5, HIE > 2.5, and HIE > 3.5 m/s) were extracted from the tracking devices. The authors modeled within-player and between-player effects of single external load variables on sRPE-TL, and multiple levels of variability, using a linear mixed model. The effect of 2 SDs of external load on sRPE-TL was evaluated with magnitude-based inferences. Results: Total distance, PlayerLoad™, PlayerLoad2D™, and HIE > 1.5 had most likely substantial within-player effects on sRPE-TL (100%–106%, very large effect sizes). Moreover, the authors observed likely substantial between-player effects (12%–19%, small to moderate effect sizes) from the majority of the external load variables and likely to very likely substantial individual responses of PlayerLoad™, high-speed running distance, very high-speed running distance, and HIE > 1.5 (19%–30% coefficient of variation, moderate to large effect sizes). Finally, sRPE-TL showed large to very large between-session variability with all external load variables. Conclusions: External load variables with low intensity-thresholds had the strongest relationship with sRPE-TL. Furthermore, the between-player effect of external load and the individual response to external load advocate for monitoring sRPE-TL in addition to external load. Finally, the large between-session variability in sRPE-TL demonstrates that substantial amounts of sRPE-TL in training sessions are not explained by single external load variables.

To explore the short-term effects of accidental head impacts and repetitive headers on circulating microRNAs, accounting for the effects of high-intensity exercise alone. Blood samples were collected from professional soccer players at rest. Repeat samples were drawn 1 h and 12 h after three conditions: (1) accidental head impacts in a match, (2) repetitive headers during training, and (3) high-intensity exercise. 89 samples were screened to detect microRNAs expressed after each exposure. Identified microRNAs were then validated in 98 samples to determine consistently deregulated microRNAs. Deregulated microRNAs were further explored using bioinformatics to identify target genes and characterize their involvement in biological pathways. Accidental head impacts led to deregulation of eight microRNAs that were unaffected by high-intensity exercise; target genes were linked to 12 specific signaling pathways, primarily regulating chromatin organization, Hedgehog and Wnt signaling. Repetitive headers led to deregulation of six microRNAs that were unaffected by high-intensity exercise; target genes were linked to one specific signaling pathway (TGF-β). High-intensity exercise led to deregulation of seven microRNAs; target genes were linked to 31 specific signaling pathways. We identified microRNAs specific to accidental head impacts and repetitive headers in soccer, potentially being useful as brain injury biomarkers.

ObjectivesDetermine how to assess the cumulative effect of training load on the risk of injury or health problems in team sports.MethodsFirst, we performed a simulation based on a Norwegian Premier League male football dataset (n players=36). Training load was sampled from daily session rating of perceived exertion (sRPE). Different scenarios of the effect of sRPE on injury risk and the effect of relative sRPE on injury risk were simulated. These scenarios assumed that the probability of injury was the result of training load exposures over the previous 4 weeks. We compared seven different methods of modelling training load in their ability to model the simulated relationship. We then used the most accurate method, the distributed lag non-linear model (DLNM), to analyse data from Norwegian youth elite handball players (no. of players=205, no. of health problems=471) to illustrate how assessing the cumulative effect of training load can be done in practice.ResultsDLNM was the only method that accurately modelled the simulated relationships between training load and injury risk. In the handball example, DLNM could show the cumulative effect of training load and how much training load affected health problem risk depending on the distance in time since the training load exposure.ConclusionDLNM can be used to assess the cumulative effect of training load on injury risk.

Top-level football referees take decisions during strenuous physical activity, and often under great mental pressure. Despite their central role in a football match, little is known about referees' health problems, particularly in female referees.To investigate the prevalence and burden of health problems in female and male top-level referees.Prospective cohort study.Fifty-five Norwegian male and female top-level referees reported health problems (injuries and illnesses) in pre-season and during the 2020 competitive season, using the Oslo Sports Trauma Research Center Questionnaire on Health Problems (OSTRC-H2).We recorded data for 49 weeks with a compliance of 98%. On average, 34% (95% CI 31-36%) of referees reported at least one health problem each week, and 20% (95% CI 19-22%) reported substantial health problems. Female referees reported more health problems than male referees, and on-field referees reported more health problems than assistant referees. Gradual-onset injuries were most prevalent and caused the greatest absence from training and matches, whereas illnesses represented only a small portion to the overall burden of health problems. The injury incidence was three injuries per athlete-year (95% CI 2.5-3.5) and 11 injuries per 1000 match hours (95% CI 7-18). The illness incidence was 1.4 illnesses per athlete-year (95% CI 1.1-1.8). Injuries to the lower legs and feet represented the highest burden of health problems.Top-level referees, especially females, reported a high prevalence of health problems. Gradual-onset injuries to the lower leg and foot represented the highest injury burden.

Background The Adductor Strengthening Programme (ASP) is the first groin specific prevention programme proven to reduce the risk of groin problems in male football. Widespread dissemination of the programme and its preventative effect is recommended, however, successful implementation require researchers acquiring comprehensive knowledge of the implementation context. Using the Reach Effectiveness Adoption Implementation Maintenance (RE-AIM) framework is recommended for this procedure. Objectives First, to investigate delivery agents’ attitudes, beliefs, and behaviour regarding the ASP using the RE-AIM framework. Second, to present a ‘best practice’ protocol based on the reported usage of the ASP in a professional team setting. Design Descriptive cross-sectional. Setting Norwegian male professional football teams. Participants The primary delivery agent of injury prevention exercise programmes in each team (n=32). Intervention Survey using a pilot tested questionnaire. Results Twenty-nine (91%) participants responded. All respondents (100%) were familiar with the ASP and its potential to mitigate the burden of groin problems. All delivery agents (100%) adopted the ASP, however, only 10% used it in accordance with the evidence-based protocol. The main modifications were that players in 72% of the teams were instructed to perform a non-progressive number of repetitions during pre-season, and 86% of the teams performed more sets, but fewer repetitions per set during in-season. In total, 97% of delivery agents planned to continue using the ASP in the subsequent season. The two most stated reasons for using the ASP, were first, its documented injury preventive effect and second, that it doesn’t require any additional equipment. Conclusion The delivery agents had positive attitudes and beliefs to the ASP. Moreover, they widely adopted and planned to maintain its usage in the next season. Most of the delivery agents modified the original ASP protocol, which warrant further investigations.

Background Top-level football referees make decisions during strenuous physical activity and often under great mental pressure. Despite their central role in a football match, little is known about referees’ health problems, particularly female referees. Objective To investigate the prevalence and burden of health problems in female and male top-level football referees. Design Prospective cohort study. Setting Female and male referees from the Norwegian female and male top divisions. Patients (or Participants) All top-level referees (n=55) were included in this study. Interventions (or Assessment of Risk Factors) Referees reported health problems (injuries and illnesses) through text messages for 49 weeks using the Oslo Sports Trauma Research Center Questionnaire on Health Problems (OSTRC-H2). Main Outcome Measurements Prevalence of all health problems. Results On average, 34% (95% CI 31–36%) of referees reported at least one health problem each week, and 20% (95% CI 19–22%) reported substantial health problems. The compliance was 98.1%. The injury incidence was 3 injuries per athlete-year (95% CI 2.5 to 3.5) and 12 injuries per 1000 match hours (95% CI 7 to 19). Gradual-onset injuries were most prevalent, with an average weekly prevalence of 23%, and caused the greatest absence from training and matches (60% of total time loss). Of the 156 reported injuries, 36% were related to the lower-leg and foot. Illnesses represented a small portion of the overall burden of health problems. Female referees reported more health problems than male referees, and on-field referees reported more health problems than assistant referees. Conclusions Top- level referees reported a high prevalence of health problems during one full season. Gradual onset injuries to the lower-leg and foot represented the highest injury burden, especially in female referees.

ObjectivesGroin injuries represent a substantial problem in male football, with the Adductor Strengthening Programme (ASP) being the only exercise programme demonstrated to significantly reduce the risk of groin problems. We aimed first, to use the Reach Adoption Effectiveness Implementation Maintenance (RE-AIM) framework to investigate attitudes, beliefs and behaviour to the ASP among primary delivery agents of injury prevention exercises in Norwegian male professional football teams. Second, we aimed to identify a real-world application of the ASP protocol used in a professional team setting.DesignA descriptive cross-sectional survey, using a questionnaire designed to cover all five dimensions of the RE-AIM framework.SettingThe top two divisions of Norwegian male professional football.Participants32 primary injury prevention delivery agents.Primary and secondary outcome measuresPrimarily, the proportion of respondents being aware of the ASP and its effect; having adopted it; having implemented it as intended; and considering maintaining using it. Secondary, the most often used ASP modifications.ResultsTwenty-nine (91%) participants responded. All (100%) respondents were aware of the ASP and its injury preventive effect. The two most stated reasons for using the ASP were its injury preventive effect and that it does not require equipment. The ASP was adopted by all (100%) delivery agents, but only 10% used it in accordance with the original protocol. The main modifications were that the players in 72% of the teams were instructed to perform a non-progressive number of repetitions during pre-season, and in 86% of the teams instructed to perform more sets, but fewer repetitions per set, during in season. In total, 97% of the delivery agents planned to continue using the ASP.ConclusionThe delivery agents have positive attitudes and beliefs to the ASP, but they frequently modify it. We identified and reported a real-world application of the ASP protocol.

Purpose Return-to-play (RTP) is an on-going challenge in professional football. Return-to-play related research is increasing. However, it is unknown to what extent the recommendations presented within research are being implemented by professional football teams, and where there are gaps between research and practice. The purposes of this study were (1) to determine if premier-league football teams worldwide follow a RTP continuum, (2) to identify RTP criteria used and (3) to understand how RTP decision-making occurs in applied practice. Methods We sent a structured online survey to practitioners responsible for the RTP programme in 310 professional teams from 34 premier-leagues worldwide. The survey comprised four sections, based on hamstring muscle injury: (1) criteria used throughout RTP phases, (2) the frequency with which progression criteria were achieved, (3) RTP decision-making process and (4) challenges to decision-making. Results One-hundred and thirty-one teams responded with a completed survey (42%). One-hundred and twenty-four teams (95%) used a continuum to guide RTP, assessing a combination of clinical, functional and psychological criteria to inform decisions to progress. One-hundred and five (80%) teams reported using a shared decision-making approach considering the input of multiple stakeholders. Team hierarchy, match- and player-related factors were common challenges perceived to influence decision-making. Conclusions General research recommendations for RTP and the beliefs and practices of practitioners appear to match with, the majority of teams assessing functional, clinical and psychological criteria throughout a RTP continuum to inform decision-making which is also shared among key stakeholders. However, specific criteria, metrics and thresholds used, and the specific involvement, dynamics and interactions of staff during decision-making are not clear.

Groin injuries represent a considerable problem in male football, accounting for 4%‐19% of all time‐loss injuries. The Adductor Strengthening Programme is the first groin‐specific prevention program shown to reduce the risk of groin problems. We aimed to use the RE‐AIM framework to examine the players’ experiences with the implementation of the program and player attitude toward groin injury prevention in football. Of the 632 players involved in the trial examining the effect of the Adductor Strengthening Programme, 501 agreed to participate in a survey at the end of the season. Most players thought that footballers are at moderate to high risk for groin injuries (87%) and that there is a need for preventive measures (96%). They also believed that a preventive program with strengthening exercises would reduce the risk of groin injuries (91%). Majority of the players reported using

Background: Wearable sensor systems have the potential to quantify head kinematic responses of head impacts in soccer. However, on-field use of sensors (eg, accelerometers) remains challenging, owing to poor coupling to the head and difficulties discriminating low-severity direct head impacts from inertial loading of the head from human movements, such as jumping and landing. Purpose: To test the validity of an in-ear sensor for quantifying head impacts in youth soccer. Study Design: Descriptive laboratory study. Methods: First, the sensor was mounted to a Hybrid III headform and impacted with a linear impactor or a soccer ball. Peak linear acceleration (PLA), peak rotational acceleration (PRA), and peak rotational velocity (PRV) were obtained from both systems; random and systematic errors were calculated with Hybrid III as reference. Then, 6 youth soccer players wore sensors and performed a structured training protocol, including heading and nonheading exercises; they also completed 2 regular soccer sessions. For each accelerative event recorded, PLA, PRA, and PRV outputs were compared with video recordings. Receiver operating characteristic curves were used to determine the sensor’s discriminatory capacity in both on-field settings, establishing cutoff values for predicting outcomes. Results: For the laboratory tests, the random error was 11% for PLA, 20% for PRA, and 5% for PRV; the systematic error was 11%, 19%, and 5%, respectively. For the structured training protocol, heading events resulted in higher absolute values (PLA = 15.6 g± 11.8 g) than nonheading events (PLA = 4.6 g± 1.2 g); the area under the curve was 0.98 for PLA. In regular training sessions, the area under the curve was >0.99 for PLA. A 9 g cutoff value yielded a positive predictive value of 100% in the structured training protocol versus 65% in the regular soccer sessions. Conclusion: The in-ear sensor displayed considerable random error and substantially overestimated head impact exposure. Despite the sensor’s excellent on-field accuracy for discriminating headings from other accelerative events in youth soccer, absolute values must be interpreted with caution, and there is a need for secondary means of verification (eg, video analysis) in real-life settings. Clinical Relevance: Wearable sensor systems can potentially provide valuable insights into head impact exposures in contact sports, but their limitations require careful consideration.

BackgroundIn a recent randomised controlled trial, we found that a commonly used training load management approach was not effective in preventing injuries and illnesses in Norwegian elite youth footballers.AimTo investigate players’ and coaches’ barriers and facilitators to a load management approach to prevent injuries and illnesses and their attitudes and beliefs of load management and injuries and illnesses in general.MethodsWe asked players and coaches about their views on injury risk in football, the benefits and limitations of load management in general and implementation of load management in football. The questionnaires used were based on similar studies using the Reach, Effectiveness, Adoption, Implementation and Maintenance framework.ResultsWe recorded answers from 250 players and 17 coaches. Most players (88%) reported that scientific evidence showing improved performance from the intervention measures is a key facilitator to completing the intervention. Similarly, coaches reported that the most important facilitator was scientific evidence that the preventive measures were effective (100%). Players reported that the coach’s attitude to preventive measures was important (86%), and similarly, 88% of coaches reported that the player’s attitude was important.ConclusionsBy having a mutual positive attitude towards the intervention, players and coaches can positively contribute to each other’s motivation and compliance. Both players and coaches reported scientific evidence for load management having injury-preventive and performance-enhancing effect and being time efficient as important facilitators.Trial registration numberTrial registration number

ObjectivesTo determine whether the relationship between training load and injury risk is non-linear and investigate ways of handling non-linearity.MethodsWe analysed daily training load and injury data from three cohorts: Norwegian elite U-19 football (n=81, 55% male, mean age 17 years (SD 1)), Norwegian Premier League football (n=36, 100% male, mean age 26 years (SD 4)) and elite youth handball (n=205, 36% male, mean age 17 years (SD 1)). The relationship between session rating of perceived exertion (sRPE) and probability of injury was estimated with restricted cubic splines in mixed-effects logistic regression models. Simulations were carried out to compare the ability of seven methods to model non-linear relationships, using visualisations, root-mean-squared error and coverage of prediction intervals as performance metrics.ResultsNo relationships were identified in the football cohorts; however, a J-shaped relationship was found between sRPE and the probability of injury on the same day for elite youth handball players (pConclusionThe relationship between training load and injury risk should be assumed to be non-linear. Future research should apply appropriate methods to account for non-linearity, such as fractional polynomials or restricted cubic splines. We propose a guide for which method(s) to use in a range of different situations.

BackgroundThe COVID-19 pandemic forces sport and exercise medicine (SEM) physicians to think differently about the clinical care of patients. Many rapidly implement eHealth and telemedicine solutions specific to SEM without guidance on how best to provide these services.AimThe aim of this paper is to present some guiding principles on how to plan for and perform an SEM consultation remotely (teleSEM) based on a narrative review of the literature. A secondary aim is to develop a generic teleSEM injury template.ResultseHealth and telemedicine are essential solutions to effective remote patient care, also in SEM. This paper provides guidance for wise planning and delivery of teleSEM. It is crucial for SEM physicians, technology providers and organisations to codesign teleSEM services, ideally involving athletes, coaches and other clinicians involved in the clinical care of athletes, and to gradually implement these services with appropriate support and education.ConclusionteleSEM provides solutions for remote athlete clinical care during and after the COVID-19 pandemic. We define two new terms—eSEM and teleSEM and discuss guiding principles on how to plan for and perform SEM consultations remotely (teleSEM). We provide an example of a generic teleSEM injury assessment guide.

Conducting field-based strength assessments is embedded within football academy development processes. Yet, there is a limited understanding of how hip and groin strength assessments relate to vital game-based tasks such as sprinting and change of direction (COD) performance. Our aim was to explore field-based strength assessments and their relationships with both sprint and COD performance in male academy footballers. Participants (n = 146; age 14.2 ± 2.2 years; stature 166.3 ± 15.4 cm; body mass 55.6 ± 15.6 kg) performed maximal countermovement jump (CMJ), Nordic hamstring strength (NHS), isometric hip adductor (ADD)/abductor (ABD), 5 m, 10 m, 20 m sprints, and modified 505 agility test. All strength measures were allometrically scaled to account for body weight. Between-limb differences were reported as imbalance scores. Principal component analysis reduced sprint and COD variables to a single "running ability" component score. Scaled strength and imbalance, when controlled for age, were associated with "running ability" (adjusted R2 = 0.78, p

BackgroundThe acute:chronic workload ratio (ACWR) is commonly used to manage training load in sports, particularly to reduce injury risk. However, despite its extensive application as a prevention intervention, the effectiveness of load management using ACWR has never been evaluated in an experimental study.AimTo evaluate the effectiveness of a load management intervention designed to reduce the prevalence of health problems among elite youth football players of both sexes.MethodsWe cluster-randomised 34 elite youth football teams (16 females, 18 males) to an intervention group (18 teams) and a control group (16 teams). Intervention group coaches planned all training based on published ACWR load management principles using a commercially available athlete management system for a complete 10-month season. Control group coaches continued to plan training as normal. The prevalence of health problems was measured monthly in both groups using the Oslo Sports Trauma Research Centre Questionnaire on Health Problems.ResultsThe between-group difference in health problem prevalence (primary outcome) was 1.8%-points (−4.1 to 7.7 %-points; p=0.55) with no reduction in the likelihood of reporting a health problem in the intervention group (relative risk 1.01 (95% CI 0.91 to 1.12); p=0.84) compared with the control group.ConclusionsWe observed no between-group difference, suggesting that this specific load management intervention was not successful in preventing health problems in elite youth footballers.Trial registration numberISRCTN18177140.

Introduction: Blood-based biomarkers can provide valuable information on the effects of repetitive head impacts in sports. This study investigated if repetitive headers or accidental head impacts in soccer could cause structural brain injury, detected as an increase in serum neurofilament light (NfL) or tau. Methods: NfL and tau were measured in professional soccer players in pre-season. Then, the effect of three short-term exposures on biomarker levels was assessed: (1) high-intensity exercise, (2) repetitive headers, and (3) head impacts in a match. Results: We analyzed 354 samples and observed no effects on NfL from any of the three short-term exposures. Tau levels rose significantly from baseline to 1 h after (1) high-intensity exercise (Δ0.50 pg/ mL, 95% CI 0.19–0.81, p < .01); the same was observed after (2) repetitive headers (Δ0.29 pg/mL, 95% CI 0.10–0.48, p < .01), but not after (3) accidental head-impact incidents (Δ0.36 pg/mL, 95% CI −0.02–0.74, p = .06). The highest absolute values were seen 1 h after high-intensity exercise (mean±SD, 1.92 ± 0.83 pg/mL). Conclusion: NfL and tau in serum were unaffected by head impacts in soccer. Importantly, tau levels seem to rise in response to exercise, emphasizing the need for control groups. Our findings highlight important characteristics and limitations when using these biomarkers in sports.

IntroductionTransitioning out of professional football is a challenging time in most players’ lives. During these preretirement and postretirement years, professional footballers may struggle with their mental, musculoskeletal, neurocognitive and cardiovascular health. Currently, longitudinal data about these health conditions are lacking. This article presents the design of a prospective cohort study with the primary aim of gathering epidemiological evidence about the onset and course of mental, musculoskeletal, neurocognitive and cardiovascular health conditions in professional footballers during their preretirement and postretirement years and evaluating the associations between risk indicators and the health conditions under study in these players.Methods and analysisAn observational prospective cohort study with repeated measurements over a follow-up period of 10 years will be conducted among at least 200 professional footballers (male; 27 (±1) years old). Mental health will be explored by assessing symptoms of distress, anxiety, depression, sleep disturbance, alcohol misuse, drug misuse and disordered eating. Musculoskeletal health will be explored by assessing severe joint injury and related surgery, clinical and radiological osteoarthritis, and joint function (hips, knees and ankles). Neurocognitive health will be explored by assessing the concussion, brain structure and functioning, and neurocognitive functioning. Cardiovascular health will be explored by assessing blood pressure, lipid profile and ECG abnormalities.Ethics and disseminationEthical approval for the study was provided by the Medical Ethics Review Committee of the Amsterdam University Medical Centers. The results of the study will be submitted to peer-reviewed journals, will be presented at scientific conferences and will be released in the media (postpublication).Trial registration numberThe Dutch Trial Registry (Drake Football Study NL7999).

At a young age, high-level youth footballers enter structured practice where they engage in regular training and matches. The academy system is considered fundamental to a young footballer's tactical, technical and physical development. Yet, with regular training and matches, high-level youth footballers may be exposed to the risk of injury.This systematic review analyses and summarises published scientific information on high-level youth football injury characteristics and calculates the risk of them sustaining an injury over the course of a typical season.The search was performed using the Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) guidelines. Of the 1346 studies found, 23 fulfilled the inclusion criteria.Quality assurance scores for the selected research articles ranged between two and five out of eight. A high degree of heterogeneity between studies was observed. The probability of sustaining a time-loss injury during a high-level youth season ranged between 1% and 96% for under 9- to under 16-year age groups and 50% and 91% for under 18- to under 21-year age groups. Pooled estimates for total (training and match) incidence per 1000 h was 5.8 for youth players aged under 9 to under 21 years, 7.9 for older players (under 17-under 21 years) and 3.7 for younger aged players (under 9-under 16 years). Training injury incidence rate ranged from 0.69 to 7.9 per 1000 h for all age groups in youth football. Match injury incidence rate for high-level youth players ranged from 0.4 to 80.0 per 1000 h. Close to one-fifth (18%) of all high-level youth football injuries were classified as severe and required 28 days recovery time. Muscle strain injury accounted for 37% of all injuries reported in youth football. High probabilities ( 90%) of sustaining a time-loss injury over one typical high-level football season were found.High-level youth players lose large portions of the seasonal development to injury, with players seemingly suffering long absences from training and matches, consequently affecting health and well-being and possibly burdening club/parental finances and healthcare systems.

Introduction Wearable sensor systems may be useful for measuring head-impact exposure. Here, we tested the validity of in-ear sensors developed to improve head coupling. Methods First, the sensor was mounted to a Hybrid III headform (HIII) and impacted with a linear impactor or football. Peak linear acceleration (PLA), peak rotational acceleration (PRA) and peak rotational velocity (PRV) were obtained from both systems; random and systematic error were calculated using HIII as reference. Then, six youth football players wore sensors and performed a structured training protocol including heading and non-heading exercises; they also completed two regular football sessions. For each accelerative event recorded, PLA, PRA and PRV outputs were compared to video recordings. Receiver operating characteristic curves were used to determine the sensor’s discriminatory capacity in both on-field settings, determining cut-off values for predicting outcomes. Results For the laboratory tests, the random error was 11% for PLA, 20% for PRA and 5% for PRV, respectively; the systematic error was 11%, 19% and 5%. For the structured training protocol, heading events yielded higher absolute values (PLA=15.6±11.8 g) than non-heading events (PLA=4.6±1.2 g); the area under the curve (AUC) was 0.98 for PLA. In regular training sessions, AUC was >0.99 for PLA. A 9 g cut-off value yielded a positive predictive value of 100% in the structured training protocol, compared to only 65% in regular football sessions. Conclusion The sensor displayed systematic overestimation with considerable random error. Despite excellent on-field accuracy for discriminating head-impacts from other accelerative events, secondary means of verifying events are still necessary.

Introduction Wearable sensor systems may be useful for measuring head-impact exposure. Here, we tested the validity of in-ear sensors developed to improve head coupling. Methods First, the sensor was mounted to a Hybrid III headform (HIII) and impacted with a linear impactor or football. Peak linear acceleration (PLA), peak rotational acceleration (PRA) and peak rotational velocity (PRV) were obtained from both systems; random and systematic error were calculated using HIII as reference. Then, six youth football players wore sensors and performed a structured training protocol including heading and non-heading exercises; they also completed two regular football sessions. For each accelerative event recorded, PLA, PRA and PRV outputs were compared to video recordings. Receiver operating characteristic curves were used to determine the sensor’s discriminatory capacity in both on-field settings, determining cut-off values for predicting outcomes. Results For the laboratory tests, the random error was 11% for PLA, 20% for PRA and 5% for PRV, respectively; the systematic error was 11%, 19% and 5%. For the structured training protocol, heading events yielded higher absolute values (PLA=15.6±11.8 g) than non-heading events (PLA=4.6±1.2 g); the area under the curve (AUC) was 0.98 for PLA. In regular training sessions, AUC was >0.99 for PLA. A 9 g cut-off value yielded a positive predictive value of 100% in the structured training protocol, compared to only 65% in regular football sessions. Conclusion The sensor displayed systematic overestimation with considerable random error. Despite excellent on-field accuracy for discriminating head-impacts from other accelerative events, secondary means of verifying events are still necessary.

Restrictions on heading in youth football have been implemented in some countries to limit head impact exposure. However, current interventions remain poorly guided by evidence. Our objective was to quantify heading exposure in youth football, assessing the effects of sex and age. Football matches played during an international youth football tournament with no heading restrictions were directly observed, including players from both sexes (11‐19 years). The elite senior level was included for comparison, using video analysis. All heading events were registered, classified, and assigned to individual players. Heading rates were calculated for each sex and age group. We observed a total of 267 matches, corresponding to 4011 player hours (1927 player hours for females, 2083 player hours for males). Males headed more frequently than females (2.7 vs 1.8 headers/player hour; P

Background There are limited data on the nature, type and incidence of illness in football. Previous studies indicate that gastrointestinal and respiratory tract illnesses are most common. Aim To describe the incidence and burden of illness in male professional football. Methods Over the 4-year study period, 2011–2014, 73 professional football teams in Europe participated, with a total of 1 261 367 player-days recorded. All time-loss illnesses were recorded by the medical staff of each club. A recordable illness episode was any physical or psychological symptom (not related to injury) that resulted in the player being unable to participate fully in training or match play. Results A total of 1914 illness episodes were recorded. The illness incidence was 1.5 per 1000 player-days, meaning that, on average, a player experienced an illness episode every second season, with a median of 3 days absence per illness episode. Severe illness (absence >4 weeks) constituted 2% of all illnesses. Respiratory tract illness was the most common (58%), followed by gastrointestinal illness (38%). Respiratory tract illness, gastrointestinal illness and cardiovascular illness caused the highest illness burden. Conclusions The illness incidence among male professional football players is low compared with the injury incidence. We found that the highest illness burden was caused by illness to the respiratory tract, gastrointestinal tract and cardiovascular system.

Controlled laboratory study; cross-sectional.To investigate the relationship among anatomical variables, knee laxity, muscle strength, and peak knee valgus angles during a vertical drop-jump landing task.Excessive knee valgus has been associated with anterior cruciate ligament injury in females; however, the influence of anatomical characteristics, knee laxity, and muscle strength on frontal plane knee motion is not completely understood.Norwegian elite female soccer players (n = 279; mean ± SD age, 21 ± 4 years; height, 167 ± 6 cm; body mass, 63 ± 7 kg) were evaluated from 2009 through 2012. The evaluation included 3-D motion analysis of a vertical drop jump, anatomical measures (height, static knee valgus, leg length, and static foot posture), knee laxity, and muscle strength (quadriceps, hamstrings, and hip abductors). Multiple linear regression analyses were used to investigate the relationships among anatomical characteristics, knee laxity, muscle strength, and peak knee valgus angles.Anatomical characteristics explained 11% of the variance in peak knee valgus angles (P.001), with height and static knee valgus being significant predictors.Greater body height and static knee valgus were associated with greater peak knee valgus angles during a vertical drop-jump landing task. However, these variables only explained 11% of the variance in peak knee valgus.

Groin injuries represent a considerable problem in male football, accounting for 4% to 19% of all time-loss injuries.1 At the elite level, 14% to 17% of all players incur a groin injury causing time-loss each season.2 During a period with match congestion, 59% of men reported at least one episode with 37 …

BackgroundPreparticipation cardiac screening of athletes aims to detect cardiovascular disease at an early stage to prevent sudden cardiac arrests and deaths. Few studies have described the cardiovascular outcomes in athletes classified as negative on screening.ObjectiveTo identify cardiovascular incidents in a cohort of male professional football players who were cleared to play after a negative screening result.MethodsThis is a retrospective 8-year follow-up study of 595 professional male football players in Norway who underwent preparticipation cardiac screening by experienced cardiologists, including electrocardiography (ECG) and echocardiography, in 2008. We performed a media search to identify sudden cardiovascular incidents between January 2008 and February 2016. Incidents were cross-checked with medical records.ResultsSix of the 595 players (1%), all classified as negative on cardiac screening, experienced severe cardiovascular incidents during follow-up. Retrospective review revealed abnormal ECG findings in one case, not recognised at the time of screening. Three players suffered a sudden cardiac arrest (all resuscitated successfully), one a myocardial infarction, one a transient ischaemic attack and one atrial flutter. Three of the players ignored chest pain, paresis, dyspnoea or near-syncope, two completed a match with symptoms before seeking medical assistance, one player’s symptoms were misinterpreted and received inappropriate treatment initially, and two players were discharged from hospital without proper follow-up, despite having serious cardiovascular symptoms.ConclusionsA comprehensive preparticipation cardiac screening did not identify a subset of 6 of 595 players who experienced subsequent cardiovascular incidents as being at risk. It is important to remind athletes that a normal cardiac screening exam does not protect against all cardiac diseases. Timely reporting of symptoms is essential.

What’s cutting edge in sports medicine?, Norway, februar 2, 2018, 16:45 – 18:00. Introduction Groin problems are highly prevalent in male football players. Previous groin-specific prevention programs have shown no effect on groin injury rates. However, a single-exercise approach targeting hip adduction strength has not been tested previously. Aim Evaluate the effect of a single-exercise approach, based on the Copenhagen Adduction exercise, to reduce the high prevalence of groin problems in male players. Materials and methods 35 semi-professional Norwegian senior football teams were cluster-randomised (18 teams, 339 players in the intervention group, 17 teams 313 players in the control group) and followed for 1 full season. An adductor strengthening programme, with three progression levels, was introduced to the intervention group to perform 3 times weekly during pre-season and once weekly during the competitive season. The main outcome measure, prevalence of groin problems, was measured weekly for 28 weeks during the competitive season using the Oslo Sports Trauma Research Centre Overuse Injury Questionnaire. Result The average prevalence of groin problems during the season was 13.5% (95% CI: 12.3% to 14.7%) in the intervention group, and 21.3% (95% CI: 20.0% to 22.6%) in the control group. This corresponds to a 41% (OR 0.59, 95% CI: 0.40 to 0.86, p=0.008) lower risk of reporting groin problems for players performing the adductor strengthening programme. Conclusion The adductor strengthening programme reduced the prevalence and risk of groin problems among male football players, and should therefore be implemented in male football teams.

ObjectiveThis review aims to analyse strength training-based sports injury prevention randomised controlled trials (RCT) and present best evidence recommendations for athletes and future research. A priori PROSPERO registration; CRD42015006970.DesignSystematic review, qualitative analysis and meta-analysis. Sorting of studies and quality assessments were performed by two independent authors. Qualitative analyses, relative risk (RR) estimate with robustness and strength of evidence tests, formal tests of publication bias and post-hoc meta-regression were performed.Data sourcesPubMed, Embase, Web of Science and SPORTDiscus were searched to July 2017.Eligibility criteria for selecting studiesRCTs on strength training exercises as primary prevention of sports injuries.ResultsSix studies analysed five different interventions with four distinct outcomes. 7738 participants aged 12–40 years were included and sustained 177 acute or overuse injuries. Studies were published in 2003–2016, five from Europe and one from Africa. Cluster-adjusted intention-to-treat analysis established RR 0.338 (0.238–0.480). The result was consistent across robustness tests and strength of evidence was high. A 10% increase in strength training volume reduced the risk of injury by more than four percentage points. Formal tests found no publication bias.ConclusionThe included studies were generally well designed and executed, had high compliance rates, were safe, and attained consistently favourable results across four different acute and overuse injury outcomes despite considerable differences in populations and interventions. Increasing strength training volume and intensity were associated with sports injury risk reduction. Three characteristically different approaches to prevention mechanisms were identified and incorporated into contemporary strength training recommendations.