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The effect of ball characteristics on head impact magnitude during purposeful heading in adolescent male and female football players
... Considering the findings from the study, coaches must promote safe heading by mastering head-to-ball contact, body positioning and jump, activation of neck muscles, and safe strategies in heading duels (where head-head, head-shoulder, and head-elbow contacts occur) to reduce risk of injury. It is also important to note that there were significant differences in starting standing position [41]. ...
Football promotes mental and physical benefits (cardiovascular, metabolic, musculoskeletal, psychological), and ensures social and emotional health. Purposeful heading is a common practice among football athletes, and rising injury rates have affected adult willingness to allow their children to participate in tackle football. Soccer has recorded a high number of injuries, more than basketball and volleyball, and carries a 1000 times higher risk compared to industrial occupations. Studies undertaken in 2012-2016 recorded that 22% soccer injuries are concussions, as a result of purposeful heading. There is an established link between purposeful heading, neurodegeneration, dementia, and motor impairment. Purposeful heading has a high incidence among youth players. Concussions may cause acute symptoms including blurred visions, loss of hunger, sleep, balance, concentration, and attention. Subconcussive impacts can cause functional and microstructural damage including ionic and metabolic shifts, microstructural damage, and impaired neurotransmission, often undiagnosable. Sometimes, loss of consciousness (LOC) may occur. Concussions can cause Traumatic Brain Injury (TBI), leading to disease, mortality, and morbidity worldwide. Concussion awareness has been rising between 2010-2019. A reduction in head impact exposure (HIE) has been addressed through the design of protective equipment, educational initiatives, and rule changes. Behavioral interventions, neck and trunk strength training, timely care, and the use of computational models are evidence-based interventions. A deeper understanding of the epidemiology of concussions is required to inform primary prevention in respective geographies and targeted age groups. Addressing safety concerns can improve participation. The text covers a Literature Review and Thematic Analysis of Influencing Factors, Consequences, Measurements, and Interventions Related to Heading in Soccer and Football.
It has been documented that up to 22% of all soccer injuries are concussions. This is in part due to players purposely using their head to direct the ball during play. To provide a more complete understanding of head trauma in soccer athletes, this study characterized the effects of four soccer ball characteristics (size, inflation pressure, mass, velocity) on the resulting peak impact force as it relates to the potential for incurring neurophysiological changes. A total of six hundred trials were performed on size 4 and 5 soccer balls as well as a novel lightweight soccer ball. Impact force was measured with a force plate and ball velocity was determined using motion capture. These data were used, in conjunction with dimensional analysis to relate impact force to ball size, mass, velocity, and pressure. Reasonable reductions in allowable ball parameters resulted in a 19.7% decrease in peak impact force. Adjustments to ball parameters could reduce a high cumulative peak translational acceleration soccer athlete down into a previously defined safer low loading range. In addition, it was noted that water absorption by soccer balls can result in masses that substantially increase impact force and quickly surpass the NCAA weight limit for game play. Additional research is required to determine whether varying soccer ball characteristics will enable soccer players to avoid persistent neurophysiological deficits or what additional interventions may be necessary and the legal implications of these data are discussed.
Purpose: To quantify the incidence and characteristics of purposeful headers and unintentional head impacts in football (soccer) in boys’ football over three seasons.
Methods: This retrospective longitudinal study analysed purposeful headers and unintentional head impacts collected over three seasons (under-10 to under-12) using match video analysis from boys’ team in Australia. Total headers and head impacts, as well as incidence rate (IR) per 1000 match-hours for different match characteristics, were calculated.
Results: Total number of headers and heading IR increased significantly (r = 0.99) with age from under-10 (n = 29; IR: 483) to under-12 (n = 149; IR: 1515). All but three players (87%) were observed to head the ball at least once during a season (mean: 10, range 0–25) with the accumulative number of headers performed by out-field players over three seasons ranging from 6 to 40. Players in defensive positions (n = 121) headed the ball more frequently than midfielders (n = 83) or attackers (n = 53). Five (IR: 22) unintentional head impacts were observed, of which four required medical attention.
Conclusion: Although the number of headers performed by young players in under-10 to under-12 age groups was low, the range of headers performed by individuals varied greatly. These results could be used to guide age-specific heading coaching practices.
There are growing concerns about the risk of neurodegenerative diseases associated with heading in football. It is essential to understand the biomechanics of football heading to guide player protection strategies to reduce the severity of the impact. The aim of this study was to assess the effect of football speed, mass and stiffness on the forces experienced during football heading using mathematical and human body computational model simulations. Previous research indicates that a football header can be modelled as a lumped mass mathematical model with elastic contact. Football headers were then reconstructed using a human body modelling approach. Simulations were run by independently varying the football mass, speed and stiffness. Peak contact force experienced by the head was extracted from each simulation. The mathematical and human body computational model simulations indicate that the force experienced by the head was directly proportional to the speed of the ball and directly proportional to the square root of the ball stiffness and mass. Over the practical range of ball speed, mass and stiffness, the force experienced by the head during football heading is mainly influenced by the speed of the ball rather than its mass or stiffness. The findings suggest that it would be more beneficial to develop player protection strategies that aim to reduce the speed at which the ball is travelling when headed by a player. Law changes reducing high ball speeds could be trialled at certain age grades or as a phased introduction to football heading.
Synopsis:
Repeated purposeful heading in soccer has come under increased scrutiny as concerns surrounding the association with long-term neurodegenerative disorders in retired players continues to grow. Whilst a causal link between heading and brain health has not been established, the 'Precautionary Principle' supports the notion that soccer governing bodies and associations should consider implementing pragmatic strategies, which can reduce head impact during purposeful heading in youth soccer whilst this relationship is being investigated. This viewpoint discusses the current evidence to support low-risk head impact reduction strategies during purposeful heading to protect young developing players; and how such strategies could be implemented now while research and debate continues on this topic. J Orthop Sports Phys Ther, Epub 22 May 2020. doi:10.2519/jospt.2020.9680.
To assess the real‐life magnitude of the heading incidence in children’s and youth’ football in eight European countries with different “football cultures” a cross‐sectional observational design, in which one match per team in 480 different teams from eight European countries (2017/18–2018/19) was recorded by video. One training session was recorded in 312 teams. Clubs with Under‐10, Under‐12 (female/male/mixed) and Under‐16 female and male teams were eligible to participate. Heading frequencies and types were analysed. Results are presented as headers per match/training and per team. Incidence rates (IR) per 1000 match/training hours were calculated. Under‐10 teams carried out the lowest average number of headers per match (8.8), followed by Under‐16 female (17.7), Under‐12 (18.4), and Under‐16 male (35.5). Total number of headers per match and team varied between countries. 80% of the total number of headers were single intentional headers, 12% heading duels, 3% unintentional headers by getting hit and 5% others (trends apparent in all age groups). Three head injuries occurred during match play corresponding to an IR of 0.70 (95% CI, 0.23‐2.16). The lowest number of headers per training and team was found in Under‐10 (21.3), followed by Under‐16 females (34.1), Under‐12 (35.8), and Under‐16 males (45.0). In conclusion, this large‐scale study presents novel data about the number and type of headers in youth’ football throughout Europe. A more precise understanding of the heading incidence, specifically in young players, is mandatory for the debate of restrictions on heading in youth football.
Objective:
To systematically review the literature to investigate the potential relationship between neck strength and head acceleration during purposeful heading in soccer.
Design:
Systematic review.
Methods:
Comprehensive search of five electronic databases: EMBASE, MEDLINE, CINAHL, SportsDiscus and Web of Science. Studies were included if they reported data on the relationship between neck strength and head impact and/or acceleration during purposeful soccer heading, published in English (or translation available).
Results:
From an initial search of 1174 potentially eligible papers, five cross-sectional studies met the eligibility criteria for inclusion in this review. Data from cross-sectional studies indicate that higher neck strength is associated with lower head acceleration during purposeful heading in soccer (p=<0.05; r<-0.5).
Conclusion:
This review provides evidence that higher neck strength may lower head acceleration during purposeful heading in soccer. Further research is required to determine the most effective method to strengthen the neck musculature in soccer players.
The importance of well trained and stable neck flexors and exten-sors as well as trunk muscles for intentional headers in soccer is increasingly discussed. The neck flexors and extensors should ensure a coupling of trunk and head at the time of ball contact to increase the physical mass hitting the ball and reduce head acceleration. The aim of the study was to analyze the influence of a 6-week strength training program (neck flexors, neck extensors) on the acceleration of the head during standing, jumping and running headers as well as after fatigue of the trunk muscles on a pendulum header. A total of 33 active male soccer players (20.3 ± 3.6 years, 1.81 ± 0.07 m, 75.5 ± 8.3 kg) participated and formed two training intervention groups (IG1: independent adult team, IG2: independent youth team) and one control group (CG: players from different teams). The training intervention consisted of three exercises for the neck flexors and extensors. The training effects were verified by means of the isometric maximum voluntary contraction (IMVC) measured by a telemetric Noraxon DTS force sensor. The head acceleration during ball contact was determined using a telemetric Noraxon DTS 3D accelerometer. There was no significant change of the IMVC over time between the groups (F=2.265, p=.121). Head acceleration was not reduced significantly for standing (IG1 0.4 ± 2.0, IG2 0..050, p = 0.362) headers as well as after fatigue of the trunk musculature for post-jumping (IG1-0.2 ± 2.1, IG2-0.6 ± 1.4; CG-0.6 ± 1.3; F = 0.184, p = 0.833) and post-running (IG1-0.3 ± 1.6, IG2-0.7 ± 1.2, CG 0.0 ± 1.4; F = 0.695, p = 0.507) headers over time between IG1, IG2 and CG. A 6-week strength training of the neck flexors and neck extensors could not show the presumed preventive benefit. Both the effects of a training intervention and the consequences of an effective intervention for the acceleration of the head while heading seem to be more complex than previously assumed and presumably only come into effect in case of strong impacts.
The present study aimed to investigate time trends of head injuries and their injury mechanisms since a rule change as monitoring may help to identify causes of head injuries and may advance head injury prevention efforts. Based on continuously recorded data from the German football magazine “kicker Sportmagazin®” as well as other media sources, a database of head injuries in the 1st German male Bundesliga was generated comprising 11 seasons (2006/07–2016/17). Injury mechanisms were analysed from video recordings. Injury incidence rates (IR) and 95% confidence intervals (95% CI) were calculated. Time trends were analysed via linear regression. Two hundred thirty-eight match head injuries occurred (IR 1.77/1000 match hours, 95% CI 1.56–2.01). There were no significant seasonal changes, expressed as annual average year-on-year change, in IRs over the 11-year period for total head injuries (p=0.693), facial/head fractures (p=0.455), lacerations/abrasions (p=0.162), and head contusions (p=0.106). The annual average year-on-year increase for concussion was 6.4% (p=0.004). Five head injury mechanisms were identified. There were no seasonal changes in injury mechanisms over the study period. The concussion subcategory increased slightly over the seasons, which may either be a result of increasing match dynamics or raised awareness among team physicians and players.
Much biomedical research is observational. The reporting of such research is often inadequate, which hampers the assessment of its strengths and weaknesses and of a study's generalisability. The Strengthening the Reporting of Observational Studies in Epidemiology (STROBE) initiative developed recommendations on what should be included in an accurate and complete report of an observational study. We defined the scope of the recommendations to cover three main study designs: cohort, case-control, and cross-sectional studies. We convened a 2-day workshop in September, 2004, with methodologists, researchers, and journal editors to draft a che-cklist of items. This list was subsequently revised during several meetings of the coordinating group and in e-mail discussions with the larger group of STROBE contributors, taking into account empirical evidence and methodological considerations. The workshop and the subsequent iterative process of consultation and revision resulted in a checklist of 22 items (the STROBE statement) that relate to the title, abstract, introduction, methods, results, and discussion sections of articles. 18 items are common to all three study designs and four are specific for cohort, case-control, or cross-sectional studies. A detailed explanation and elaboration document is published separately and is freely available on the websites of PLoS Medicine, Annals of Internal Medicine, and Epidemiology. We hope that the STROBE statement will contribute to improving the quality of reporting of observational studies.
Inertial sensors are commonly used to measure human head motion. Some sensors have been tested with dummy or cadaver experiments with mixed results, and methods to evaluate sensors in vivo are lacking. Here we present an in vivo method using high speed video to test teeth-mounted (mouthguard), soft tissue-mounted (skin patch), and headgear-mounted (skull cap) sensors during 6–13 g sagittal soccer head impacts. Sensor coupling to the skull was quantified by displacement from an ear-canal reference. Mouthguard displacements were within video measurement error (<1 mm), while the skin patch and skull cap displaced up to 4 and 13 mm from the ear-canal reference, respectively. We used the mouthguard, which had the least displacement from skull, as the reference to assess 6-degree-of-freedom skin patch and skull cap measurements. Linear and rotational acceleration magnitudes were over-predicted by both the skin patch (with 120% NRMS error for amag, 290% for αmag) and the skull cap (320% NRMS error for amag, 500% for αmag). Such over-predictions were largely due to out-of-plane motion. To model sensor error, we found that in-plane skin patch linear acceleration in the anterior–posterior direction could be modeled by an underdamped viscoelastic system. In summary, the mouthguard showed tighter skull coupling than the other sensor mounting approaches. Furthermore, the in vivo methods presented are valuable for investigating skull acceleration sensor technologies.
The available scientific research regarding injury prevention practices in international football is sparse. The purpose of this study was to quantify current practice with regard to (1) injury prevention of top-level footballers competing in an international tournament, and (2) determine the main challenges and issues faced by practitioners in these national teams.
A survey was administered to physicians of the 32 competing national teams at the FIFA 2014 World Cup. The survey included 4 sections regarding perceptions and practices concerning non-contact injuries: (1) risk factors, (2) screening tests and monitoring tools, (3) preventative strategies and (4) reflection on their experience at the World Cup.
Following responses from all teams (100%), the present study revealed the most important intrinsic (previous injury, accumulated fatigue, agonist:antagonist muscle imbalance) and extrinsic (reduced recovery time, training load prior to and during World Cup, congested fixtures) risk factors during the FIFA 2014 World Cup. The 5 most commonly used tests for risk factors were: flexibility, fitness, joint mobility, balance and strength; monitoring tools commonly used were: medical screen, minutes/matches played, subjective and objective wellness, heart rate and biochemical markers. The 5 most important preventative exercises were: flexibility, core, combined contractions, balance and eccentric.
The present study showed that many of the National football (soccer) teams' injury prevention perceptions and practices follow a coherent approach. There remains, however, a lack of consistent research findings to support some of these perceptions and practices.
Published by the BMJ Publishing Group Limited. For permission to use (where not already granted under a licence) please go to http://group.bmj.com/group/rights-licensing/permissions.
Recently developed methods for power analysis expand the options available for study design. We demonstrate how easily the methods can be applied by (1) reviewing their formulation and (2) describing their application in the preparation of a particular grant proposal. The focus is a complex but ubiquitous setting: repeated measures in a longitudinal study. Describing the development of the research proposal allows demonstrating the steps needed to conduct an effective power analysis. Discussion of the example also highlights issues that typically must be considered in designing a study. First, we discuss the motivation for using detailed power calculations, focusing on multivariate methods in particular. Second, we survey available methods for the general linear multivariate model (GLMM) with Gaussian errors and recommend those based on F approximations. The treatment includes coverage of the multivariate and univariate approaches to repeated measures, MANOVA, ANOVA, multivariate regression, and univariate regression. Third, we describe the design of the power analysis for the example, a longitudinal study of a child's intellectual performance as a function of mother's estimated verbal intelligence. Fourth, we present the results of the power calculations. Fifth, we evaluate the tradeoffs in using reduced designs and tests to simplify power calculations. Finally, we discuss the benefits and costs of power analysis in the practice of statistics. We make three recommendations: Align the design and hypothesis of the power analysis with the planned data analysis, as best as practical.Embed any power analysis in a defensible sensitivity analysis.Have the extent of the power analysis reflect the ethical, scientific, and monetary costs. We conclude that power analysis catalyzes the interaction of statisticians and subject matter specialists. Using the recent advances for power analysis in linear models can further invigorate the interaction.
Background:
Soccer is currently the most popular and fastest-growing sport worldwide. Similar to many sports, soccer carries an inherent risk of injury, including concussion. Soccer is also unique in the use of 'heading'. The present paper provides a comprehensive review of the research examining the incidence, mechanisms, biomarkers of injury and neurocognitive outcomes of concussions and heading in soccer.
Methods:
Seven databases were searched for articles from 1806 to 24 May 2013. Articles obtained by the electronic search were reviewed for relevance, with 229 selected for review. Ultimately, 49 articles met criteria for inclusion in the present review.
Results:
Female soccer players have a higher incidence of concussions than males. The most frequent injury mechanism is player-to-player contact for both genders. Few studies examined the effects of concussion in soccer players; however, neurocognitive outcomes were similar to those reported in the larger sport concussion literature, while the effect of heading is less clear.
Conclusion:
Despite variation in research designs and study characteristics, the outcomes of concussions in soccer align with the greater concussion literature. This review makes recommendations for future research to increase standardization of research for improved understanding of concussions in soccer as well as the effects of heading.
Background:
Soccer heading is using the head to directly contact the ball, often to advance the ball down the field or score. It is a skill fundamental to the game, yet it has come under scrutiny. Repeated subclinical effects of heading may compound over time, resulting in neurologic deficits. Greater head accelerations are linked to brain injury. Developing an understanding of how the neck muscles help stabilize and reduce head acceleration during impact may help prevent brain injury.
Hypothesis:
Neck strength imbalance correlates to increasing head acceleration during impact while heading a soccer ball.
Study Design:
Observational laboratory investigation.
Methods:
Sixteen Division I and II collegiate soccer players headed a ball in a controlled indoor laboratory setting while player motions were recorded by a 14-camera Vicon MX motion capture system. Neck flexor and extensor strength of each player was measured using a spring-type clinical dynamometer.
Results:
Players were served soccer balls by hand at a mean velocity of 4.29 m/s (±0.74 m/s). Players returned the ball to the server using a heading maneuver at a mean velocity of 5.48 m/s (±1.18 m/s). Mean neck strength difference was positively correlated with angular head acceleration (rho = 0.497; P = 0.05), with a trend toward significance for linear head acceleration (rho = 0.485; P = 0.057).
Conclusion:
This study suggests that symmetrical strength in neck flexors and extensors reduces head acceleration experienced during low-velocity heading in experienced collegiate players.
Clinical Relevance:
Balanced neck strength may reduce head acceleration cumulative subclinical injury. Since neck strength is a measureable and amenable strength training intervention, this may represent a modifiable intrinsic risk factor for injury.
We administered neurocognitive batteries to 49 youth soccer athletes (9–15 yr), who were selected from competitive soccer teams in Central Florida. We collected observational data on soccer heading, self-reported soccer heading, as well as demographics, including school, medical, and soccer history. Both the frequency and intensity of heading the ball in soccer was low in comparison with adolescents and adults. In our sample, the vast majority of soccer headings were of low to moderate intensity and direct (i.e., the incoming flight of the ball was perpendicular to the forehead). Age significantly correlated with frequent heading. Parents were reliable observers of their children’s soccer heading behavior and other at-risk behaviors during games. The majority of soccer headings were direct rather than flicks. Almost half of our participants reported headache and one-fourth reported dizziness after instances of heading the ball. Frequency of soccer heading was not related to neuropsychological score data.
Cognitive deficits observed in professional soccer players may be related to heading of a soccer ball. To assess the severity of a single instance of heading a soccer ball, this study experimentally and theoretically evaluated the linear and angular accelerations experienced by the human head during a frontal heading maneuver.
Accelerations were measured using a set of three triaxial accelerometers mounted to the head of each of four adult male subjects. These measurements (nine signals) were used to estimate the linear acceleration of the mass center and the angular acceleration of the head. Results were obtained for ball speeds of 9 and 12 m.s(-1) (approximately 20 and 26 mph). A simple mathematical model was derived for comparison.
At 9 m.s(-1), peak linear acceleration of the head was 158 +/- 19 m.s(-2) (mean +/- standard deviation) and peak angular acceleration was 1302 +/- 324 rad.s(-2); at 12 m.s(-1), the values were 199 +/- 27 m.s-2 and 1457 +/- 297 rad.s-2, respectively. The initial acceleration pulses lasted approximately 25 ms. Measured head accelerations confirmed laboratory headform measurements reported in the literature and fell within the ranges predicted by the theoretical model.
Linear and angular acceleration levels for a single heading maneuver were well below those thought to be associated with traumatic brain injury, as were computed values of the Gadd Severity Index and the Head Injury Criterion. However, the effect of repeated acceleration at this relatively low level is unknown.
Although soccer has a lower injury rate than does American football, injuries to the head and neck do occur. Indeed, soccer is classified as a contact sport. The potential for cervical injuries from the maneuver known as "heading" are of particular concern. This review provides a synopsis of soccer-related head and neck injuries, an overview of the biomechanics of trauma, and a rational approach to evaluating patients.
This review was conducted to assess and evaluate existing literature on the biomechanics of the act of heading in soccer and the potential for acute and long-term injury to the head and neck.
The resulting work is based on literature searches of the PubMed and Medline databases, textbook reviews, and bibliographies of articles and textbooks obtained during the search. Findings from several studies were summarized and critiqued. Biomechanics, anatomy, pathophysiology, and their relation to the act of heading in soccer were also synthesized into the discussion. Relevant studies of athletes in other sports where activity can affect the neck and head in a manner similar to heading were also considered.
The act of heading in soccer involves the athlete's entire body, and studies have used electromyography to define the activity of neck musculature during heading. The majority of head and neck injuries in soccer occur secondary to impacts other than those that occur during heading, however, rare case reports of serious injury exist. Degenerative bony changes in the cervical spine of soccer players have been noted in a few studies, but the connection with heading is not well established. Data from research in other sports, particularly American football and rugby, suggest a predisposition to degenerative disease of the neck secondary to axial loading mechanisms; the exact relevance of these studies to heading and soccer is unclear.
The complex biomechanics of heading in soccer are not completely defined, especially with regard to long-term effects on the neck and cervical spine. Existing studies of long-term effects suggest a predisposition to degenerative changes of the cervical spine, though they are somewhat limited, even when coupled with data regarding athletes in other sports. Further research in this area is needed with studies that assess biomechanical forces under simulated play conditions and control for impacts and stresses to the neck and spine that occur from non-heading activity.
Objectives
To quantify the incidence and characteristics of purposeful headers and non-intentional head impacts during male and female youth football (soccer) games in Australia.
Design
Cross-sectional observational study.
Methods
Ten match-videos (total n = 110) per playing age (under 13-20 males; under 13-17 females) from the 2019 National Premier League season were coded for purposeful headers and non-intentional head impacts. Total headers and head impacts as well as incidence rate (IR) per 1000 match-hours for different match characteristics were calculated.
Results
Purposeful headers accounted for 99% (n = 4615, IR:1618) of total head impacts. The IR of purposeful headers per 1000 match-hours was highest for under-15 males (IR:2117) and under-17 females (IR:2090) followed by under-20 males (IR:1761). Midfielders completed the most headers in all female age groups (mean IR:713) and under 13-14 males (mean IR:891), with defenders completing the most headers in under 15-20 males (mean IR:760). Heading duels accounted for 16% of total headers with most headers performed during free play (68%), throw-ins (15%), free kicks (12%) and corner kicks (5%). Only 57 head impacts (IR:20) were coded as non-intentional head impacts resulting from being struck by the ball or opponent body part with 4 (IR:1.4) requiring medical attention.
Conclusions
Heading is a complex skill. Given the propensity of youth players of all ages to purposefully head the ball, consideration should be given to coaching heading technique based on specific game scenarios for their playing position and age group. The findings of this study can be used to inform heading guidelines.
Exposure to head impacts is common in soccer and, in some cases, has been associated with neurocognitive and physiological consequences in soccer players. Ball-to-head impacts are particularly frequent, as soccer players regularly use their heads to pass, clear, and shoot the ball during game play and practice. The attenuation of head accelerations resulting from impact is of interest to promoting athlete brain health and numerical models have suggested that reducing soccer ball inflation pressure can lower head accelerations from ball-to-head impacts. The present study sought to test the effect of ball inflation pressure on peak linear acceleration and peak rotational acceleration of the head in a biomechanical reconstruction of ball-to-head impacts using an anthropomorphic testing device head and neck. Adult-sized soccer balls were inflated to five different pressures (34, 48, 55, 62, and 76 kPa), a range that spanned the lower bound on inflation pressure regulated by Fédération Internationale de Football Association and the National Collegiate Athletic Association (60 kPa). Balls were then thrown via a ball launcher at the forehead of the anthropomorphic testing device at three different velocities (17.3, 19.7, and 22.2 m/s). Repeated-measures analyses of variance, with pressure and velocity as repeated measures, revealed an increase in peak linear acceleration (p = 0.001) and peak rotational acceleration (p = 0.002) with higher ball velocities, and a decrease in peak linear acceleration (p < 0.001) and peak rotational acceleration (p < 0.001) with lower ball pressures. Consistent with previous numerical models, the results of this study suggest that reducing soccer ball inflation pressure may reduce head accelerations of ball-to-head impacts.
There has been an increased focus and awareness of head injury and sport-related concussion (SRC) across all sports from the medical and scientific communities, sports organisations, legislators, the media and the general population. Soccer, in particular, has been a focus of attention due to the popularity of the game, the frequency of SRC and the hypothesised effects of repetitive heading of the ball. Major League Soccer, US Soccer and the National Women’s Soccer League jointly hosted a conference entitled, ‘Head Injury in Soccer: From Science to the Field’, on 21–22 April 2017 in New York City, New York. The mission of this conference was to identify, discuss and disseminate evidence-based science related to the findings and conclusions of the fifth International Conference on Concussion in Sport held by the Concussion in Sport Group and apply them to the sport of soccer. In addition, we reviewed information regarding the epidemiology and mechanism of head injuries in soccer at all levels of play, data regarding the biomechanics and effects of repetitive head impacts and other soccer-specific considerations. We discussed how to release the information raised during the summit to key stakeholders including athletes, parents, coaches and healthcare providers. We identified future areas for research and collaboration to enhance the health and safety of soccer (football) players.
There is increasing societal concern about the long-term effects of repeated impacts from soccer heading, but there is little information about ways to reduce head impact severity. The purpose of this study was to identify factors that contribute to head acceleration during soccer heading. One-hundred soccer players completed 12 controlled soccer headers. Peak linear (PLA) and rotational (PRA) accelerations were measured using a triaxial accelerometer and gyroscope. Head acceleration contributing factors were grouped into 3 categories: size (head mass, neck girth), strength (sternocleidomastoid, upper trapezius) and technique [kinematics (trunk, head-to-trunk range-of-motion), sternocleidomastoid and upper trapezius activity]. Multiple regression analyses indicated size variables explained 22.1% of the variance in PLA and 23.3% of the variance in PRA; strength variables explained 13.3% of the variance in PLA and 17.2% of the variance in PRA; technique variables did not significantly predict PLA or PRA. These findings suggest that head and neck size and neck strength predict PLA and PRA. Anthropometric and neck strength measurements should be considered when determining an athlete’s readiness to begin soccer heading.
Background
Absolute numbers of head injuries in football (soccer) are considerable because of its high popularity and the large number of players. In 2006 a rule was changed to reduce head injuries. Players were given a red card (sent off) for intentional elbow-head contact.
Aims
To describe the head injury mechanism and examine the effect of the rule change.
Methods
Based on continuously recorded data from the German football magazine “kicker”, a database of all head injuries in the 1st German Male Bundesliga was generated comprising seasons 2000/01-2012/13. Injury mechanisms were analysed from video recordings. Injury incidence rates (IR) and 95% confidence intervals (95% CI) as well as incidence rate ratios (IRR) to assess differences before and after the rule change were calculated.
Results
356 head injuries were recorded (IR 2.22, 95% CI 2.00 to 2.46 per 1000 match hours). Contact with another player caused most head injuries, more specifically because of head-head (34%) or elbow-head (17%) contacts. After the rule change, head injuries were reduced by 29% (IRR 0.71, 95% CI 0.57 to 0.86, p=0.002). Lacerations/abrasions declined by 42% (95% CI 0.39 to 0.85), concussions by 29% (95% CI 0.46 to 1.09), contusions by 18% (95% CI 0.43 to 1.55) and facial fractures by 16% (95% CI 0.55 to 1.28).
Conclusions
This rule change appeared to reduce the risk of head injuries in men’s professional football.
Objective:
Intraclass correlation coefficient (ICC) is a widely used reliability index in test-retest, intrarater, and interrater reliability analyses. This article introduces the basic concept of ICC in the content of reliability analysis.
Discussion for researchers:
There are 10 forms of ICCs. Because each form involves distinct assumptions in their calculation and will lead to different interpretations, researchers should explicitly specify the ICC form they used in their calculation. A thorough review of the research design is needed in selecting the appropriate form of ICC to evaluate reliability. The best practice of reporting ICC should include software information, "model," "type," and "definition" selections.
Discussion for readers:
When coming across an article that includes ICC, readers should first check whether information about the ICC form has been reported and if an appropriate ICC form was used. Based on the 95% confident interval of the ICC estimate, values less than 0.5, between 0.5 and 0.75, between 0.75 and 0.9, and greater than 0.90 are indicative of poor, moderate, good, and excellent reliability, respectively.
Conclusion:
This article provides a practical guideline for clinical researchers to choose the correct form of ICC and suggests the best practice of reporting ICC parameters in scientific publications. This article also gives readers an appreciation for what to look for when coming across ICC while reading an article.
This Viewpoint provides an overview of US Soccer’s initiatives to improve concussion awareness and management. On November 9, 2015, the US Soccer Federation, US Youth Soccer Association, American Youth Soccer Organization, US Club Soccer, and California’s Youth Soccer Associations (collectively referred to hereafter as US Soccer) issued a joint statement1 announcing the soon-to-be-released comprehensive campaign for safety in youth soccer, a sport that has grown dramatically in the past 4 decades. The sweeping initiative comes on the heels of a 2014 lawsuit, eliminating heading soccer balls for youth players younger than 10 years and limiting the practice of heading for children ages 11 to 13 years.1
Soccer, originally introduced as a safer sport for children and adolescents, has seen a rapid increase in popularity in the United States over the past 3 decades. Recently, concerns have been raised regarding the safety of soccer ball heading (when an athlete attempts to play the ball in the air with his or her head) given the rise in concussion rates, with some calling for a ban on heading among soccer players younger than 14 years.
To evaluate trends over time in boys' and girls' soccer concussions, to identify injury mechanisms commonly leading to concussions, to delineate soccer-specific activities during which most concussions occur, to detail heading-related soccer concussion mechanisms, and to compare concussion symptom patterns by injury mechanism.
Retrospective analysis of longitudinal surveillance data collected from 2005-2006 through 2013-2014 in a large, nationally representative sample of US high schools. Participants were boys and girls who were high school soccer players.
Concussions sustained during high school-sanctioned soccer games and practices.
Mechanism and sport-specific activity of concussion.
Overall, 627 concussions were sustained during 1 393 753 athlete exposures (AEs) among girls (4.50 concussions per 10 000 AEs), and 442 concussions were sustained during 1 592 238 AEs among boys (2.78 concussions per 10 000 AEs). For boys (68.8%) and girls (51.3%), contact with another player was the most common concussion mechanism. Heading was the most common soccer-specific activity, responsible for 30.6% of boys' concussions and 25.3% of girls' concussions. Contact with another player was the most common mechanism of injury in heading-related concussions among boys (78.1%) and girls (61.9%). There were few differences in concussion symptom patterns by injury mechanism.
Although heading is the most common activity associated with concussions, the most frequent mechanism was athlete-athlete contact. Such information is needed to drive evidence-based, targeted prevention efforts to effectively reduce soccer-related concussions. Although banning heading from youth soccer would likely prevent some concussions, reducing athlete-athlete contact across all phases of play would likely be a more effective way to prevent concussions as well as other injuries.
Soccer is the world's most popular sport and unique in that players use their unprotected heads to intentionally deflect, stop, or redirect the ball for both offensive and defensive strategies. Headed balls travel at high velocity pre- and postimpact. Players, coaches, parents, and physicians are justifiably concerned with soccer heading injury risk. Furthermore, risk of long-term neurocognitive and motor deficits caused by repetitively heading a soccer ball remains unknown. We review the theoretical concerns, the results of biomechanical laboratory experiments, and the available clinical data regarding the effects of chronic, subconcussive head injury during heading in soccer.
Three soccer header types (shooting, clearing and passing) and two heading approaches (standing and jumping) were manipulated to quantify impact forces and neck muscle activity in elite female soccer players. The 15 participants were Division I intercollegiate soccer players. Impact forces were measured by a 15-sensor pressure array secured on the forehead. The electromyographic (EMG) activity of the left and right sternocleidomastoid and trapezius muscles was recorded using surface electrodes. Maximum impact forces and impulses as well as the EMG data were analysed with separate repeated-measures analyses of variance. Impact forces and impulses did not differ among the header types or approaches. Higher values were found for jumping versus standing headers in the mean normalized EMG for the right sternocleidomastoid. In addition, the integrated EMG was greater for the right sternocleidomastoid and right and left trapezius (P < 0.05). The sternocleidomastoid became active earlier than the trapezius and showed greater activity before ball contact. The trapezius became active just before ball contact and showed greater activity after ball contact. The increased muscle activity observed in the neck during the jumping approach appears to stabilize the connection between the head and body, thereby increasing the stability of the head-neck complex.
There is increasing concern that repetitive blows to the head, such as those from heading a soccer ball, can cause measurable cognitive impairment. Reducing acceleration of impact could reduce neurologic sequelae.
To measure the effectiveness of four different types of soccer headgear in reducing the acceleration of impact.
A standard magnesium headform was instrumented with a triaxial accelerometer. A soccer ball was propelled at the headform at three different speeds known to occur in soccer play: 9, 12, and 15 m/sec (20, 26, and 34 mph). The main outcome was the peak acceleration of the headform associated with these impacts with and without protective headgear.
Peak accelerations were found in a range from 144 m/s(2) to 289 m/s(2) (14.67-29.5 G, G = 9.81 m/s(2)). Using multivariate analysis of variance (MANOVA) methods to compare the headbands and controls, there was no significant difference in the measured accelerations at the center of gravity with or without headgear (p = 0.50). However, the interaction term of headbands, pressure, and speed was significant at F = 5.51 and p = 0.00001. Using contrasts within conditions, some headbands were found to cause a decrease in peak acceleration at the highest speed and pressure.
Currently available headgear for soccer heading shows little ability to attenuate impact during simulated soccer heading. However, statistically significant decreases are present at the highest speeds and pressures tested, suggesting the headbands may play a role in decreasing impact for more forceful blows.
The objective of this study was to theoretically model, based on the Hertz contact theory, the impact force and contact time, as well as the linear and angular head accelerations during heading in children using two neck stiffness conditions (infinite and negligible stiffness).
The following mathematical model inputs were obtained: elastic modulus and mass of size three, four, and five balls at inflation pressures of 10, 12, and 14 psi, head modulus, head mass, head length, head and trunk moment of inertia, and the precontact ball velocity. The model outputs consisted of linear and angular head acceleration, impact force, contact time between the ball and head, and head impact criteria (HIC) all at the point of impact. Head mass and length were obtained as a percentage of body weight and height, respectively, based on age.
With an increase in head mass, there is a decrease in the linear and angular head acceleration. With an increase in ball size, for the same head mass, there is an increase in the contact time between the head and the ball. Changing ball inflation pressure has little effect on the impact characteristics. Infinite neck stiffness decreased linear and angular head acceleration and HIC.
Head mass and ball size have an effect on linear and angular head acceleration and contact time, respectively, whereas ball inflation pressure has a minimal effect on the impact characteristics. These results indicate that children should be restricted to using the appropriate ball for their age. Smaller head size within an age group is an underemphasized though important identifier of a player's injury risk.
Head impacts from footballs are an essential part of the game but have been implicated in mild and acute neuropsychological impairment. Ball characteristics have been noted in literature to affect the impact response of the head; however, the biomechanics are not well understood. The present study determined whether ball mass, pressure, and construction characteristics help reduce head and neck can impact response.
Head responses under ball impact (6-7 m/s) were measured with a biofidelic numerical human model and controlled human subject trials (n = 3). Three ball masses and four ball pressures were investigated for frontal heading. Further, the effect of ball construction in wet/dry conditions was studied with the numerical model. The dynamic ball characteristics were determined experimentally. Head linear and angular accelerations were measured and compared with injury assessment functions comprising peak values and head impact power. Neck responses were assessed with the numerical model.
Ball mass reductions up to 35% resulted in decreased head responses up to 23-35% for the numerical and subject trials. Similar decreases in neck axial and shear responses were observed. Ball pressure reductions of 50% resulted in head and neck response reductions up to 10-31% for the subject trials and numerical model. Head response reductions up to 15% were observed between different ball constructions. The wet condition generally resulted in greater head and neck responses of up to 20%.
Ball mass, pressure, and construction can reduce the impact severity to the head and neck. It is foreseeable that the benefits can be extended to players of all ages and skill levels.
Effect of football size and mass in youth football head impacts. Multidisciplinary Digital Publishing Institute Proceedings, 2020. 29. Football Association (England). 2020. Updated heading guidance
- M Dunn
- D Davies
- J Hart
Dunn, M., Davies, D. & Hart, J. Effect of football size and mass in youth football head impacts.
Multidisciplinary Digital Publishing Institute Proceedings, 2020. 29.
Football Association (England). 2020. Updated heading guidance. [Online]. Available at:
https://www.thefa.com/news/2020/feb/24/updated-heading-guidance-announcement-240220. Accessed 26th May 2020.