Heading in football. Part 3: effect of ball properties on head response

The Acute Effects of Ball Pressure on Anticipation Timing Following a Series of Purposeful Headers in Adult Football (Soccer) Players

The purpose of this study is to investigate the acute effects of ball pressure on anticipation timing following a series of purposeful headers in adult football (soccer) players. There is evidence to suggest acute neurophysiological changes to the brain following purposeful heading; this may lead to altered anticipation timing as a result, potentially having future safety implications for players. A repeated measures crossover design was used. Seventeen participants aged between 20 and 30 years performed (i) 20 rotational headers with a lower-pressure match ball (58.6 kPa; 8.5 psi), (ii) 20 rotational headers with a higher-pressure match ball (103.4 kPa; 15 psi), or (iii) 20 non-headers (kicks) as a control each on separate days. The effect of ball pressure on anticipation timing accuracy, measured as absolute, constant, and variable errors, was assessed before and immediately after each intervention session using an anticipation timing task. Differences between group means were compared using repeated measures ANOVA and linear mixed effects models, with p-values of <0.05 considered statistically significant. No significant differences in anticipation timing accuracy across interventions were detected between control, occluded, and non-occluded trials. This finding differs from the previous literature regarding the measurable, acute effects of purposeful heading. The anticipation timing task may lack sensitivity for detecting the effects of repeated heading on brain function.

Head trauma analysis of laboratory reconstructed headers using 1966 Slazenger Challenge and 2018 Telstar 18 soccer balls

Retired soccer players are presenting with early onset neurodegenerative diseases, potentially from heading the ball. It has been proposed that the older composition of soccer balls places higher strains on brain tissues. The purpose of this research was to compare the dynamic head response and brain tissue strain of laboratory reconstructed headers using replicas of the 1966 Slazenger Challenge and 2018 Telstar 18 World Cup soccer balls. Head-to-ball impacts were physically conducted in the laboratory by impacting a Hybrid III head form at three locations and four velocities using dry and wet soccer ball conditions, and computational simulation was used to measure the resulting brain tissue strain. This research showed that few significant differences were found in head dynamic response and maximum principal strain between the dry 1966 and 2018 balls during reconstructed soccer headers. Headers using the wet 1966 soccer ball resulted in higher head form responses at low-velocity headers and lower head responses as velocities increased. This study demonstrates that under dry conditions, soccer ball construction does not have a significant effect on head and brain response during headers reconstructed in the laboratory. Although ball construction didn't show a notable effect, this study revealed that heading the ball, comparable to goalkeeper kicks and punts at 22 m/s, led to maximum principal strains exceeding the 50% likelihood of injury risk threshold. This has implications for the potential risks associated with repetitive heading in soccer for current athletes.

Where are We Headed? Evidence to Inform Future Football Heading Guidelines

Given the scientific and public concern regarding the short-, medium- and long-term consequences of heading on brain health, being proactive about developing and implementing guidelines that help reduce the burden (volume, impact magnitude and injury risk) of heading in young and beginner players appears justified. This narrative review explores the evidence underpinning strategies that could be incorporated into future heading guidelines to reduce heading burden in players across all levels of football. A four-step search strategy was utilised to identify all data-based papers related to heading in football. Eligibility criteria for inclusion were: (1) original data, (2) study population included football players, (3) outcome measures included one or more of the following: number of headers, measurement of head acceleration during heading, or head/brain injury incidence, and (4) published in English or English translation available. In total, 58 papers were included that outlined strategies based on (1) game or team development, (2) player skill development and (3) equipment. In particular, greater emphasis existed for small-sided games (particularly in young players) where fewer headers are observed when compared with the conventional 11 versus 11 game, as well as reducing headers from goal kicks and corners. Evidence also existed for developing a heading coaching framework that focusses on technical proficiency as well as neuromuscular neck exercises integrated into general injury reduction exercise programs, enforcement of rules related to deliberate head contact and using lower-pressure match and training balls. To mitigate potential risks of heading on brain health, a number of pragmatic strategies have been examined in scientific studies and may be considered as part of future heading guidelines.

Head Impact Exposure in Female Collegiate Soccer by Activity Type

Soccer, one of the most popular sports in the world, has one of the highest rates of sports-related concussions. Additionally, soccer players are frequently exposed to nonconcussive impacts from intentionally heading the ball, a fundamental component of the sport. There have been many studies on head impact exposure in soccer, but few focus on soccer practices or practice activities. This study aimed to characterize the frequency and magnitude of head impacts in National Collegiate Athletic Association Division I female soccer practice activities using a custom-fit instrumented mouthpiece. Sixteen players were instrumented over the course of 54 practice sessions. Video analysis was performed to verify all mouthpiece-recorded events and classify practice activities. Category groupings of practice activities include technical training, team interaction, set pieces, position-specific, and other. Differences in head impact rates and peak resultant kinematics were observed across activity types and category groupings. Technical training had the highest impact rate compared to other category groupings. Impacts occurring during set piece activities had the highest mean kinematic values. Understanding drill exposure can help inform coaches on training plans aimed to reduce head impact exposure for their athletes.

A Systematic Review of Head Impacts and Acceleration Associated with Soccer

Epidemiological studies of the neurological health of former professional soccer players are being undertaken to identify whether heading the ball is a risk factor for disease or premature death. A quantitative estimate of exposure to repeated sub-concussive head impacts would provide an opportunity to investigate possible exposure-response relationships. However, it is unclear how to formulate an appropriate exposure metric within the context of epidemiological studies. We have carried out a systematic review of the scientific literature to identify the factors that determine the magnitude of head impact acceleration during experiments and from observations during playing or training for soccer, up to the end of November 2021. Data were extracted from 33 experimental and 27 observational studies from male and female amateur players including both adults and children. There was a high correlation between peak linear and angular accelerations in the observational studies (p < 0.001) although the correlation was lower for the experimental data. We chose to rely on an analysis of maximum or peak linear acceleration for this review. Differences in measurement methodology were identified as important determinants of measured acceleration, and we concluded that only data from accelerometers fixed to the head provided reliable information about the magnitude of head acceleration from soccer-related impacts. Exposures differed between men and women and between children and adults, with women on average experiencing higher acceleration but less frequent impacts. Playing position appears to have some influence on the number of heading impacts but less so on the magnitude of the head acceleration. Head-to-head collisions result in high levels of exposure and thus probably risk causing a concussion. We concluded, in the absence of evidence to the contrary, that estimates of the cumulative number of heading impacts over a playing career should be used as the main exposure metric in epidemiological studies of professional players.

Immediate effects of an acute bout of repeated soccer heading on cognitive performance

Purpose: There isgrowing concern surrounding the harmful effects of soccer heading on cognitive function. The present study aims to examine the immediate effects of heading.Methods: 30 recreational male soccer players were divided into three groups that undertook 20 consecutive headers with a soft (8.8 psi), hard (16.2 psi), or no (control) ball. A battery of neuropsychological tests was completed before and after heading: King-Devick, trail-making (TM) (A, B), digit span (DS) and spatial span (SS) (forward, backward).Results: Significant increase in the time (M = 4.44 s) and errors (M = 1.45) for the King-Devick test within the hard and soft groups, although there was no significant difference for TM-A and TM-B. Significant decline for SS forward within the hard and soft groups (M= -16%), although the declines for SS backward (M = -16%), DS forward (M= -23%) and DS backward (M = -25%) were present only for the hard group (ps <.05).Discussion: While outside of regular match-play, this study showed that heading negatively influenced one indicator of a suspected concussion (King-Devick), as well as working memory (DS, SS) that is essential for daily life. These findings contribute to the growing debate surrounding heading safety.

The effect of ball characteristics on head acceleration during purposeful heading in male and female youth football players

Objective: The objective of this cross-sectional study was to explore the effects of different ball types and characteristics on head acceleration during purposeful heading in youth football players. Methods: Experienced male and female players (n = 61) aged between 12-17 years completed heading trials with 4 different balls (Ball 1 mass 192 grams (g), pressure 5.0 pounds per square inch (psi); Ball 2 432 g, 5.0 psi; Ball 3 255 g, 5.0 psi; Ball 4 430 g, 10.5 psi) whilst wearing a head-mounted accelerometer and gyroscope. Balls 1, 2 and 4 were size 5 balls; Ball 3 was a size 4 ball.Results: Multivariate analysis of variance and post-hoc univariate analyses revealed a statistically significant difference between ball type and head acceleration during heading for both linear acceleration (adjusted R² = 0.68; F = 140.90; p = <0.001) and angular velocity (adjusted R² = 0.28; F = 26.52; p = <0.001). Ball 1 (lightest size 5 ball) and Ball 3 (size 4 ball) demonstrated linear head accelerations up to 59% lower (p = <0.01) when compared with Ball 4 (size 5 regulated match ball).Discussion: Head acceleration during purposeful heading is influenced by changes to ball pressure, ball size and/or ball mass. Changing ball characteristics, particularly in youth football training when heading is being taught, should be an easy strategy to implement.

Heading incidence in boys' football over three seasons

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.

REPIMPACT - a prospective longitudinal multisite study on the effects of repetitive head impacts in youth soccer

Repetitive head impacts (RHI) are common in youth athletes participating in contact sports. RHI differ from concussions; they are considered hits to the head that usually do not result in acute symptoms and are therefore also referred to as “subconcussive” head impacts. RHI occur e.g., when heading the ball or during contact with another player. Evidence suggests that exposure to RHI may have cumulative effects on brain structure and function. However, little is known about brain alterations associated with RHI, or about the risk factors that may lead to clinical or behavioral sequelae. REPIMPACT is a prospective longitudinal study of competitive youth soccer players and non-contact sport controls aged 14 to 16 years. The study aims to characterize consequences of exposure to RHI with regard to behavior (i.e., cognition, and motor function), clinical sequelae (i.e., psychiatric and neurological symptoms), brain structure, function, diffusion and biochemistry, as well as blood- and saliva-derived measures of molecular processes associated with exposure to RHI (e.g., circulating microRNAs, neuroproteins and cytokines). Here we present the structure of the REPIMPACT Consortium which consists of six teams of clinicians and scientists in six countries. We further provide detailed information on the specific aims and the design of the REPIMPACT study. The manuscript also describes the progress made in the study thus far. Finally, we discuss important challenges and approaches taken to overcome these challenges.

Force experienced by the head during heading is influenced more by speed than the mechanical properties of the football

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 modeled as a lumped mass mathematical model with elastic contact. Football headers were then reconstructed using a human body modeling 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 traveling when headed by a player. Law changes reducing high ball speeds could be trialed at certain age grades or as a phased introduction to football heading.

Purposeful Heading in Youth Soccer: Time to Use Our Heads

Repeated purposeful heading in soccer has come under increased scrutiny as concerns surrounding the association with long-term neurodegenerative disorders in retired players continue to grow. Although 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 that can reduce head impact during purposeful heading in youth soccer while 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 continue on this topic. J Orthop Sports Phys Ther 2020;50(8):415-417. doi:10.2519/jospt.2020.0608.

Injury mechanism of midfacial fractures in football causes in over 40% typical neurological symptoms of minor brain injuries

PURPOSE

The injury mechanisms of midfacial fractures may be typical causes of concussion, but hardly any scientific data on midfacial injuries sustained in football are available. Head and brain trauma represent frequent injuries in athletes of different sports that require appropriate treatment by sports and trauma physicians. This study investigated the management of midfacial fractures in football and the association of such fractures with concomitant brain injury.

METHODS

In a prospective cohort study lasting 24 months (2012 to 2013), midfacial injuries of football players were analysed with regard to the injury mechanisms, first aid procedures on the field, treatment and return-to-play. To analyse concomitant and potentially overlooked minor brain injuries due to the trauma, we retrospectively investigated the neurological symptoms of the study population.

RESULTS

The study included 132 football players (37 semi-professionals and 95 amateurs) with midfacial fractures. The main injury mechanisms were head-to-head and head-to-elbow trauma. The mean period of return-to-play after trauma was 33.5 days, which was significantly shortened if a protective face mask was worn (mean 10.4 days earlier, p = 0.0006). Semi-professional football players returned to play earlier (p = 0.009) and more often used protective face masks (p = 0.001). 55 players (41.6%) had neurological symptoms immediately after trauma as a possible sign of concomitant minor brain injury. 5 of 132 players with concussion had been hospitalised for 24 h, but no persistent neurological symptoms were detected.

CONCLUSION

In football, midfacial fractures represent moderate-to-severe injuries with time away from sports of more than 4 weeks. Over 40% of athletes with a midfacial fracture showed concomitant neurological symptoms as a sign of minor brain injury. Therefore, sports physicians and other staff supervising athletes in daily practice should be aware of the presence of neurological symptoms.

LEVEL OF EVIDENCE

Level III.

Head and neck injuries in football (soccer)

The incidence for concussions in football (soccer) is equivalent to other contact sports such as American football and ice hockey. The risk of concussion is increased in goalkeepers, females and perhaps young players. Head to head contact between athletes is the most common mechanism for concussion, while heading does not appear to be a frequent cause. Research is providing evidence that neck muscle development and protective headgear may play a role in the prevention of concussions. The presence and pathophysiology of a chronic encephalopathy secondary to a cumulative subconcussive blows obtained in football is still controversial. Neck injuries are not as common as head injuries and are not frequently reported in the literature. The biomechanics of neck injuries are different between children and adults which may account for the different types of injuries in these populations. Spinal cord injuries are rarely seen in football and are usually associated with major fractures/dislocations.

Risk management: FIFA's approach for protecting the health of football players

BACKGROUND

Sport and exercise have long-term health benefits, but there is also a risk that participants will sustain injuries and/or ill health from these activities. For this reason, international sports governing bodies have a responsibility to identify the risks that exist within their sport and to provide guidance to participants and other stakeholders on how these risks can be controlled within acceptable levels.

PURPOSE

To demonstrate how Fédération Internationale de Football Association (FIFA), as football's governing body, uses a risk management framework to identify, quantify, mitigate and communicate the risks of injury and ill health in football for men, women and children in all environments.

METHOD

All the research papers published by FIFA's Medical Assessment and Research Centre (F-MARC) during the period 1994 to 2011 were reviewed and categorised according to an established sport-related risk management framework.

CONCLUSIONS

F-MARC investigated and mitigated 17 areas of risk to footballers' health in a coherent and consistent approach through the process of risk management.

Validation of a wireless head acceleration measurement system for use in soccer play

Soccer heading has been studied previously with conflicting results. One major issue is the lack of knowledge regarding what actually occurs biomechanically during soccer heading impacts. The purpose of the current study is to validate a wireless head acceleration measurement system, head impact telemetry system (HITS) that can be used to collect head accelerations during soccer play. The HIT system was fitted to a Hybrid III (HIII) head form that was instrumented with a 3-2-2-2 accelerometer setup. Fifteen impact conditions were tested to simulate impacts commonly experienced during soccer play. Linear and angular acceleration were calculated for both systems and compared. Root mean square (RMS) error and cross correlations were also calculated and compared for both systems. Cross correlation values were very strong with r = .95 ± 0.02 for ball to head forehead impacts and r = .96 ± 0.02 for head to head forehead impacts. The systems showed a strong relationship when comparing RMS error, linear head acceleration, angular head acceleration, and the cross correlation values.

Epidemiology of acute head injuries in Canadian children and youth soccer players

BACKGROUND

Limited studies have been done to assess head injury characteristics for children and youth soccer players in Canada.

OBJECTIVES

To describe acute head injury characteristics in children and youth soccer players and identify the characteristics of patients who required hospital admission.

METHODS

Analysis was based on the Canadian Hospitals Injury Reporting and Prevention Program (CHIRPP). Soccer-related head injuries amongst 5-19 year old children presenting at 16 hospital emergency departments during 1994-2004 were selected in the study. All head injury-related variables (nature of injury, mechanism of injury, location of play, soccer type and season of play) were stratified by age and sex. A logistic regression model, consisting of the injury-related variables, sex and age as the independent variables, was performed to examine the characteristics of those head-injured patients who required hospital admission.

RESULTS

Overall, there were 4720 head injury cases identified (15% of all soccer-related emergency department visits). The highest proportion of head injuries was amongst males (70%) and children aged 10-14 years (50%). Of head injury cases, 35% were superficial and/or open wounds, 28% minor head injuries, 11% concussions, 9% eye injuries and 5% fractures. The total number of cases that required hospital admission was 164 (3.5%). Based on logistic regression analysis, head-injured youth aged 15-19 years were almost two times more likely to be admitted to hospital than their younger counterparts (OR=2.2, 95% CI: 1.3-3.6). Compared to ball contact injuries, contact with structures/surfaces, other players/persons and other unspecified objects increased the odds of hospital admission at least by two-folds. Moreover, those who played unorganised soccer were significantly more likely to be admitted to the hospital as compared to those who played organised soccer (OR=1.7, 95% CI: 1.2-2.6). Finally, playing in the non-winter seasons had increased likelihood of hospital admissions.

CONCLUSIONS

Head injuries constituted a significant proportion of soccer-related injuries presenting to emergency departments. Future studies need to evaluate the nature and safety of the playing surfaces/turf and other structures on or around the field of play.

Sport-related concussion

Sport-related concussion is a common injury in children and adolescents. Athletes seldom report concussive symptoms, which makes the diagnosis a challenge. The management of sport-related concussion has changed significantly over the last several years. The previously used grading systems and return-to-play guidelines have been abandoned in favor of more individualized assessment and management. Neuropsychological testing is being used more frequently to assist in management. After recovery, it is recommended that an athlete's return-to-play progress in a gradual, stepwise fashion while being monitored by a health care provider. Proper assessment and management of a sport-related concussion is crucial, because repeat concussions can result in decreased neurocognitive functioning, increased symptomatology, and, at times, catastrophic outcomes.

Do UK university football club players suffer neuropsychological impairment as a consequence of their football (soccer) play?

Male players from football and rugby clubs and sportsmen from a variety of noncontact sports clubs at a UK university were compared on biographical and neuropsychological test measures. A data analysis paradigm was developed and employed to control the inflation of Type 1 error rate due to multiple hypotheses testing. Rugby players sustained most head injuries in their chosen sport, but neuropsychological tests of attention, memory, and executive function provided no evidence of performance impairment attributable to the number of head injuries sustained or the football, rugby, or noncontact sport groups. Footballers' heading frequency was related to the number of football head injuries sustained, but no relationship was detected between footballers' heading frequency and their neuropsychological test performance. Following discussion of pertinent methodological limitations it is concluded that there was no evidence in this dataset of neuropsychological impairment consistent with either mild head injury incidence or football heading frequency. However, a need for further research examining the long-term neuropsychological consequences of such head injuries was identified.

Pediatric sport-related concussion: a review of the clinical management of an oft-neglected population

Athletic concussion is a growing focus of attention for pediatricians. Although numerous literature reviews and clinical guidelines are now available pertaining to athletic concussion, few have focused on the pediatric athlete in particular. Sport-related concussions occur relatively frequently in children and adolescents, and primary health care providers are often responsible for coordinating clinical management. Here we summarize the scientific literature pertinent to the care of young athletes. We examine how concussion affects younger and older athletes differently at biomechanical, pathophysiological, neurobehavioral, and contextual levels. We also discuss important issues in clinical management, including preparticipation assessment, concussion evaluation and recovery tracking, and when and how to return pediatric athletes to play sports. We also briefly cover non-sport-related interventions (eg, school support). With proper management, most children and adolescents sustaining a sport-related concussion can be expected to recover fully.

Heading in football. Part 2: biomechanics of ball heading and head response

OBJECTIVES

Controversy surrounding the long term effects of repeated impacts from heading has raised awareness among the public and the medical community. However, there is little information about the human response to the impacts and what measures can be taken to alter their effect. The objective of the current study was to gain a better understanding of heading biomechanics through the implementation of a numerical model and subsequent investigation of parameters related to heading technique and ball characteristics.

METHODS

A controlled laboratory study was carried out with seven active football players, aged 20-23 years who underwent medical screening and were instrumented with accelerometers mounted in bite plates and electromyographic electrodes on the major neck muscle groups. Balls were delivered at two speeds (6 m/s and 8 m/s) as the subjects demonstrated several specific heading manoeuvres. Photographic targets were tracked via high speed video to measure heading kinematics. One subject demonstrating reasonably averaged flexion-extension muscle activity phased with head acceleration data and upper torso kinematics was used to validate a biofidelic 50th percentile human numerical model with detailed representation of the head and neck.

RESULTS

Heading kinematics and subject responses were used with a detailed numerical model to simulate impact biomechanics for a baseline heading scenario. Changes to heading techniques and ball characteristics which mitigated head impact response were identified.

CONCLUSION

A numerical model combined with biomechanical measurement techniques is an important tool for parametric investigation of strategies to reduce head impact severity via changes in heading technique or the physical properties of the ball.

Heading in football. Part 1: development of biomechanical methods to investigate head response

OBJECTIVES

There has been growing controversy regarding long term effects of repeated low severity head impacts such as when heading a football. However, there are few scientific data substantiating these concerns in terms of the biomechanical head response to impact. The present study aimed to develop a research methodology to investigate the biomechanical response of human subjects during intentional heading and identify strategies for reducing head impact severity.

METHODS

A controlled laboratory study was carried out with seven active football players, aged 20-23 and of average stature and weight. The subjects were fitted with photographic targets for kinematic analysis and instrumented to measure head linear/angular accelerations and neck muscle activity. Balls were delivered at two speeds (6 m/s and 8 m/s) as the subjects executed several specific forward heading manoeuvres in the standing position. Heading speeds up to 11 m/s were seen when the head closing speed was considered. One subject demonstrating averaged flexion-extension muscle activity phased with head acceleration data and upper torso kinematics was used to validate a biofidelic 50th percentile human model with a detailed head and neck. The model was exercised under ball incoming speeds of 6-7 m/s with parameter variations including torso/head alignment, neck muscle tensing, and follow through. The model output was subsequently compared with additional laboratory tests with football players (n = 3). Additional heading scenarios were investigated including follow through, non-active ball impact, and non-contact events. Subject and model head responses were evaluated with peak linear and rotational accelerations and maximum incremental head impact power.

RESULTS

Modelling of neck muscle tensing predicted lower head accelerations and higher neck loads whereas volunteer head acceleration reductions were not consistent. Modelling of head-torso alignment predicted a modest reduction in volunteer head accelerations. Exaggerated follow through while heading reduced volunteer head accelerations modestly.

CONCLUSION

Biomechanical methods were developed to measure head impact response. Changing the biomechanics of currently accepted heading techniques will have inconsistent benefits towards the reduction of head loading. Furthermore, mathematical modelling suggested an increased risk of neck loads with one alternative technique. No consistent recommendations can be made on the basis of the current study for altering heading techniques to reduce impact severity.