The number of purposeful headers female youth soccer players experience during games depends on player age but not player position

Heading in football: a systematic review of descriptors, definitions, and reporting methods used in heading incidence studies

The primary objective of this systematic review was to describe the number and type of heading descriptors used in all published studies which report on heading incidence in football. The secondary objective was to detail the data collection and reporting methods used in the included studies to present heading incidence data. Eligible studies were identified through searches of five electronic databases: Ovid MEDLINE, CINAHL, EMBASE, SPORTDiscus, and Web of Science, using a combination of free-text keywords (inception to 12th September 2023). Manual searching of reference lists and retrieved systematic reviews was also performed. A descriptive overview and synthesis of the results is presented. From 1620 potentially eligible studies, 71 studies were included, with the following key findings: 1) only 61% of studies defined a header with even fewer (23%) providing an operational definition of a header within the methods; 2) important study and player demographic data including year and country were often not reported; 3) reported heading descriptors and their coding options varied greatly; 4) visual identification of headers was essential when inertial measurement units were used to collect heading incidence data; and 5) there was a lack of standardisation in the reporting methods used in heading incidence studies making comparison between studies challenging. To address these findings, the development of a standardised, internationally supported, operational definition of a header and related heading descriptors should be prioritised. Further recommendations include the development of minimum reporting criteria for heading incidence research.

Quantitative Analysis of Ball-Head Impact Exposure in Youth Soccer Players

Since the implementation of the US Soccer heading guidelines released in 2015, little to no research on ball-head impact exposure in the United States youth soccer population has been conducted. The purpose was to compare ball-head impact exposure across sex and age in youth soccer players over a weekend tournament. Ten male and female games for each age group (Under-12 [U12], U13, and U14) were video recorded at a weekend tournament for a total of 60 games. Ball-head impact exposure for each game was then coded following a review of each recording. Male players were 2.8 times more likely to have ball-head impacts than female players, (p < 0.001) particularly in the U14 age group when compared to the U12 age group (p = 0.012). Overall 92.4% of players experienced 0-1 ball-head impacts per game with the remaining players experiencing 2+ ball-head impacts per game. Ball-head impact exposure levels are low in the youth players. Most youth soccer players do not head the soccer ball during match play and those that did, only headed the ball on average once per game. Overall, the difference in ball-head impact exposure per player was less than 1 between all the groups, which may have no clinical meaning.

Heading Exposure in Elite Football (Soccer): A Study in Adolescent, Young Adult, and Adult Male and Female Players

PURPOSE

This study aims to quantify heading exposure in real-life elite football at the level of individual male and female adolescents, young adults, and adults.

METHODS

Heading exposure was determined by video analysis in combination with a structured electronic registration tool and observation training, to comprehensively register heading characteristics. Characteristics of heading events were registered in 116 official matches (96 male, 20 female) of Dutch national teams.

RESULTS

Mean exposure for male players based on full match participation was 4.2 headers, with maximum heading exposure at 10.6 headers. Mean heading exposure was higher in adult than adolescent players ( P = 0.049), whereas maximum heading exposure was higher for adult than for young adult players ( P = 0.045). Maximum heading exposure was higher in male than in female players ( P = 0.015). Defenders had the greatest mean and maximum heading exposure ( P < 0.001). Longer flight courses of the ball had greater contribution to mean and maximum heading exposure than shorter courses ( P < 0.01). Frontal headers had greater contribution to exposure than other points of contact on player's head ( P < 0.001), whereas linear headers had greater contribution than rotational headers ( P = 0.016). Defensive headers had greater contribution to exposure than other heading types ( P < 0.014). Unintentional head contacts in elite football players were, in most cases (80%), not related to heading situations.

CONCLUSIONS

This study provides real-life quantifications of mean and maximum heading exposure in elite football, with strong relevance for policy makers and researchers. The results highlight the roles of player and heading characteristics in heading exposure, informing current discussions on the role of heading in football.

A systematic review of match-play characteristics in women's soccer

This review aimed to (1) systematically review the scientific literature evaluating the match-play characteristics of women's soccer, (2) determine the methods adopted to quantify match-play characteristics of women's soccer, and (3) present the physical, technical and tactical characteristics of women's soccer match-play across age-groups, playing standards and playing positions. A systematic search of electronic databases was conducted in May 2021; keywords relating to the population, soccer and match-play characteristics were used. Studies which quantified physical, technical or tactical performance of women's soccer players during match-play were included. Excluded studies included adapted match-play formats and training studies. Sixty-nine studies met the eligibility criteria. Studies predominantly quantified match-play characteristics of senior international (n = 27) and domestic (n = 30) women's soccer match-play, with only seven studies reporting youth match-play characteristics. Physical (n = 47), technical (n = 26) and tactical characteristics (n = 2) were reported as whole-match (n = 65), half-match (n = 21), segmental (n = 17) or peak (n = 8) characteristics. Beyond age-groups, playing standard, and playing position, fourteen studies quantified the impact of contextual factors, such as environment or match outcome, on match-play characteristics. Distance was the most commonly reported variable (n = 43), as outfield women's soccer players covered a total distance of 5480-11160 m during match-play. This systematic review highlights that physical match-performance increases between age-groups and playing standards, and differs between playing positions. However, further research is warranted to understand potential differences in technical and tactical match-performance. Coaches and practitioners can use the evidence presented within this review to inform population-specific practices, however, they should be mindful of important methodological limitations within the literature (e.g. inconsistent velocity and acceleration/deceleration thresholds). Future research should attempt to integrate physical, technical and tactical characteristics as opposed to quantifying characteristics in isolation, to gain a deeper and more holistic insight into match-performance.

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.

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.

Head Impact Exposure and Biomechanics in University Varsity Women's Soccer

Soccer is a unique sport where players purposefully and voluntarily use their unprotected heads to manipulate the direction of the ball. There are limited soccer head impact exposure data to further study brain injury risks. The objective of the current study was to combine validated mouthpiece sensors with comprehensive video analysis methods to characterize head impact exposure and biomechanics in university varsity women’s soccer. Thirteen female soccer athletes were instrumented with mouthpiece sensors to record on-field head impacts during practices, scrimmages, and games. Multi-angle video was obtained and reviewed for all on-field activity to verify mouthpiece impacts and identify contact scenarios. We recorded 1307 video-identified intentional heading impacts and 1011 video-verified sensor impacts. On average, athletes experienced 1.83 impacts per athlete-exposure, with higher exposure in practices than games/scrimmages. Median and 95th percentile peak linear and peak angular accelerations were 10.0, 22.2 g, and 765, 2296 rad/s², respectively. Long kicks, top of the head impacts and jumping headers resulted in the highest impact kinematics. Our results demonstrate the importance of investigating and monitoring head impact exposure during soccer practices, as well as the opportunity to limit high-kinematics impact exposure through heading technique training and reducing certain contact scenarios.

Purposeful Heading Performed by Female Youth Soccer Players Leads to Strain Development in Deep Brain Structures

Head impacts in soccer have been associated with both short- and long-term neurological consequences. Youth players' brains are especially vulnerable given that their brains are still developing, and females are at an increased risk of traumatic brain injury (TBI) compared to males. Approximately 90% of head impacts in soccer occur from purposeful heading. Accordingly, this study assessed the relationship between kinematic variables and brain strain during purposeful headers in female youth soccer players. A convenience sample of 36 youth female soccer players (13.4 [0.9] years of age) from three elite youth soccer teams wore wireless sensors to quantify head impact magnitudes during games. Purposeful heading events were categorized by game scenario (e.g., throw-in, goal kick) for 60 regular season games (20 games per team). A total of 434 purposeful headers were identified. Finite element model simulations were performed to calculate average peak maximum principal strain (APMPS) in the corpus callosum, thalamus, and brainstem on a subset of 110 representative head impacts. Rotational velocity was strongly associated with APMPS in these three regions of the brain (r = 0.83-0.87). Linear acceleration was weakly associated with APMPS (r = 0.13-0.31). Game scenario did not predict APMPS during soccer games (p > 0.05). Results demonstrated considerable APMPS in the corpus callosum (mean = 0.102) and thalamus (mean = 0.083). In addition, the results support the notion that rotational velocity is a better predictor of brain strain than linear acceleration and may be a potential indicator of changes to the brain.

Heading in Football: Incidence, Biomechanical Characteristics and the Association with Acute Cognitive Function-A Three-Part Systematic Review

BACKGROUND

There is growing concern surrounding the role of repetitive sub-concussive head impacts, such as football heading, on brain health.

OBJECTIVES

Three questions were addressed while only considering studies that observed heading exposure directly: (1) how frequently does heading occur within football training and matches, (2) what are the biomechanical characteristics of heading, and (3) is cognitive function affected by heading?

METHODS

This review followed the steps described in the Preferred Reporting Items for Systematic Reviews and Meta-analysis (PRISMA) guidelines. Electronic databases including MEDLINE and SPORTDiscus were searched from the earliest entry to July 2020. Studies that reported independently quantified heading exposure, biomechanical characteristics of heading or the relationship between heading and cognitive function were included. Data were extracted and used to populate summary tables with reference to each research question.

RESULTS

Heading incidence ranged between one to nine headers per player per match. The number of headers observed in small-sided games during training varied depending on the exact format used but generally speaking ranged between zero to one per player per game. The three most commonly reported biomechanical variables were head acceleration, head rotational velocity and overall movement kinematics during the heading action. Average head acceleration ranged from approximately four to 50 g. Nine out of 12 included studies did not observe a negative impact on cognitive test performance following exposure to heading and while three did, these negative effects were limited to specific outcome measures: reaction time and memory function.

CONCLUSION

The current weight of evidence summarised herein does not support the notion that heading is deleterious to cognitive performance in the short term; however, this conclusion is tentative due to methodological shortcomings in the existing evidence base.

Purposeful Heading in Youth Soccer: A Review

Recent public concern over the short- and long-term effects of repetitive head impacts (RHI) associated with purposeful heading in soccer has led researchers to study a multitude of variables related to this important aspect of the game. Of particular interests are the effects of soccer heading in the youth population (≤ 13 years old) whose brains are undergoing rapid development. We conducted a review on youth soccer heading that includes purposeful heading frequency, head impact biomechanics, head injuries, clinical outcomes, and modifying factors. We have concluded that youth soccer players head the ball at a low frequency that typically increases with age and with a finding that boys head the ball more often than girls do. Interestingly, although girls head the ball less frequently than boys do, they tend to sustain higher head impact magnitudes. Head injuries are more likely to occur in girls versus boys and during games because of contact with another player. Clinical outcome measures of concussion are often utilized to study the effects of soccer heading, in both field and laboratory environments. Immediately following soccer heading, youth often report having a headache and demonstrate some deficits in balance measures. Modifying factors that may benefit soccer players participating in purposeful heading activities include stronger neck musculature, wearing headgear, and the use of mouthguards. Research involving youth soccer players needs to be expanded and funded appropriately to better understand the consequences of RHI in both the short and long term.

Performing more than 20 purposeful gameplay headers in a soccer season may alter autonomic function in female youth soccer players

This study evaluated the effects of cumulative purposeful soccer heading on autonomic nervous system function in 22 female youth soccer players (13.3 ± 0.9 years). A 10 minute electrocardiogram recording was collected at baseline and following the 20 game season (post-season) to calculate measures of heart rate variability (HRV), including standard deviation of the normal-normal intervals, total power, high frequency (HF), low frequency (LF), LF:HF, normalized HF and normalized LF. Participants were categorized into low- (<20 headers per season; n = 13) and high- (>20 headers per season; n = 9) exposure groups. Mann-Whitney U tests demonstrated no significant differences between groups for any HRV metric. However, the increased normalized LF power (low exposure 8.67 and high exposure -31.17, respectively; r = 0.35) and LF:HF power (-6.39 and 15.80, respectively; r = 0.35), between groups had moderate practical significance. Therefore, female youth players who perform more than 20 purposeful headers during a soccer season may exhibit altered autonomic function.

The incidence and characteristics of purposeful heading in male and female youth football (soccer) within Australia

OBJECTIVES

To quantify the incidence and characteristics of purposeful headers and unintentional 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 unintentional 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 unintentional 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.

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.

The UEFA Heading Study: Heading incidence in children's and youth' football (soccer) in eight European countries

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 analyzed. 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.