Higher neck strength is associated with lower head acceleration during purposeful heading in soccer: A systematic review

Heading in Football: insights from stakeholders in amateur football

Despite emerging research questioning the long-term effect of purposeful heading on players' brain health, heading-related perspectives and behaviours of stakeholders in amateur football in Australia (a country without heading guidelines) remain unknown. This study aimed to explore the current heading-related perspectives and behaviours of football stakeholders. In total, 290 players (aged over 11 years), 54 coaches, 34 non-coaching staff and 14 medical staff completed the survey. Of the 290 players, 56.5% reported being formally trained in heading, with female players less likely to be trained than male players (p < 0.05). Players were the least concerned about the long-term effects of heading, while medical staff were the most concerned (33.1% and 57.1%, respectively). From proposed strategies to reduce heading burden, a heading ban for all ages was least popular (2.3%), while teaching heading technique was most popular (67.3%). Our study provides insights into football stakeholders' heading-related perspectives, which could be used, along with scientific evidence, to inform pragmatic future heading guidelines.

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.

Neck strength alone does not mitigate adverse associations of soccer heading with cognitive performance in adult amateur players

OBJECTIVES

Soccer heading is adversely associated with neurocognitive performance, but whether greater neck strength or anthropometrics mitigates these outcomes is controversial. Here, we examine the effect of neck strength or anthropometrics on associations of soccer heading with neurocognitive outcomes in a large cohort of adult amateur players.

METHODS

380 adult amateur league soccer players underwent standardized measurement of neck strength (forward flexion, extension, left lateral flexion, right lateral flexion) and head/neck anthropometric measures (head circumference, neck length, neck circumference and neck volume). Participants were assessed for heading (HeadCount) and cognitive performance (Cogstate) on up to 7 visits over a period of two years. Principal components analysis (PCA) was performed on 8 neck strength and anthropometric measures. We used generalized estimating equations to test the moderation effect of each of the three PCs on 8 previously identified adverse associations of 2-week and 12-month heading estimates with cognitive performance (psychomotor speed, immediate verbal recall, verbal episodic memory, attention, working memory) and of unintentional head impacts on moderate to severe central nervous system symptoms.

RESULTS

3 principal components (PC's) account for 80% of the variance in the PCA. In men, PC1 represents head/neck anthropometric measures, PC2 represents neck strength measures, and PC3 represents the flexor/extensor (F/E) ratio. In women, PC1 represents neck strength, PC2 represents anthropometrics, and PC3 represents the F/E ratio. Of the 48 moderation effects tested, only one showed statistical significance after Bonferroni correction, which was not robust to extensive sensitivity analyses.

CONCLUSION

Neither neck strength nor anthropometrics mitigate adverse associations of soccer heading with cognitive performance in adult amateur players.

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.

Decrease in aerial challenges after revision of goal kick rules in Japan Professional Soccer League: explorative study of the possibility of a risk reduction for head injury, concussion, and brain damage by a rule revision

In 2019, FIFA revised the goal kick (GLK) rule such that a GLK could be performed even if the kicker had teammates in the penalty area. This study aimed to examine whether the rule revision reduced the frequency of aerial challenge (AC) and long GLKs (LGLKs), which are risk factors for head injury and concussion in soccer. We analyzed all official league matches (306 matches/season) of the Japan Professional Soccer League 1st Division before (2018 season) and after the rule revision (2020 season). The analysis categorized GLKs into short GLKs (SGLKs) and LGLKs, depending on the GLK distance, and included the frequency and causes of AC, in each match following a GLK, which were compared between the 2018 and 2020 seasons. The average number of LGLKs per match in the 2020 season (8.85) decreased compared to that in the 2018 season (14.20). Additionally, for ACs following a GLK, the frequency of ACs decreased from 6.08 to 3.92 per match. Meanwhile, the frequency of LGLKs tended to increase toward the end of the first and second halves in matches. The results of this study revealed that the 2019 GLK rule revision reduced the number of LGLKs and ACs.

Examining the influence of the Get aHEAD Safely in Soccer™ program on head impact kinematics and neck strength in female youth soccer players

The objective was to examine the efficacy of the Get aHEAD Safely in Soccer™ intervention on head impact kinematics and neck strength in female youth soccer players. The control group (CG) consisted of 13 players (age: 11.0 ± 0.4 yrs), while the experimental group (EG) consisted of 14 players (age: 10.6 ± 0.5 yrs). Head impact kinematics included peak linear acceleration (PLA), peak rotational acceleration (PRA), and peak rotational velocity (PRV). Pre- and post-season measures included strength measures of neck/torso flexion (NF/TF) and extension (NE/TE). Data were analysed using a multilevel linear model and ANOVA techniques. No differences in PLA, PRA, or PRV were observed between groups. The EG showed significant improvement in NF strength while the CG showed significant improvement in NE strength. Both groups significantly improved in TF pre- to post-season. The foundational strength components of the Get aHEAD Safely in Soccer program appear to show a benefit in youth soccer players beginning to learn the skill of purposeful heading.

The Relationship Between Neck Strength and Sports-Related Concussion in Team Sports: A Systematic Review With Meta-analysis

OBJECTIVE: We aimed to quantify the relationship between neck strength and sports-related concussion (SRC) for athletes participating in team sports. DESIGN: Etiology systematic review with meta-analysis. LITERATURE SEARCH: PubMed, PsycINFO, MEDLINE, CINAHL, CENTRAL, and Scopus were searched on March 17, 2022, and updated on April 18, 2023. STUDY SELECTION CRITERIA: Team sports where an opponent invades the player's territory (eg, football, rugby, basketball) that reported at least 1 measure of neck strength, and 1 measure of SRC incidence, using cohort, case-control, or cross-sectional study designs. The Newcastle-Ottawa scale was used to assess risk of bias; certainty of evidence was assessed using the Grading of Recommendations, Assessment, Development, and Evaluation approach. DATA SYNTHESIS: Studies were summarized qualitatively and quantitatively. To understand the relationship between neck strength and future SRC incidence, random-effects meta-analysis was conducted on prospective longitudinal studies. RESULTS: From a total of 1445 search results, eight studies including 7625 participants met the inclusion criteria. Five studies reported a relationship between greater neck strength or motor control and reduced concussion incidence. Pooled results from 4 studies indicated small (r = 0.08-0.14) nonsignificant effects with substantial heterogeneity (I2>90%). The considerable heterogeneity is likely a result of synthesized studies with vastly different sample characteristics, including participant age, playing level, and sports. CONCLUSIONS: There was very low-certainty evidence suggesting a small, nonsignificant relationship between greater neck strength and a lower risk of sustaining a SRC. J Orthop Sports Phys Ther 2023;53(10):1-9. Epub: 10 July 2023. doi:10.2519/jospt.2023.11727.

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.

Injury-Reduction Programs Containing Neuromuscular Neck Exercises and the Incidence of Soccer-Related Head and Neck Injuries

CONTEXT

Concern is growing among soccer players, coaches, and parents regarding head and neck injuries, including concussion, particularly from heading a ball. Thus, we need to explore soccer-specific head injury risk-reduction initiatives. One such initiative is to condition the neck musculature of young players by adding neuromuscular neck exercises to existing injury-reduction exercise programs.

OBJECTIVE

To investigate the effect of neuromuscular neck exercises completed as part of an injury risk-reduction exercise program on the incidence of soccer-related head and neck injuries in adolescent soccer players.

DESIGN

Prospective cohort study.

SETTING

Two sports high schools and 6 soccer clubs during the 2021 soccer season.

PATIENTS OR OTHER PARTICIPANTS

A total of 364 male and female soccer players, aged 12 to 18 years.

INTERVENTION(S)

Members of 1 sports high school and 2 soccer clubs performed neuromuscular neck exercises as part of an injury-reduction program during training (neck training group). Members of another sports high school and 4 soccer clubs performed an injury-reduction program but without neck exercises (comparison group).

MAIN OUTCOME MEASURE(S)

Self-reported injury data were collected from each player at the end of the season and used to calculate incidence rate ratios (IRRs) with 95% CIs.

RESULTS

In total, 364 players completed the study, including 146 players in the neck training group and 218 players in the comparison group. Despite players in the neck training group being less likely to self-report a concussion (IRR = 0.23; 95% CI = 0.03, 1.04) and pain on heading a ball (IRR = 0.62; 95% CI = 0.34, 1.07), only a lower incidence of possible concussive events (IRR = 0.38; 95% CI = 0.14, 0.90; P < .05) was significant.

CONCLUSIONS

Integrating neuromuscular neck exercises into injury-reduction exercise programs has the potential to reduce the risk of adolescent soccer players sustaining a possible concussive event, concussion, or pain on heading a ball.

Reliability of a neck strength test in schoolboy rugby players

BACKGROUND

In rugby union, a bracing mechanism of the neck and trunk is normally adopted in contact situations where high linear and angular forces are produced, which may contribute to the risk for sports-related concussion (SRC).

OBJECTIVES

To examine the feasibility of and test-retest reliability, both inter-rater and intra-rater reliability, of a novel neck strength test in schoolboy rugby players and to summarize neck strength values for this cohort, including rugby position-specific estimates.

MATERIALS AND METHODS

52 male schoolboy rugby union players completed the neck strength test protocol twice, eight days apart using a novel device.

RESULTS

Intra-class correlation coefficients (ICCs) were good to excellent for test-retest reliability (range from 0.86 to 0.92) in all four directions. Intra-rater (ICCs range from 0.706 to 0.981) and inter-rater (ICCs range from 0.669 to 0.982) ranges were calculated. Significant differences were identified between forwards and backs for non-normalised force measures but no significant difference when normalised to bodyweight. The flexor:extensor ratio was 0.68 (SD 0.2) for forwards, 0.71 (SD 0.16) for backs and 0.67 (SD 0.16) for the cohort.

DISCUSSION & CONCLUSION

While there is limited direct evidence to support a direct link between neck strength and SRC risk at present, investigating the relationship of neck strength, stiffness and impact anticipation might be a useful direction for further research. In conclusion, we describe a portable, user-friendly and safe neck strength test with good-to-excellent test-retest reliability, and intra-, inter-rater reliability. Test-retest ICC values compare favourably to gold standard fixed-frame dynamometry and are superior to hand-held dynamometry.

Head and Neck Characteristics as Risk Factors For and Protective Factors Against Mild Traumatic Brain Injury in Military and Sporting Populations: A Systematic Review

BACKGROUND

Investigators have proposed that various physical head and neck characteristics, such as neck strength and head and neck size, are associated with protection from mild traumatic brain injury (mTBI/concussion).

OBJECTIVES

To systematically review the literature and investigate potential relationships between physical head and neck characteristics and mTBI risk in athletic and military populations.

METHODS

A comprehensive search of seven databases was conducted: MEDLINE, EMBASE, CINAHL, Scopus, SPORTDiscus, Cochrane Library, and Web of Science. Potential studies were systematically screened and reviewed. Studies on military and athletic cohorts were included if they assessed the relationship between physical head-neck characteristics and mTBI risk or proxy risk measures such as head impact kinematics.

RESULTS

The systematic search yielded a total of 11,723 original records. From these, 22 studies met our inclusion criteria (10 longitudinal, 12 cross-sectional). Relevant to our PECO (Population, Exposure, Comparator, and Outcomes) question, exposures included mTBI incidence and head impact kinematics (acceleration, velocity, displacement) for impacts during sport play and training and in controlled laboratory conditions. Outcome characteristics included head and neck size (circumference, mass, length, ratios between these measures), neck strength and endurance, and rate of force development of neck muscles.

DISCUSSION

We found mixed evidence for head and neck characteristics acting as risk factors for and protective factors against mTBI and increased susceptibility to head impacts. Head-neck strength and size variables were at times associated with protection against mTBI incidence and reduced impact kinematics (14/22 studies found one or more head-neck variable to be associated with protection); however, some studies did not find these relationships (8/22 studies found no significant associations or relationships). Interestingly, two studies found stronger and larger athletes were more at risk of sustaining high impacts during sport. Strength and size metrics may have some predictive power, but impact mitigation seems to be influenced by many other variables, such as behaviour, sex, and impact anticipation. A meta-analysis could not be performed due to heterogeneity in study design and reporting.

CONCLUSION

There is mixed evidence in the literature for the protective capacity of head and neck characteristics. We suggest field-based mTBI research in the future should include more dynamic anthropometric metrics, such as neck stiffness and response to perturbation. In addition, laboratory-based mTBI studies should aim to standardise design and reporting to help further uncover these complicated relationships.

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.

The Effect of the FIFA 11 + with Added Neck Exercises on Maximal Isometric Neck Strength and Peak Head Impact Magnitude During Heading: A Pilot Study

BACKGROUND

Higher neck strength has been postulated to reduce head impact magnitude during purposeful heading in football.

OBJECTIVES

This pilot trial explored the effect of a neck exercise programme on (1) neck strength and (2) head impact magnitude during heading in male and female adolescent football players.

METHODS

Boys and girls (aged 12-17 years) were randomised by team to the intervention (5 weeks of supervised neuromuscular neck exercises integrated into part 2 of the FIFA 11 + , completed three times per week) or the control group (usual part 2 of the FIFA 11 + , no neck exercises). Outcomes included isometric neck strength and head impact magnitude (peak linear acceleration and peak angular velocity) during standardised heading from a throw-in (at baseline and 6 weeks) plus completion of an evaluation survey by intervention players and coaches.

RESULTS

In total, 52 players (n = 31 intervention; n = 21 control) completed the study. Mixed-model analysis of variance (ANOVA) revealed significant differences in neck strength variables (p < 0.001), peak linear acceleration (p = 0.04) and peak angular velocity (p = 0.04) between the intervention and control groups over time. Intervention players demonstrated increases in mean composite neck strength (53.8% intervention vs 15.6% control) as well as decreases in mean peak linear head acceleration during heading (- 11.8% vs - 5.0%) from baseline to follow-up. Reduction in peak angular velocity was more pronounced in girls (- 27.7%) than boys (- 11.5%) in the intervention group. The addition of neck exercises into part 2 of the FIFA 11 + was feasible and accepted by players and coaches.

CONCLUSION

On average, players who completed neck exercises demonstrated an increase in isometric neck strength and a decrease in head impact magnitude during heading. These exercises were easily incorporated into usual training. Australian New Zealand Clinical Trials Registry (no: ACTRN12619001375145).

Header biomechanics in youth and collegiate female soccer

Concerns about the effects of intentional heading in soccer have led to regulatory restrictions on headers for youth players. However, there is limited data describing how header exposure varies across age levels, and few studies have attempted to compare head impact exposure across different levels of play with the same sensor. Additionally, little is known about the biomechanical response of the brain to header impacts. The objective of this study was to evaluate head kinematics and the resulting tissue-level brain strain associated with intentional headers among youth and collegiate female soccer players. Six youth and 13 collegiate participants were instrumented with custom mouthpiece-based sensors measuring six-degree-of-freedom head kinematics of headers during practices and games. Kinematics of film-verified headers were used to drive impact simulations with a detailed brain finite element model to estimate tissue-level strain. Linear and rotational head kinematics and strain metrics, specifically 95th percentile maximum principal strain (ε_1,95) and the area under the cumulative strain damage measure curve (VSM₁), were compared across levels of play (i.e., youth vs. collegiate) while adjusting for session type and ball delivery method. A total of 483 headers (n = 227 youth, n = 256 collegiate) were analyzed. Level of play was significantly associated with linear acceleration, rotational acceleration, rotational velocity, ε_1,95, and VSM₁. Headers performed by collegiate players had significantly greater mean head kinematics and strain metrics compared to those performed by youth players (all p < .001). Targeted interventions aiming to reduce head impact magnitude in soccer should consider factors associated with the level of play.

Neck strength in Rugby Union players: a systematic review of the literature

The incidence and severity of concussion injuries are increasing every year. Scientific evidence indicates that neck strength and girth could play a role in preventing head and neck injuries, or at least mitigating their severity. We aimed to examine the scientific literature addressing neck strength in Rugby Union with a focus on the potential role of neck strength on injury incidence, neck assessment protocols, neck strength measures, and neck strengthening exercises.We conducted a systematic search of the literature in January 2021 to locate published peer-reviewed articles from PubMed, SPORTDiscus^TM, Web of Science®, and Scopus® e-databases. Overall, senior elite male players were stronger than younger-aged players. Forwards were stronger in extension than any other directions assessed, and were generally stronger and possessed larger necks and greater cross-sectional areas when compared to backs. Implementation of isometric exercise routines in professional players was reported to improve neck strength in all directions. There were no studies evaluating the incidence of concussion and neck strength or neck strengthening strategies in Rugby Union. Strengthening the neck continues to be one of the targeted modifiable risk factors with respect to limiting the severity and temporal effects of head injuries in Rugby Union, despite limited evidence regarding direct associations between neck strength and concussion.

Why are female soccer players experiencing a concussion more often than their male counterparts? A scoping review

BACKGROUND

The risk of concussion is particularly high in female soccer players. There is no consensus as to why female soccer players are at an elevated risk.

OBJECTIVE

To synthesise current evidence investigating reasons for the increased concussion rate in female soccer players.

SOURCES

Searching of six databases (MEDLINE, Scopus, CINAHL, SportDiscus, Web of Science and the Cochrane Library) and grey literature was performed between 13/07/2020-31/07/2020. Keywords were concussion-related terms, terms relating to female football/soccer and terms relating to the mechanism/cause. No constraints were placed on publication date and quantitative or exploratory studies meeting inclusion criteria were eligible. Exclusion criteria were studies not published in English and qualitative studies.

RESULTS

Several hypotheses were identified to explain increased concussion rates in female soccer players, these include, reduced neck strength/anthropometrics, increased head acceleration, increased ball-to-head concussions, differences in hormones and brain structure/function, and reduced visual awareness.

CONCLUSION

Promising ideas/reasons have been identified for increased concussion rates in female soccer players. Despite hypothesis generation there is scarce high-level evidence which is required to guide injury prevention and/or rule changes to protect female soccer players. The level of evidence for included studies is level 2-3 with most being observational cross-sectional or cohort studies.

Injury Reduction Programs for Reducing the Incidence of Sport-Related Head and Neck Injuries Including Concussion: A Systematic Review

BACKGROUND

Sport-related head and neck injuries, including concussion, are a growing global public health concern with a need to explore injury risk reduction strategies such as neck exercises.

OBJECTIVES

To systematically review the literature to investigate: (1) the relationship between neck strength and sport-related head and neck injuries (including sport-related concussion (SRC); and (2) whether neck exercise programs can reduce the incidence of (a) sport-related head and neck injuries; and (b) SRC.

METHODS

Five databases (Ovid MEDLINE, CINAHL, EMBASE, SPORTDiscus, and Web of Science) and research lists of included studies were searched using a combination of medical subject headings and keywords to locate original studies which reported the association between incidence of head and/or neck injury and neck strength data, or included a neck exercise intervention either in isolation or as part of a more comprehensive exercise program.

RESULTS

From an initial search of 593 studies, six were included in this review. A narrative synthesis was performed due to the heterogeneity of the included studies. The results of two observational studies reported that higher neck strength, but not deep neck flexor endurance, is associated with a lower risk of sustaining a SRC. Four intervention studies demonstrated that injury reduction programs that included neck exercises can reduce the incidence of sport-related head and neck injuries including SRC.

CONCLUSION

Consideration should be given towards incorporating neck exercises into injury reduction exercise programs to reduce the incidence of sport-related head and neck injuries, including SRC.

SYSTEMATIC REVIEW REGISTRATION

PROSPERO (registration number: 194217).

Analysis of Head Impact Biomechanics in Youth Female Soccer Players Following the Get aHEAD Safely in Soccer™ Heading Intervention

The effects of repetitive head impacts associated with soccer heading, especially in the youth population, are unknown. The purpose of this study was to examine balance, neurocognitive function, and head impact biomechanics after an acute bout of heading before and after the Get aHEAD Safely in Soccer™ program intervention. Twelve youth female soccer players wore a Triax SIM-G head impact sensor during two bouts of heading, using a lightweight soccer ball, one before and one after completion of the Get aHEAD Safely in Soccer™ program intervention. Participants completed balance (BESS and SWAY) and neurocognitive function (ImPACT) tests at baseline and after each bout of heading. There were no significant changes in head impact biomechanics, BESS, or ImPACT scores pre- to post-season. Deficits in three of the five SWAY positions were observed from baseline to post-season. Although we expected to see beneficial changes in head impact biomechanics following the intervention, the coaches and researchers observed an improvement in heading technique/form. Lightweight soccer balls would be a beneficial addition to header drills during training as they are safe and help build confidence in youth soccer players.

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.

Relation between Isometric Neck Strength and White Matter Organization in Collegiate Athletes

Soccer athletes frequently experience repetitive head impacts (RHI) during games and practices, which may affect neural integrity over time and lead to altered brain structure. Neck strength is hypothesized to limit the transfer of force to the brain and decrease the effect of RHI on brain structure. The goal of our work was to examine whether greater neck strength is associated with more intact white matter organization (WMO) in collegiate athletes exposed to RHI. Collegiate soccer (n = 17) and limited/non-contact sport (n = 39) athletes were assessed prior to their athletic seasons. Participants completed neck strength assessments using handheld dynamometry in six test positions and diffusion tensor imaging. Fractional anisotropy (FA), mean diffusivity (MD), radial diffusivity (RD), and axial diffusivity (AD) were calculated for 20 white matter (WM) regions. A multi-variate approach was used to examine the relationship between neck strength and diffusion measures in soccer and limited/non-contact athletes. Neck strength was positively associated with FA and negatively associated with RD across several WM regions in soccer players only. Neck strength was not significantly associated with MD or AD in either group. Greater neck strength was related to more intact WMO in athletes with high exposure to RHI, particularly in regions prone to damage from brain trauma such as the basal ganglia, superior longitudinal fasciculus, and frontoparietal WM. Future studies should examine neck strength as a factor to moderate neural outcomes in athletes with exposure to RHI.

Heading in the Right Direction: A Critical Review of Studies Examining the Effects of Heading in Soccer Players

The practice of heading in soccer has become a public concern because of the potential for subconcussive impacts to cause cumulative concussive-like effects; however, experimental evidence for this hypothesis has been mixed. This systematic review used pre-defined search parameters to assess primary literature that examined changes in cognitive, behavioral, structural, and/or biological processes after acute heading exposure in youth and young adult soccer players. The findings were synthesized into a concise and comprehensive summary of the research following the preferred reporting items for systematic reviews and meta-analyses (PRISMA) format, and suggestions for standardization of acute heading protocols are described. A total of 1189 articles were considered for this review, with 19 articles meeting all of the inclusion criteria for full analysis. An attempt was made to identify methods with significant sensitivity and reliability by grouping studies based on their outcome measures. Because of lack of standardization across intervention types and data collection protocols, no sensitive and reliable methods could be identified conclusively to assess the effects of acute heading exposure in soccer players. Based on this review, there is not enough evidence to either support or refute the potential of effects of subconcussive events from acute soccer heading exposure. Recommendations for standardization of acute heading exposure studies based on the included literature are discussed. Standardization is required to better understand the impact of acute heading exposure in soccer players, while allowing for the development of guidelines that mitigate any potential risks and allowing athletes to remain active and develop their skills.

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.