It’s a New Year — CSJM Blog Journal Club 2019 Starts Now

Japan (and its iconic Mt. Fuji) will be one of the places on the globe that will be enjoying an exciting 2019 in the world of sport.

We here at CJSM hope all of our readers have enjoyed a festive and relaxing holiday season.  I am sure for most of us reading this post, ‘things’ have picked back up, because the global sports world never sleeps.  From Australian Open tennis to the NFL playoffs to the English Premiership, and beyond, the sports (and sports medicine) scenes have been ushered in with a bang.

2019 promises to be an exciting year in sports all over, but perhaps in no place quite like Japan, as it hosts the Rugby World Cup at year’s end and busily prepares for the 2020 Summer Olympic Games in Tokyo.  I just spent my holidays there and fell in love with the country.  I am looking forward to posting more about the upcoming global events Japan is hosting this year and next.

CJSM has entered the new year with a bang as well, as we begin our 29th year with an issue that is full of interesting offerings.

Among the pieces of original research we have just published in this January 2019 issue is this one: Head Impact Exposure in Youth Soccer and Variation by Age and Sex. This piece has already received a good deal of attention. The accompanying editorial arguing (relatively speaking) against a ban on heading in youth soccer has realized a comparable buzz.

Jason Zaremski MD, Junior Associate Editor CJSM

We thought this would be a particularly good study to ‘de-construct’ in the Journal Club, and so we contacted our regular correspondent Jason Zaremski MD to pen one of his ever popular, recurring posts.  Thanks Dr. Zaremski, as always.



Chrisman SPD, Ebel BE, Stein E, Sarah J. Lowry SJ, Rivara FP. Head Impact Exposure in Youth Soccer and Variation by Age and Sex. Clin J Sport Med 2019;29:3–10.


The newest edition of the Journal Club commentary for the Clinical Journal of Sports Medicine (CJSM) will be a review of an original research manuscript highlighting a very interesting topic, heading in “soccer” (referred to as “football” outside the United States) and its effects on our youth athletes. As the authors note, there are more than ¼ of a billion soccer players worldwide. In the USA, there are approximately 24 million soccer players and more than 37% are youth players. In the past few years there have been growing concerns about heading in youth soccer and possible associations with concussions and sub-concussive head impact exposures (HIE). Due to these concerns, individuals and some leagues (from local levels to national) have suggested a ban of heading to limit body contact and potential HIE. However, prior research has suggested that the actual number of youth players heading a soccer ball as well as intentional impacts with head to ball are low and heading restrictions may not be indicated. (Comstock et al JAMA Ped 2015, Lynall et al MSSE 2016, Press and Rowson CJSM 2016). Therefore, in order to obtain more objective data, the authors of this study wanted to objectively measure HIE in males and females at the youth level.

Purpose/Specific Aim(s):

The purpose of this study was to measure HIE using adhesive-mounted accelerometers during 1 month of soccer. The goals were to describe variations in sex and age as well as any changes in concussion symptoms, health-related quality of life, and cognitive testing after exposure to 1 month of soccer-related head impacts.


This was a prospective cohort study with IRB approval.  All subjects and parents completed consent and assent.


46 youth soccer players aged 11-14 years old (25 female, 21 male from U12 and U14 select and premier teams in the Seattle Area). Participants were primarily white (80%) and had played soccer for 6+ years (85%). Interestingly, while 10% of males and 20% of females had a previous concussion, a secondary finding in this study confirms previous studies suggesting underreporting of head injuries in sports:  more than 50% of youth, as well as parents, reported a previous hit to their head during sports after which they  ‘did not feel right.’


Prior to testing, all participants and parents completed a baseline survey. All assessments were administered in a computer room overseen by the study research assistant.


Variables in this survey included:

  • Age
  • Years playing soccer
  • Migraine history
  • Mental health diagnoses
  • Income
  • Household size
  • Parental educational level
  • Socioeconomic status (>73% of all participants were in a household that earned >$100,000)
  • Parents also reported on any previous concussions their child sustained that were diagnosed by a clinician


Measures at baseline and 1 month after soccer included:

  • Concussion symptoms (aka Postconcussion Symptom Scale (PCSS))
  • Health-related quality of life (Pediatric Quality of Life Inventory or PedsQL)
  • Neuropsychological testing (via Immediate Post-Concussion Assessment and Cognitive Testing (ImPACT) as well as the King–Devick (K-D) test)
  • Comparison of the quantity and magnitude of HIE by sex and age level
  • Changes in outcome measures after 1 month of exposure to soccer related HIE


Parents and youth were screened weekly for potential concussive injury through written surveys, with follow-up telephone calls for any positive responses.

Data Acquisition:

HIE data collection was obtained via a Head Impact monitoring system called the xPatch ( The authors describe the xPatch is an adhesive-mounted 1×2-cm device that is placed over the mastoid bone and measures tri-axial linear acceleration of head impacts.  The device measures acceleration continuously and records when it measures an impact greater than 10 g. If an impact exceeds the threshold, the device saves 10 ms before that impact and 90 ms after the impact. Then, peak linear acceleration (PLA) for each impact is then calculated. It was noted that rotational velocity was not measured, only quantity of head impacts and magnitude of head impact.


Research assistants attended all soccer games during the study period in order to place the xPatch appropriately and obtain the head impact data.  Head impact data was only recorded if witnessed and measured by the xPatch. Research assistants recorded the exact time of collision, the players involved, and the mechanism of collision (heading vs non-heading).


The threshold of 15g was chosen based on previous research that has suggested that impacts less than the 15g threshold are unlikely to cause injury.

Statistical Measures:  As the authors note, statistical analysis was performed using Stata versions 12.1 and 14.1 (StataCorp 2011 and 2016, College Station, Texas). HIE data was placed into graphical form and compared for normality. Median HIE quantity and HIE magnitude were compared across groups using Wilcoxon rank sum. HIE quantity (no head impact >15 g vs at least 1 head impact >15 g) was compared using Pearson x2 tests. Poisson regression models were used to examine effects of age and sex on the quantity of HIE. The strength and directionality of the relationship between the quantity and magnitude of HIE was determined using the Pearson correlation coefficient. Concussion symptoms, health-related quality of life, and neuropsychological testing were compared between baseline and follow-up using Student paired t tests.


Two participants (1 male and 1 female) dropped out during the season: the male player sustained an extremity injury and the female player moved out of the region. Both athletes were included in the comparisons of quantity and magnitude of HIE, as they had completed the baseline measures and had been monitored for approximately 1 month of soccer play. Neither athlete had follow-up data and was included in the analysis comparing measures at baseline and follow-up.


Males more so than females had at least 1 HIE greater than 15gs (P=0.02). 57% of all athletes sustained a HIE greater than 15g (74% Males, 40% Females). Females sustained a HIE magnitude of 47.4g on average compared to males (33.3g) (p = 0.04). 85% of athletes on the U14 team sustained a HIE greater than 15g as opposed to only 15% of the U12 team (p = 0.001).   The U12 female team had no athletes who sustained head impacts above the threshold, whereas other teams had multiple individuals with head impacts above the threshold. Data indicated that age effects were only significant for females.


There was a strong positive correlation between the quantity of head impacts and the magnitude of the greatest head impact (r = 0.62). There was also significant individual variation in the quantity of HIE sustained during the 1-month period. On the U14 female team, 2 athletes sustained no head impacts >15 whereas 5 athletes each sustained more than 10 such head impacts. The authors found similar patterns for each team with a majority of players accounting for the HIE with a maximum of 21 head impacts for 1 individual during the 1-month time period.


The authors did document that no athlete reported a concussion during the study as well as that HIE varied by team. Final analysis also revealed that HIE was significant for females only. In addition, concussion symptoms, health-related quality of life, and neuropsychological testing compared from baseline to follow-up did not have any significant differences.


  • Data acquisition was appropriate using a reputable device
  • HIE criteria was based on prior studies
  • Very thorough data comparison using health report quality of life measures
  • These data fill a hole in the soccer and heading literature by comparing sex (male vs female) in the same age group.


  • As the authors suggest, different positions on the soccer field (aka the pitch) are more likely to head the ball than others. However, that data point was not examined in this study.
  • The sample size was small, the length of the study was short, and the subjects were primarily a homogenous sample of high socioeconomic status club soccer youth. As the authors indicate, this study may not generalize to other populations of youth who play soccer.
  • The ability to include rotational velocity measurement (not included in this study) would be of value to analyze if rotational HIE resulted in >15g were at lower thresholds than non-rotational HIE.
  • As the authors state, the xpatch devices are small and thus are only able to sample at 1 kHz versus 30 kHz, which is the gold standard for a laboratory-based accelerometer.
  • Given that there was such variation in players that sustained HIE >15g, it would be interesting if heading technique could have been assessed prior to the start of the study and during with video analysis and correlate with any HIE >15g. Including cervical neck strength prior to the start of the study would be also useful, since data indicated that males have great cervical strength than females. (Tierney R, et al. Gender differences in head-neck segment dynamic stabilization during head acceleration. MSSE 2005)


The authors concluded there is variation in HIE in youth soccer players aged 11-14 years old with an influence of age and sex. Additionally, HIE in youth soccer may be related to heading.

Clinical Relevance:

Health care providers who care for athletes who participate in soccer should be aware of this study. It would be adventitious to make sure all youth soccer players participate in some form of practice of heading prior to live game participation to improve technique. Parents should be aware that younger, female soccer players may be at greater risk for sustaining a sub concussive HIE than males in this age group as data has indicated females sustain impacts of more than 14gs greater than males in this cohort.

**As of 2015 US Soccer has eliminated heading for U11 team members (children 10 and under) and limited heading in practice for children between the ages of 11 and 13 (Heading training limited to maximum of 30 minutes per week with no more than 15-20 headers per player, per week). This study was performed just prior to the initiation of these recommendations. (US Soccer:



About sportingjim
I work at Nationwide Children's Hospital in Columbus, Ohio USA, where I am a specialist in pediatric sports medicine. My academic appointment as an Associate Professor of Pediatrics is through Ohio State University. I am a public health advocate for kids' health and safety. I am also the Deputy Editor for the Clinical Journal of Sport Medicine.

Comments are closed.

%d bloggers like this: