It is the 98th minute in the 2003 World Cup final between Germany and Sweden. Extra time, free kick for Germany. Renate Lingor lobs the ball sensitively into the center of the penalty area - header specialist Nia Künzer rises high and blasts the ball over goalkeeper Caroline Jönssen into the goal. The rest is history: Germany is World Champion for the first time.
20 years after the German team's first World Cup triumph and Künzer's header to the World Cup title, the next Women's World Cup is coming up in Australia and New Zealand. On the occasion of this event, questions about the long-term consequences - keyword: brain damage caused by headers - are becoming more intense again, including in women's football. A potential danger lurks in headers, which is an elementary component of the sport of football.
Jan Kern, Research Associate at the Chair of Human Movement Science, is investigating the "Impact of football headers on brain structure and function" as part of his doctoral thesis. Under the title "A Prospective Investigation of the Effects of Soccer Heading on Cognitive and Sensorimotor Performances in Semi-Professional Female Players" (currently still in the review process), Kern is looking at the analysis of possible health risks in female footballers that could arise from regular headers during training and matches.
The Federal Institute for Sport Sciences funded the project to research the influences of headers in football on cognition, sensorimotor functions, and brain structure. Prof. Dr. Joachim Hermsdörfer, head of the Chair of Human Movement Science, is leading the project: "The fact that we have devoted ourselves specifically to women's football in our project naturally takes on an extraordinary significance due to the upcoming Women's World Cup in Australia and New Zealand," explains the human movement scientist.
On the occasion of the FIFA Women's World Cup in Australia and New Zealand, which starts today, on July 20, 2023, we interviewed Jan Kern:
What dangers can arise from headers?
Jan Kern: "Impacts on the head - including head balls and the associated mechanical impact on the brain - are a potential health hazard. Individual head balls do not pose a long-term risk to brain health due to the low impact of force. However, there is concern that the subtle effects of repeated headers may accumulate throughout a football career and ultimately contribute to the development of neurodegenerative diseases such as dementia or Parkinson's disease. However, even though this connection is often presented as proven, no scientifically sound evidence proves beyond doubt that playing headers is responsible for developing these diseases. Given the current state of research, this question can not be answered conclusively."
Are there differences between men and women?
Jan Kern: "While the results of previous studies suggest that women play fewer headers on average than their male colleagues, there is reason to believe that women experience comparatively higher head accelerations during titles. This is related to anthropometric differences, such as a smaller head circumference and a smaller head mass. The often weaker neck muscles may also play a role in this context. However, we cannot yet make a scientifically sound statement about head balls' possible adverse health effects."
Why did you choose women's football to study the effects of headers?
Jan Kern: "Apart from the reasons mentioned above of a possibly increased susceptibility of women to headers, the main reason was that female football players have largely yet to be considered in previous studies on the possibly harmful effects of titles. While football is still male-dominated, women's football has gained enormous popularity in recent years, reflected not least in the steadily increasing number of female players in clubs of the German Football Association (DFB). We wanted to take this development into account with our project."
What exactly did you research in your current study?
Jan Kern: "Our study aimed to investigate the possibly harmful effects of headers on various domains of cognition, sensorimotor functions, and brain structure. In contrast to most previous studies, we chose a prospective design and followed 28 female football players over almost two years. The study also included a control group of 15 female athletes who do not play contact sports."
How did the studies proceed?
Jan Kern: "At the beginning of the study, the female football players and the control subjects underwent an initial examination, including behavioral tests and MRI scans. The analyses were repeated after each of the two subsequent seasons. Throughout the seasons, the games of the female footballers were recorded using video cameras to determine the individual number of headers of each player from these recordings. For some of the matches, the footballers were also equipped with portable accelerometers to assess the intensity of their titles. Initially, the study was scheduled for an extended period, but this was unfortunately prevented by the outbreak of the COVID-19 pandemic and the resulting suspension of match operations."
What are the key findings of your study?
Jan Kern: "While the MRI scans have not yet been finally evaluated, we could not find any valid evidence for a negative effect of head ball play on the domains we analyzed for the cognition and motor skills tests. Only in individual aspects of fine motor skills and balance performance did the female footballers show subtle deteriorations compared to the control group."
What are the implications of the upcoming Women's World Cup and women's football results?
Jan Kern: "The article on our study is still in review, which is why the direct impact on the upcoming World Cup will be relatively small. The transfer of previous research results into football practice - especially in the professional sector - is rather complex, mainly due to the ambiguous research situation that only allows for minimal reliable recommendations for action. The publication of our research results can hopefully have the potential to create a higher level of awareness among the people involved, i.e., officials, coaches, and also players, and in this context, point out the importance of the topic in the field of women's football. In the best case, this can lead to an increased willingness by the national associations and football clubs to recognize research in this area as necessary and to support it accordingly."
What are the recommendations for action about women's headers?
Jan Kern: "Recently, the DFB published updated guidelines on headers, but they do not explicitly differentiate between male and female players and also refer exclusively to the youth level. While other national associations, such as those in the USA and Great Britain, have imposed restrictions and, in some cases, even bans on headers for specific age groups at the youth level, the DFB's guidelines focus on reducing the frequency of headers in younger age groups. On the one hand, forms of play with a reduced pitch size were introduced, in which hardly any headers occurred. On the other hand, the players should learn the correct header technique as risk-free as possible - balloons and foam balls are used for this purpose, among others. According to current estimates, the technically clean execution of headers can reduce the resulting head accelerations."
What could future research projects look like?
Jan Kern: "Due to the still ambiguous state of research regarding the potentially harmful effects of headers, there is a great need for further research in this area. In addition to longer-term prospective studies with more significant cases, experimental laboratory studies that enable the best possible control of external influencing factors also represent an essential component within the research field. One topic that we have already taken up at the Chair of Human Movement Science and want to explore further in future studies is the question of the role of expertise - i.e., whether and to what extent a clean heading technique can represent a protective factor. In this context, multimodal approaches also play an essential role, which, in addition to behavioral examinations or MRI scans, also include the recording of kinematic data or biomarkers as possible injury predictors."
Thank you very much for the interview!
Prof. Dr. Joachim Hermsdörfer
Chair of Human Movement Science
Georg-Brauchle Ring 60/62
phone: 089 289 24550
Chair of Human Movement Science
Georg-Brauchle Ring 60/62
phone: 089 289 24643
Text: Bastian Daneyko