The goal of this observational study is to evaluate the safety of heading in football. We will study the release of biomarkers in blood that reflect microscopic neural damage. The main questions this study aims to answer are:

• Does participation in a football match lead to a change in biomarkers that reflect microscopic neural damage?
• Is the dose of exposure during a football match related to the magnitude of change in biomarkers that reflect microscopic neural damage?

Participants will participate in a regular football match and provide blood samples before and right after the football match. The football match will be recorded on video to count the number of headers of all participants.

The objective of this prospective observational study is to determine the potential impact of ball heading in football on brain integrity as assessed by blood biomarkers for neural damage in a real-world setting. Healthy amateur football players will be recruited to participate in the study. Participants will be invited to play a regular football match for investigation purposes. They will provide a blood sample within one hour before the start of the match and a second blood sample within one hour after the match. Participants will be asked to provide a third blood sample within 48 hours after participation, but this is not obligatory. The football match will be recorded on video to determine the number of head impacts of all participants. Furthermore, participants will wear heart rate sensors and local positioning sensors to determine the internal and external training load and account for the possible confounding effects of exercise on neural blood biomarkers.

Inclusion Criteria:

• Member of the KNVB;
• 18 years or older;
• Male
• Self-reported fitness to play 70-90 minutes (absence of injury).

Exclusion Criteria:

• Sustained a head injury in the last year;
• History or current neurological condition;
• Regular participation in other contact sports (e.g. rugby, American football, ice hockey, fighting sports);
• (Former) military personnel with a history of fighting/blast exposure

All senior amateur football players will be invited to participate in the study. An amateur population is chosen because of the great number of participants and the resulting societal relevance of the research question.

We intend to make IPD available to other researchers. However, we still need to develop the plan in collaboration with the privacy officer and legal research support.