Headaches are extremely common illnesses with a combined lifetime prevalence of 90-99% in Europe. Despite this high prevalence, there are persons who have never, in their whole life, encountered a headache.

The aim of the study is to identify factors that protect against headache by studying pain perception, muscle tenderness and pain tolerance in people who never have had a headache (headache resistant) versus non-resistant controls.

The investigators hope to contribute with novelty to the current understanding of headache pathophysiology and development of more efficient treatment of headache.

The investigator examining:

Quantitative sensory testing (cold pain threshold and heat pain threshold), Muscle tenderness (total tenderness score) and cold pressor test (time in the water and pain rating). All tests are performed the same day, by one investigator who are blinded to the grouping of the participants.

Inclusion Criteria:

• Headache resistant and non-resistant male participants from the Danish Blood Donor Study.
• Weight: 45 kg to 95 kg

Exclusion Criteria:

• Daily consumption of any medication.
• Consumption of any medication less than 12 hours prior to the study day.
• Headache on the study day or 48 hours prior to the study day.
• Amnestic or clinical signs of hypertension (systolic blood pressure >150 mmHg and/or diastolic blood pressure >100 mmHg) or hypotension (systolic blood pressure <90 mmHg and/or diastolic blood pressure <50 mmHg).
• Any severe cardiovascular disease, including cerebrovascular illness.
• Amnestic or clinical signs of current mental illness.
• Amnestic or clinical signs of current substance or drug abuse.
• Amnestic or clinical signs of any illness the responsible doctor considers relevant for participation in the study.

50 Headache resistant and 50 non-resistant male participants from the Danish Blood Donor Study.