The purpose of this prospective study is to investigate how close Heat Pain Detection Threshold is associated with the area of secondary hyperalgesia, elicited by the clinical pain model Brief Thermal Sensitization.

Furthermore we wish to investigate how close the clinical pain model: Pain during 1 min. heating of the skin (45 degrees celsius), and the psychological tests, Pain Catastrophizing Scale and Hospital Anxiety and Depression Scale are associated with the area of secondary hyperalgesia, elicited by the clinical pain model Brief Thermal Sensitization.

The study participants will be tested with 3 types of clinical pain models on two separate identical study days. A minimum of 7 days will separate the two study days, thus, the minimum length of the study is 7 days, but can be higher.

The 3 types of pain conditioning consist of 1) Brief thermal sensitisation (BTS), 2) Heat pain detection threshold (HPDT), and pain during 1 min. thermal stimulation (p-TS.

The order of the stimulations (HPDT and BTS) is randomised for each patient and each study day, by a random allocation sequence, computer-generated by Copenhagen Trial Unit and stored in sealed and opaque envelopes to secure adequate allocation concealment. p-TS is conducted subsequent to BTS and HPDT.

The participants will complete the psychological tests Pain Catastrophizing Scale (PCS) and Hospital Anxiety and Depression Scale (HADS) in their private home prior to study day 1. The completed tests will be placed in opaque sealed envelopes to secure blinding of the investigator and outcome assessor.

Inclusion Criteria:

• Age >18 years and <35 years
• Speak and understand Danish
• Male gender
• Study participants who have understood and signed the informed consent
• No prescription medicine during the last 30 days.

Exclusion Criteria:

• Study participants that cannot cooperate to the test.
• Study participants who have a weekly intake of >21 units of alcohol, or a have consumed >3 units of alcohol within 24 hours before experimental day.
• Study participants with a substance abuse, assessed by the investigator.
• Study participants, who have consumed analgesics less than 3 days before experimental day.
• Study participants, who have consumed antihistamines less than 48 hours before experimental day.
• Study participants, who have consumed antidepressant medication during the last 30 days before experimental day.
• Study participants with chronic pain.
• Study participants with neurological illnesses.
• Study participants with psychiatric diagnoses.
• Study participants with tattoos on the extremities.
• Study participants with eczema, wounds or sunburns on the sites of stimulation.
• Study participants with a Body Mass Index of >30 kg/m2 or <18 kg/m2