In this study, we use positron emission tomography (PET) and functional magnetic resonance imaging (fMRI) to study brain mechanisms that contribute to physical exercise-induced reward. We examine whether acute physical exercise releases endogenous opioids in the brain, and whether it modulates brain responses to viewing appetizing foods. Unraveling these mechanism are instrumental from a public health perspective, given the undisputed positive health effects of physical exercise.

Inclusion Criteria:

1. Native Finnish speaker
2. Age > 18 years
3. Western Caucasian origin

Exclusion Criteria:

1. Age < 18 or > 65
2. History or current mental disorder
3. BMI > 27 kg/m2
4. Use of drugs that influence the central nervous system, including nicotine
5. Poor compliance
6. Any chronic medical defect or injury which hinder or interfere everyday life
7. Eating disorder
8. Current or past excessive use of alcohol or substance abuse
9. Past dose of radiation from medical research such that the annual effective dose will exceed 10 mSv
10. Any other condition that in the opinion of the investigator could create a hazard to the subject safety, endanger the study procedures or interfere with the interpretation of study results
11. Presence of any ferromagnetic objects that would make MR imaging contraindicated