The main aim for this study is to investigate to what extent physical activity of moderate or low intensity, relative to prolonged inactivity, may acutely alter neural activity-related prefrontal cortex oxygenated hemoglobin during a cognitive demanding task in 13- 15 year-old adolescents. The study is primarily focused on investigating these effects in ecologically valid conditions, i.e. activity patterns that closely resemble a typical day in school and using activity modes that are suitable in a school setting.

The study will be a controlled crossover experimental trial with three conditions. Each participant will complete each of the three experimental conditions, separated by a washout period of minimum four days. Physical activity behaviours and sleep will be monitored the day/night before each test day. The first visit will be a familiarization session for the collection of demographic data, fitness testing, and acquaintance with experimental procedures. On the second, third, and fourth visits, participants will undergo three different standardized 80-minutes interventions in a randomized order. Before and immediately after the 80-minutes interventions, blood pressure, augmentation index, and cerebral hemodynamic response of the prefrontal cortex during standardized cognitive tasks (nback test) will be measured. Additionally, saliva samples will be collected the morning of the test day, and before and after the interventions.

Exclusion Criteria:

• Ongoing medication that can affect central circulation or brain circulation
• Ongoing infection
• Inability to apprehend information about the study or to perform the tests