Procedure

All procedures will be carried out in line with the ethical standards laid out in the Declaration of Helsinki [32]. All procedures were approved by the Research Ethics Committee of the University of Thessaly, ref approval no. 39 (date of approval: 19/11/2020), the Ethics Committee of the Department of Physical Education & Sport Science, ref approval no. 1701 (date of approval: 09/12/2020) and the ethical review board of Northwest and Central Switzerland, ref approval no. AO_2020-00036 (date of approval: 26/11/2020). Prior to data assessment, all participants will sign written informed consent. On the consent form, participants will be asked if they agree to use of their data should they choose to withdraw from the trial. Participants will also be asked for permission for the research team to share relevant data with people from the universities taking part in the research or from regulatory authorities, where relevant. They will also be informed that the trial involves collecting blood specimen (10 drops) from every individual at each measurement occasion. Allocation to groups will be done randomly by a computer-generated code after the baseline assessment has taken place. In order to reduce random differences between the two groups, we will use the “OxMaR” software (Oxford Minimization and Randomization), taking into account the following stratification variables: gender, age, time fleeing and PTSD symptom severity. All data assessments will be made by trained research staff. At the post- and follow-up data assessment, assessors will be blinded with regard to group allocation. Since many participants will have limited English skills, all questionnaires will be provided in English, Arabic, Farsi, French and Greek, and a translator will be present during the data assessment. Main languages spoken in the camp are Arabic, Farsi, Koyrmatzi, Sorani, Somali and French.

Inclusion criteria are (a) written informed consent, (b) aged 16–59 years, (c) living in the selected refugee camp, (d) not having any contra-indications for moderate-intensity physical activity (based on the Physical Activity Readiness Questionnaire) [33], (e) being able to exercise at least two times per week for 60 min at moderate intensity and (f) being able to read English, Arabic, Farsi, French or Greek. In case of contra-indications, consultation with a medical doctor will be held. At the baseline, we will assess information about further concomitant care and interventions (e.g. use of antidepressants), in order to account for these factors as potential confounders/moderators.