Background: Psychological distress is highly prevalent in mid-aged adults (i.e., aged 40 to 64 years) and is associated with adverse physical and mental health outcomes and economic burden. Mastery and physical activity are potential independent resources to mitigate distress, however, most research has examined these constructs independently. Therefore, the aim of this Clinical PhD research program was to understand the inter-relationship of mastery and physical activity with psychological distress in Australian mid-aged adults. [...]