Introduction
depressive disorder, MDD, depressive symptoms
DISORDER
Major depressive disorder (MDD) is a prevailing mental health disorder, including among U.S. service members [Fortunately, existing evidence-based treatments, such as cognitive behavioral therapy and antidepressant medications, are efficacious in treating MDD [Given the variability in treatment tolerance and response [The effectiveness of physical activity on improving mental health may be due to several factors. One factor, social interaction, is associated with improved psychological health [Although hiking/walking is physical activity that can incorporate social interaction within a natural environment, a water-based environment or “blue space” [Surfing is a water-based activity shown to have beneficial effects for mental health in military samples. Among veterans and service members, surf therapy—an intervention using surfing to promote well-being (International Surf Therapy Organization, 2019; Despite preliminary evidence for the psychological benefits of surf therapy, there are limitations in the literature. Currently, few studies [This study aims to address these limitations and evaluate the efficacy of activity-based interventions for MDD. Importantly, there are no published studies examining the effects of surf therapy using a randomized controlled trial (RCT) design or evaluating depressive symptoms following hike therapy in those with MDD. The rigorous design allows for the examination of both surf and hike therapy, providing clinical knowledge of intervention effects for service members with MDD. As a control condition, hiking is a sound comparison to surfing. Hiking is a physical activity with similar energy expenditure to surfing [