Hoarding disorder (HD) is characterized by difficulty discarding personal possessions due to significant emotional distress when parting with personal items. This leads to the accumulation of excessive clutter which compromises the normal use of living spaces. In addition to emotional distress, individuals with HD experience significant impairment in physical health. One study found an 11-fold increase in stroke risk, a 10-fold increase in cancer risk, and a 7-fold increase in cardiovascular disease in individuals with HD relative to a general population comparison group. Patients with HD are also more likely to experience obesity and metabolic diseases such as diabetes. The short-term goal of the proposed study is to determine whether a brief exercise intervention improves discarding-related distress and brain-derived neurotropic factor (BDNF) in individuals with HD relative to a relaxation control condition. Preliminary evidence suggests that BDNF may be associated with greater body mass index and more severe HD symptoms in patients with HD. BDNF is a well-studied growth factor which is involved in neuronal transmission, plasticity, and survival of many neuron systems that have been implicated in psychiatric disorders, including serotonin, glutamate, and dopamine. BDNF has been proposed as a mechanism of exercise interventions for psychiatric disorders, as even one session of exercise has been shown to increase BDNF levels. This study represents an initial first step towards the long-term goal of improving current treatments for HD. This is important because although current cognitive-behavioral treatments (CBT) are effective, only 35% of patients who receive these treatments actually benefit from them. In the proposed pilot study, the investigators will test whether 30 minutes of moderate-intensity exercise reduces the distress associated with discarding and increases BDNF levels in individuals with HD relative to a relaxation control. The investigators will recruit 22 individuals with a primary diagnosis of HD. They will be randomly assigned to exercise or control. Following the intervention, the investigators will assess BDNF via serum. Participants will complete a standardized discarding task which consists of sorting and discarding personal possessions. The central hypothesis is that those in the exercise condition will demonstrate lower distress during the discarding task and greater BDNF levels as compared to those in the relaxation control condition. Should the hypothesis be confirmed, the investigators will be well poised to conduct large-scale clinical trials testing exercise interventions as adjunctive or alternative treatments to standard CBT.

Inclusion Criteria:

• Primary diagnosis of hoarding disorder
• Age 45-65 years

Exclusion Criteria:

• Contraindications to engaging in exercise, including cardiovascular, metabolic, or renal disease, thyroid problems, uncontrolled hypertension
• Significant mobility issues that would preclude brisk walking
• Schizophrenia, bipolar disorder, serious suicidal risk, active substance use disorder, and cognitive impairment that may preclude the ability to provide informed consent and/or participate in study procedures

Participants and investigators will not know the condition assignment until the intervention is about to begin. So the informed consent process, the study eligibility interview, and the self-report measures will be completed prior to condition assignment.