Considerable research (\>500 studies) has examined the association between physical (in)activity and cancer incidence. Reviews of observational studies have led to the conclusion that there is some evidence for a reduced risk of 11 different cancer sites when comparing the highest to the lowest levels of physical activity (PA). Specifically, there is "strong" evidence that PA reduces the risk of bladder, breast, colon, endometrial, esophageal adenocarcinoma, and gastric cancers. As a result, public health agencies (e.g., Public Health Agency of Canada) promote PA as an important part of a healthy lifestyle and note that regular PA can help to reduce the risk of premature death and chronic diseases including breast cancer. The Canadian Society for Exercise Physiology (CSEP; https://csepguidelines.ca/guidelines/adults-18-64/) published recommendations for adults (aged 18-64) that include: (a) performing at least 150 minutes of moderate-to-vigorous intensity PA each week (i.e., activities that get your heart beating faster), (b) performing muscle strengthening activities at least twice a week, (c) limiting time spent sitting or laying down to 8 hours or less a day, and (d) achieving good quality and consistent sleep (i.e., 7 to 9 hours, with consistent bed and wake-up times).

Efforts to promote PA in adults at higher-than-average risk for breast cancer (reflected by their enrollment in the Ontario Breast Screening Program), are critical to reduce their risk of breast cancer. Despite the effectiveness of PA recommendations delivered through health care providers (HCPs), most individuals do not receive them during routine care as HCPs report barriers to promoting PA (e.g., inadequate training, lack of time/knowledge). Research needs to focus on developing sustainable interventions that can be implemented broadly using distance-based approaches and available infrastructure (e.g., patient registries) without burdening HCPs to increase the consistency with which PA is promoted to adults at higher-than-average risk for breast cancer. Unlike self-guided PA interventions, supervised face-to-face PA interventions can be costly, unsustainable, and have limited ability to reach individuals unable (or unwilling) to travel to a facility where interventions are delivered. Thus, online interventions should be explored as a means to expand support to adults at higher-than-average risk for breast cancer, as a complement to offering PA recommendations. When self-guided, these interventions are easily scalable at a relatively low marginal cost per additional participant. When self-guided, these interventions are easily scalable at a relatively low marginal cost per additional participant, accessible, self-paced, and available around the clock. Accordingly, they are frequently valued for their accessibility and convenience. Additionally, as interventions incorporating behaviour change techniques, such as goal setting and problem-solving, show greater sustained PA levels post-intervention, it is critical to embed those evidence-based techniques and PA materials (e.g., printed materials, logbook, webinars and education sessions) into online interventions if they are to be effective.

Accordingly, this team of researchers and HCPs have partnered to develop and evaluate an intervention comprising of a copy of PA recommendations for adults (18-64 years) plus a motivation package (intervention arm) that can be implemented using a distance-based approach and sustained in the current healthcare system without burdening HCPs. This study aims to test the following hypothesis: the effects of the intervention on PA (primary outcome), quality of life (QoL) (secondary outcome), and body mass index (BMI; secondary outcome) in adults at high-risk of breast cancer will be greater in comparison to standard care plus a copy of PA recommendations for adults (control arm).