The study will evaluate the utility of hypoxic exercise training to improve cardiovascular and metabolic health among obese breast cancer survivors. While participants exercise, a lower fraction of inspired oxygen will be used to simulate a higher altitude. This approach removes the mechanical strain needed to sustain moderate-to-vigorous exercise intensity which is believed to support exercise tolerance. Participants are randomized to either the treatment (walking+simulated-altitude) or control (walking under normoxic conditions).

Cancer survivors have a two-fold greater risk of having one or more functional limitations compared to those without a history of cancer. Though exercise interventions in breast cancer survivors exist, a large portion of women (61%) exhibit some form of lower-body dysfunction that severely restricts participation in physical activity and exercise. Both physical and emotional well-being are negatively affected by the combination of increased adiposity, orthopedic problems and muscle weakness, thus reinforcing a cycle of physical inactivity.

For these reasons, obese breast cancer survivors with walking limitations are faced with a barrier that greatly increases the difficulty of meeting prescribed exercise guidelines (≥150 weekly minutes of moderate-to-vigorous intensity exercise). Though previous investigations have demonstrated the safety and benefits of exercise+simulated altitude to improve body fat, physical endurance and insulin sensitivity, results have been limited to non-cancer participants only. Given the comorbidities common to breast cancer survivors, specifically, heart disease risk, lower body joint problems, low aerobic capacity, and fatigue, further research is needed.

Inclusion Criteria:

1. Physician's medical clearance for participation
2. English-speaking women
3. 18-70 years of age with a history of Stage 0-III breast cancer
4. Preferred walking speed of less than 2.9 mph as measured by a timed 10 meter walk test (to be performed on-site after consent during preliminary screening) "OR" the inability to complete a 6-minute walk without stopping (to be performed on-site after consent during preliminary screening)
5. Body mass index between 30-45 kg/m2
6. ≥1 year post-treatment and not currently receiving or planning to receive chemo/radiation therapies
7. Not participating in a structured exercise routine
8. In the previous 6 months, not engaging in (on average) ≥60 minutes of moderate or ≥30 minutes of vigorous physical activity per week.

Exclusion Criteria:

1. Males
2. Dementia
3. Medical, psychological, and/or social characteristics that may interfere with the ability to fully participate in the proposed study activities/assessments (e.g., psychosis, schizophrenia)
4. Contraindication to participate in regular exercise training
5. Unwilling to complete prescribed exercise
6. Inability to walk
7. Pregnant
8. Resting oxygen saturation via pulse oximetry below 90%
9. Using home oxygen therapy