PURPOSE: This trial aimed to demonstrate feasibility of high-intensity interval training (HIIT) in post-menopausal, overweight/obese women at high-risk of invasive breast cancer, and explore HIIT on changes in cardiorespiratory fitness (CRF), body weight, and body mass index (BMI) compared to moderate-intensity continuous training (MICT) and usual care (UC). METHODS: Forty-four women were randomized to HIIT, MICT or UC for a 12-week, thrice weekly, supervised exercise intervention. HIIT included a 5-minute warm-up at 50 to 70% peak heart rate (HR), four cycles of four minutes at 90 to 100% peak HR followed by three minutes at 50 to 70% peak HR. MICT consisted of 41 minutes at 60 to 70% peak HR. Feasibility was assessed by consent, adherence, compliance and retention rates. CRF, body weight and BMI were measured at baseline and end-of-study. Repeated measures linear mixed models were used to assess within- and between-group differences. RESULTS: Average age was 63.9 +/- 8.8 years. BMI was 30.9 +/- 5.7 kg/m2. Participants completed 90% and 89% of HIIT and MICT workouts respectively, with 100% compliance to the exercise prescriptions. No serious adverse events were reported. Compared to MICT and UC, HIIT exhibited improvements in change in treadmill time (101 seconds greater than MICT, and 125 seconds greater than UC, respectively, p < 0.001). Compared to UC, HIIT exhibited improvement in changes in absolute and relative VO2peak (a 0.15 increase in L/min, p = 0.005; and 2.3 increase in ml/kg/min, p = 0.004). There were no significant differences between groups for body weight or BMI (p > 0.05). CONCLUSIONS: HIIT is feasible, safe, and appears to promote greater improvements in CRF compared to MICT and UC in women at high risk for breast cancer.

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