Treatment of cancer patients should not only involve removing the cancer, but should also focus on maintaining good health and well-being and quality of life. This can be done by offering patients suitable rehabilitation programmes. Previous research has shown that such programmes need to involve exercise alongside other components, such as psychological support. To date most studies have looked at the positive effects of moderate-intensity exercise such as brisk walking, but this type of exercise is time-consuming and often not done by many patients. Shorter-duration exercise routines consisting of repeated short sprints have been found to improve general health just as well, but one of the most time-efficient routines (termed 'reduced-exertion high-intensity interval training', or 'REHIT') has not been studied in cancer patients. REHIT involves 3 exercise sessions per week, each only 10 minutes long. This makes it an ideal routine to combine with other components of a cancer rehabilitation programme. The present study will determine whether REHIT can improve important markers of health and well-being in newly diagnosed breast cancer patients. To achieve this the investigators will recruit up to 30 patients and divide them into a group who will do REHIT before and for up to 6 weeks after their cancer surgery, and a control group who will receive standard care. Markers of health and well-being will be measured at the start of the study, ~1 week after surgery, and ~7 weeks after surgery. Any changes will be compared between the exercise group and the control group. If beneficial effects are found with the REHIT intervention then this could be more widely implemented as part of cancer treatment. This study is funded by Nuffield Health and will be performed in Oxford, UK.