 Neoadjuvant chemoradiotherapy NACRT prior to surgery for lower gastrointestinal colon and rectal cancer is associated with improved survival, but also adversely affects physical fitness, potentially rendering patients unfit for major surgery or increasing the risk of adverse outcome death and serious complications after major surgery. The investigators have pilot data using an upper gastrointestinal cancer patient cohort showing that neoadjuvant chemotherapy NACreduces objectively measured exercise capacity fitness. The investigators therefore propose a blinded, single centre, prospective interventional trial of patients undergoing NACRT prior to elective colorectal cancer resection in an NHS teaching hospital. 