The trial objectives are as follows: Primary: To evaluate the effect of a prehabilitation programme during neo-adjuvant therapy on CPX performance prior to resection for oesophago-gastric cancer. Secondary: To investigate the impact of neo-adjuvant chemotherapy on insulin resistance; to determine whether a prehabilitation exercise programme is feasible during neo-adjuvant chemotherapy; to determine whether rehabilitation has a positive impact on quality of life outcomes; to investigate the impact of prehabilitation on clinical outcomes; to assess the effect of prehabilitation on nutritional status; to determine whether prehabilitation affects the stress response to surgery.