Background: Treatment of locally advanced oesophago-gastric adenocarcinoma usually entails neo-adjuvant chemotherapy (NAC) and surgery. Surgery is associated with high morbidity and mortality. Cardiopulmonary reserve of patients having major surgery is related to postoperative outcomes. Complications are associated with poorer quality of life and may affect prognosis. Preventing complications may be beneficial to both of these and have cost implications. Prehabilitation may improve recovery from surgery by increasing a patients' fitness before surgery. Designing a potentially cost and resource effective regimen which improves cardiopulmonary reserve may have a beneficial impact on patient outcomes after surgery. Methods: The ChemoFit study is a non-randomised, single-arm and single-centre pilot study designed to investigate the feasibility of a home-based prehabilitation exercise intervention for patients receiving neoadjuvant treatment prior to oesophago-gastric surgery. Forty patients will be recruited at a single high-volume centre. The simple, home-based exercise intervention involves patients increasing their daily step-count during and after NAC and in the weeks leading up to surgical resection of the cancer. Additionally, quality of life assessments (QLQ-C30 and QLQ-OG25), oncological treatment delivery and participant perceptions of the study assessed by focus groups and questionnaires will be performed. The primary outcomes are to assess feasibility of the exercise intervention. The secondary outcomes will evaluate changes in cardiopulmonary reserve, sarcopenia and fat composition. Discussion: It is anticipated that during an important teachable moment, the diagnosis and treatment of cancer, our patients will be open to the possibility of improving their fitness during chemotherapy and before major cancer surgery. It is possible that the negative impact of NAC on cardiopulmonary fitness could be prevented by implementing a home-based prehabilitation programme during and after NAC, prior to surgery for oesophago-gastric adenocarcinoma. Trial registration: This study has been approved by the Health Research Authority (REC 18/WA/0427). Newcastle upon Tyne Hospitals NHS Foundation Trust (NUTH) will act as the study sponsor and the work is funded by a grant awarded by The Jon Moulton Charitable Foundation, supported by a research post funded by the Sir Bobby Robson Foundation.