 The investigators propose a prospective blinded observational cohort study of patients undergoing NAC prior to elective upper gastrointestinal cancer resection oesophagectomy and gastrectomy in three NHS teaching hospitals. Exercise capacity fitness before and after NAC will be assessed using CPET and the relationship between the derived variables AT, VO2 peak and clinical outcomes will be described. Postoperative outcomes will be objective recorded clinically meaningful and will include mortality 1 year after surgery and short term postoperative harm described by the PostOperative Morbidity Survey POMS Quality of lifer using the EQ5D questionnaire and resource use e.g. hospital bed utilization. The hypotheses will be tested by constructing predictive models incorporating exercise variables and factors known to be related to outcome following surgery e.g. age, gender, open versus laparoscopic surgery. For example, for the Primary Hypothesis, models will be developed to predict the risk of one year mortality using i baseline exercise capacity and ii baseline exercise capacity and the relative decrease in exercise capacity. The aim will be to compare the predictive ability of both models to ascertain how prognostic the relative decrease in exercise capacity is, after adjusting for baseline exercise. In addition, Hypothesis 1 will be investigated by comparing AT before and after NAC using a paired t-test and Hypothesis 2 will be investigated by comparing the risk of 1year mortality between patients who stay in the same AT band and those who deteriorate using a chi squared test. Logistic regression will be used to repeat the analysis adjusting for potential confounders. 