Inclusion Criteria post-oesophagectomy or -gastrectomy group:  is 18 years or older, and below 90 years of age, AND be able to walk, run or cycle a short distance, AND has been diagnosed with or already treated for oesophageal or gastric cancer if already receiving treatment, any type of treatment is included, either surgical resection for early-stage disease or definitive chemotherapy for advanced disease, AND use and Android phone  Inclusion Criteria healthy controls:  is 18 years or older, and below 90 years of age, AND no previous history of upper gastrointestinal cancer, AND not diagnosed with or undergoing treatment for active cancer since active cancer or cancer-related treatment might influence physical activity levels and quality of life, AND be able to walk, run or cycle a short distance, AND use an Android phone  Exclusion Criteria:  lacks capacity or is unable to provide informed consent, OR below 18 years of age or over 90 years of age, OR cannot walk, run or cycle a short distance, OR is diagnosed with or undergoing treatment for active cancer other than oesophageal or gastric cancer, OR is pregnant, OR is not using an Android phone, as Google Location History data is only accessible from an Android device