Prehabilitation to Enhance Preoperative Function in Elderly Undergoing Abdominal Malignancy Surgery

Inclusion Criteria: * Diagnosed with intraabdominal malignancy (e.g., colorectal, esophageal, gastric, pancreatic, hepatic, biliary tract, urinary bladder, or endometrial malignancies). * Schedules for elective major surgery and formally enrollment in the ERAS program at Siriraj Hospital. (at Siriraj Hospital, patients scheduled for pre-specific elective major surgeries are enrolled into the ERAS program as individual hospital protocols for each ERAS module. All patients are informed about the ERAS program by their surgical team.) * Referred to the SiPAP center for prehabilitation in accordance with the ERAS preoperative protocol, with a minimum preoperative time of 14 days before the scheduled surgery date. * Able to understand the study protocol and provide written informed consent. Exclusion Criteria: * Have emergency surgery * Reschedule the surgery for an earlier date, allowing less than 14 days for prehabilitation. * Severe cardiopulmonary or musculoskeletal conditions that contraindicate exercise (e.g., unstable angina, decompensated heart failure, severe COPD, or orthopedic disability). * Cognitive impairment or psychiatric illness precluding participation in prehabilitation. * Refusal to participate. * Inability to comply with the protocol.