The goal of this observational study is to evaluate the effectiveness of the multimodal prehabilitation program at the Siriraj Integrated Preoperative and Prehabilitation Center (SiPAP) on improving preoperative walking capacity and functional status in patients undergoing elective intraabdominal cancer surgery. The main question it aims to answer is:

- Does the prehabilitation program lead to a significant change in 6-minute walk distance (6MWD) at preoperative admission as compared to at baseline assessment? Participants will receive the structured multimodal prehabilitation program, which represents the standard of care for patients in the ERAS protocol at the study site. Outcomes will be measured at preoperative admission and at 1 and 3 months after surgery.

Surgical resection remains the mainstay of treatment for patients with intraabdominal malignancies such as colorectal, gastric, hepatobiliary, and pancreatic cancers. However, patients with cancer often present with impaired physical function, malnutrition, sarcopenia, and psychological distress, which may negatively impact their ability to tolerate surgery and recover postoperatively. Intraabdominal cancer surgery, particularly major procedures, imposes significant physiological stress, and reduced preoperative physical fitness has been associated with poor postoperative outcomes, including longer length of stay, increased complications, and delayed return to baseline function.

Prehabilitation, defined as the process of enhancing a patient's functional capacity before surgery to improve postoperative outcomes, has emerged as a promising strategy to address these challenges. Multimodal prehabilitation, typically involving aerobic and resistance exercise, nutritional optimization, and psychological support, has been shown to improve preoperative functional capacity, measured by objective tests such as the Six-Minute Walk Test (6MWT), and to enhance postoperative recovery.

The 6MWT is a simple, reproducible tool that reflects integrated cardiopulmonary and musculoskeletal function, and it has been widely used as a functional assessment in the preoperative setting. A minimal clinically important difference (MCID) of 20-30 meters has been suggested in various populations.Studies in colorectal and upper gastrointestinal cancer surgery have demonstrated that prehabilitation can lead to meaningful improvements in 6MWT distance, muscle strength, and health-related quality of life before surgery.

However, most existing studies have been conducted in Western countries, and there is limited data regarding the feasibility and benefits of prehabilitation in Asian populations, including Thailand, where differences in patient characteristics, healthcare systems, and cultural factors may influence outcomes. Furthermore, many prior studies have focused on postoperative endpoints, whereas preoperative functional improvement-as a modifiable, short-term goal-is less frequently studied despite its potential clinical and prognostic significance.

This prospective observational cohort study aims to evaluate the effectiveness of the multimodal prehabilitation program at the Siriraj Integrated Preoperative and Prehabilitation Center (SiPAP) on improving preoperative walking capacity and functional status in patients undergoing elective intraabdominal cancer surgery. The SiPAP at Siriraj Hospital, Bangkok, Thailand, has incorporated this multimodal prehabilitation program as part of the standard of care within the Enhanced Recovery After Surgery (ERAS) protocol. The findings of this study will clarify the feasibility and clinical utility of implementing prehabilitation in Thai patients undergoing cancer surgery and may inform the design of future randomized controlled trials or support the development of evidence-based guidelines.

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.

The patients who enroll to Enhanced Recovery After Surgery (ERAS) program, Siriraj Hospital and referred to the SiPAP program.