Inclusion and exclusion criteria for participants.

Adults with the following inclusion criteria are eligible to participate: (1) aged 18 years old and over, (2) scheduled for elective major abdominal surgery, (3) able to perform the 6-Minute Walk Test (6MWT), and (4) able to provide written informed consent. Excluded are patient with: (1) emergency operation for major abdominal surgery, (2) medically unstable or severe comorbidities that contraindicate exercise (e.g., unstable cardiovascular disease), (3) impaired cognition or confusion, and (4) impaired vision, cognition or physical impairment of upper and lower limbs in functional task components.

Informed consent.

Eligible patients who fulfil the inclusion criteria will be approached by the research team and invited to participate in the study. They will be provided with an information sheet outlining the study objectives, procedures, and expected time commitment together with the informed consent form prior to enrolment into the study. Upon obtaining written informed consent, participants will be formally enrolled in the study. Participants retain the autonomy to withdraw from the study at any point. Furthermore, if the principal investigator assesses that continued participation poses significant risk or harm to the participant, they will be withdrawn from the study to ensure their safety.

Randomisation and allocation.

Following recruitment and baseline assessments, participants will be randomly assigned to one of two groups which will be control group (MICT) or the intervention group (HIIT) using a computer-generated random number sequence. Allocation will be conducted by an independent individual utilizing a block randomization method (5 blocks of 14). An administrative assistant, independent of the trial, will prepare 70 sequentially numbered opaque envelopes, each containing a group allocation. A physiotherapist, trained in the study protocol, will deliver the intervention. Participants in the control group will receive moderate-intensity continuous training (MICT), while those in the intervention group will engage in high-intensity interval training (HIIT) preoperatively. Both groups will commence and conclude sessions with a warm-up and cool down to mitigate the risk of adverse events.

Blinding.

Patients and outcome assessors, will remain blinded to treatment allocation. However, the treating physiotherapists cannot be blinded due to the nature of the intervention. To maintain blinding, details of the intervention will not be recorded in the medical records. Outcome assessments will be conducted by a blinded assessor based off-site from the outpatient department, ensuring impartiality in both inpatient and outpatient settings. Intervention sessions will occur on different days from those scheduled for outcome assessments to further reduce the risk of unblinding. If a participant from the intervention group discloses details of their intervention to the assessor, this will be documented and reported, with the rationale recorded. All analyses will be performed on an intention-to-treat basis once randomization is unblinded.

Trial intervention.

The intervention will be delivered by the same physiotherapists at outpatient setting, based on the group allocation. All physiotherapists involved are senior clinicians with more than 5 years of experience in abdominal surgery. To ensure uniformity, the physiotherapists will have a standardized training in treating the patients. The prehabilitation exercise program is design based on recommendations from the current ERAS guidelines for major abdominal surgery [18,32]. Specifically, the program adapted from previously published protocols used in preoperative populations [1,2,14,33,34] with modifications tailored to the local clinical setting and characteristics of the target patient population.

Standard care for control group (MICT).

This will be a tailored and supervised by a single physiotherapist (more than 10 years clinical experiences in cardiorespiratory) in outpatient hospital setting. Participants will engage in an aerobic (moderate intensity continuous training), strengthening exercise and inspiratory muscles training program prior to the date of their surgery.

For aerobic exercise this will be a low intensity in week one with graduation to moderate intensity. Moderate intensity continuous training (MICT) will allow 55–75% of maximum heart rate (MHR) [35]. Aerobic exercise training (e.g.,: treadmill, cycling, walking exercise) 1–3 times per week (60 minutes) for overall duration typical 2–4 week prior to date of surgery. Patients’ Maximum Heart rate (210-age) and Karvonen Formula will be used for targeted heart rate. Patients’ heart rate will be monitored along the aerobic training using smart watch. However, the Karvonen formula may not be suitable for all patient populations, particularly those on beta-blockers or with underlying cardiac conditions. In such cases, training intensity will be guided by the patient’s Rating of Perceived Exertion (RPE) of 10–13 RPE score, and appropriate modifications will be made to ensure safety. This approach allows for individualized intensity adjustment while maintaining the safety and effectiveness of the intervention.

For the progressive resistance exercise, the following muscle groups will be targeted: biceps brachii, triceps brachii, pectoralis major and minor, latissimus dorsi, deltoid and rhomboids using free weights. The intensity will be 70–80% of estimated 10 repetitions maximum. The load not provided joint pain or severe muscle fatigue and/or arm fatigue on RPE of 10–13 on 6–20 RPE score [34]. Aim for a total session duration of about 45–60 minutes, including warm-up and cool-down. This includes 30–45 minutes of MICT, depending on the patient’s tolerance. Sessions will be done 1–3 times per week [34].

In addition to the PVC weighted bar, we also used different types of resistance training such as band, dumbbells, kettlebells. Inspiratory muscles training will be given 20 minutes per day with 30% of maximum inspiratory pressure (MIP) [14].

Participants will also be given an illustrated handout to assist further training support by the carer (advice regarding maintaining a set amount of aerobic/strength exercise per week standard [1,2,14]. Detailed session attendance checklist and vital sign will be recorded for every attendance for adherence.

Intervention group (HIIT).

Participants in the intervention group will receive the same care as the standard care group. Additionally, for aerobic exercise this will be a moderate intensity which is 55–75% of maximum heart rate (MHR) in week one, with graduation to high intensity in week two on > 80% of MHR [24]. Aerobic exercise training (e.g.,: Treadmill, Cycle ergometer, body weight exercises) 1–3 times per week (30 minutes) for an overall duration typically 2–4 weeks prior to the date of surgery. Patients’ Maximum Heart rate (210-age) and Karvonen Formula will be used for the targeted heart rate. Patients’ heart rate will be monitored along the aerobic training using a smartwatch. However, those patients who are on beta-blockers or with underlying cardiac conditions, training intensity will be guided by the RPE between 16–18 RPE score with appropriate adjustments made to ensure safety. The interval training will be 30–60 seconds of high-intensity training with 1–2 minutes of active recovery (light activity or complete rest) between intervals to facilitate recovery. This will be repeated for a total of 5–10 cycles [33].

In addition to aerobic training, participants will receive the same progressive resistance exercise and inspiratory muscle training, with intensity matched to that of the standard care of MICT group. Aim for a total session duration of about 20–30 minutes, including warm-up and cool-down. This includes 10–15 minutes of HIIT, depending on the patient’s tolerance. Sessions will be done 1–3 times per week, with rest days in between to allow for recovery. Participants will also receive an illustrated handout to guide continued training support by caregivers, including recommendations on maintaining a standard amount of aerobic and strength exercise per week. A detailed session attendance checklist and vital signs will be recorded at each session to monitor adherence.

All other aspects of patient care such as preoperative management, general anaesthesia, intraoperative ventilation settings, fluid administration, prophylactic antibiotic use, pain management, management of lines and drains, general nursing care, and discharge planning will be administered at the discretion of nurses and physicians in accordance with routine clinical practices at hospital for both groups.

The 6-Minute Walk Test (6MWT).

The 6MWT is a widely used measure to assess the submaximal level of functional capacity [36]. The test involves walking back and forth along a 30-meter indoor track for as many laps as possible within a 6-minute period [37,38]. Following the American Thoracic Society (ATS) guidelines, the test will be conducted before initiating prehabilitation, with the better result from two attempts recorded as the baseline measurement [39]. Participants will be informed of the elapsed time at the end of each minute during the test, but no additional encouragement will be provided [39].

Maximal inspiratory pressure.

Inspiratory muscle strength will be assessed by measuring the maximum inspiratory pressure (MIP) generated at the mouth using the PowerBreathe K2 device. Patients will be seated in an upright position and instructed to exhale fully to their residual volume before performing a maximal and rapid inspiratory effort lasting 3 seconds. The highest 1-second average value from each trial will be recorded. To ensure reliability, three consistent measurements (defined as having a coefficient of variation <10%) will be selected from 5 to 8 maximal trials, with each trial separated by a 60-second rest interval [40].

1 Minute Sit to Stand Test (1MSTST).

The 1MSTST is recognized as a tool for assessing functional status and predicting fall risk. It has shown a good correlation with exercise capacity in patients with chronic obstructive pulmonary disease (COPD) [41]. Studies have demonstrated a significant correlation between the number of repetitions completed in the 1MSTST and essential functional outcomes in patients with COPD, including the 6-minute walk distance (6MWD), quadriceps muscle strength, and physical activity levels [41–43]. These findings suggest that the 1MSTST may serve as a valid measure of exercise capacity following respiratory rehabilitation, especially in populations with comorbid of pulmonary complications, which is common in patients with major abdominal surgery.

Short Physical Performance Battery (SPPB).

The SPPB will be used to assess lower extremity physical performance status. It is an objective outcome measures of balance, lower extremity strength, and functional capacity which includes three domains (walking, sit-to-stand and balance) [44]. SPPB had an excellent interrater reliability (ICC = 0.92) among people with respiratory condition [45]. Besides, it may serve as a reliable surrogate endpoint for all-cause mortality in clinical trials aiming to evaluate the efficacy of specific treatments or rehabilitation programs in improving health outcomes [46].

The hospital anxiety and depression scale.

Anxiety and depression will be measured using the 14-item Hospital Anxiety and Depression Scale (HADS), which comprises two subscales: one for anxiety (HADS-A) and one for depression (HADS-D), each containing seven items [47]. Each item is scored on a 4-point Likert scale ranging from 0 (not present) to 3 (maximum), with a maximum subscale score of 21 points [48]. A cut-off score of ≥8 points will be applied to identify cases of anxiety or depression, as this threshold has been shown to optimize sensitivity and specificity for both subscales [48]. The HADS is a validated and reliable instrument, with Cronbach’s α values of 0.81 for HADS-A and 0.88 for HADS-D [48,49]. It has been widely translated and extensively utilized in international research [48,50], demonstrating high internal consistency in inpatient populations, including those undergoing median sternotomy [50].

Hand grip strength.

Hand grip strength will be measured in kilogram using a hand-held dynamometer with three attempts to assess physical fitness that related to muscular strength. The peak pressure of each 5-second attempt and the highest value will be recorded [51]. This hand-held dynamometer has excellent reliability (ICC = 0.98) and construct validity of r = 0.99 (very high correlation) with Rolyan dynamometers [52].

EuroQol (EQ-5D-5L).

Health related quality of life will be evaluated using self-assessment questionnaire EuroQol EQ-5D-5L. It consisted of five component scales, namely mobility, self-care, usual activities, pain, and anxiety. Recent evidence suggested that the newer 5-level version of the EQ-5D had improved measurement properties, including feasibility, ceiling effects, sensitivity, and convergent validity [53]. The EQ-5D-5L had good test-retest reliability, as indicated by intraclass correlation coefficients (ICCs) ranging from 0.65 to 0.91 for the EQ-5D index [54].

Self-assessment of physical activity questionnaire (SAQ).

Self-Assessment of Physical Activity Questionnaire (SAQ) will be used for physical capacity. The SAQ is a 13-item, self-administered activity questionnaire assessing common physical activities associated with personal care, ambulation, household tasks and recreation [55]. All these activities have a known metabolic equivalent (MET) obtained from the Compendium of Physical Activities. Each question required a ‘yes’ or ‘no’ response. A SAQ score will be obtained by recording the corresponding MET value of the most demanding activity that the participant perceived they could complete without symptoms [55]. All scores will be correlated against measured of peak oxygen consumption [55].

Fatigue severity scale (FSS).

The Fatigue Severity Scale (FSS) is a method of evaluating the impact of fatigue. The Fatigue Severity Scale (FSS) is widely used to assess the impact of fatigue on daily functioning. Its psychometric properties have been evaluated in various populations, demonstrating its reliability and validity [56]. The FSS is a short questionnaire that requires patients to rate their level of fatigue. The FSS questionnaire contains nine statements that rate the severity of fatigue symptoms. Read each statement and circle a number from 1 to 7, based on how accurately it reflects the condition during the past week and the extent to which patients agree or disagree that the statement applies to patients [57].

The global rating of change scale.

This is a self-reported measure of patients perceived change. It will be administered prior to the performance-based assessments preoperatively, prior to discharge, 4 weeks and 3 months postoperatively. Participants will be asked: ‘Overall, how do your arms function now, compared with how your arms functioned at the initial assessment before surgery?’ Responses will be recorded according to a 7-point scale from ‘very much improved’ to ‘very much worse’. It has been previously reported that when participants rate their change as ‘minimally improved’, ‘no change’ or ‘minimally worse’, it is unlikely that a clinically important difference has occurred; therefore, these patients are grouped into an ‘unchanged’ category [58]. Responses of ‘much worse’, ‘very much worse’, ‘much improved’ and ‘very much improved’ indicate a clinically important difference has occurred and therefore these patients are grouped into a ‘changed’ category [58].

Bio-electrical impedance analysis.

An InBody device utilizing Bio-electrical Impedance Analysis will be used to assess body composition by estimating key components such as lean body mass, fat mass, and total body water. This method involves passing a low-level electrical current through the body and measuring the resulting impedance to estimate body composition parameters, including total body water, extracellular water, intracellular water, fat mass, fat-free mass, body fat percentage, and bone mineral content [59].

Bioelectrical Impedance Analysis has been validated as a reliable method for assessing body composition, showing strong correlations with CT-derived measurements of torso fat volume and waist fat area, with correlation coefficients ranged from 0.86 to 0.95 in both men and women (p < 0.001) [60]. InBody devices showed a 98% correlation with dual-energy X-ray absorptiometry (DXA), with strong agreement across all body mass index (BMI) categories [61].