This clinical trial aims to determinate whether a structured exercise program, supported by telerehabilitation, can help individuals with severe obesity who are going to undergo bariatric surgery.

The main objective of this study is whether a structured exercise program, including both supervised and home-based workouts, leads to greater body fat loss and improved strength compared to usual care. Furthermore, it also aims to evaluate other potentially affected aspects, such as body composition and functionality, quality of life, cardiovascular fitness, and various genetic and metabolic factors.

This study is a randomized clinical trial with two groups:

• The intervention group will follow a structured exercise program both pre- and post- surgery.
• The control group will receive standard care, including nutritional counseling and general health advice.

The study will include 72 adults with severe obesity (36 men and 36 women), all of whom will be randomly assigned to either the intervention or control group.

Participants in the exercise group will follow these steps:

1. Before Surgery (Prehabilitation): A 26-week program with aerobic and strength exercises, done in-person or remotely 2-4 times per week.
2. Pre-Surgery Maintenance: A flexible period before surgery where participants continue exercising on their own.
3. After Surgery (Rehabilitation): A 20-week program focused on recovery and strength.
4. Post-Surgery Maintenance: A long-term, self-guided phase to maintain progress.

Participants in the exercise group will also receive the same care as the control group, including nutrition counseling and medical checkups.

To evaluate participant progress, a series of measurements will be carried out, including:

• BMI and body composition
• Physical function assessed through isometric strength tests and other measures such as the Sit-to-Stand test and the 6-Minute Walk Test
• Quality of life and lifestyle assessed using validated questionnaires
• Daily physical activity measured with pedometers
• Metabolic and genetic analysis from blood samples

If proven effective, this program could help establish structured exercise with telerehabilitation as a standard component of obesity care. The results may support the integration of exercise programs into clinical practice, leading to improved long-term outcomes for individuals with severe obesity undergoing bariatric surgery. Additionally, insights into genetic and metabolic factors may contribute to the development of personalized treatment strategies.

INTRODUCTION Severe obesity represents a growing public health challenge in Spain, with a marked increase in prevalence and significant implications for morbidity, mortality, and healthcare expenditure. In 2022, nearly 400,000 individuals were affected by class III obesity, reflecting an increase of more than 200% since the 1990s. This condition is strongly associated with serious comorbidities, including cardiovascular disease, type 2 diabetes, and certain cancers, and is linked to a substantial reduction in life expectancy. From an economic perspective, overweight and obesity are estimated to account for approximately 10% of national healthcare costs, with severe obesity contributing significantly through both direct medical expenses and indirect costs related to productivity loss.

Conventional treatment strategies, such as dietary interventions and physical activity (PA), offer limited long-term effectiveness in individuals with severe obesity. Although physical exercise (PE)-a structured form of PA-has shown benefits beyond weight reduction, including improvements in body composition and cardiorespiratory fitness, the majority of participants find it difficult to sustain behavioral changes over time. Furthermore, the degree of weight loss required in this population frequently exceeds what lifestyle interventions alone can achieve.

Bariatric surgery has emerged as an effective alternative, providing substantial short-term weight reduction and improvement in obesity-related comorbidities. However, it is not without limitations, including the loss of lean body mass and the risk of long-term weight regain, particularly in the absence of adequate PA following surgery. Recent studies have shown that postoperative PE programs may improve these outcomes, although the evidence on the benefits of preoperative exercise (prehabilitation) remains limited.

In this context, telerehabilitation appears to be a promising strategy for enhancing accessibility, adherence, and continuity of care. Remote supervision of structured exercise programs, supported by wearable technologies such as activity trackers, may help overcome common barriers and increase participant engagement. Additionally, the substantial variability in individual responses to obesity treatment highlights the need for personalized interventions. Genetic, metabolic, and epigenetic factors likely contribute to treatment resistance in certain individuals, and the identification of predictive biomarkers may help guide more effective and individualized obesity management strategies.

OBJECTIVES:

Primary Objective To evaluate whether a structured PE and PA promotion program, incorporating both supervised in-person and home-based sessions through telerehabilitation tools, is more effective than standard care guidelines in reducing fat percentage and increasing lower-limb strength in candidates for bariatric surgery.

Secondary Objectives

To determine whether the structured PE and PA program is more effective than standard care in achieving:

1. Improved physical functionality.
2. Greater cardiovascular capacity.
3. Enhanced quality of life.
4. Superior outcomes in other body composition variables.

Additional secondary objectives include:

1. Evaluating adherence to the recommended session frequency and prescribed training volume.
2. Analyzing the relative contribution, adjusted for sex, of fat percentage reduction and lower-limb strength improvement to functionality and quality of life.
3. Assessing the effects of the PE and PA program on plasma levels of adipokines, exerquines, and cytokines.
4. Investigating epigenetic modifications induced by the PE program.
5. Identifying differences in metabolic, genetic, and epigenetic profiles according to physical fitness level and total volume of PE and PA performed (stratified by activity level, independent of group allocation).
6. Exploring associations between body composition and functional variables with metabolic, genetic, and epigenetic factors.

METHODOLOGY The methodology of the study is included in the initial summary and detailed in the subsequent sections (study design, arms and interventions, outcomes measures and elegibility) .

SAMPLE SIZE The sample size for this clinical trial was determined based on the two coprimary outcomes: fat percentage and lower-limb strength. For fat percentage, the calculation aimed to detect a 2% reduction in the experimental group compared to the control group, with 80% statistical power and a 5% significance level, resulting in an estimated minimum of 13 participants per group. Similarly, for lower-limb strength, assessed via the 5-repetition Sit-to-Stand (5STS) test, a 30% improvement was considered clinically relevant, requiring only 6 participants per group under the same statistical assumptions.

Given that the variable with the higher sample size requirement was fat percentage, it was used to guide the final sample size. To allow for subgroup analyses by sex, the study was designed to include 30 participants per group-15 women and 15 men. To accommodate an anticipated dropout rate of 20%, the final sample size was increased to 36 participants in each group, with equal sex distribution (18 women and 18 men per group).

STATISTICAL METHODS Data management and statistical analyses will be performed using SPSS software. A dedicated study database will be created, and data accuracy will be verified through random cross-checks with original records. Prior to analysis, data cleaning will be conducted to ensure consistency and completeness, followed by the creation of derived variables where necessary.

The analysis will begin with a flowchart of participant progression throughout the study, alongside a comparison of baseline characteristics between groups to assess equivalence at enrollment. Descriptive statistics will be used: categorical variables will be reported as frequencies and percentages, while continuous variables will be expressed as means and standard deviations or medians and interquartile ranges, depending on data distribution.

To evaluate the primary outcomes, a mixed-model ANOVA will be conducted, with time (baseline, end of prehabilitation, and pre-surgery) as the within-subject factor and group allocation (intervention vs. control) as the between-subject factor. The assumptions of normality and homogeneity will be tested using the Shapiro-Wilk and Levene's tests, respectively. When assumptions are violated, appropriate statistical corrections will be applied.

Effect sizes will be reported using partial eta squared (η²), and post hoc analyses will include Bonferroni correction when significant group-time interactions are detected. The magnitude of observed effects will be interpreted using Cohen's d.

The same statistical approach will be applied to secondary outcomes, such as physical function, cardiovascular fitness, quality of life, and body composition. Intervention adherence will be quantified by the proportion of completed sessions and those performed at the prescribed intensity, followed by between-group comparisons using non-parametric tests as appropriate.

To assess the influence of fat mass reduction and improved lower-limb strength on clinically relevant outcomes (e.g., Six-Minute Walk Test [6MWT], Impact of Weight on Quality of Life [IWQOL]), participants will be dichotomized based on whether they achieved a minimally clinically important difference. Multivariate logistic regression models will be constructed, using these two variables and sex as predictors. Model refinement will be carried out via backward elimination, and results will be presented as odds ratios with 95% confidence intervals.

Finally, linear regression models will be used to explore associations between body composition and functional outcomes with genetic, metabolic, and epigenetic markers.

SUBSTUDY 2: POSTOPERATIVE REHABILITATION FOLLOWING BARIATRIC SURGERY In addition to the main study, a subgroup of participants will be enrolled exclusively in the postoperative phase, forming part of Substudy 2. This substudy targets individuals already on the bariatric surgery waiting list and focuses solely on postoperative rehabilitation and maintenance.

The study design and intervention protocols are identical to those of the main study, but the follow-up period is limited to 12 months. Measurements will be conducted at three time points: prior to surgery, 6 months post-surgery, and 12 months post-surgery.

The key differences between the two substudies are as follows:

• Primary Outcome Measures: Given the exclusive postoperative focus of Substudy 2, the primary endpoints differ from those in the main study:

  • Lean Mass Reduction: Assessed via bioelectrical impedance analysis (BIA), this outcome is prioritized over fat percentage reduction, as substantial fat mass loss is expected in all participants following surgery.
  • Lower-Limb Strength: Evaluated using the Five-Repetition Sit-to-Stand (5STS) test, which serves as a functional indicator of muscular performance and recovery.

• Sample Size: The sample size was calculated to detect a directional hypothesis of a 25% smaller decrease in lean mass in the experimental group compared to the control group (effect size f = 0.8), with 80% power and a 5% significance level. This calculation yielded a minimum requirement of 15 participants per group.

To allow for sex-based subgroup analyses, each group (intervention and control) must include 30 participants-15 women and 15 men. Considering an expected dropout rate of approximately 15% in this substudy, the final sample size will be increased to 34 participants per group, resulting in a total of 68 participants overall.

Aside from the differences outlined above, all remaining aspects of Substudy 2-including methodology, intervention content, and assessment procedures-will follow the same protocols described in the main study.

Inclusion Criteria:

• Age: 18-65 years
• BMI ≥35 with comorbidities, or ≥40, regardless of comorbidity presence

Exclusion Criteria:

• Participation in a structured physical exercise program within the past 6 months
• Presence of musculoskeletal or systemic diseases that prevent participation in a physical exercise program
• Uncontrolled hypertension
• Uncontrolled diabetes, particularly in the presence of severe complications (neuropathy and/or diabetic foot, proliferative retinopathy)
• Uncontrolled or unstable cardiovascular disease (acute myocardial infarction within the past year, angina, heart failure, peripheral artery disease)

Eligible participants who consent to participate will be randomly assigned to either the standard care group or a physical exercise (PE) program incorporating telerehabilitation. Randomization will be performed using permuted blocks of six participants to ensure balanced allocation and concealment. The randomization sequence will be generated by an independent researcher not involved in participant recruitment or group assignment, and will be concealed in sequentially numbered, opaque, and sealed envelopes.

After the baseline assessment, study personnel will open the next envelope in the sequence, and the assigned intervention will commence immediately. To preserve methodological rigor, both the evaluators conducting participant assessments and the researchers performing data analyses will remain blinded to group allocation throughout the study.