Concurrent Exercise Effects in Post-Bariatric Patients

Bariatric surgery is an effective intervention for the treatment of severe obesity; however, the early postoperative period, characterized by rapid weight loss, is often accompanied by unfavorable changes in body composition, including loss of lean mass and decreased muscle function. These alterations may negatively affect functional recovery and quality of life. In this context, physical exercise has been proposed as a key strategy within metabolic rehabilitation; nevertheless, there is limited evidence regarding the effectiveness of short-term concurrent exercise programs initiated in the early postoperative phase, particularly in relation to muscle quality.

The aim of this study is to evaluate the effect of a 5-week concurrent exercise program on rectus femoris muscle quality in individuals undergoing bariatric surgery, compared with a control group receiving usual care. Additionally, changes in body composition, functional response, and quality of life will be assessed, and the association between adherence to the exercise program and the magnitude of observed changes will be explored under a dose-response framework.

This is a single-center, prospective, longitudinal, non-randomized controlled clinical trial. The study will include two groups: an intervention group and a control group. A total of 84 adults aged 18 to 60 years who have undergone sleeve gastrectomy or Roux-en-Y gastric bypass at BUPA Clinic Santiago and have a medical indication for metabolic rehabilitation will be recruited. Participants will enter the study at postoperative week 4, when baseline assessments will be performed.

Participants will then be allocated to either the intervention or control group according to criteria defined by the research team. The intervention group will begin a concurrent exercise program immediately after baseline assessment, while the control group will continue with usual clinical care without participating in a structured exercise program during the study period.

The intervention will consist of a 5-week concurrent exercise program combining aerobic and resistance training. The program will include two supervised in-person sessions per week (10 sessions in total), each lasting approximately 60 minutes, and one recommended weekly home-based session guided by an individualized exercise plan. Training progression will be gradual and tailored to each participant's tolerance and clinical safety criteria. Aerobic exercise intensity will be monitored using the Borg Rating of Perceived Exertion scale, while resistance training will be adjusted according to individual capacity using estimated one-repetition maximum (1RM). The home-based session will be considered complementary and will not be included in adherence calculations.

After completing the 5-week intervention, a 1-week period without supervised sessions will be observed to minimize acute exercise effects on outcome measurements. The final assessment will be conducted at week 7 from baseline. Therefore, outcomes will be measured at two time points: baseline (pre-intervention) and 7 weeks after baseline (following 5 weeks of intervention and 1 week of rest).

The primary outcome will be rectus femoris muscle quality assessed by musculoskeletal ultrasound, using echo intensity as the main indicator. Secondary outcomes will include body composition assessed by bioelectrical impedance analysis, functional response measured using the one-minute sit-to-stand test (1min-STST), and quality of life assessed using the Moorehead-Ardelt II questionnaire.

Adherence to the exercise program will be assessed exclusively in the intervention group as the percentage of attendance at supervised sessions (adherence = attended sessions/10 × 100). For descriptive purposes, adherence will be categorized as high (≥80%), moderate (60-79%), or low (\<60%). Additionally, its association with the magnitude of changes in outcomes will be analyzed under a dose-response framework.

Statistical analyses will be performed using SPSS (v29). Data distribution will be assessed using the Shapiro-Wilk test. Continuous variables will be presented as mean ± standard deviation or median (interquartile range), as appropriate, and categorical variables as frequencies and percentages.

Changes in outcomes (Δ = post - pre) will be analyzed both within and between groups. Within-group analyses will be conducted using paired t-tests or Wilcoxon signed-rank tests, depending on data distribution. Between-group comparisons will be performed using independent t-tests or Mann-Whitney U tests. Additionally, repeated-measures analysis of variance (two-way ANOVA: group × time) or equivalent linear models may be used to evaluate interaction effects.

Effect sizes (e.g., Cohen's d) will be estimated to support clinical interpretation. To explore associations, Pearson or Spearman correlation coefficients will be used. Furthermore, multivariable linear regression models will be conducted to examine the association between adherence (continuous variable) and changes in primary and secondary outcomes within the intervention group, adjusting for relevant variables such as weight change during the intervention period (Δweight).

• Change in percent body fat (%) [Time frame: Baseline (pre-intervention) and 7 weeks after baseline (after 5 weeks of exercise and 1 week of rest).]
• Change in fat mass (kg) [Time frame: Baseline (pre-intervention) and 7 weeks after baseline (after 5 weeks of exercise and 1 week of rest).]
• Change in skeletal muscle mass (kg) [Time frame: Baseline (pre-intervention) and 7 weeks after baseline (after 5 weeks of exercise and 1 week of rest).]
• Change in 1-minute Sit-to-Stand performance (1min-STST) [Time frame: Baseline (pre-intervention) and 7 weeks after baseline (after 5 weeks of exercise and 1 week of rest).]
• Adherence to the exercise program (supervised in-clinic sessions) [Time frame: During the 5-week intervention period (calculated at the end of the program based on attendance to the 10 supervised sessions).]
• Change in visceral fat area (cm²) [Time frame: Baseline (pre-intervention) and 7 weeks after baseline (after 5 weeks of exercise and 1 week of rest).]
• Change in basal metabolic rate (kcal/day) [Time frame: Baseline (pre-intervention) and 7 weeks after baseline (after 5 weeks of exercise and 1 week of rest).]
• Change in rectus femoris muscle thickness (cm) [Time frame: Baseline (pre-intervention) and 7 weeks after baseline (after 5 weeks of exercise and 1 week of rest).]
• Change in rectus femoris cross-sectional area (cm²) [Time frame: Baseline (pre-intervention) and 7 weeks after baseline (after 5 weeks of exercise and 1 week of rest).]
• Change in fat infiltration measured by ultrasound in the rectus femoris (cm) [Time frame: Baseline (pre-intervention) and 7 weeks after baseline (after 5 weeks of exercise and 1 week of rest).]
• Change in quality of life assessed by the Moorehead-Ardelt II questionnaire [Time frame: Baseline (pre-intervention) and 7 weeks after baseline (after 5 weeks of exercise and 1 week of rest).]