The Muscle Paradox in Bariatric Surgery: Early Post-opertative Loss of Muscle Mass without Functional Decline

The Muscle Paradox in Bariatric Surgery: Early Post-opertative Loss of Muscle Mass without Functional Decline | Research Square window.SnipcartSettings = { analytics: { enabled: false } }; (function() { var accessVector = localStorage.getItem('access_vector') || ''; window.dataLayer = window.dataLayer || []; if (accessVector) { window.dataLayer.push({ user: { profile: { profileInfo: { snid: accessVector } } } }); } })(); (function(w,d,s,l,i){w[l]=w[l]||[];w[l].push({'gtm.start':new Date().getTime(),event:'gtm.js'});var f=d.getElementsByTagName(s)[0],j=d.createElement(s),dl=l!='dataLayer'?'&l='+l:'';j.async=true;j.src='https://www.googletagmanager.com/gtm.js?id='+i+dl;f.parentNode.insertBefore(j,f);})(window,document,'script','dataLayer','GTM-K279D39R'); Browse Preprints In Review Journals COVID-19 Preprints AJE Video Bytes Research Tools Research Promotion AJE Professional Editing AJE Rubriq About Preprint Platform In Review Editorial Policies Our Team Advisory Board Help Center Sign In Submit a Preprint Cite Share Download PDF Research Article The Muscle Paradox in Bariatric Surgery: Early Post-opertative Loss of Muscle Mass without Functional Decline Tamyris Silva, Regina Silva, Patricia Lisboa, Iala Bertasso, Luiz Guilherme Kraemer-Aguiar, and 1 more This is a preprint; it has not been peer reviewed by a journal. https://doi.org/ 10.21203/rs.3.rs-9360148/v1 This work is licensed under a CC BY 4.0 License Status: Under Review Version 1 posted 6 You are reading this latest preprint version Abstract Background Bariatric and metabolic surgery (BMS) induces rapid weight loss, often accompanied by reductions in lean mass. However, early postoperative adaptations in muscle function and sarcopenic obesity (SO) remain incompletely understood. This study investigated short-term changes in muscle mass, muscle strength, muscle quality, and SO prevalence, according to ESPEN/EASO criteria, within 6 months after Roux-en-Y gastric bypass (RYGB). Methods In this prospective study, adults with severe obesity undergoing RYGB were evaluated before surgery and 6 months postoperatively. Body composition was assessed by dual-energy X-ray absorptiometry, and appendicular skeletal muscle mass (ASM) was calculated. Muscle strength was evaluated by handgrip strength (HGS) and chair stand test. Muscle quality was estimated using the muscle quality index (MQI = HGS/ASM). Metabolic, inflammatory, and muscle-related biomarkers were also analyzed. Results Forty participants (46.5 ± 9.6 years; 92% women) were included. Body weight, BMI, ASM, and fat-free mass decreased significantly over follow-up, whereas ASM/weight increased significantly. Absolute muscle strength remained stable, with no significant changes in HGS or chair stand performance. MQI showed a modest but significant increase over time. Metabolic parameters improved substantially, including reductions in fasting glucose, HbA1c, insulin, triglycerides, total cholesterol, LDL-c, and hs-CRP, while vitamin D increased significantly. IL-6 decreased significantly, whereas TNF-α and myostatin remained unchanged. The prevalence of SO decreased descriptively according to both functional definitions, although these changes were not statistically significant. In an exploratory multivariable model, only ΔIL-6 was independently associated with ΔMQI. Conclusion Despite significant reductions in absolute muscle mass during the first 6 months after RYGB, absolute muscle strength was preserved. These findings suggest that early postoperative loss of muscle mass does not necessarily translate into measurable short-term functional decline and support the inclusion of functional assessment in postoperative follow-up. bariatric surgery sarcopenic obesity muscle quality index muscle strength Introduction Obesity is a chronic disease associated with metabolic dysfunction, systemic inflammation, reduced physical function, and increased risk of multiple comorbidities, substantially impairing quality of life. Among available treatment options, bariatric and metabolic surgery (BMS) is the most effective intervention for severe obesity, producing substantial and sustained weight loss together with important metabolic benefits. Roux-en-Y gastric bypass (RYGB) remains one of the most widely performed procedures and is associated with marked improvements in glycemic control and cardiometabolic risk. 1–5 Despite these benefits, preservation of skeletal muscle health during the postoperative period remains an important clinical concern. Rapid weight loss after bariatric surgery is frequently accompanied by reductions in lean mass and fat-free mass, which may raise concern regarding physical function and long-term musculoskeletal health. 5,6 In this context, assessment of postoperative adaptation should not rely exclusively on body weight or lean mass estimates, since changes in muscle quantity do not necessarily reflect changes in functional status. 6,7 Sarcopenic obesity (SO), defined as the coexistence of excess adiposity and impaired muscle mass and function, has gained increasing attention as a clinically relevant phenotype associated with adverse outcomes. 8–11 The 2022 ESPEN/EASO consensus provided a standardized framework for the diagnosis of SO, emphasizing the integration of body composition and functional performance. 10 However, SO remains insufficiently investigated in bariatric populations, particularly during the early postoperative period, when the most pronounced changes in body composition occur. 10,11 In addition to muscle mass and strength, derived indices such as the muscle quality index (MQI) may provide complementary information by relating strength to appendicular muscle mass. 12,13 Nevertheless, the interpretation of such indices in the context of rapid postoperative weight loss remains challenging, and early changes in muscle mass, function, muscle quality, and SO after RYGB are still incompletely understood. 6,12,13 Therefore, this prospective study aimed to investigate short-term changes in body composition, muscle strength, muscle quality, and SO prevalence during the first 6 months after RYGB, together with metabolic and inflammatory changes that may accompany postoperative adaptation. Methods This was a prospective longitudinal study conducted at the Obesity Unit, Multiuser Clinical Research Center (CePeM), Hospital Universitário Pedro Ernesto, State University of Rio de Janeiro, Rio de Janeiro, Brazil. Adults aged 20–65 years with severe obesity were eligible if they had a body mass index (BMI) ≥ 35 kg/m² with obesity-related comorbidities or BMI ≥ 40 kg/m² regardless of comorbidities. Exclusion criteria were body weight > 160 kg (equipment limit), previous bariatric or major gastrointestinal surgery, chronic neuromuscular or inflammatory disease, use of medications known to affect muscle metabolism, or refusal to provide informed consent. Participants were evaluated preoperatively and again 6 months after Roux-en-Y gastric bypass (RYGB). The study was conducted in accordance with the Declaration of Helsinki and was approved by the local Research Ethics Committee. All participants provided written informed consent before enrollment. Anthropometry and body composition Anthropometric measurements were obtained according to World Health Organization recommendations 14 . Body composition was assessed by dual-energy X-ray absorptiometry (DXA; GE Medical Systems, Lunar, Madison, WI, USA) using Encore software version 13.60. Appendicular skeletal muscle mass (ASM) was calculated as the sum of lean mass from both arms and legs. Relative ASM was expressed as ASM adjusted for body weight (ASM/weight × 100) 15,16 . Total fat mass (FM) and fat-free mass (FFM) were obtained directly from DXA measurements. Muscle Strength, Muscle Quality, and Sarcopenic Obesity Muscle strength was assessed by handgrip strength (HGS) using a JAMAR hydraulic dynamometer (model SH5001, Saehan Corporation, Korea). Three maximal attempts were performed using the dominant hand, and the highest value was used for analysis. Low handgrip strength was defined as < 32 kg for men and < 19 kg for women, according to the normative reference values adopted in the ESPEN/EASO consensus for sarcopenic obesity 10,17 . Lower-limb performance was assessed using the five-repetition chair stand test. Low lower-limb strength/performance was defined as a completion time ≥ 17 seconds for both sexes 10 . Muscle quality was assessed using the Muscle Quality Index (MQI), calculated as the ratio between handgrip strength and appendicular skeletal muscle mass (MQI = HGS/ASM). MQI was analyzed as a continuous derived index and also categorized using previously proposed sex-specific thresholds: normal (> 1.53), low muscle quality (1.35 < MQI ≤ 1.53 for women; 1.36 < MQI ≤ 1.53 for men), and poor muscle quality (≤ 1.35 for women; ≤ 1.36 for men). For descriptive analyses of muscular vulnerability, participants classified as having low or poor muscle quality were grouped together 13 . Sarcopenic obesity (SO) was defined according to the 2022 ESPEN/EASO consensus, integrating DXA-derived muscle mass with functional measures, including HGS and chair stand performance. SO prevalence was examined using both functional definitions combined with ASM/weight 10 . Weight Loss Outcomes Weight loss was assessed using percentage total weight loss (%TWL) and percentage excess weight loss (%EWL), according to standardized reporting recommendations. %TWL was calculated as: (preoperative weight − postoperative weight) / preoperative weight × 100. %EWL was calculated as: [(preoperative weight − postoperative weight) / (preoperative weight − ideal weight)] × 100,where ideal weight was defined as the weight corresponding to a BMI of 25 kg/m². 19 Physical Activity Assessment Physical activity was assessed at both time points using the short form of the International Physical Activity Questionnaire (IPAQ-SF). Participants were classified according to IPAQ-SF scoring guidelines into five categories: inactive, irregularly active A, irregularly active B, active, and very active. Laboratory and Biomarker Assessments Fasting blood samples were collected preoperatively and at 6 months after surgery to measure glucose, glycated hemoglobin (HbA1c), insulin, lipid profile, vitamin D, and high-sensitivity C-reactive protein (hs-CRP) using standard laboratory methods. Circulating cytokines and muscle-related biomarkers were measured in serum samples using a magnetic bead-based multiplex immunoassay (MILLIPLEX MAP Human Cytokine/Chemokine/Angiogenesis Panel, Merck KGaA, Darmstadt, Germany) on a Luminex 200 system (Luminex Corp, Austin, TX, USA), according to the manufacturer’s instructions. The following analytes were quantified: interleukin-6 (IL-6), tumor necrosis factor-alpha (TNF-α), and myostatin. Detection sensitivities were 0.9 pg/mL for IL-6, 0.1 pg/mL for TNF-α, and 163 pg/mL for myostatin. All samples were analyzed in duplicate, and data were processed using BeadView software. Statistical Analysis Paired changes (Δ) were calculated as the 6-month postoperative value minus the preoperative value. Positive Δ values indicated an increase over time, whereas negative Δ values indicated a decrease. Data distribution was assessed using the Shapiro–Wilk test. Continuous variables with approximately normal distribution were expressed as mean ± standard deviation (SD), whereas non-normally distributed variables were expressed as median [interquartile range]. Comparisons between preoperative and 6-month postoperative values were performed using the paired t-test or Wilcoxon matched-pairs signed-rank test, as appropriate. For parametric paired changes, 95% confidence intervals (95% CI) were also calculated. Changes in sarcopenic obesity prevalence between time points were assessed using the exact McNemar test. Changes in the global distribution of IPAQ-SF categories between baseline and 6 months were assessed using a marginal homogeneity approach for paired categorical data. Correlations between continuous variables were evaluated using Pearson or Spearman coefficients, according to data distribution. An exploratory multivariable linear regression model was used to investigate factors independently associated with the change in MQI (ΔMQI), including age, %TWL, hs-CRP, and change in IL-6 (ΔIL-6) as covariates. Given the sample size and the derived nature of MQI, this model was interpreted as exploratory. Statistical significance was set at p < 0.05 Results A total of 40 participants were included in the longitudinal analysis of anthropometry, body composition, muscle function, and SO prevalence. At 6 months after RYGB, mean total weight loss (%TWL) was 23.8 ± 5.4, corresponding to an excess weight loss (%EWL) of 56.7 ± 14.6. As shown in Table 1 , body weight decreased from 120.5 ± 16.6 to 88.4 ± 13.0 kg (Δ = -32.2 ± 24.3 kg; 95% CI -39.8 to -24.5; p < 0.0001), and BMI decreased from 45.8 ± 5.0 to 33.7 ± 4.2 kg/m² (Δ = -12.1 ± 7.3 kg/m²; 95% CI -14.4 to -9.8; p < 0.0001). ASM also decreased significantly, from 25.7 ± 5.1 to 22.7 ± 3.9 kg (Δ = -3.0 ± 6.5 kg; 95% CI -5.0 to -1.0; p = 0.0042), whereas ASM/weight increased from 21.3 ± 3.4% to 25.6 ± 2.6% (Δ = 4.3 ± 4.4; 95% CI 2.9 to 5.7; p < 0.0001). Fat-free mass also decreased significantly during follow-up. Table 1 Longitudinal changes in anthropometry, body composition, muscle function, and physical activity from baseline to 6 months after RYGB Variable Baseline 6 months Δ (T6 − T0) 95% CI for Δ p-value Anthropometric and body composition Weight (kg) 120.5 ± 16.6 88.4 ± 13.0 -32.2 ± 24.3 -39.8 to -24.5 < 0.0001 BMI (kg/m²) 45.8 ± 5.0 33.7 ± 4.2 -12.1 ± 7.3 -14.4 to -9.8 < 0.0001 ASM (kg) 25.7 ± 5.1 22.7 ± 3.9 -3.0 ± 6.5 -5.0 to -1.0 0.0042 ASM/weight (%) 21.3 ± 3.4 25.6 ± 2.6 4.3 ± 4.4 2.9 to 5.7 < 0.0001 FFM (kg) 58.1 ± 7.6 51.6 ± 7.4 −6.5 ± 8.8 58.1 ± 7.6 < 0.0001 Muscle function and quality HGS (kg) 30.8 ± 9.0 29.3 ± 6.6 -1.5 ± 10.6 -4.8 to 1.8 0.3648 Chair stand test (s) 13.7 ± 4.1 12.3 ± 3.6 -1.4 ± 5.4 -3.1 to 0.3 0.1020 MQI 1.2 (0.3) 1.3 (0.2) 0.1 ± 0.4 -0.0 to 0.2 0.0101 Physical activity level, n (%) Inactive 23 (54.8) 3 (7.1) < 0.0001 Irregularly active B 4 (9.5) 3 (7.1) Irregularly active A 13 (31.0) 7 (16.7) Active 1 (2.4) 19 (45.2) Very active 1 (2.4) 10 (23.8) Continuous variables are presented as mean ± standard deviation when analyzed with the paired t-test and as median [interquartile range] when analyzed with the Wilcoxon signed-rank test. Δ values are presented as mean ± standard deviation or median [interquartile range], as appropriate. 95% confidence intervals are shown for mean paired changes only. ASM, appendicular skeletal muscle mass; FFM, fat-free mass; HGS, handgrip strength; MQI, muscle quality index. No significant changes were observed in absolute muscle function measures (Table 1 ). Handgrip strength remained unchanged from baseline to 6 months (30.8 ± 9.0 vs. 29.3 ± 6.6 kg; p = 0.3648), and chair stand test performance also did not differ significantly over time (13.7 ± 4.1 vs. 12.3 ± 3.6 s; p = 0.1020). In contrast, MQI showed a modest but statistically significant increase over follow-up (1.2 [0.3] vs. 1.3 [0.2]; p = 0.0101). Given the derived nature of MQI, this finding should be interpreted cautiously. Self-reported physical activity improved significantly after surgery (Table 1 ). The proportion of inactive participants decreased from 54.8% at baseline to 7.1% at 6 months, whereas the proportion classified as active or very active increased from 4.8% to 69.0% (global p < 0.0001). Metabolic and inflammatory parameters improved substantially over the study period (Table 2 ). Fasting glucose, HbA1c, insulin, hs-CRP, total cholesterol, triglycerides, and LDL-c all decreased significantly from baseline to 6 months, whereas vitamin D increased significantly. HDL-c did not change significantly. Among inflammatory and muscle-related biomarkers, IL-6 decreased from 5.2 ± 1.7 to 4.0 ± 1.4 pg/mL (Δ = -1.2 ± 2.3; 95% CI -2.4 to -0.1; p = 0.0365), whereas TNF-α and myostatin remained unchanged. Table 2 Longitudinal changes in metabolic, inflammatory, and muscle-related biomarkers from baseline to 6 months after RYGB Variable Baseline 6 months Δ (T6 − T0) 95% CI for Δ p-value Metabolic profile Fasting glucose (mg/dL) 105.2 [96.0–121.7] 88.8 [82.7–97.3] -16.6 [-29.3–-5.1] — < 0.0001 HbA1c (%) 5.7 [5.4–6.4] 5.4 [5.1–5.6] -0.5 [-1.0–0.0] — 0.0007 Insulin (mUI/mL) 18.6 [14.8–22.6] 8.4 [6.2–11.3] -10.1 [-14.8–-6.7] — < 0.0001 hs-CRP (mg/L) 9.9 [7.2–14.8] 2.2 [0.9–5.5] -6.4 [-10.4–-1.2] — < 0.0001 Total cholesterol (mg/dL) 179.4 ± 31.1 157.0 ± 23.9 -22.4 ± 33.4 -32.8 to -12.0 < 0.0001 Triglycerides (mg/dL) 120.0 [84.8–151.2] 71.0 [56.0–91.0] -33.5 [-77.5–-10.8] — < 0.0001 HDL-c (mg/dL) 47.0 ± 10.5 47.4 ± 10.4 0.4 ± 15.0 -4.3 to 5.1 0.8621 LDL-c (mg/dL) 111.5 ± 27.7 97.4 ± 28.7 -14.1 ± 28.5 -23.0 to -5.2 0.0026 Vitamin D (ng/mL) 27.0 ± 7.6 34.9 ± 10.0 8.0 ± 11.8 4.3 to 11.7 < 0.0001 Inflammatory and muscle-related markers IL-6 (pg/mL) 5.2 ± 1.7 4.0 ± 1.4 -1.2 ± 2.3 -2.4 to -0.1 0.0365 TNF-α (pg/mL) 11.2 ± 3.6 11.6 ± 4.2 0.4 ± 3.6 -0.9 to 1.7 0.5444 Myostatin (pg/mL) 832.8 [655.3–1011.6] 1043.8 [753.4–1653.5] 138.0 [-100.0–522.9] — 0.0755 Continuous variables are presented as mean ± standard deviation when analyzed with the paired t-test and as median [interquartile range] when analyzed with the Wilcoxon signed-rank test. Δ values are presented as mean ± standard deviation or median [interquartile range], as appropriate. 95% confidence intervals are shown for mean paired changes only. hs-CRP, high-sensitivity C-reactive protein; HbA1c, glycated hemoglobin. The prevalence of SO varied according to the functional criterion applied (Table 3 ). At baseline, 10.0% of participants met SO criteria when the chair stand test was combined with ASM/weight, whereas 2.5% met the criteria when handgrip strength was used. At 6 months, no participants met SO criteria by either definition. However, these reductions were not statistically significant according to the exact McNemar test. Table 3 Prevalence of sarcopenic obesity according to the functional criterion applied at baseline and 6 months after RYGB Variable Baseline 6 months p-value SO based on chair stand test + ASM/weight, n (%) 4 (10.0) 0 (0.0) 0.1250 SO based on handgrip strength + ASM/weight, n (%) 1 (2.5) 0 (0.0) 1.0000 Values are presented as n (%). p-values were obtained using the exact McNemar test. SO, sarcopenic obesity; ASM, appendicular skeletal muscle mass. An exploratory multivariable linear regression model was performed to assess factors associated with changes in MQI at 6 months (Table 4 ). The model explained 41.2% of the variance in ΔMQI (R² = 0.412; adjusted R² = 0.385; overall model p = 0.028). Among the variables included, only ΔIL-6 was independently associated with ΔMQI (β = 0.0673; 95% CI 0.003 to 0.132; p = 0.041), whereas %TWL, age, and hs-CRP were not significantly associated. Table 4 Exploratory multivariable linear regression analysis of factors associated with the change in Muscle Quality Index (ΔMQI) at 6 months after RYGB Variable Coefficient (β) SE 95% CI t p-value Intercept -0.3807 0.551 -1.581 to 0.819 0.691 0.502 ΔIL-6 (pg/mL) 0.0673 0.029 0.003 to 0.132 2.277 0.041 %TWL 0.0020 0.014 -0.028 to 0.033 0.146 0.886 Age (years) 0.0090 0.011 -0.014 to 0.032 0.824 0.425 hs-CRP (mg/L) 0.0425 0.037 -0.038 to 0.123 1.147 0.273 Model fit summary : R 2 = 0.412; Adjusted R² = 0.385; Overall model p-value = 0.028 Abbreviations: SE, standard error; CI, confidence interval; %TWL, total weight loss percentage; hs-CRP, high-sensitivity C-reactive protein; IL-6, interleukin-6; RYGB, Roux-en-Y gastric bypass. This model should be interpreted as exploratory given the sample size and the derived nature of MQI. Discussion The main finding of this prospective study is that the first 6 months after RYGB were characterized by significant reductions in body weight, BMI, ASM, and fat-free mass, without significant deterioration in absolute muscle strength or chair stand performance. In parallel, substantial improvements were observed in metabolic and inflammatory parameters, including reductions in fasting glucose, HbA1c, insulin, hs-CRP, and IL-6. Together, these findings indicate that early postoperative loss of muscle mass does not necessarily translate into measurable short-term functional decline after bariatric surgery. The reduction in ASM observed in the present study is consistent with previous reports showing that a considerable proportion of early postoperative weight loss is accompanied by loss of lean mass and fat-free mass. 5 , 8 , 21 This pattern is expected during the rapid catabolic phase after surgery and reinforces the importance of monitoring body composition in addition to total weight loss. At the same time, the significant increase in ASM/weight suggests that the proportional reduction in total body mass exceeded the decline in appendicular muscle mass. Thus, although absolute muscle mass decreased, its relative representation in relation to body weight improved over time 22 , 33 , 34 . Despite the reduction in ASM, no significant changes were observed in handgrip strength or chair stand performance. This finding is clinically relevant because it suggests preservation of measurable muscle function during the early postoperative period. Previous studies have similarly shown that declines in lean mass after bariatric surgery are not always accompanied by worsening in functional performance, particularly over the short term. 3 , 8 , 21 , 35 In this context, the dissociation between muscle quantity and function may help explain why substantial changes in body composition can occur without immediate impairment in strength-based outcomes. MQI showed a modest increase over follow-up; however, this finding should be interpreted cautiously. MQI is mathematically dependent on ASM and may therefore be influenced by changes in the denominator rather than reflecting true physiological improvement. 12 , 13 , 28 Accordingly, although the increase in MQI may suggest relative preservation of function in relation to muscle mass, it should not be interpreted as definitive evidence of improved muscle quality. In the present study, the more robust functional message is that absolute strength remained stable despite significant reductions in ASM. The marked metabolic improvements observed in this study are consistent with the well-established systemic benefits of bariatric surgery. 2 , 3 , 4 , 24 In addition to reductions in glucose- and lipid-related markers, hs-CRP and IL-6 also declined significantly, indicating attenuation of systemic inflammation. Chronic low-grade inflammation has been implicated in anabolic resistance, impaired muscle protein turnover, and reduced physical performance in obesity. 2 , 16 , 27 Therefore, the reduction in inflammatory burden observed after surgery may represent a more favorable systemic environment for functional preservation, even in the context of reduced muscle mass. However, the present study was not designed to establish a mechanistic link between inflammatory improvement and muscle adaptation, and this interpretation should remain hypothesis-generating rather than causal. TNF-α and myostatin did not change significantly over follow-up. This suggests that not all inflammatory and muscle-related biomarkers respond similarly during the first postoperative months. In particular, the absence of a significant change in myostatin may reflect the complexity of muscle remodeling during the early postoperative period, when weight loss, caloric restriction, and changes in physical activity may occur simultaneously. 30 , 31 Although myostatin is biologically relevant as a negative regulator of muscle mass, the present results do not support a measurable role for this pathway in explaining the functional findings observed here. Self-reported physical activity improved substantially after surgery, with a marked reduction in inactivity and a parallel increase in the proportion of participants classified as active or very active. This shift is clinically relevant and consistent with previous literature showing that bariatric surgery may facilitate improvements in mobility and physical activity behavior. 20 , 32 However, IPAQ is based on self-report and does not capture exercise modality, intensity, or resistance training exposure. Therefore, although physical activity clearly improved at the behavioral level, the extent to which it contributed to the preservation of muscle function in this cohort cannot be determined from the present data. The prevalence of SO varied according to the functional criterion applied, underscoring the clinical complexity of this phenotype. At baseline, a greater proportion of participants met SO criteria when the chair stand test was used than when handgrip strength was used, which is in line with the ESPEN/EASO framework emphasizing the combination of body composition and functional performance. 10 , 11 Although no participants met SO criteria at 6 months, these reductions were not statistically significant, likely because of the small number of baseline cases. Therefore, the present findings suggest a descriptive reduction in SO frequency after surgery, but they do not allow strong inferential conclusions regarding changes in prevalence. The exploratory multivariable model identified ΔIL-6 as the only variable independently associated with ΔMQI, whereas %TWL, age, and hs-CRP were not significant predictors. This finding should be interpreted with caution for two reasons. First, the model was exploratory and based on a limited sample size. Second, MQI is a derived index with known mathematical limitations. 12 , 28 Therefore, while the regression may suggest a possible relationship between inflammatory changes and relative functional adaptation, it should not be overinterpreted as evidence of mechanism. Rather, it may serve as a basis for future studies incorporating larger samples and direct measures of muscle composition and performance. This study has several limitations. The sample size was small, the follow-up period was limited to 6 months, and most participants were women, which restricts generalizability. In addition, the number of observations varied across laboratory and biomarker analyses, and physical activity was assessed by self-report. MQI, although clinically appealing, is a derived variable influenced by ASM and should be interpreted cautiously. Finally, no direct assessments of dietary protein intake, resistance training, intramuscular adipose tissue, or neuromuscular function were available. On the other hand, the study also has important strengths, including its prospective design, the use of DXA, the incorporation of functional tests, and the application of contemporary ESPEN/EASO criteria for SO. 10,21 From a clinical perspective, these findings support the inclusion of functional assessment in postoperative follow-up rather than relying exclusively on weight loss or lean mass estimates. The early postoperative period appears to be characterized by substantial loss of muscle mass without measurable decline in absolute muscle function, which may represent an important therapeutic window for interventions aimed at preserving musculoskeletal health. In this context, resistance exercise and adequate protein intake are likely to be relevant components of postoperative care and should be investigated more directly in future studies. 6 , 8 , 22 , 32 Clinical implications and Future directions From a clinical perspective, these findings suggest that postoperative follow-up should extend beyond weight monitoring and include routine functional assessment of skeletal muscle. Targeted interventions, particularly resistance training and adequate protein intake, may be important to preserve muscle function and support musculoskeletal health during the phase of rapid weight loss. Future studies should incorporate direct measures of muscle composition and quality, such as imaging techniques, together with more comprehensive functional assessments. In addition, factors such as protein intake, exercise modality, and neuromuscular adaptations should be further explored. Longer-term follow-up is needed to determine whether these early postoperative adaptations are sustained or eventually progress to functional impairment later after surgery. Conclusion Six months after bariatric surgery, skeletal muscle strength remained stable despite significant reductions in body weight and absolute muscle mass. MQI increased modestly, although this finding should be interpreted cautiously given the derived nature of this index. The prevalence of sarcopenic obesity decreased descriptively when functional criteria were applied, alongside substantial improvements in metabolic and inflammatory parameters. These preliminary findings suggest that bariatric surgery enhances metabolic health and early postoperative loss of muscle mass does not necessarily translate into measurable short-term functional decline and support the inclusion of functional assessment alongside body composition monitoring in postoperative care, and highlighted that muscle quality, rather that absolute mass, should be the primary focus for functional monitoring in postoperative care. Declarations Author Contribution Conception and design of the study : TLS and APM. Recruitment and data curation: TLS and RRAS. Methodolody: TLS, RRAS, PL; Writing -original drift :TLS . Writing- review and editing: APM Supervision: APM, Resources: APM, LGKA. All authors reviewed the manuscript. Acknowledgement Carlos Chagas Filho Foundation for Research Support in the State of Rio de Janeiro (FAPERJ). References World Obesity Federation. World Obesity Atlas 2025 . London: World Obesity Federation; 2025. 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Obesity . 2012;20(10):2101-2106. doi:10.1038/oby.2012.20 Dodds RM, et al. Grip strength across the life course: normative data from twelve British studies. PLoS One . 2014;9(12):e113637. doi:10.1371/journal.pone.0113637 Harris EK, Yasaka T. On the calculation of a “reference change” for comparing two consecutive measurements. Clin Chem . 1983;29(1):25-30. Brethauer SA, et al. Standardized outcomes reporting in metabolic and bariatric surgery. Surg Obes Relat Dis . 2015;11(3):489-506. doi:10.1016/j.soard.2015.02.003 Lee PH, et al. Validity of the International Physical Activity Questionnaire Short Form (IPAQ-SF): a systematic review. Int J Behav Nutr Phys Act . 2011;8:115. doi:10.1186/1479-5868-8-115 Cardoso P, Santos TV, Ramon-Krauel M, et al. Impact of Bariatric and Metabolic Surgery on Sarcopenia-Related Parameters According to the EWGSOP2 Consensus Criteria in Persons Living with Obesity. Obes Surg . 2025;35(5):1900-1910. doi:10.1007/s11695-025-07816-6 Nuijten MAH, et al. The magnitude and progress of lean body mass, fat-free mass, and skeletal muscle mass loss following bariatric surgery: A systematic review and meta-analysis. Obes Rev . 2022;23(1):e13370. doi:10.1111/obr.13370 Zhang M, et al. Muscle quality index is correlated with insulin resistance and type 2 diabetes mellitus: a cross-sectional population-based study. BMC Public Health . 2025;25(1):497. doi:10.1186/s12889-025-21734-3 Reczkowicz J, Mika A, Antosiewicz J, et al. Bariatric surgery induced changes in blood cholesterol are modulated by vitamin D status. Nutrients . 2022;14(10):2000. doi:10.3390/nu14102000 Barbat-Artigas S, et al. Muscle quantity is not synonymous with muscle quality. J Am Med Dir Assoc . 2013;14(11):852.e1-7. doi:10.1016/j.jamda.2013.06.003 Persad LS, Wang Z, Pino PA, et al. Specific tension of human muscle in vivo: a systematic review. J Appl Physiol (1985) . 2024;137(4):945-962. doi:10.1152/japplphysiol.00296.2024 Illán-Gómez F, et al. Obesity and inflammation: change in adiponectin, C-reactive protein, tumour necrosis factor-alpha and interleukin-6 after bariatric surgery. Obes Surg . 2012;22(6):950-5. doi:10.1007/s11695-012-0643-y Archie JP Jr. Mathematic coupling of data: a common source of error. Ann Surg . 1981;193(3):296-303. doi:10.1097/00000658-198103000-00008 Grosicki GJ, Barrett BB, Englund DA, et al. Circulating Interleukin-6 Is Associated with Skeletal Muscle Strength, Quality, and Functional Adaptation with Exercise Training in Mobility-Limited Older Adults. J Frailty Aging . 2020;9(1):1-10. doi:10.14283/jfa.2020.1 Stefanakis K, et al. The impact of weight loss on fat-free mass, muscle, bone and hematopoiesis health: implications for emerging pharmacotherapies aiming at fat reduction and lean mass preservation. Metabolism . 2024;161:156057. doi:10.1016/j.metabol.2024.156057 Orioli L, Thissen JP. Myokines as potential mediators of changes in glucose homeostasis and muscle mass after bariatric surgery. Front Endocrinol (Lausanne) . 2025;16:1554617. doi:10.3389/fendo.2025.1554617 James JD, Hardeman W, Goodall M, et al. A systematic review of interventions to increase physical activity and reduce sedentary behaviour following bariatric surgery. Obes Rev . 2021;22(7):e13258. doi:10.1111/obr.13258 Martínez M, et al. The Impact of Bariatric Surgery on the Muscle Mass in Patients with Obesity: 2-Year Follow-up. Obes Surg . 2022;32(3):625-633. doi:10.1007/s11695-021-05837-5 Carvalho CP, et al. Effects of preoperative sarcopenia-related parameters on the musculoskeletal and metabolic outcomes after bariatric surgery: a one-year longitudinal study in females. Sci Rep . 2023;13(1):13373. doi:10.1038/s41598-023-40404-z Alba DL, et al. Changes in Lean Mass, Absolute and Relative Muscle Strength, and Physical Performance After Gastric Bypass Surgery. J Clin Endocrinol Metab . 2019;104(3):711-720. doi:10.1210/jc.2018-0095 Additional Declarations No competing interests reported. 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Also discoverable on Platform About Our Team In Review Editorial Policies Advisory Board Help Center Resources Author Services Accessibility API Access RSS feed Manage Cookie Preferences © Research Square 2026 | ISSN 2693-5015 (online) Privacy Policy Terms of Service Do Not Sell My Personal Information {"props":{"pageProps":{"initialData":{"identity":"rs-9360148","acceptedTermsAndConditions":true,"allowDirectSubmit":false,"archivedVersions":[],"articleType":"Research Article","associatedPublications":[],"authors":[{"id":630513517,"identity":"d32958e8-092e-469a-b9fa-487eadb74189","order_by":0,"name":"Tamyris Silva","email":"","orcid":"","institution":"Rio de Janeiro State University","correspondingAuthor":false,"prefix":"","firstName":"Tamyris","middleName":"","lastName":"Silva","suffix":""},{"id":630513519,"identity":"bdda2463-9cdd-457a-9f64-35975fce3b9c","order_by":1,"name":"Regina Silva","email":"","orcid":"","institution":"Rio de Janeiro State University","correspondingAuthor":false,"prefix":"","firstName":"Regina","middleName":"","lastName":"Silva","suffix":""},{"id":630513521,"identity":"431fb3e9-1b25-4397-a4ab-b5a2f5eea8de","order_by":2,"name":"Patricia Lisboa","email":"","orcid":"","institution":"Rio de Janeiro State University","correspondingAuthor":false,"prefix":"","firstName":"Patricia","middleName":"","lastName":"Lisboa","suffix":""},{"id":630513524,"identity":"f2fe41f3-479f-48b6-9c3c-6f3c172be4da","order_by":3,"name":"Iala Bertasso","email":"","orcid":"","institution":"Rio de Janeiro State University","correspondingAuthor":false,"prefix":"","firstName":"Iala","middleName":"","lastName":"Bertasso","suffix":""},{"id":630513526,"identity":"96f60da0-891f-4a97-bb7a-b460abed5332","order_by":4,"name":"Luiz Guilherme Kraemer-Aguiar","email":"","orcid":"","institution":"Rio de Janeiro State University","correspondingAuthor":false,"prefix":"","firstName":"Luiz","middleName":"Guilherme","lastName":"Kraemer-Aguiar","suffix":""},{"id":630513528,"identity":"f8a42d74-2ad0-479f-b6bc-e52fd7b4024a","order_by":5,"name":"Alessandra Mulder","email":"data:image/png;base64,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","orcid":"","institution":"Rio de Janeiro State University","correspondingAuthor":true,"prefix":"","firstName":"Alessandra","middleName":"","lastName":"Mulder","suffix":""}],"badges":[],"createdAt":"2026-04-08 18:08:24","currentVersionCode":1,"declarations":"","doi":"10.21203/rs.3.rs-9360148/v1","doiUrl":"https://doi.org/10.21203/rs.3.rs-9360148/v1","draftVersion":[],"editorialEvents":[],"editorialNote":"","failedWorkflow":false,"files":[{"id":108491503,"identity":"498510b9-0709-4065-af2a-69c08639ee9e","added_by":"auto","created_at":"2026-05-05 09:54:12","extension":"pdf","order_by":0,"title":"","display":"","copyAsset":false,"role":"manuscript-pdf","size":359645,"visible":true,"origin":"","legend":"","description":"","filename":"manuscript.pdf","url":"https://assets-eu.researchsquare.com/files/rs-9360148/v1/059a8cd7-a2c7-48ce-b208-e11d47744102.pdf"},{"id":108235960,"identity":"8888ac03-fd1c-4bd0-8161-109bdad70d2a","added_by":"auto","created_at":"2026-04-30 18:50:47","extension":"png","order_by":1,"title":"","display":"","copyAsset":false,"role":"supplement","size":5261161,"visible":true,"origin":"","legend":"","description":"","filename":"graphicalabstract.pngNotebookLm.png","url":"https://assets-eu.researchsquare.com/files/rs-9360148/v1/2a9bc21d68083280bf02e99a.png"}],"financialInterests":"No competing interests reported.","formattedTitle":"The Muscle Paradox in Bariatric Surgery: Early Post-opertative Loss of Muscle Mass without Functional Decline","fulltext":[{"header":"Introduction","content":"\u003cp\u003eObesity is a chronic disease associated with metabolic dysfunction, systemic inflammation, reduced physical function, and increased risk of multiple comorbidities, substantially impairing quality of life. Among available treatment options, bariatric and metabolic surgery (BMS) is the most effective intervention for severe obesity, producing substantial and sustained weight loss together with important metabolic benefits. Roux-en-Y gastric bypass (RYGB) remains one of the most widely performed procedures and is associated with marked improvements in glycemic control and cardiometabolic risk. \u003csup\u003e1\u0026ndash;5\u003c/sup\u003e\u003c/p\u003e \u003cp\u003eDespite these benefits, preservation of skeletal muscle health during the postoperative period remains an important clinical concern. Rapid weight loss after bariatric surgery is frequently accompanied by reductions in lean mass and fat-free mass, which may raise concern regarding physical function and long-term musculoskeletal health. \u003csup\u003e5,6\u003c/sup\u003e In this context, assessment of postoperative adaptation should not rely exclusively on body weight or lean mass estimates, since changes in muscle quantity do not necessarily reflect changes in functional status. \u003csup\u003e6,7\u003c/sup\u003e\u003c/p\u003e \u003cp\u003eSarcopenic obesity (SO), defined as the coexistence of excess adiposity and impaired muscle mass and function, has gained increasing attention as a clinically relevant phenotype associated with adverse outcomes. \u003csup\u003e8\u0026ndash;11\u003c/sup\u003e The 2022 ESPEN/EASO consensus provided a standardized framework for the diagnosis of SO, emphasizing the integration of body composition and functional performance. \u003csup\u003e10\u003c/sup\u003e However, SO remains insufficiently investigated in bariatric populations, particularly during the early postoperative period, when the most pronounced changes in body composition occur. \u003csup\u003e10,11\u003c/sup\u003e\u003c/p\u003e \u003cp\u003eIn addition to muscle mass and strength, derived indices such as the muscle quality index (MQI) may provide complementary information by relating strength to appendicular muscle mass. \u003csup\u003e12,13\u003c/sup\u003e Nevertheless, the interpretation of such indices in the context of rapid postoperative weight loss remains challenging, and early changes in muscle mass, function, muscle quality, and SO after RYGB are still incompletely understood. \u003csup\u003e6,12,13\u003c/sup\u003e\u003c/p\u003e \u003cp\u003eTherefore, this prospective study aimed to investigate short-term changes in body composition, muscle strength, muscle quality, and SO prevalence during the first 6 months after RYGB, together with metabolic and inflammatory changes that may accompany postoperative adaptation.\u003c/p\u003e"},{"header":"Methods","content":"\u003cp\u003eThis was a prospective longitudinal study conducted at the Obesity Unit, Multiuser Clinical Research Center (CePeM), Hospital Universit\u0026aacute;rio Pedro Ernesto, State University of Rio de Janeiro, Rio de Janeiro, Brazil. Adults aged 20\u0026ndash;65 years with severe obesity were eligible if they had a body mass index (BMI) \u0026ge; 35 kg/m\u0026sup2; with obesity-related comorbidities or BMI \u0026ge; 40 kg/m\u0026sup2; regardless of comorbidities. Exclusion criteria were body weight \u0026gt; 160 kg (equipment limit), previous bariatric or major gastrointestinal surgery, chronic neuromuscular or inflammatory disease, use of medications known to affect muscle metabolism, or refusal to provide informed consent. Participants were evaluated preoperatively and again 6 months after Roux-en-Y gastric bypass (RYGB). The study was conducted in accordance with the Declaration of Helsinki and was approved by the local Research Ethics Committee. All participants provided written informed consent before enrollment.\u003c/p\u003e\n\u003cp\u003eAnthropometry and body composition\u003c/p\u003e\n\u003cp\u003eAnthropometric measurements were obtained according to World Health Organization recommendations\u003csup\u003e14\u003c/sup\u003e. Body composition was assessed by dual-energy X-ray absorptiometry (DXA; GE Medical Systems, Lunar, Madison, WI, USA) using Encore software version 13.60. Appendicular skeletal muscle mass (ASM) was calculated as the sum of lean mass from both arms and legs. Relative ASM was expressed as ASM adjusted for body weight (ASM/weight \u0026times; 100)\u003csup\u003e15,16\u003c/sup\u003e. Total fat mass (FM) and fat-free mass (FFM) were obtained directly from DXA measurements.\u003c/p\u003e\n\u003ch3\u003eMuscle Strength, Muscle Quality, and Sarcopenic Obesity\u003c/h3\u003e\n\u003cp\u003eMuscle strength was assessed by handgrip strength (HGS) using a JAMAR hydraulic dynamometer (model SH5001, Saehan Corporation, Korea). Three maximal attempts were performed using the dominant hand, and the highest value was used for analysis. Low handgrip strength was defined as \u0026lt; 32 kg for men and \u0026lt; 19 kg for women, according to the normative reference values adopted in the ESPEN/EASO consensus for sarcopenic obesity\u003csup\u003e10,17\u003c/sup\u003e. Lower-limb performance was assessed using the five-repetition chair stand test. Low lower-limb strength/performance was defined as a completion time \u0026ge; 17 seconds for both sexes\u003csup\u003e10\u003c/sup\u003e.\u0026nbsp;\u003c/p\u003e\n\u003cp\u003eMuscle quality was assessed using the Muscle Quality Index (MQI), calculated as the ratio between handgrip strength and appendicular skeletal muscle mass (MQI = HGS/ASM). MQI was analyzed as a continuous derived index and also categorized using previously proposed sex-specific thresholds: normal (\u0026gt; 1.53), low muscle quality (1.35 \u0026lt; MQI \u0026le; 1.53 for women; 1.36 \u0026lt; MQI \u0026le; 1.53 for men), and poor muscle quality (\u0026le; 1.35 for women; \u0026le; 1.36 for men). For descriptive analyses of muscular vulnerability, participants classified as having low or poor muscle quality were grouped together\u003csup\u003e13\u003c/sup\u003e.\u0026nbsp;\u003c/p\u003e\n\u003cp\u003eSarcopenic obesity (SO) was defined according to the 2022 ESPEN/EASO consensus, integrating DXA-derived muscle mass with functional measures, including HGS and chair stand performance. SO prevalence was examined using both functional definitions combined with ASM/weight\u003csup\u003e10\u003c/sup\u003e.\u003c/p\u003e\n\u003ch3\u003eWeight Loss Outcomes\u003c/h3\u003e\n\u003cp\u003eWeight loss was assessed using percentage total weight loss (%TWL) and percentage excess weight loss (%EWL), according to standardized reporting recommendations. %TWL was calculated as: (preoperative weight \u0026minus; postoperative weight) / preoperative weight \u0026times; 100. %EWL was calculated as: [(preoperative weight \u0026minus; postoperative weight) / (preoperative weight \u0026minus; ideal weight)] \u0026times; 100,where ideal weight was defined as the weight corresponding to a BMI of 25 kg/m\u0026sup2;.\u003csup\u003e19\u003c/sup\u003e\u0026nbsp;\u003c/p\u003e\n\u003ch3\u003ePhysical Activity Assessment\u003c/h3\u003e\n\u003cp\u003ePhysical activity was assessed at both time points using the short form of the International Physical Activity Questionnaire (IPAQ-SF). Participants were classified according to IPAQ-SF scoring guidelines into five categories: inactive, irregularly active A, irregularly active B, active, and very active.\u0026nbsp;\u003c/p\u003e\n\u003ch3\u003eLaboratory and Biomarker Assessments\u003c/h3\u003e\n\u003cp\u003eFasting blood samples were collected preoperatively and at 6 months after surgery to measure glucose, glycated hemoglobin (HbA1c), insulin, lipid profile, vitamin D, and high-sensitivity C-reactive protein (hs-CRP) using standard laboratory methods.\u0026nbsp;\u003c/p\u003e\n\u003cp\u003eCirculating cytokines and muscle-related biomarkers were measured in serum samples using a magnetic bead-based multiplex immunoassay (MILLIPLEX MAP Human Cytokine/Chemokine/Angiogenesis Panel, Merck KGaA, Darmstadt, Germany) on a Luminex 200 system (Luminex Corp, Austin, TX, USA), according to the manufacturer\u0026rsquo;s instructions. The following analytes were quantified: interleukin-6 (IL-6), tumor necrosis factor-alpha (TNF-\u0026alpha;), and myostatin. Detection sensitivities were 0.9 pg/mL for IL-6, 0.1 pg/mL for TNF-\u0026alpha;, and 163 pg/mL for myostatin. All samples were analyzed in duplicate, and data were processed using BeadView software.\u0026nbsp;\u003c/p\u003e\n\u003ch3\u003eStatistical Analysis\u003c/h3\u003e\n\u003cp\u003ePaired changes (\u0026Delta;) were calculated as the 6-month postoperative value minus the preoperative value. Positive \u0026Delta; values indicated an increase over time, whereas negative \u0026Delta; values indicated a decrease.\u0026nbsp;\u003c/p\u003e\n\u003cp\u003eData distribution was assessed using the Shapiro\u0026ndash;Wilk test. Continuous variables with approximately normal distribution were expressed as mean \u0026plusmn; standard deviation (SD), whereas non-normally distributed variables were expressed as median [interquartile range]. Comparisons between preoperative and 6-month postoperative values were performed using the paired t-test or Wilcoxon matched-pairs signed-rank test, as appropriate. For parametric paired changes, 95% confidence intervals (95% CI) were also calculated.\u0026nbsp;\u003c/p\u003e\n\u003cp\u003eChanges in sarcopenic obesity prevalence between time points were assessed using the exact McNemar test. Changes in the global distribution of IPAQ-SF categories between baseline and 6 months were assessed using a marginal homogeneity approach for paired categorical data. Correlations between continuous variables were evaluated using Pearson or Spearman coefficients, according to data distribution.\u0026nbsp;\u003c/p\u003e\n\u003cp\u003eAn exploratory multivariable linear regression model was used to investigate factors independently associated with the change in MQI (\u0026Delta;MQI), including age, %TWL, hs-CRP, and change in IL-6 (\u0026Delta;IL-6) as covariates. Given the sample size and the derived nature of MQI, this model was interpreted as exploratory. Statistical significance was set at p \u0026lt; 0.05\u003c/p\u003e"},{"header":"Results","content":"\u003cp\u003eA total of 40 participants were included in the longitudinal analysis of anthropometry, body composition, muscle function, and SO prevalence. At 6 months after RYGB, mean total weight loss (%TWL) was 23.8\u0026thinsp;\u0026plusmn;\u0026thinsp;5.4, corresponding to an excess weight loss (%EWL) of 56.7\u0026thinsp;\u0026plusmn;\u0026thinsp;14.6. As shown in Table\u0026nbsp;\u003cspan refid=\"Tab1\" class=\"InternalRef\"\u003e1\u003c/span\u003e, body weight decreased from 120.5\u0026thinsp;\u0026plusmn;\u0026thinsp;16.6 to 88.4\u0026thinsp;\u0026plusmn;\u0026thinsp;13.0 kg (Δ = -32.2\u0026thinsp;\u0026plusmn;\u0026thinsp;24.3 kg; 95% CI -39.8 to -24.5; p\u0026thinsp;\u0026lt;\u0026thinsp;0.0001), and BMI decreased from 45.8\u0026thinsp;\u0026plusmn;\u0026thinsp;5.0 to 33.7\u0026thinsp;\u0026plusmn;\u0026thinsp;4.2 kg/m\u0026sup2; (Δ = -12.1\u0026thinsp;\u0026plusmn;\u0026thinsp;7.3 kg/m\u0026sup2;; 95% CI -14.4 to -9.8; p\u0026thinsp;\u0026lt;\u0026thinsp;0.0001). ASM also decreased significantly, from 25.7\u0026thinsp;\u0026plusmn;\u0026thinsp;5.1 to 22.7\u0026thinsp;\u0026plusmn;\u0026thinsp;3.9 kg (Δ = -3.0\u0026thinsp;\u0026plusmn;\u0026thinsp;6.5 kg; 95% CI -5.0 to -1.0; p\u0026thinsp;=\u0026thinsp;0.0042), whereas ASM/weight increased from 21.3\u0026thinsp;\u0026plusmn;\u0026thinsp;3.4% to 25.6\u0026thinsp;\u0026plusmn;\u0026thinsp;2.6% (Δ\u0026thinsp;=\u0026thinsp;4.3\u0026thinsp;\u0026plusmn;\u0026thinsp;4.4; 95% CI 2.9 to 5.7; p\u0026thinsp;\u0026lt;\u0026thinsp;0.0001). Fat-free mass also decreased significantly during follow-up.\u003c/p\u003e \u003cp\u003e \u003cdiv class=\"gridtable\"\u003e\u003ctable float=\"Yes\" id=\"Tab1\" border=\"1\"\u003e \u003ccaption language=\"En\"\u003e \u003cdiv class=\"CaptionNumber\"\u003eTable 1\u003c/div\u003e \u003cdiv class=\"CaptionContent\"\u003e \u003cp\u003eLongitudinal changes in anthropometry, body composition, muscle function, and physical activity from baseline to 6 months after RYGB\u003c/p\u003e \u003c/div\u003e \u003c/caption\u003e \u003ccolgroup cols=\"6\"\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c1\" colnum=\"1\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c2\" colnum=\"2\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c3\" colnum=\"3\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c4\" colnum=\"4\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c5\" colnum=\"5\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c6\" colnum=\"6\"\u003e\u003c/div\u003e \u003cthead\u003e \u003ctr\u003e \u003cth align=\"left\" colname=\"c1\"\u003e \u003cp\u003e Variable\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c2\"\u003e \u003cp\u003eBaseline\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c3\"\u003e \u003cp\u003e6 months\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c4\"\u003e \u003cp\u003eΔ (T6\u0026thinsp;\u0026minus;\u0026thinsp;T0)\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c5\"\u003e \u003cp\u003e95% CI for Δ\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c6\"\u003e \u003cp\u003ep-value\u003c/p\u003e \u003c/th\u003e \u003c/tr\u003e \u003ctr\u003e \u003cth align=\"left\" colspan=\"6\" nameend=\"c6\" namest=\"c1\"\u003e \u003cp\u003eAnthropometric and body composition\u003c/p\u003e \u003c/th\u003e \u003c/tr\u003e \u003c/thead\u003e \u003ctbody\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eWeight (kg)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e120.5\u0026thinsp;\u0026plusmn;\u0026thinsp;16.6\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e88.4\u0026thinsp;\u0026plusmn;\u0026thinsp;13.0\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e-32.2\u0026thinsp;\u0026plusmn;\u0026thinsp;24.3\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e-39.8 to -24.5\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c6\"\u003e \u003cp\u003e\u003cb\u003e\u0026lt;\u0026thinsp;0.0001\u003c/b\u003e\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eBMI (kg/m\u0026sup2;)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e45.8\u0026thinsp;\u0026plusmn;\u0026thinsp;5.0\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e33.7\u0026thinsp;\u0026plusmn;\u0026thinsp;4.2\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e-12.1\u0026thinsp;\u0026plusmn;\u0026thinsp;7.3\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e-14.4 to -9.8\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c6\"\u003e \u003cp\u003e\u003cb\u003e\u0026lt;\u0026thinsp;0.0001\u003c/b\u003e\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eASM (kg)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e25.7\u0026thinsp;\u0026plusmn;\u0026thinsp;5.1\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e22.7\u0026thinsp;\u0026plusmn;\u0026thinsp;3.9\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e-3.0\u0026thinsp;\u0026plusmn;\u0026thinsp;6.5\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e-5.0 to -1.0\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c6\"\u003e \u003cp\u003e\u003cb\u003e0.0042\u003c/b\u003e\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eASM/weight (%)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e21.3\u0026thinsp;\u0026plusmn;\u0026thinsp;3.4\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e25.6\u0026thinsp;\u0026plusmn;\u0026thinsp;2.6\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e4.3\u0026thinsp;\u0026plusmn;\u0026thinsp;4.4\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e2.9 to 5.7\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c6\"\u003e \u003cp\u003e\u003cb\u003e\u0026lt;\u0026thinsp;0.0001\u003c/b\u003e\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eFFM (kg)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e58.1\u0026thinsp;\u0026plusmn;\u0026thinsp;7.6\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e51.6\u0026thinsp;\u0026plusmn;\u0026thinsp;7.4\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e\u0026minus;6.5\u0026thinsp;\u0026plusmn;\u0026thinsp;8.8\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e58.1\u0026thinsp;\u0026plusmn;\u0026thinsp;7.6\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c6\"\u003e \u003cp\u003e\u003cb\u003e\u0026lt;\u0026thinsp;0.0001\u003c/b\u003e\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colspan=\"6\" nameend=\"c6\" namest=\"c1\"\u003e \u003cp\u003e\u003cb\u003eMuscle function and quality\u003c/b\u003e\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eHGS (kg)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e30.8\u0026thinsp;\u0026plusmn;\u0026thinsp;9.0\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e29.3\u0026thinsp;\u0026plusmn;\u0026thinsp;6.6\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e-1.5\u0026thinsp;\u0026plusmn;\u0026thinsp;10.6\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e-4.8 to 1.8\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c6\"\u003e \u003cp\u003e0.3648\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eChair stand test (s)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e13.7\u0026thinsp;\u0026plusmn;\u0026thinsp;4.1\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e12.3\u0026thinsp;\u0026plusmn;\u0026thinsp;3.6\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e-1.4\u0026thinsp;\u0026plusmn;\u0026thinsp;5.4\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e-3.1 to 0.3\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c6\"\u003e \u003cp\u003e0.1020\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eMQI\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e1.2 (0.3)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e1.3 (0.2)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e0.1\u0026thinsp;\u0026plusmn;\u0026thinsp;0.4\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e-0.0 to 0.2\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c6\"\u003e \u003cp\u003e\u003cb\u003e0.0101\u003c/b\u003e\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colspan=\"6\" nameend=\"c6\" namest=\"c1\"\u003e \u003cp\u003e\u003cb\u003ePhysical activity level, n (%)\u003c/b\u003e\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eInactive\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e23 (54.8)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e3 (7.1)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\" morerows=\"4\" rowspan=\"5\"\u003e \u003cp\u003e\u0026lt;\u0026thinsp;0.0001\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e\u0026nbsp;\u003c/td\u003e \u003ctd align=\"left\" colname=\"c6\"\u003e\u0026nbsp;\u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eIrregularly active B\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e4 (9.5)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e3 (7.1)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e\u0026nbsp;\u003c/td\u003e \u003ctd align=\"left\" colname=\"c6\"\u003e\u0026nbsp;\u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eIrregularly active A\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e13 (31.0)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e7 (16.7)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e\u0026nbsp;\u003c/td\u003e \u003ctd align=\"left\" colname=\"c6\"\u003e\u0026nbsp;\u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eActive\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e1 (2.4)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e19 (45.2)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e\u0026nbsp;\u003c/td\u003e \u003ctd align=\"left\" colname=\"c6\"\u003e\u0026nbsp;\u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eVery active\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e1 (2.4)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e10 (23.8)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e\u0026nbsp;\u003c/td\u003e \u003ctd align=\"left\" colname=\"c6\"\u003e\u0026nbsp;\u003c/td\u003e \u003c/tr\u003e \u003c/tbody\u003e \u003c/colgroup\u003e \u003ctfoot\u003e \u003ctr\u003e\u003ctd colspan=\"6\"\u003e\u003cem\u003eContinuous variables are presented as mean\u0026thinsp;\u0026plusmn;\u0026thinsp;standard deviation when analyzed with the paired t-test and as median [interquartile range] when analyzed with the Wilcoxon signed-rank test. Δ values are presented as mean\u0026thinsp;\u0026plusmn;\u0026thinsp;standard deviation or median [interquartile range], as appropriate. 95% confidence intervals are shown for mean paired changes only. ASM, appendicular skeletal muscle mass; FFM, fat-free mass; HGS, handgrip strength; MQI, muscle quality index.\u003c/em\u003e\u003c/td\u003e\u003c/tr\u003e \u003c/tfoot\u003e \u003c/table\u003e\u003c/div\u003e \u003c/p\u003e \u003cp\u003eNo significant changes were observed in absolute muscle function measures (Table\u0026nbsp;\u003cspan refid=\"Tab1\" class=\"InternalRef\"\u003e1\u003c/span\u003e). Handgrip strength remained unchanged from baseline to 6 months (30.8\u0026thinsp;\u0026plusmn;\u0026thinsp;9.0 vs. 29.3\u0026thinsp;\u0026plusmn;\u0026thinsp;6.6 kg; p\u0026thinsp;=\u0026thinsp;0.3648), and chair stand test performance also did not differ significantly over time (13.7\u0026thinsp;\u0026plusmn;\u0026thinsp;4.1 vs. 12.3\u0026thinsp;\u0026plusmn;\u0026thinsp;3.6 s; p\u0026thinsp;=\u0026thinsp;0.1020). In contrast, MQI showed a modest but statistically significant increase over follow-up (1.2 [0.3] vs. 1.3 [0.2]; p\u0026thinsp;=\u0026thinsp;0.0101). Given the derived nature of MQI, this finding should be interpreted cautiously.\u003c/p\u003e \u003cp\u003eSelf-reported physical activity improved significantly after surgery (Table\u0026nbsp;\u003cspan refid=\"Tab1\" class=\"InternalRef\"\u003e1\u003c/span\u003e). The proportion of inactive participants decreased from 54.8% at baseline to 7.1% at 6 months, whereas the proportion classified as active or very active increased from 4.8% to 69.0% (global p\u0026thinsp;\u0026lt;\u0026thinsp;0.0001).\u003c/p\u003e \u003cp\u003eMetabolic and inflammatory parameters improved substantially over the study period (Table\u0026nbsp;\u003cspan refid=\"Tab2\" class=\"InternalRef\"\u003e2\u003c/span\u003e). Fasting glucose, HbA1c, insulin, hs-CRP, total cholesterol, triglycerides, and LDL-c all decreased significantly from baseline to 6 months, whereas vitamin D increased significantly. HDL-c did not change significantly. Among inflammatory and muscle-related biomarkers, IL-6 decreased from 5.2\u0026thinsp;\u0026plusmn;\u0026thinsp;1.7 to 4.0\u0026thinsp;\u0026plusmn;\u0026thinsp;1.4 pg/mL (Δ = -1.2\u0026thinsp;\u0026plusmn;\u0026thinsp;2.3; 95% CI -2.4 to -0.1; p\u0026thinsp;=\u0026thinsp;0.0365), whereas TNF-α and myostatin remained unchanged.\u003c/p\u003e \u003cp\u003e \u003cdiv class=\"gridtable\"\u003e\u003ctable float=\"Yes\" id=\"Tab2\" border=\"1\"\u003e \u003ccaption language=\"En\"\u003e \u003cdiv class=\"CaptionNumber\"\u003eTable 2\u003c/div\u003e \u003cdiv class=\"CaptionContent\"\u003e \u003cp\u003eLongitudinal changes in metabolic, inflammatory, and muscle-related biomarkers from baseline to 6 months after RYGB\u003c/p\u003e \u003c/div\u003e \u003c/caption\u003e \u003ccolgroup cols=\"6\"\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c1\" colnum=\"1\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c2\" colnum=\"2\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c3\" colnum=\"3\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c4\" colnum=\"4\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c5\" colnum=\"5\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c6\" colnum=\"6\"\u003e\u003c/div\u003e \u003cthead\u003e \u003ctr\u003e \u003cth align=\"left\" colname=\"c1\"\u003e \u003cp\u003eVariable\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c2\"\u003e \u003cp\u003eBaseline\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c3\"\u003e \u003cp\u003e6 months\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c4\"\u003e \u003cp\u003eΔ (T6\u0026thinsp;\u0026minus;\u0026thinsp;T0)\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c5\"\u003e \u003cp\u003e95% CI for Δ\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c6\"\u003e \u003cp\u003ep-value\u003c/p\u003e \u003c/th\u003e \u003c/tr\u003e \u003ctr\u003e \u003cth align=\"left\" colspan=\"6\" nameend=\"c6\" namest=\"c1\"\u003e \u003cp\u003eMetabolic profile\u003c/p\u003e \u003c/th\u003e \u003c/tr\u003e \u003c/thead\u003e \u003ctbody\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eFasting glucose (mg/dL)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e105.2 [96.0\u0026ndash;121.7]\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e88.8 [82.7\u0026ndash;97.3]\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e-16.6 [-29.3\u0026ndash;-5.1]\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e\u0026mdash;\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c6\"\u003e \u003cp\u003e\u0026lt;\u0026thinsp;0.0001\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eHbA1c (%)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e5.7 [5.4\u0026ndash;6.4]\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e5.4 [5.1\u0026ndash;5.6]\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e-0.5 [-1.0\u0026ndash;0.0]\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e\u0026mdash;\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c6\"\u003e \u003cp\u003e0.0007\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eInsulin (mUI/mL)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e18.6 [14.8\u0026ndash;22.6]\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e8.4 [6.2\u0026ndash;11.3]\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e-10.1 [-14.8\u0026ndash;-6.7]\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e\u0026mdash;\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c6\"\u003e \u003cp\u003e\u0026lt;\u0026thinsp;0.0001\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003ehs-CRP (mg/L)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e9.9 [7.2\u0026ndash;14.8]\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e2.2 [0.9\u0026ndash;5.5]\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e-6.4 [-10.4\u0026ndash;-1.2]\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e\u0026mdash;\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c6\"\u003e \u003cp\u003e\u0026lt;\u0026thinsp;0.0001\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eTotal cholesterol (mg/dL)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e179.4\u0026thinsp;\u0026plusmn;\u0026thinsp;31.1\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e157.0\u0026thinsp;\u0026plusmn;\u0026thinsp;23.9\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e-22.4\u0026thinsp;\u0026plusmn;\u0026thinsp;33.4\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e-32.8 to -12.0\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c6\"\u003e \u003cp\u003e\u0026lt;\u0026thinsp;0.0001\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eTriglycerides (mg/dL)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e120.0 [84.8\u0026ndash;151.2]\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e71.0 [56.0\u0026ndash;91.0]\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e-33.5 [-77.5\u0026ndash;-10.8]\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e\u0026mdash;\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c6\"\u003e \u003cp\u003e\u0026lt;\u0026thinsp;0.0001\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eHDL-c (mg/dL)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e47.0\u0026thinsp;\u0026plusmn;\u0026thinsp;10.5\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e47.4\u0026thinsp;\u0026plusmn;\u0026thinsp;10.4\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e0.4\u0026thinsp;\u0026plusmn;\u0026thinsp;15.0\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e-4.3 to 5.1\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c6\"\u003e \u003cp\u003e0.8621\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eLDL-c (mg/dL)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e111.5\u0026thinsp;\u0026plusmn;\u0026thinsp;27.7\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e97.4\u0026thinsp;\u0026plusmn;\u0026thinsp;28.7\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e-14.1\u0026thinsp;\u0026plusmn;\u0026thinsp;28.5\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e-23.0 to -5.2\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c6\"\u003e \u003cp\u003e0.0026\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eVitamin D (ng/mL)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e27.0\u0026thinsp;\u0026plusmn;\u0026thinsp;7.6\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e34.9\u0026thinsp;\u0026plusmn;\u0026thinsp;10.0\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e8.0\u0026thinsp;\u0026plusmn;\u0026thinsp;11.8\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e4.3 to 11.7\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c6\"\u003e \u003cp\u003e\u0026lt;\u0026thinsp;0.0001\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colspan=\"6\" nameend=\"c6\" namest=\"c1\"\u003e \u003cp\u003e\u003cb\u003eInflammatory and muscle-related markers\u003c/b\u003e\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eIL-6 (pg/mL)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e5.2\u0026thinsp;\u0026plusmn;\u0026thinsp;1.7\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e4.0\u0026thinsp;\u0026plusmn;\u0026thinsp;1.4\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e-1.2\u0026thinsp;\u0026plusmn;\u0026thinsp;2.3\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e-2.4 to -0.1\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c6\"\u003e \u003cp\u003e0.0365\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eTNF-α (pg/mL)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e11.2\u0026thinsp;\u0026plusmn;\u0026thinsp;3.6\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e11.6\u0026thinsp;\u0026plusmn;\u0026thinsp;4.2\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e0.4\u0026thinsp;\u0026plusmn;\u0026thinsp;3.6\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e-0.9 to 1.7\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c6\"\u003e \u003cp\u003e0.5444\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eMyostatin (pg/mL)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e832.8 [655.3\u0026ndash;1011.6]\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e1043.8 [753.4\u0026ndash;1653.5]\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e138.0 [-100.0\u0026ndash;522.9]\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e\u0026mdash;\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c6\"\u003e \u003cp\u003e0.0755\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003c/tbody\u003e \u003c/colgroup\u003e \u003ctfoot\u003e \u003ctr\u003e\u003ctd colspan=\"6\"\u003e\u003cem\u003eContinuous variables are presented as mean\u0026thinsp;\u0026plusmn;\u0026thinsp;standard deviation when analyzed with the paired t-test and as median [interquartile range] when analyzed with the Wilcoxon signed-rank test. Δ values are presented as mean\u0026thinsp;\u0026plusmn;\u0026thinsp;standard deviation or median [interquartile range], as appropriate. 95% confidence intervals are shown for mean paired changes only. hs-CRP, high-sensitivity C-reactive protein; HbA1c, glycated hemoglobin.\u003c/em\u003e\u003c/td\u003e\u003c/tr\u003e \u003c/tfoot\u003e \u003c/table\u003e\u003c/div\u003e \u003c/p\u003e \u003cp\u003eThe prevalence of SO varied according to the functional criterion applied (Table\u0026nbsp;\u003cspan refid=\"Tab3\" class=\"InternalRef\"\u003e3\u003c/span\u003e). At baseline, 10.0% of participants met SO criteria when the chair stand test was combined with ASM/weight, whereas 2.5% met the criteria when handgrip strength was used. At 6 months, no participants met SO criteria by either definition. However, these reductions were not statistically significant according to the exact McNemar test.\u003c/p\u003e \u003cp\u003e \u003cdiv class=\"gridtable\"\u003e\u003ctable float=\"Yes\" id=\"Tab3\" border=\"1\"\u003e \u003ccaption language=\"En\"\u003e \u003cdiv class=\"CaptionNumber\"\u003eTable 3\u003c/div\u003e \u003cdiv class=\"CaptionContent\"\u003e \u003cp\u003ePrevalence of sarcopenic obesity according to the functional criterion applied at baseline and 6 months after RYGB\u003c/p\u003e \u003c/div\u003e \u003c/caption\u003e \u003ccolgroup cols=\"4\"\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c1\" colnum=\"1\"\u003e\u003c/div\u003e \u003cdiv align=\"char\" char=\".\" class=\"colspec\" colname=\"c2\" colnum=\"2\"\u003e\u003c/div\u003e \u003cdiv align=\"char\" char=\".\" class=\"colspec\" colname=\"c3\" colnum=\"3\"\u003e\u003c/div\u003e \u003cdiv align=\"char\" char=\".\" class=\"colspec\" colname=\"c4\" colnum=\"4\"\u003e\u003c/div\u003e \u003cthead\u003e \u003ctr\u003e \u003cth align=\"left\" colname=\"c1\"\u003e \u003cp\u003eVariable\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c2\"\u003e \u003cp\u003eBaseline\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c3\"\u003e \u003cp\u003e6 months\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c4\"\u003e \u003cp\u003ep-value\u003c/p\u003e \u003c/th\u003e \u003c/tr\u003e \u003c/thead\u003e \u003ctbody\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eSO based on chair stand test\u0026thinsp;+\u0026thinsp;ASM/weight, n (%)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e \u003cp\u003e4 (10.0)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e0 (0.0)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e \u003cp\u003e0.1250\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eSO based on handgrip strength\u0026thinsp;+\u0026thinsp;ASM/weight, n (%)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e \u003cp\u003e1 (2.5)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e0 (0.0)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e \u003cp\u003e1.0000\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003c/tbody\u003e \u003c/colgroup\u003e \u003ctfoot\u003e \u003ctr\u003e\u003ctd colspan=\"4\"\u003e\u003cem\u003eValues are presented as n (%). p-values were obtained using the exact McNemar test. SO, sarcopenic obesity; ASM, appendicular skeletal muscle mass.\u003c/em\u003e\u003c/td\u003e\u003c/tr\u003e \u003c/tfoot\u003e \u003c/table\u003e\u003c/div\u003e \u003c/p\u003e \u003cp\u003eAn exploratory multivariable linear regression model was performed to assess factors associated with changes in MQI at 6 months (Table\u0026nbsp;\u003cspan refid=\"Tab4\" class=\"InternalRef\"\u003e4\u003c/span\u003e). The model explained 41.2% of the variance in ΔMQI (R\u0026sup2; = 0.412; adjusted R\u0026sup2; = 0.385; overall model p\u0026thinsp;=\u0026thinsp;0.028). Among the variables included, only ΔIL-6 was independently associated with ΔMQI (β\u0026thinsp;=\u0026thinsp;0.0673; 95% CI 0.003 to 0.132; p\u0026thinsp;=\u0026thinsp;0.041), whereas %TWL, age, and hs-CRP were not significantly associated.\u003c/p\u003e \u003cp\u003e \u003cdiv class=\"gridtable\"\u003e\u003ctable float=\"Yes\" id=\"Tab4\" border=\"1\"\u003e \u003ccaption language=\"En\"\u003e \u003cdiv class=\"CaptionNumber\"\u003eTable 4\u003c/div\u003e \u003cdiv class=\"CaptionContent\"\u003e \u003cp\u003eExploratory multivariable linear regression analysis of factors associated with the change in Muscle Quality Index (ΔMQI) at 6 months after RYGB\u003c/p\u003e \u003c/div\u003e \u003c/caption\u003e \u003ccolgroup cols=\"6\"\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c1\" colnum=\"1\"\u003e\u003c/div\u003e \u003cdiv align=\"char\" char=\".\" class=\"colspec\" colname=\"c2\" colnum=\"2\"\u003e\u003c/div\u003e \u003cdiv align=\"char\" char=\".\" class=\"colspec\" colname=\"c3\" colnum=\"3\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c4\" colnum=\"4\"\u003e\u003c/div\u003e \u003cdiv align=\"char\" char=\".\" class=\"colspec\" colname=\"c5\" colnum=\"5\"\u003e\u003c/div\u003e \u003cdiv align=\"char\" char=\".\" class=\"colspec\" colname=\"c6\" colnum=\"6\"\u003e\u003c/div\u003e \u003cthead\u003e \u003ctr\u003e \u003cth align=\"left\" colname=\"c1\"\u003e \u003cp\u003eVariable\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c2\"\u003e \u003cp\u003eCoefficient (β)\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c3\"\u003e \u003cp\u003eSE\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c4\"\u003e \u003cp\u003e95% CI\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c5\"\u003e \u003cp\u003et\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c6\"\u003e \u003cp\u003ep-value\u003c/p\u003e \u003c/th\u003e \u003c/tr\u003e \u003c/thead\u003e \u003ctbody\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eIntercept\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e \u003cp\u003e-0.3807\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e0.551\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e-1.581 to 0.819\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e \u003cp\u003e0.691\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c6\"\u003e \u003cp\u003e0.502\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eΔIL-6 (pg/mL)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e \u003cp\u003e0.0673\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e0.029\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e0.003 to 0.132\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e \u003cp\u003e2.277\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c6\"\u003e \u003cp\u003e0.041\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e%TWL\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e \u003cp\u003e0.0020\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e0.014\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e-0.028 to 0.033\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e \u003cp\u003e0.146\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c6\"\u003e \u003cp\u003e0.886\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eAge (years)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e \u003cp\u003e0.0090\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e0.011\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e-0.014 to 0.032\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e \u003cp\u003e0.824\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c6\"\u003e \u003cp\u003e0.425\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003ehs-CRP (mg/L)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e \u003cp\u003e0.0425\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e0.037\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e-0.038 to 0.123\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e \u003cp\u003e1.147\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c6\"\u003e \u003cp\u003e0.273\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003c/tbody\u003e \u003c/colgroup\u003e \u003ctfoot\u003e \u003ctr\u003e\u003ctd colspan=\"6\"\u003e\u003cb\u003eModel fit summary\u003c/b\u003e: R\u003csup\u003e2\u003c/sup\u003e\u0026thinsp;=\u0026thinsp;0.412; Adjusted R\u0026sup2; = 0.385; Overall model p-value\u0026thinsp;=\u0026thinsp;0.028\u003c/td\u003e\u003c/tr\u003e \u003ctr\u003e\u003ctd colspan=\"6\"\u003eAbbreviations: SE, standard error; CI, confidence interval; %TWL, total weight loss percentage; hs-CRP, high-sensitivity C-reactive protein; IL-6, interleukin-6; RYGB, Roux-en-Y gastric bypass. This model should be interpreted as exploratory given the sample size and the derived nature of MQI.\u003c/td\u003e\u003c/tr\u003e \u003c/tfoot\u003e \u003c/table\u003e\u003c/div\u003e \u003c/p\u003e"},{"header":"Discussion","content":"\u003cp\u003eThe main finding of this prospective study is that the first 6 months after RYGB were characterized by significant reductions in body weight, BMI, ASM, and fat-free mass, without significant deterioration in absolute muscle strength or chair stand performance. In parallel, substantial improvements were observed in metabolic and inflammatory parameters, including reductions in fasting glucose, HbA1c, insulin, hs-CRP, and IL-6. Together, these findings indicate that early postoperative loss of muscle mass does not necessarily translate into measurable short-term functional decline after bariatric surgery.\u003c/p\u003e \u003cp\u003eThe reduction in ASM observed in the present study is consistent with previous reports showing that a considerable proportion of early postoperative weight loss is accompanied by loss of lean mass and fat-free mass.\u003csup\u003e\u003cspan citationid=\"CR5\" class=\"CitationRef\"\u003e5\u003c/span\u003e,\u003cspan citationid=\"CR8\" class=\"CitationRef\"\u003e8\u003c/span\u003e,\u003cspan citationid=\"CR21\" class=\"CitationRef\"\u003e21\u003c/span\u003e\u003c/sup\u003e This pattern is expected during the rapid catabolic phase after surgery and reinforces the importance of monitoring body composition in addition to total weight loss. At the same time, the significant increase in ASM/weight suggests that the proportional reduction in total body mass exceeded the decline in appendicular muscle mass. Thus, although absolute muscle mass decreased, its relative representation in relation to body weight improved over time\u003csup\u003e\u003cspan citationid=\"CR22\" class=\"CitationRef\"\u003e22\u003c/span\u003e,\u003cspan citationid=\"CR33\" class=\"CitationRef\"\u003e33\u003c/span\u003e,\u003cspan citationid=\"CR34\" class=\"CitationRef\"\u003e34\u003c/span\u003e\u003c/sup\u003e.\u003c/p\u003e \u003cp\u003eDespite the reduction in ASM, no significant changes were observed in handgrip strength or chair stand performance. This finding is clinically relevant because it suggests preservation of measurable muscle function during the early postoperative period. Previous studies have similarly shown that declines in lean mass after bariatric surgery are not always accompanied by worsening in functional performance, particularly over the short term.\u003csup\u003e\u003cspan citationid=\"CR3\" class=\"CitationRef\"\u003e3\u003c/span\u003e,\u003cspan citationid=\"CR8\" class=\"CitationRef\"\u003e8\u003c/span\u003e,\u003cspan citationid=\"CR21\" class=\"CitationRef\"\u003e21\u003c/span\u003e,\u003cspan citationid=\"CR35\" class=\"CitationRef\"\u003e35\u003c/span\u003e\u003c/sup\u003e In this context, the dissociation between muscle quantity and function may help explain why substantial changes in body composition can occur without immediate impairment in strength-based outcomes.\u003c/p\u003e \u003cp\u003eMQI showed a modest increase over follow-up; however, this finding should be interpreted cautiously. MQI is mathematically dependent on ASM and may therefore be influenced by changes in the denominator rather than reflecting true physiological improvement.\u003csup\u003e\u003cspan citationid=\"CR12\" class=\"CitationRef\"\u003e12\u003c/span\u003e,\u003cspan citationid=\"CR13\" class=\"CitationRef\"\u003e13\u003c/span\u003e,\u003cspan citationid=\"CR28\" class=\"CitationRef\"\u003e28\u003c/span\u003e\u003c/sup\u003e Accordingly, although the increase in MQI may suggest relative preservation of function in relation to muscle mass, it should not be interpreted as definitive evidence of improved muscle quality. In the present study, the more robust functional message is that absolute strength remained stable despite significant reductions in ASM.\u003c/p\u003e \u003cp\u003eThe marked metabolic improvements observed in this study are consistent with the well-established systemic benefits of bariatric surgery.\u003csup\u003e\u003cspan citationid=\"CR2\" class=\"CitationRef\"\u003e2\u003c/span\u003e,\u003cspan citationid=\"CR3\" class=\"CitationRef\"\u003e3\u003c/span\u003e,\u003cspan citationid=\"CR4\" class=\"CitationRef\"\u003e4\u003c/span\u003e,\u003cspan citationid=\"CR24\" class=\"CitationRef\"\u003e24\u003c/span\u003e\u003c/sup\u003e In addition to reductions in glucose- and lipid-related markers, hs-CRP and IL-6 also declined significantly, indicating attenuation of systemic inflammation. Chronic low-grade inflammation has been implicated in anabolic resistance, impaired muscle protein turnover, and reduced physical performance in obesity.\u003csup\u003e\u003cspan citationid=\"CR2\" class=\"CitationRef\"\u003e2\u003c/span\u003e,\u003cspan citationid=\"CR16\" class=\"CitationRef\"\u003e16\u003c/span\u003e,\u003cspan citationid=\"CR27\" class=\"CitationRef\"\u003e27\u003c/span\u003e\u003c/sup\u003e Therefore, the reduction in inflammatory burden observed after surgery may represent a more favorable systemic environment for functional preservation, even in the context of reduced muscle mass. However, the present study was not designed to establish a mechanistic link between inflammatory improvement and muscle adaptation, and this interpretation should remain hypothesis-generating rather than causal.\u003c/p\u003e \u003cp\u003eTNF-α and myostatin did not change significantly over follow-up. This suggests that not all inflammatory and muscle-related biomarkers respond similarly during the first postoperative months. In particular, the absence of a significant change in myostatin may reflect the complexity of muscle remodeling during the early postoperative period, when weight loss, caloric restriction, and changes in physical activity may occur simultaneously.\u003csup\u003e\u003cspan citationid=\"CR30\" class=\"CitationRef\"\u003e30\u003c/span\u003e,\u003cspan citationid=\"CR31\" class=\"CitationRef\"\u003e31\u003c/span\u003e\u003c/sup\u003e Although myostatin is biologically relevant as a negative regulator of muscle mass, the present results do not support a measurable role for this pathway in explaining the functional findings observed here.\u003c/p\u003e \u003cp\u003eSelf-reported physical activity improved substantially after surgery, with a marked reduction in inactivity and a parallel increase in the proportion of participants classified as active or very active. This shift is clinically relevant and consistent with previous literature showing that bariatric surgery may facilitate improvements in mobility and physical activity behavior.\u003csup\u003e\u003cspan citationid=\"CR20\" class=\"CitationRef\"\u003e20\u003c/span\u003e,\u003cspan citationid=\"CR32\" class=\"CitationRef\"\u003e32\u003c/span\u003e\u003c/sup\u003e However, IPAQ is based on self-report and does not capture exercise modality, intensity, or resistance training exposure. Therefore, although physical activity clearly improved at the behavioral level, the extent to which it contributed to the preservation of muscle function in this cohort cannot be determined from the present data.\u003c/p\u003e \u003cp\u003eThe prevalence of SO varied according to the functional criterion applied, underscoring the clinical complexity of this phenotype. At baseline, a greater proportion of participants met SO criteria when the chair stand test was used than when handgrip strength was used, which is in line with the ESPEN/EASO framework emphasizing the combination of body composition and functional performance.\u003csup\u003e\u003cspan citationid=\"CR10\" class=\"CitationRef\"\u003e10\u003c/span\u003e,\u003cspan citationid=\"CR11\" class=\"CitationRef\"\u003e11\u003c/span\u003e\u003c/sup\u003e Although no participants met SO criteria at 6 months, these reductions were not statistically significant, likely because of the small number of baseline cases. Therefore, the present findings suggest a descriptive reduction in SO frequency after surgery, but they do not allow strong inferential conclusions regarding changes in prevalence.\u003c/p\u003e \u003cp\u003eThe exploratory multivariable model identified ΔIL-6 as the only variable independently associated with ΔMQI, whereas %TWL, age, and hs-CRP were not significant predictors. This finding should be interpreted with caution for two reasons. First, the model was exploratory and based on a limited sample size. Second, MQI is a derived index with known mathematical limitations.\u003csup\u003e\u003cspan citationid=\"CR12\" class=\"CitationRef\"\u003e12\u003c/span\u003e,\u003cspan citationid=\"CR28\" class=\"CitationRef\"\u003e28\u003c/span\u003e\u003c/sup\u003e Therefore, while the regression may suggest a possible relationship between inflammatory changes and relative functional adaptation, it should not be overinterpreted as evidence of mechanism. Rather, it may serve as a basis for future studies incorporating larger samples and direct measures of muscle composition and performance.\u003c/p\u003e \u003cp\u003eThis study has several limitations. The sample size was small, the follow-up period was limited to 6 months, and most participants were women, which restricts generalizability. In addition, the number of observations varied across laboratory and biomarker analyses, and physical activity was assessed by self-report. MQI, although clinically appealing, is a derived variable influenced by ASM and should be interpreted cautiously. Finally, no direct assessments of dietary protein intake, resistance training, intramuscular adipose tissue, or neuromuscular function were available. On the other hand, the study also has important strengths, including its prospective design, the use of DXA, the incorporation of functional tests, and the application of contemporary ESPEN/EASO criteria for SO.\u003csup\u003e10,21\u003c/sup\u003e\u003c/p\u003e \u003cp\u003eFrom a clinical perspective, these findings support the inclusion of functional assessment in postoperative follow-up rather than relying exclusively on weight loss or lean mass estimates. The early postoperative period appears to be characterized by substantial loss of muscle mass without measurable decline in absolute muscle function, which may represent an important therapeutic window for interventions aimed at preserving musculoskeletal health. In this context, resistance exercise and adequate protein intake are likely to be relevant components of postoperative care and should be investigated more directly in future studies.\u003csup\u003e\u003cspan citationid=\"CR6\" class=\"CitationRef\"\u003e6\u003c/span\u003e,\u003cspan citationid=\"CR8\" class=\"CitationRef\"\u003e8\u003c/span\u003e,\u003cspan citationid=\"CR22\" class=\"CitationRef\"\u003e22\u003c/span\u003e,\u003cspan citationid=\"CR32\" class=\"CitationRef\"\u003e32\u003c/span\u003e\u003c/sup\u003e\u003c/p\u003e \u003cdiv id=\"Sec11\" class=\"Section2\"\u003e \u003ch2\u003eClinical implications and Future directions\u003c/h2\u003e \u003cp\u003eFrom a clinical perspective, these findings suggest that postoperative follow-up should extend beyond weight monitoring and include routine functional assessment of skeletal muscle. Targeted interventions, particularly resistance training and adequate protein intake, may be important to preserve muscle function and support musculoskeletal health during the phase of rapid weight loss. Future studies should incorporate direct measures of muscle composition and quality, such as imaging techniques, together with more comprehensive functional assessments. In addition, factors such as protein intake, exercise modality, and neuromuscular adaptations should be further explored. Longer-term follow-up is needed to determine whether these early postoperative adaptations are sustained or eventually progress to functional impairment later after surgery.\u003c/p\u003e \u003c/div\u003e"},{"header":"Conclusion","content":"\u003cp\u003eSix months after bariatric surgery, skeletal muscle strength remained stable despite significant reductions in body weight and absolute muscle mass. MQI increased modestly, although this finding should be interpreted cautiously given the derived nature of this index. The prevalence of sarcopenic obesity decreased descriptively when functional criteria were applied, alongside substantial improvements in metabolic and inflammatory parameters. These preliminary findings suggest that bariatric surgery enhances metabolic health and early postoperative loss of muscle mass does not necessarily translate into measurable short-term functional decline and support the inclusion of functional assessment alongside body composition monitoring in postoperative care, and highlighted that muscle quality, rather that absolute mass, should be the primary focus for functional monitoring in postoperative care.\u003c/p\u003e"},{"header":"Declarations","content":"\u003ch2\u003eAuthor Contribution\u003c/h2\u003e\u003cp\u003eConception and design of the study : TLS and APM. Recruitment and data curation: TLS and RRAS. Methodolody: TLS, RRAS, PL; Writing -original drift :TLS . Writing- review and editing: APM Supervision: APM, Resources: APM, LGKA. All authors reviewed the manuscript.\u003c/p\u003e\u003ch2\u003eAcknowledgement\u003c/h2\u003e\u003cp\u003eCarlos Chagas Filho Foundation for Research Support in the State of Rio de Janeiro (FAPERJ).\u003c/p\u003e"},{"header":"References","content":"\u003col\u003e\n \u003cli\u003eWorld Obesity Federation. \u003cem\u003eWorld Obesity Atlas 2025\u003c/em\u003e. London: World Obesity Federation; 2025. Accessed March 1, 2026. \u0026nbsp; \u0026nbsp;https://data.worldobesity.org/publications/?cat=23\u003c/li\u003e\n \u003cli\u003eKalinkovich A, Livshits G. Sarcopenic obesity or obese sarcopenia: A cross talk between age-associated adipose tissue and skeletal muscle inflammation as a main mechanism of the pathogenesis. \u003cem\u003eAgeing Res Rev\u003c/em\u003e. 2017;35:200-221. doi:10.1016/j.arr.2016.09.008\u003c/li\u003e\n \u003cli\u003eCoral RV, et al. 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Changes in Lean Mass, Absolute and Relative Muscle Strength, and Physical Performance After Gastric Bypass Surgery. \u003cem\u003eJ Clin Endocrinol Metab\u003c/em\u003e. 2019;104(3):711-720. doi:10.1210/jc.2018-0095\u003c/li\u003e\n\u003c/ol\u003e"}],"fulltextSource":"","fullText":"","funders":[],"hasAdminPriorityOnWorkflow":false,"hasManuscriptDocX":true,"hasOptedInToPreprint":true,"hasPassedJournalQc":"","hasAnyPriority":false,"hideJournal":false,"highlight":"","institution":"","isAcceptedByJournal":false,"isAuthorSuppliedPdf":false,"isDeskRejected":"","isHiddenFromSearch":false,"isInQc":false,"isInWorkflow":false,"isPdf":false,"isPdfUpToDate":true,"isWithdrawnOrRetracted":false,"journal":{"display":true,"email":"[email protected]","identity":"obesity-surgery","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":false,"externalIdentity":"obsu","sideBox":"Learn more about [Obesity Surgery](https://link.springer.com/journal/11695)","snPcode":"11695","submissionUrl":"https://submission.springernature.com/new-submission/11695/3","title":"Obesity Surgery","twitterHandle":"","acdcEnabled":true,"dfaEnabled":true,"editorialSystem":"stoa","reportingPortfolio":"Springer Hybrid","inReviewEnabled":true,"inReviewRevisionsEnabled":false},"keywords":"bariatric surgery, sarcopenic obesity, muscle quality index, muscle strength","lastPublishedDoi":"10.21203/rs.3.rs-9360148/v1","lastPublishedDoiUrl":"https://doi.org/10.21203/rs.3.rs-9360148/v1","license":{"name":"CC BY 4.0","url":"https://creativecommons.org/licenses/by/4.0/"},"manuscriptAbstract":"\u003cp\u003e\u003cb\u003eBackground\u003c/b\u003e\u003c/p\u003e \u003cp\u003eBariatric and metabolic surgery (BMS) induces rapid weight loss, often accompanied by reductions in lean mass. However, early postoperative adaptations in muscle function and sarcopenic obesity (SO) remain incompletely understood. This study investigated short-term changes in muscle mass, muscle strength, muscle quality, and SO prevalence, according to ESPEN/EASO criteria, within 6 months after Roux-en-Y gastric bypass (RYGB).\u003c/p\u003e\u003cp\u003e\u003cb\u003eMethods\u003c/b\u003e\u003c/p\u003e \u003cp\u003eIn this prospective study, adults with severe obesity undergoing RYGB were evaluated before surgery and 6 months postoperatively. Body composition was assessed by dual-energy X-ray absorptiometry, and appendicular skeletal muscle mass (ASM) was calculated. Muscle strength was evaluated by handgrip strength (HGS) and chair stand test. Muscle quality was estimated using the muscle quality index (MQI\u0026thinsp;=\u0026thinsp;HGS/ASM). Metabolic, inflammatory, and muscle-related biomarkers were also analyzed.\u003c/p\u003e\u003cp\u003e\u003cb\u003eResults\u003c/b\u003e\u003c/p\u003e \u003cp\u003eForty participants (46.5\u0026thinsp;\u0026plusmn;\u0026thinsp;9.6 years; 92% women) were included. Body weight, BMI, ASM, and fat-free mass decreased significantly over follow-up, whereas ASM/weight increased significantly. Absolute muscle strength remained stable, with no significant changes in HGS or chair stand performance. MQI showed a modest but significant increase over time. Metabolic parameters improved substantially, including reductions in fasting glucose, HbA1c, insulin, triglycerides, total cholesterol, LDL-c, and hs-CRP, while vitamin D increased significantly. IL-6 decreased significantly, whereas TNF-α and myostatin remained unchanged. The prevalence of SO decreased descriptively according to both functional definitions, although these changes were not statistically significant. In an exploratory multivariable model, only ΔIL-6 was independently associated with ΔMQI.\u003c/p\u003e\u003cp\u003e\u003cb\u003eConclusion\u003c/b\u003e\u003c/p\u003e \u003cp\u003eDespite significant reductions in absolute muscle mass during the first 6 months after RYGB, absolute muscle strength was preserved. These findings suggest that early postoperative loss of muscle mass does not necessarily translate into measurable short-term functional decline and support the inclusion of functional assessment in postoperative follow-up.\u003c/p\u003e","manuscriptTitle":"The Muscle Paradox in Bariatric Surgery: Early Post-opertative Loss of Muscle Mass without Functional Decline","msid":"","msnumber":"","nonDraftVersions":[{"code":1,"date":"2026-04-30 18:50:41","doi":"10.21203/rs.3.rs-9360148/v1","editorialEvents":[{"type":"communityComments","content":0},{"type":"editorInvitedReview","content":"","date":"2026-05-18T15:26:31+00:00","index":"hide","fulltext":""},{"type":"reviewerAgreed","content":"176629805148947797934598793156189864464","date":"2026-04-27T16:45:03+00:00","index":"hide","fulltext":""},{"type":"reviewersInvited","content":"","date":"2026-04-22T16:38:15+00:00","index":"","fulltext":""},{"type":"editorAssigned","content":"","date":"2026-04-21T14:56:39+00:00","index":"","fulltext":""},{"type":"checksComplete","content":"","date":"2026-04-21T01:19:29+00:00","index":"","fulltext":""},{"type":"submitted","content":"Obesity Surgery","date":"2026-04-08T18:03:42+00:00","index":"","fulltext":""}],"status":"published","journal":{"display":true,"email":"[email protected]","identity":"obesity-surgery","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":false,"externalIdentity":"obsu","sideBox":"Learn more about [Obesity Surgery](https://link.springer.com/journal/11695)","snPcode":"11695","submissionUrl":"https://submission.springernature.com/new-submission/11695/3","title":"Obesity Surgery","twitterHandle":"","acdcEnabled":true,"dfaEnabled":true,"editorialSystem":"stoa","reportingPortfolio":"Springer Hybrid","inReviewEnabled":true,"inReviewRevisionsEnabled":false}}],"origin":"","ownerIdentity":"42b795a2-bad7-430a-a1fd-3a2008ccaf79","owner":[],"postedDate":"April 30th, 2026","published":true,"recentEditorialEvents":[{"type":"editorInvitedReview","content":"","date":"2026-05-18T15:26:31+00:00","index":17,"fulltext":""}],"rejectedJournal":[],"revision":"","amendment":"","status":"under-review","subjectAreas":[],"tags":[],"updatedAt":"2026-04-30T18:50:41+00:00","versionOfRecord":[],"versionCreatedAt":"2026-04-30 18:50:41","video":"","vorDoi":"","vorDoiUrl":"","workflowStages":[]},"version":"v1","identity":"rs-9360148","journalConfig":"researchsquare"},"__N_SSP":true},"page":"/article/[identity]/[[...version]]","query":{"redirect":"/article/rs-9360148","identity":"rs-9360148","version":["v1"]},"buildId":"XKTyCvWXoU3ODBz1xrDgd","isFallback":false,"isExperimentalCompile":false,"dynamicIds":[84888],"gssp":true,"scriptLoader":[]}