Abstract
Introduction
According to the 2020 national census data from the National Bureau of Statistics, the population aged 60 and above in China is nearly 270 million, accounting for 18.7% of the total population, while those aged 65 and above have surpassed 190 million, constituting 13.5% of the total population. 1 With China gradually transitioning into an aging society, degenerative conditions such as sarcopenia emerge as significant health concerns for the elderly population. Sarcopenia (SP) is a chronic syndrome characterized by a decline in overall muscle mass, reduced muscle strength, and physiological function decline. 2 It can result in impaired limb mobility, an elevated risk of falls, and fractures. 3 Recent research indicates that the prevalence of sarcopenia among elderly individuals residing in Chinese communities can reach approximately 12%. However, the overall prevalence of sarcopenia among elderly populations in both community and hospital settings is even higher, ranging from 20% to 30%. Among women in nursing homes, the prevalence of sarcopenia can be as high as 33.7%. 4 The InBody body composition analyzer employs bioelectrical impedance analysis (BIA) to detect and analyze body composition and content, including proteins, water, minerals, etc. Research has identified a close association between human body composition and the occurrence and development of malnutrition, as well as various chronic diseases,5–7 including sarcopenia. Compared to dual-energy X-ray absorptiometry (DXA), BIA offers advantages such as simple and convenient operation, lower cost, non-radioactivity, and ease of repeat measurements. 8 Thus, it can be applied in hospitals and even at the primary healthcare level.9–11 In this study, we employed the InBody body composition analyzer in conjunction with the diagnostic and treatment consensus proposed by the 2019 Asian Working Group for Sarcopenia. 12 We analyzed the body composition results of 1258 hospitalized patients, identified individuals meeting the diagnostic criteria for sarcopenia, and examined the influencing factors contributing to its occurrence. This research aims to provide a theoretical basis for reducing or preventing the onset of sarcopenia. Additionally, it suggests that healthcare professionals should early identify the risk factors of sarcopenia as well as effectively screen and manage high-risk populations.
Methods
Patients
The study cohort comprised 1258 patients admitted for inpatient treatment in the General Medicine Department of Tongji Medical College Affiliated Union Hospital, Huazhong University of Science and Technology, from December 2021 to October 2023. Our study is a retrospective research.
Inclusion criteria
Admission for inpatient care in the General Medicine Department between December 2021 and October 2023.
Underwent a body composition examination using the InBody analyzer while hospitalized.
Provided comprehensive informed consent to participate in this study and volunteered.
Exclusion criteria
Did not undergo body composition assessment using the InBody analyzer while hospitalized.
Were unable to cooperate in completing the required assessments.
Diagnosis
This study utilized the 2019 Asian Working Group for Sarcopenia diagnostic consensus, 12 which defines sarcopenia as a condition characterized by a reduction in muscle mass accompanied by a decrease in muscle strength, with or without a decline in muscle function. The assessment of skeletal muscle mass was conducted using bioelectrical impedance analysis (InBody body composition analyzer), and the Appendicular Skeletal Muscle Index (ASMI) was calculated. ASMI is calculated as the appendicular skeletal muscle mass (in kilograms) divided by the square of the height (in meters): ASMI = Appendicular Skeletal Muscle Mass (kg) / Height (m)². Sarcopenia is diagnosed when the ASMI is less than 7.0 kg/m² for males and less than 5.7 kg/m² for females.
Data collection
This study was conducted in the General Medicine Department of Tongji Medical College Affiliated Union Hospital, Huazhong University of Science and Technology. General patient information was extracted from the hospital's Haitai inpatient system, while body composition analysis data were obtained from the InBody body composition analyzer (InBody270, provided by BISON Medical Trading (Shanghai) Co., Ltd). For eligible study participants meeting the inclusion criteria, informed and trained research personnel from our department explained the research objectives and precautions. Patient confidentiality was maintained, and participants, under the guidance of trained research personnel, completed the body composition analysis examination. Prior to testing, participants were advised to avoid vigorous exercise, dietary changes, or excessive fluid intake to ensure optimal conditions for measurement. Participants were instructed to remove footwear and socks, stand in the designated position on the instrument with slightly separated legs, ensuring full contact of both feet with the InBody electrode plate. Participants maintained an upright position, ensuring good contact with the instrument, with arms slightly apart and naturally hanging. The testing environment remained quiet and stable throughout the measurement process until completion. To minimize operational errors, research personnel underwent professional training, and all measurements were conducted by the same trained individual. This approach aimed to ensure consistency and reliability in the data collection process.
Statistic analysis
Statistical analysis was conducted using SPSS 25.0 and Excel 2021 software for data analysis, and GraphPad Prism 9.5 software was utilized for graphical representation. Metric data with a normal distribution were expressed as mean ± standard deviation (x ± s), and inter-group comparisons were performed using independent sample t-tests. Data with skewed distribution were presented as the median with interquartile range [M (P25, P75)], and group comparisons were performed using the Mann-Whitney U test. Qualitative data were expressed as frequencies and percentages (%), and inter-group comparisons were conducted using the chi-square test. Logistic stepwise regression analysis was applied to analyze all detection indicators of the InBody analyzer, aiming to identify potentially meaningful indicators. Subsequently, binary logistic regression analysis was employed to identify significant indicators influencing the development of sarcopenia. Two-sided tests were employed, with a significance level set at α = 0.05. Finally, ROC curves were generated to assess the diagnostic capability of each individual indicator and the combined multi-indicator approach in predicting sarcopenia. The AUC values were calculated and evaluated to assess the diagnostic performance.
Results
Baseline data
This study included a total of 1258 participants, with ages ranging from 31 to 93 years and an average age of (58.48 ± 10.86) years. Among them, there were 691 males and 567 females, with 340 cases diagnosed with sarcopenia and 918 without, resulting in a prevalence rate of 27%. As indicated in Table 1, significant statistical differences (P < 0.05) were observed between the sarcopenia and non-sarcopenia groups in general characteristics such as age, gender, height, weight, and BMI. Based on Table 2, the incidence of sarcopenia gradually increases with age. Between the ages of 30 and 80, the incidence of sarcopenia increases by approximately 10% per decade. After the age of 80, the incidence of sarcopenia can reach up to 70.2%. According to the results from the InBody analyzer (Table 3), significant statistical differences (P < 0.05) were found between the two groups in total body water, protein, minerals, body fat mass, fat mass index, fat-free mass, fat-free mass index, and InBody score. Additionally, the InBody analyzer could display the normal ranges for various indicators based on the subjects’ age, gender, and other basic information. Evaluation of these indicators within their respective ranges, such as low total body water, low protein, high body fat mass, and high waist-to-hip ratio, was conducted in a binary format (Yes/No). The statistical analysis using the chi-square test revealed significant differences (P < 0.05) between the two groups. Furthermore, all count data from the measurement indicators were presented in a categorical bar chart, as illustrated in Figure 1.

Count data of InBody composition analysis.
Baseline characteristics of the study population.
The morbidity of sarcopenia varies across different age group.
Inbody body composition analysis results.
Analysis of factors influencing sarcopenia
Utilizing the presence or absence of sarcopenia as the dependent variable (1 = sarcopenia, 0 = non-sarcopenia), Logistic Stepwise Regression analysis was initially conducted, incorporating all variables from Tables 1 and 3 as independent variables. Drawing upon relevant literature and clinical experience, the analysis identified significant factors potentially influencing the occurrence of sarcopenia. The selected factors included low protein, low total body water, low minerals, gender, high body fat mass, low basal metabolic rate, high visceral fat level, high waist-to-hip ratio, high percent body fat, high obesity degree, age, BMI, fat-free mass index, and InBody score. Subsequently, the aforementioned variables were entered as independent variables into Binary Logistic Regression analysis, and the results are presented in Table 4. The findings revealed that low protein, low total body water, low minerals, low basal metabolic rate, and age were identified as risk factors for sarcopenia (OR > 1, P < 0.05). Conversely, being male, having a higher BMI, greater fat-free mass index, and a higher InBody score were identified as protective factors against sarcopenia (OR < 1, P < 0.05). The odds ratios (OR) were visually represented as shown in Figure 2.

Or visual processing.
Results of binary multiple-factor logistic regression analysis.
Predictive analysis of sarcopenia based on inbody body composition analysis
Based on the conclusions drawn from Section 2.2, it is evident that low protein, low total body water, low minerals, low basal metabolic rate, and age are risk factors associated with the occurrence of sarcopenia. Conversely, being male, having a higher BMI, greater fat-free mass index, and a higher InBody score are identified as protective factors against sarcopenia. Incorporating these variables into the diagnostic model, a ROC curve was plotted (Figure 3). Table 5 presents the predictive value of different indicators for sarcopenia. Among the single-factor indicators, low protein exhibited an AUC of 0.871 (95% CI = 0.845–0.897, P = 0.000), with sensitivity of 82.2% and specificity of 93%; low total body water demonstrated an AUC of 0.846 (95% CI = 0.817–0.874, P = 0.000), with sensitivity of 75.6% and specificity of 93.6%; low minerals showed an AUC of 0.757 (95% CI = 0.723–0.790, P = 0.000), with sensitivity of 61.8% and specificity of 89.5%; low basal metabolic rate presented an AUC of 0.645 (95% CI = 0.611–0.678, P = 0.000), with sensitivity of 75.9% and specificity of 53.1%; and age exhibited an AUC of 0.649 (95% CI = 0.614–0.684, P = 0.000), with sensitivity of 46.2% and specificity of 76.1%. Finally, combining these five indicators, a new model incorporating low protein, low total body water, low minerals, low basal metabolic rate, and age was established (Figure 4). The AUC for the new model was 0.932 (95% CI = 0.916–0.947, P = 0.000), demonstrating higher predictive performance. Sensitivity (83.2%) and specificity (92.6%) also showed improvement (Table 6).

ROC curves for different indicators in predicting sarcopenia.

ROC curve for the combined model (low protein, low total body water, low minerals, low basal metabolic rate, age) in predicting sarcopenia.
Predictive value of different indicators for sarcopenia.
Predictive value of the combined model (low protein, low total body water, low minerals, low basal metabolic rate, age) for sarcopenia.
Discussion
Sarcopenia is an age-related geriatric syndrome characterized by progressive loss of muscle mass, strength, and/or decline in muscle physiological function. According to statistics, there are currently 50 million sarcopenia patients worldwide, with an estimated increase to 500 million by the year 2050. 13 Human muscle mass peaks at the age of 25, and a decline of 3%–5% in muscle mass occurs every decade from the age of 40, followed by a 1%–2% reduction per year after the age of 50.14,15 The prevalence of sarcopenia among individuals aged 80 and above is reported to be as high as 67.1%. 16 Additionally, sarcopenia often coexists with osteoporosis (OP), collectively referred to as "sarcopenia-osteoporosis (OS)," thereby significantly increasing the risk of falls, fractures, and hospitalization in the elderly. The InBody body composition analyzer, utilizing the principle of bioelectrical impedance analysis (BIA), is widely employed as a non-invasive, convenient, cost-effective, and easily repeatable method for assessing and analyzing human body composition, including proteins, water, minerals, and fat. In recent years, it has gained popularity as a diagnostic tool that is ionizing radiation-free, thus making it more readily accepted by patients compared to dual-energy X-ray absorptiometry (DXA) examinations. In this study, we employed the InBody analyzer to assess the body composition characteristics of sarcopenia patients in China, analyzed influencing factors, and ultimately conducted predictive analysis for sarcopenia based on identified influencing factors.
Low protein, low total body water, low minerals, and low basal metabolic rate are risk factors for the occurrence of sarcopenia
The findings of this study suggest that inadequate protein intake significantly increases the risk of sarcopenia, in line with prior research. 17 Protein is a major component of muscle tissue and plays a vital role in muscle synthesis and repair. Inadequate protein intake can result in suboptimal muscle protein synthesis, consequently precipitating sarcopenia. The recommended dietary nutrient reference intake for Chinese residents in 2018 is 65 g/d protein intake for adult men and 55 g/d for women.18 According to the European Society for Clinical Nutrition and Metabolism guidelines, healthy elderly individuals are advised to consume 1.0–1.2 g of protein per kilogram of body weight per day, while those engaging in resistance exercise should aim for 1.2 g/kg/day. For elderly patients with chronic diseases, the recommendation is 1.2–1.5 g/kg/day, and for individuals facing severe illness, intake exceeding 1.5 g/kg/day is suggested. 19 Disparities in body composition between domestic and international populations may necessitate additional investigation into daily protein requirements. This result underscores the significance of incorporating protein intake into dietary planning, particularly for high-risk groups susceptible to sarcopenia. Augmenting protein intake could serve as a potential preventive measure. Furthermore, future research endeavors should prioritize elucidating the precise role of protein in the mechanisms governing muscle synthesis. This entails investigating variables such as protein type, timing of consumption, and quantity, aiming to foster a more holistic comprehension of the intricate pathways through which protein influences the onset of sarcopenia.
Muscle tissue contains a substantial proportion of water, and age-related cellular fluid loss can contribute to reduced body water content, potentially exacerbating sarcopenia. Minerals are primarily located in the skeleton, and insufficient mineral levels can predispose individuals to bone metabolic disorders such as osteoporosis. Nevertheless, our research demonstrates that decreased mineral content also influences the development of sarcopenia. Intriguingly, sarcopenia frequently coexists with osteoporosis, referred to as OS, 20 thereby underscoring the intimate connection between these two conditions. 21 Notably, vitamin D and calcium emerge as pivotal factors. Results from a multicenter, double-blind, randomized controlled trial indicate that vitamin D supplementation upregulates gene expression and muscle protein synthesis, thereby enhancing muscle mass and lower limb function in elderly individuals with diminished skeletal muscle mass, ultimately improving strength and balance. 22 This highlights the significant role that minerals play in preserving skeletal and muscle health.
The basal metabolic rate (BMR) indicates the body's energy expenditure during a state of rest. Our findings suggest that a diminished BMR may influence the onset of sarcopenia, likely due to decreased energy utilization efficiency, which could impair the maintenance and repair processes of muscle tissue. Moreover, metabolic rate closely correlates with energy balance, which is critical for preserving the health of muscle tissue. Diminished BMR may signify decreased energy requirements during rest, potentially resulting in reduced protein utilization by muscles. This physiological condition may induce muscle tissue to enter a negative energy balance, consequently precipitating sarcopenia. Furthermore, the body's metabolic rate is subject to regulation by the endocrine system, including thyroid hormones and insulin, 23 among other factors. These hormones can directly or indirectly influence the synthesis and breakdown processes of muscle tissue.
Male gender, BMI, and fat-free mass index are protective factors against sarcopenia
The study findings suggest that females exhibit a higher susceptibility to sarcopenia compared to males, contradicting certain previous research findings. 24 Males typically possess greater muscle mass and density, with androgen secretion potentially contributing to enhanced muscle protein synthesis, thus retarding the decline in muscle mass. 25 Conversely, in females, the substantial reduction in estrogen levels following menopause, a hormone crucial for musculoskeletal health maintenance, underscores the necessity for heightened awareness of musculoskeletal diseases among the elderly female demographic. Our observation revealed a decreased risk of sarcopenia among individuals with higher BMI. This finding underscores the significance of BMI in preserving muscle mass, as individuals with higher BMI may possess greater muscle mass, offering a protective advantage against muscle decline. Moderate fat storage may positively contribute by furnishing supplementary energy reserves to facilitate muscle synthesis and repair. Nevertheless, the protective impact of BMI may extend beyond muscle mass and should encompass the balance between fat and muscle, as observed in individuals with sarcopenic obesity. 26 Hence, evaluating muscle mass and strength remains essential for diagnosing sarcopenia, even in individuals with a normal BMI. In contrast to BMI, the fat-free mass index (FFMI) excludes fat from body weight, primarily assessing the quality of non-fat mass, notably muscle. Thus, FFMI is regarded as a superior indicator of muscle mass. Elevated FFMI levels may indicate a reduced risk of sarcopenia development. Nonetheless, this should be evaluated alongside overall muscle strength and functionality for a comprehensive assessment.
Regarding the predictive analysis of sarcopenia
This study integrated factors significantly linked to sarcopenia occurrence into a diagnostic model, and ROC curves were generated. Low levels of protein, total body water, minerals, basal metabolic rate, and age exhibited favorable AUC values, sensitivity, and specificity. Subsequently, we amalgamated these five indicators to formulate a novel predictive model, yielding an AUC of 0.932, accompanied by commendable sensitivity (83.2%) and specificity (92.6%). Prior research has suggested that in the absence of DXA, BIA serves as a viable method for evaluating muscle mass and diagnosing sarcopenia.27,28 BIA quantifies muscle mass and body composition via whole-body impedance, presenting a convenient, cost-effective, and radiation-free option for recurrent assessments, applicable across diverse settings including community and care facilities. Despite the excellent predictive capability of our new model, it depends on BIA/DXA measurements to derive these indicators. This underscores the importance that even if muscle mass assessed by BIA/DXA fails to meet the diagnostic criteria for sarcopenia in the elderly population, healthcare professionals should remain vigilant regarding the potential development of sarcopenia when the aforementioned indicators are low or borderline. In such instances, educating patients about the significance of supplementing protein, vitamin D, calcium, and participating in suitable physical exercises becomes imperative for averting sarcopenia and enhancing quality of life.
Limitations and constraints
While the sample size in this study is adequate, a comprehensive assessment and calculation of the sample size were not performed. Moreover, this study overlooks the investigation of Socioeconomic Status (SES) indicators, including educational level, economic status, and family environment of the subjects, which could influence the health status of the subjects and may consequently limit the comprehensiveness of this study. Finally, this study does not include an assessment of muscle function, such as the Timed Up and Go (TUG) test and the time taken for five sit-to-stand repetitions. The absence of muscle function assessments may limit the accuracy of sarcopenia diagnosis and the evaluation of its severity, thereby constituting limitations of this study.
Conclusion
Sarcopenia exhibits a relatively high prevalence among elderly individuals in China, emerging as a primary degenerative disease that poses a substantial threat to the health and quality of life of the aging population. The study employed the InBody analyzer, focusing on body composition analysis, to delineate the key influencing factors of sarcopenia. This study furnishes a theoretical foundation for the clinical prevention or treatment of sarcopenia, contributing to enhanced management strategies for individuals with sarcopenia. Moreover, the practicality and safety of the InBody make it a viable candidate for promotion in community settings and even larger hospital facilities. Subsequent research endeavors could contemplate conducting a comparative study between Bioelectrical Impedance Analysis (BIA) and the gold standard for body composition analysis, Dual-Energy X-ray Absorptiometry (DXA), to thoroughly validate the accuracy of BIA. Owing to the merits of BIA, including its non-radiative nature and capacity for repeated measurements, consideration could be given to substituting DXA with BIA as an innovative detection method.
