1 INTRODUCTION

Sarcopenia is an aging syndrome characterized by decreased muscle mass, strength, and function with increasing age.^{1, 2} Sarcopenia increases the risk of falls and fractures, is accompanied by disability and a decreased ability to perform activities of daily living, and is closely associated with impaired mobility, falls, low bone mass and metabolic disorders.^{3, 4} At present, numerous institutions have proposed diagnostic standards that rely on muscle size and muscle performance, employing different thresholds and diverse assessment instruments.⁵ In the assessment of sarcopenia, dual-energy X-ray absorptiometry (DXA) is presently the primary option for quantitative evaluations, although magnetic resonance imaging (MRI), computed tomography (CT), or bioimpedance analysis (BIA) may be utilized depending on the specific circumstances.⁶ Internationally, there are different diagnostic criteria for sarcopenia. DXA measures the appendicular skeletal muscle mass index (ASMI), which represents muscle mass, while grip strength serves as the muscle strength index, and daily gait speed indicates the physical fitness index.⁷ Sarcopenia can be diagnosed when the corresponding measurements are lower than the above values.

Over the past few years, there has been a proposal and enhancement of systematic constitutional theory in traditional Chinese medicine (TCM).⁸ TCM constitutions have been extensively studied in a variety of diseases.^9-11 According to Chinese medicine, the constitution of the body is a relatively stable characteristic inherent in the morphological structure and functional activities of human individuals, formed by congenital inheritance and acquisition.¹¹ The differences in individual physique are reflected in certain differences in response and adaptation to external stimuli in the physiological state, as well as in susceptibility to certain pathogenic factors in the pathogenesis process and in the tendency for disease development.^{12, 13} Hence, investigating body constitutions aids in scrutinizing the emergence and progression of illnesses, thereby establishing a foundation for diagnosing and treating ailments.^{14, 15} In recent years, it has been reported that eight kinds of biased TCM constitutions are closely related to the occurrence and development of diseases in the elderly population and can be used to guide individual prevention and treatment.^{16, 17} This cross-sectional study revealed that Qi-deficiency and Yin-deficiency are related to a decrease in neurocognitive function in elderly people and that Yang-deficiency is closely related to osteoporosis and knee joint disease.^{16, 18} The China Association for Traditional Chinese Medicine issued standards for determining constitutions in TCM.¹⁹ The standard questionnaire can be used to evaluate one's constitution based on the symptoms presented. Therefore, our investigation focused on examining the associations between nine constitutional factors and skeletal muscle mass in the sarcopenia group.

2 METHODS

3 RESULTS

3.3 The predictive value of indicators for sarcopenia

By calculating the AUC, we evaluated the diagnostic accuracy of TCM for detecting low muscle mass among individuals in the sarcopenia cohort. Furthermore, we constructed an ROC curve to analyze TCM performance (Table 3). We found that in all participants, the original body condition score of Neutral AUC = 0.644 [95% CI: 0.596–0.691] and Yang-deficiency AUC = 0.613 [95% CI: 0.560–0.666] had better predictive value than the other parameters (Figure 1). In male participants, the original body condition scores for Qi-deficiency and Yin-deficiency also showed diagnostic potential, with AUCs of 0.642 and 0.634, respectively, and a cut-off value of 10.5, but these values were not significant in female participants. Then, we aggregated the parameters of all the AUCs and discovered that the AUC of the nine original body condition score mixtures in male participants reached 0.778, while that in female participants reached 0.676 (Figure 2).

TABLE 3. The results of ROC analysis of various TCM constitutions for the diagnosis of sarcopenia.

TCM constitution	All participants (n = 1441) AUC (95% CI)	Cut-off values	Sensitivity	Specificity	Male participants (n = 355) AUC (95% CI)	Cut-off values	Sensitivity	Specificity	Female participants (n = 1086) AUC (95% CI)	Cut-off values	Sensitivity	Specificity
Neutral constitution/original score	0.644 (0.596, 0.691)	27.5	55.8	66.2	0.682 (0.587, 0.776)	29.5	70.7	58.4	0.634 (0.578, 0.689)	27.5	60.4	62.3
Qi-deficiency constitution/original score	0.568 (0.517, 0.62)	12.5	59.2	53.2	0.642 (0.551, 0.734)	10.5	78	42.9	0.549 (0.488, 0.611)	12.5	63.2	48.4
Yang-deficiency constitution/original score	0.613 (0.56, 0.666)	13.5	48.3	72.2	0.647 (0.548, 0.745)	11.5	51.2	74.4	0.607 (0.545, 0.67)	17.5	34	87
Yin-deficiency constitution/original score	0.577 (0.526, 0.628)	12.5	57.8	57	0.634 (0.547, 0.72)	10.5	80.5	47.7	0.563 (0.501, 0.625)	12.5	59.4	54.7
Phlegm-damp constitution/original score	0.535 (0.485, 0.584)	12.5	40.8	66.5	0.516 (0.425, 0.606)	9.5	80.5	31.2	0.543 (0.484, 0.602)	12.5	43.4	65.7
Damp-heat constitution/original score	0.514 (0.462, 0.566)	12.5	23.1	84.3	0.52 (0.423, 0.618)	11.5	34.1	74	0.51 (0.448, 0.571)	12.5	22.6	85.3
Blood-stagnation constitution/original score	0.611 (0.562, 0.66)	12.5	54.4	61.6	0.617 (0.523, 0.711)	10.5	73.2	47.7	0.616 (0.559, 0.673)	15.5	32.1	84.6
Qi-stagnation constitution/original score	0.546 (0.520, 0.572)	7.5	69.4	38.0	0.547 (0.454, 0.640)	8.5	48.8	56.5	0.551 (0.492, 0.610)	10.5	38.7	68.9
Special diathesis constitution/original score	0.554 (0.528, 0.580)	10.5	34.7	75.1	0.619 (0.521, 0.717)	9.5	53.7	68.5	0.530 (0.473, 0.586)	7.5	69.8	37.9

4 DISCUSSION

Sarcopenia is a progressive and systemic skeletal muscle disorder associated with an increased likelihood of adverse outcomes, including falls, fractures, physical disability, and death, and is preventable and treatable in its early stages.^{22, 23} In TCM, health maintenance and disease treatment are guided by a complex conceptual framework.²⁴ According to the TCM theory, both innate and acquired factors can influence individual body constitutions, which determine disease susceptibility and development. Previous research has investigated the associations between TCM body constitutions and various diseases and conditions, including systemic lupus erythematosus, sleep disorders, hypertension, diabetes, dysmenorrhea, stroke, neoplasm of the breast, and fatty liver disease.^{16, 25, 26} A large body of research has explored a wide range of diseases, but little has been done on patients with sarcopenia.^{17, 27}

In this investigation, we initially identified certain TCM constitutions connected to sarcopenia among elderly Chinese participants with XMAT. Participants with sarcopenia had noticeably lower original Neutral constitution scores (p < 0.050). Compared with individuals without sarcopenia, those with sarcopenia exhibited notably higher original Qi-deficiency, Yang-deficiency, Blood-stagnation, Yin-deficiency, and Qi-stagnation scores (p < 0.050). Based on the principles of TCM theory, an individual may have either a single or a blend of body constitutions.²⁸ Within TCM, Neutral is the only healthy constitution, and it is more important to balance a disharmonious condition to a gentleness constitution than to treat a particular illness.²⁹ Our results showed that sarcopenia participants tended to receive a lower original score in the Neutral TCM constitution group than in the other eight constitutions group.

Based on the multivariate logistic regression analysis, we included different indicators in the multivariate model and established ROC curves to identify the best diagnostic indicators in the sarcopenia cohort. Neutral (OR = 0.903), Qi-deficiency (in males, OR = 1.126), Yang-deficiency (OR = 1.062), Phlegm-damp (in males, OR = 0.833), and Blood-stagnation (in females, OR = 1.089) were identified as risk factors for low skeletal muscle mass in sarcopenia patients. The AUC of the original Neutral constitution score was the highest, followed by those of the Qi-deficiency and Phlegm-damp scores (0.644, 0.613, and 0.611, respectively), and the AUC of the mixture of the nine constitution original scores in males reached 0.778.

This study has many limitations. First, this was a cross-sectional study with inherent limitations. Second, in this study, we only found a correlation between TCM constitutions and sarcopenia, not a causal relationship. Third, due to ethical limitations, the investigation of sarcopenia patients in this paper did not involve patients with serious physical and mental diseases or a loss of self-care ability and focused only on local patients with independent mobility in Xiamen. It was difficult to obtain data from patients who were severely ill or bedridden, which resulted in some bias in the results of the TCM syndrome analysis. The sample in this study was mainly concentrated in Xiamen, which may limit the generalizability of the findings, so it is necessary to conduct comprehensive and in-depth multicenter studies with larger samples and longer time spans in the future.

5 CONCLUSIONS

In this cross-sectional study of Chinese elderly people aged over 50 years from the XMAT, a mixture of nine original constitution scores was associated with sarcopenia in males and risk factors for low muscle mass.

AUTHOR CONTRIBUTIONS

This work was substantially, directly, and intellectually contributed by all the authors, and their final approval was obtained.

FUNDING INFORMATION

This research is supported by Grant No. 2020YFC2005600 from the National Key R&D Program of China.

CONFLICT OF INTEREST STATEMENT

The authors affirm that the study was carried out without any potential conflicts of interest, either commercial or financial.

ETHICAL APPROVAL

This research was approved by the Medical Ethics Committee of West China Hospital of Sichuan University (ethics approval No. 2017445), and the registration number is ChiCTR 1800018895. Prior to their inclusion, all participants consented to participate in the study and provided written informed consent.