We found that the prevalence of possible sarcopenia among the community-dwelling participants over 60 years old in Tianjin totally was 11.11%, 8.33% in males and 12.47% in females. These results were lower than the 31.1% prevalence of possible sarcopenia reported by Wu et al. in Chinese cities . The reason may be that there are greater differences among old adults in cities across the country, however, participants in our study were only the community-dwelling old adults in the municipality directly under the central government, the urban socioeconomic level and the living standard and lifestyle of them may be relatively higher and better, then the prevalence may be lower. Kim et al. reported that the prevalence of possible sarcopenia among the community-dwelling old adults aged 70–84 in South Korea was 24.6% (20.1% in men and 29.2% in women) , which was higher than the results of our study, which may be related to the older participants than ours’. Ageing is an important risk factor of possible sarcopenia, and the prevalence of possible sarcopenia in people over 70 years old is 50.6–78.1% . Our participants were aged 60 to 89 years old, and the inclusion of younger old adults reduced the prevalence of possible sarcopenia. Miura et al. reported that the prevalence of possible sarcopenia in Japanese 65-year-old adults was 2.9% , which is much lower than the results of our study. The reason may be related to younger elderly in their subjects. We found that the age of the people with possible sarcopenia was about 68 years old on average. Although the prevalence of possible sarcopenia in community-dwelling old adults in Tianjin is relatively lower than South Korea, according to the 2020 census data, there were as many as more than 3 million old adults over the age of 60 in Tianjin . The screening of possible sarcopenia therefore needs to be paid more attention to sarcopenia early prevention and its negative healthy outcomes.
According to AWGS2019 criteria, we found the prevalence of sarcopenia among the community-dwelling participants was 9.17% for males and 10.84% for females, which was similar to the prevalence of AWGS2019  and Wu’s report. , who had the average age of 72 years old. However, the results of our study were lower than South Korean people over 70 years old whose prevalence of sarcopenia was 22.8%, which may be related to higher age. Wu also found that the risk of sarcopenia increased significantly with ageing. The prevalence of sarcopenia in old adults aged 60–69, 70–79 and 80 years old and above was 11.5%, 27.2% and 52.0%, respectively, and the prevalence of old adults over 70 years old with sarcopenia is even higher than Korea .
Our study shows that ageing is an independent risk factor of possible sarcopenia and sarcopenia, indicating that possible sarcopenia and sarcopenia may occur gradually in physiological characteristics, and neuromuscular function with ageing, followed by degenerative changes in skeletal muscle structure and mass. These results are also consistent with previous studies, human may lose 20%-30% of skeletal muscle mass from 20 to 80 . Muscle strength begins to decline around age 30 and declines rapidly around age 50 . With the increase of age, motor unit remodeling increases, the rate of muscle fiber denervation increases, protein synthesis decreases, and the number of muscle satellite cells required for skeletal muscle growth and repair decreases [21–24], this can lead to a decreased in muscle fiber cross-sectional area. Old adults lose more type II muscle fibers than that of type I muscle fibers, and the loss of maximal muscle strength is obvious. Therefore, AWGS recommends that the old adults should be early screened for possible sarcopenia to prevent its development [5, 25].
We found that low physical activity level was associated to possible sarcopenia and sarcopenia. The grip strength of old adults with possible sarcopenia and sarcopenia both decreased significantly, and the lower the level of physical activity, the lower the grip strength , the more severe the decline in physical function, and the higher the risk of possible sarcopenia and sarcopenia . Low physical activity level leads to impaired muscle cell metabolic function, resulting in loss of muscle mass and strength, while high physical activity level may maintain or improve muscle strength in old adults by promoting protein synthesis, improving low-level chronic inflammatory states, increasing antioxidant capacity, improving the skeletal muscle cell metabolic function, and increasing mitochondrial numbers [28–30]. Therefore, it is suggested that promoting old adults to actively participate in physical activities in the early stage of old age is very significant to prevent the occurrence and development of sarcopenia, reduce disability, and improve their quality of life.
Cognitive dysfunction is associated with sarcopenia. Skeletal muscle is not only a part of the motor system, but also an endocrine organ. Myokines produced by skeletal muscle contraction play autocrine, paracrine and endocrine effects , and are involved in muscle proliferation, differentiation and regeneration [32, 33]. They also mediate signal transduction between muscle and bone, brain, liver, pancreas, adipose tissue, vascular bed, and skin . Although the exact mechanism between cognitive dysfunction and sarcopenia is unclear, current studies have shown that myokines are involved in regulating brain functions, including mood, learning, active movement and protecting nerves from damage, confirming the existence of crosstalk between muscles and the brain . In addition, increase physical activity can delay or even prevent the loss of skeletal muscle mass, maintain or restore cognitive function , and improve the progression of neurological diseases . Studies have shown that patients with sarcopenia have various degrees of cognitive dysfunction that results in reducing executive ability and processing speed, which reduce their activities of daily living, the ability and willingness to participate in exercise, and the ability to follow and implement treatment regimens . Therefore, the prevention of cognitive dysfunction is one of the important means to prevent sarcopenia.
Our study found that higher BMI is a protective factor for sarcopenia, which is consistent with previous findings [11,39−41]. The average BMI of the participants with sarcopenia in our study was 21.93 kg/m2, which was similar to the result of Landi’s result, who found that old adults with a BMI greater than 21 kg/m2 had 0.76 times the risk of sarcopenia compared with those with a BMI of less than 21kg/m2 . Miura  reported that the average BMI of 65-year-old Japanese people with sarcopenia was only 19 kg/m2, indicating that BMI reduction increases the risk of sarcopenia.
Increased body fat mass was an associated risk factor of sarcopenia in our study, which seems to suggest that only a larger BMI with increased lean body mass is more beneficial in reducing the risk of sarcopenia. BMI is one of the criteria for measuring obesity, and some studies suggest that obesity may reduce the risk of sarcopenia by increasing energy reserves and thus improving survivability , however, BMI doesn’t distinguish from various body components such as fat, muscle and bone. Measurement of body fat composition can be used to show in greater detail what kind of body composition increase associated with increased BMI may be beneficial in reducing the risk of sarcopenia. Studies have shown that obesity is one of the important factors leading to sarcopenia. Obesity increases the level of pro-inflammatory factors, promoting insulin resistance and sarcopenia . Ageing and changes in lifestyle, dietary habits and hormone levels lead to changes in body composition in older adults . We incorporated body fat percentage into the analysis equation and found that high body fat percentage was associated with sarcopenia, which is also an important finding of this study. Fat mass increases with ageing and can gradually infiltrate into skeletal muscle, resulting in changes in muscle fiber structure and contracting property, leading to loss of skeletal muscle mass, strength and function . The molecular biological mechanism of the increase of intramuscular fat content with ageing is not clear. From the perspective of inflammation theory, adipose tissue can release a large amount of IL-6 and TNF-α, which leads to the occurrence of low-level chronic inflammation, reduces insulin sensitivity, impairs the ability of protein synthesis, promotes protein hydrolysis, and leads to the loss of skeletal muscle mass . In addition, the most abundant stem cells and progenitor cells in skeletal muscle are muscle satellite cells and fibro-adipogenic progenitor cells, the former usually differentiate into skeletal muscle cells, while the latter usually differentiate into adipocytes. Ageing may affect the proliferation and differentiation of muscle satellite cells by changing the cytokine secretion, leading to decreased myogenic differentiation and increasing adipogenic differentiation . Shen. performed aerobic and strength training for 12 weeks in old adults with osteosarcopenic obesity syndrome, which significantly reduced the body fat mass, increased muscle mass, and improved physical function , indicating that increased BMI with increased lean body mass may be a more favorable factor for maintaining and improving physical function and reducing the risk of sarcopenia in older adults.
Sarcopenia is the core pathological basis of frailty which increases the risk of death . When old adults have sarcopenia, their physical functions are already greatly impaired. Therefore, early prevention of sarcopenia is critical to the health. The prevalence and its associated risk factors of possible sarcopenia was just attracted an attention in recent years. Accurate understanding of the associated factors of possible sarcopenia and sarcopenia may lead to more advanced preventive measure of sarcopenia and more meaningful for early prevention of sarcopenia. Our study provides a basis for the prevention of sarcopenia. Improving the early identification of sarcopenia in old adults, and promoting the old adults, especially the young-old elderly, to actively increase the physical activity level, reducing body fat mass, and increasing lean body mass to achieve the purpose of preventing sarcopenia is the important inspiration of our study.
There are still some limitations in our study. The experimental design should be optimized, and the compliance of participants should be improved. In addition, further follow-up studies can be conducted to explore the long-term impact of various associated factors on disease development and physical function in patients with possible sarcopenia and sarcopenia.