Background
Fall is a major cause of bone fractures [
1], restricted activity [
2], and mortality [
3]. Fall-related injuries cause a significant burden on the healthcare system and economic system [
4]. There are many factors related with fall, including limitations of functional performance, pain, stiffness, impaired proprioception, and obesity [
5‐
7]. Gender is also associated with fall. Women have higher incidence of fall than men (nearly twice as high) [
7].
Physiological [
8], psychological [
9,
10], cognitive [
11], and performance-based [
12] assessments have been proposed to evaluate the potential fall risk. The risk factors of fall included age, disability, poor performance on physical tests, depressive symptom [
9,
10]. Despite enormous fall-prevention researches, the prevalence of falls remains unchanged. Approximately one in three people over 65 years reported at least one fall each year [
13]. This may also be due to risk factors that have never been well understood.
Weak grip strength signifies impaired function, further increasing the risk of injuries. There is evidence showing that those in the lowest quarter of grip strength were at over 1.5-fold the risk of death during follow-up compared to those in the highest quarter [
14]. Vitamin B12 deficiency [
15], older age [
16‐
18], female [
16‐
18],depression [
17] ,physical activity [
17], and work status [
19] were potential risk factors of weak grip strength. The prevalence of weak grip strength was 34.4% in China [
16]. However, few researchers studied the potential risk factors of weak grip strength involving in a large number of Chinese participants.
China has the largest ageing population and one of the highest ageing rates in the world today [
20]. It is projected that the proportion of those aged 65 or older will increase from 7% of the population in 2010 to 26% in 2050 [
21]. The old-age support ratio (defined as the number of prime-age adults aged 15 to 64 divided by the number of adults aged 65 or above) will drop from about 9.9:1 in 2010 to 2.3:1 in 2050 [
21]. The population in China is ageing and ageing-related burden on society is serious. According to the above literature, falls and weak grip strength are two important ageing-related problems which can impair function and put enormous burden on economy or healthcare. The muscle mass and muscle strength of Asian are different from White [
22]. Besides, bone microstructure of Chinese is also different from White [
23,
24]. The rates of fall and hip fracture of Chinese women are lower than in white women [
24]. The risk factors, which are closely associated with weak muscle strength and fall, are also probably different. Some studies assessed the potential factors [
9,
10] but few researchers assessed the similar characteristics between fall and weak grip strength among Chinese in a study.
This study used data from the China Health and Retirement Longitudinal Study (CHARLS) to assess the factors associated with fall and weak grip strength and found similar characteristics between them to instruct preventions.
Discussion
The primary purpose of this study was to determine the risk factors of fall and weak grip strength. We used data from CHARLS and observed that fall and weak grip strength had many similar risk factors. Depression, age, symptomatic knee osteoarthritis were risk factors of both weak grip strength and fall. Furthermore, female with ischemic stroke and kidney disease had higher risk of fall. People living in rural area had higher risk of weak grip strength.
Depression was always accompanied by several psychophysiological changes, such as disturbances in appetite, sleep [
35,
36]. According to WHO, 350 million people suffered from depression all over the world [
36]. Depression can also not be considered a normal procedure of ageing. Many adolescents exhibited depressive symptoms. Some researchers found no relationship between weak grip strength and depression [
37‐
39], while other researchers suggested a relationship between depressive symptoms with weak grip strength [
40‐
43]. Our study found that depression is a risk factor of weak grip strength. Depressed individuals may perform limited physical activities, causing weaker muscle strength. Especially, depressed participants may not fully squeeze the handle due to lack of motivation [
44]. Therefore, depressed participants were recorded with weak grip strength results.
Considering fall, as we showed, depressed people got higher risks of fall. The actual mechanism why depressive mood predisposed to falls is unknown. Maybe depressed people can’t take care of themselves and thus perform high risk behavior to fall more often [
45]. In particular, depressed people may show impaired protective responses, leading to increased risk of injury [
45].
Our study showed no relationship between body mass with fall as the result of logistic regression. But many studies [
46,
47] had shown that disabled older people, especially female with lower BMI, are more likely to fall. A low body mass may indicate poor nutritional status or health status [
47,
48]. There is also some evidence reflecting that in female, a high body mass may increase the concentration of estrogen, which may have a positive effect on bone construction [
49,
50]. Our research did not show this. It may be that our study mixed normal and disabled people. A low body mass may reflect poor nutritional status or may only indicate slimness. Moreover, the body mass of Chinese people is commonly lower than western people. We got more normal BMI or just overweight people.
PA contributes to muscle strength a lot and the mechanisms include reduced apoptosis, reduced oxidative stress, anti-inflammation, improved insulin-glucose dynamics, enhanced quality and quantity of muscle proteins and mitochondria, skeletal muscle hypertrophy, positive neuromuscular adaptations, and enhanced muscle blood supply [
51].
Some evidences revealed that high PA indicated higher muscle mass, muscle strength and better physical performance compared with low and moderate PA levels [
52,
53]. But others did not suggest such association [
54,
55]. In a systematic review, Beckwée et al. concluded that exercise contributed to improving muscle strength [
56]. Conversely, Yoshimura et al. suggested that exercise had no significant effects on muscle strength [
57]. It is still controversial. Also, some studies showed that physical activity associates positively with lower-limb strength but less with grip strength [
58,
59]. Resistance exercise is currently the primary recommendation for enhancing muscle strength [
60,
61].WHO recommends that at least 150 min of moderate aerobic PA or 75 min of vigorous aerobic PA per week for older adults (65 years and above) [
62].
Our study showed no association between grip strength with physical activities. On one hand, our definition of PA is based on IPAQ, a reflect of daily activities. On the other hand, there are no sedentary time related questions in CHARLS questionnaire. Thus, targeted exercise is not involved, which is considered to improve muscle strength.
PA restriction could be beneficial for safety by reducing risk exposure [
63]. However, long-term PA restriction on various activities leads to increased risk of falls [
63]. Higher levels of physical activity were associated with higher frequencies of fall [
64].
Muscle strength of lower limbs is considered as an important factor affecting individual fall [
65]. In our study, we found that grip strength can also reflect the risk of fall in Chinese people. In clinical practice, grip strength is easier to measure [
65]. Doctors can evaluate the muscle strength via grip strength to predict the risk of fall.
In addition, we found that older age, female, ischemic stroke, rheumatoid arthritis, kidney disease were risk factors of fall. Ischemic stroke and rheumatoid arthritis can directly affect balance and gait [
66,
67]. And kidney disease affects the homeostasis [
68]. Thus, these people get worse muscle function.
The strength of this study is that our study was based on CHARLS, involving 150 countries/districts, 450 villages/urban communities across the country and using proper sampling strategy [
20]. Thus, the sample could be well representative. However, some limitations still exist. First, CHARLS was a short follow-up survey. This still requires long-term follow-up to explore risk factors for fall and weak grip strength. Second, many covariates such as chronic diseases in CHARLS were self-reported, which may increase the risk of residual confounding. Third, because data involves health information and personal information, people may withhold relevant information. Some information is to make people recall some life and health conditions more than one year ago. These all could lead to bias. Finally, our research was based on the previous studies. The variables involved in this study were based on the previous studies and our clinical experience. There may be some influencing factors that were not included in our study that led to bias.
Conclusion
Age and depression were risk factors of both weak grip strength and fall. Other risk factors, including female, ischemic stroke, rheumatoid arthritis, and kidney disease were risk factors of fall; living in rural area and symptomatic knee osteoarthritis were risk factors of weak grip strength. Through our research involving thousands of participants, we found that people who fell and people with weak grip strength have many similar characteristics. It is of great value for us to unify the management of such people with common characteristics in the future and reduce the cost of health service systems. At the same time, personalized management of people with weak grip strength or people who fell should not be lost.
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