Handgrip strength: A simple and effective tool to recognize decreased intrinsic capacity in Chinese older adults

Objectives: Intrinsic capacity impairment results in poor outcomes among older adults. Here we tested handgrip strength as a screening tool for IC impairment in community-dwelling older adults in Xinjiang, China. We assessed the diagnostic accuracy and established optimal cut-off points for handgrip strength in the detection of intrinsic capacity impairment. Methods: In total, 1072 participants were included using a multilevel random sampling method. Intrinsic capacity was constructed according to the definition of the Integrated Care for Older People screening tool proposed by the WHO. Results: Altogether, 73.4 % (787/1072) participants had intrinsic capacity impairment. The prevalence of intrinsic capacity impairment for hearing, vision, mobility, cognition, psychological, and vitality domains was 8.6 %, 4.8 %, 39.6 %, 47.3 %, 12.0 %, and 18.8 %, respectively. The adjusted odds ratios [95 % confidence interval) for handgrip strength was 0.935 [0.914 – 0.956]. The area under the curve of the receiver operating characteristic curve for handgrip strength of older men, and handgrip strength of older women with intrinsic capacity impairment were 0.7278, and 0.7534, respectively. The handgrip strength cut-off points were 28.47 kg (60 – 69 years), 25.76 kg (70 – 79 years), and 24.45 kg ( ≥ 80 years) for men, and 20.75 kg (60 – 69 years), 19.90 kg (70 – 79 years), and 16.17 kg ( ≥ 80 years) for women. Conclusions: Handgrip strength can be used as a convenient tool for evaluating intrinsic capacity. Weak handgrip strength and low education level were associated with intrinsic capacity impairment in community-dwelling older adults in Xinjiang. Using the cut-off points of handgrip strength for different age groups and genders, older adults with impaired intrinsic capacity can be identified, which may reduce the occurrence of adverse outcomes.


Introduction
Global population aging is the one of the most pressing medical and social demographic problems.Healthy aging, as defined by the World Health Organization (WHO), is the process of developing and maintaining functional capacity that enables well-being in older age, which was published in the World Report on Aging and Health (Beard et al., 2016).In 2016, the WHO's global strategy launched a new model of Integrated Care for Older People (ICOPE) that focuses on assessing individuals across the five domains of intrinsic capacity in order to better implement this concept (Tavassoli et al., 2022; WHO Guidelines Approved by the Guidelines Review Committee, 2017).The focus of the ICOPE model is assessing and promoting intrinsic capacity, including locomotion, cognition, vitality, sensory (visual and auditory), and psychological capacities (WHO Guidelines Approved by the Guidelines Review Committee, 2017).The five domains of intrinsic capacity are related to a reduction in physical and mental capacities and independently predict mortality and care dependence in older adults (Beard et al., 2019).Traditional research on 'biological aging' tends to focus on physical and cognitive performance (Beard et al., 2019).However, intrinsic capacity inferred this concept as it also takes into account the psychological, sensory, and energetic abilities that are crucial for healthy aging (Beard et al., 2016).Ma et al. provided evidence that the ICOPE screening tool was useful for identifying older adults with impaired physical and mental functions in a sample of 376 older Chinese adults, of which 69.1 % had impairment in at least one intrinsic capacity domain (Ma et al., 2020).Meanwhile, intrinsic capacity could predict incident adverse outcomes among community-dwelling older adults.Assessing intrinsic capacity would facilitate early identification of older adults at high risk of adverse outcomes and prompt targeted interventions (Ma et al., 2020).WHO-Guidance on person-centred assessment and pathways in primary care explicitly states that health and care workers must ensure that any limitation in capacity identified by the ICOPE screening tool always triggers further in-depth assessment, making it particularly suitable for undertake a person-centered assessment in primary care in Xinjiang, should inform the development of the personalized care plan.
In clinical settings, handgrip strength is widely used as a measure of overall muscle strength and it is a simple and valid parameter of skeletal muscle function can be conducted on older adults in community medical service stations, even in more remote rural areas.Several studies have shown significant associations of handgrip strength with single domains of intrinsic capacity, such as cognition, depression, and other healthrelated outcomes, including frailty, mortality and vitality (Ramírez-Vélez et al., 2019;Arokiasamy et al., 2021;Michel et al., 2021).Several studies have found significant associations between weaker handgrip strength and increased depressive symptoms among older adults in China (Zhao et al., 2020;Zhang et al., 2021).A Chinese study also found that higher handgrip strength is associated with improved cognitive capacity and a slower decline in cognition with age (Liu et al., 2019).Although extensive research has been conducted on the association between handgrip strength and functional phenotypes, most studies have focused on single functional phenotype, instead of comprehensive assessment, for example intrinsic capacity.Whether handgrip strength, a straightforward and easily accessible approach, can be used to detect or anticipate intrinsic capacity impairment in older adults has not been determined.A tool that may help identify intrinsic capacity impairment would enable rapid intervention strategies, potentially mitigating the adverse outcomes.
Xinjiang is located in northwestern China, Eurasia hinterland.Since ancient times, Xinjiang has been a multiethnic, multicultural and multireligious place.Xinjiang spans a large latitude and longitude and has large differences in altitude, temperature (in southern and northern Xinjiang) and residents' genetic background, cultural customs and eating habits.At present, there have been no large-scale surveys or analyses of the prevalence of intrinsic capacity impairment in the older population of Xinjiang.For the first time, the intrinsic capacity assessment was conducted on community-dwelling older adults in Xinjiang.Accordingly, we evaluated the association of handgrip strength with intrinsic capacity in a large sample of community-dwelling older adults in Xinjiang.Another aim of this study was to determine the best cut-off points for handgrip strength for estimating intrinsic capacity impairment among different sexes and ages, groups, we can formulate specific intervention measures against intrinsic capacity impairment to prevent, manage and reduce occurrence of adverse outcomes and the economic burden of medical insurance.

Material and methods
The cross-sectional study of community-dwelling older adults in Xinjiang was reviewed and approved by the Ethics Committee of People's Hospital of Xinjiang Uygur Autonomous Region.All participants provided written informed consent.For illiterate or have language barriers participants, we coordinated with the legal guardian and translated the questionnaire into the local language.The informed consent form was signed by the legal guardian.

Study population
Xinjiang is divided into three distinct sub-regions (north, south and east) according to natural settings and climate patterns.Multi-level random samples, collected from January 2020 to May 2022, consisting of community-dwelling older adults in Xinjiang were examined in the study.In the first stage, two sub-regions (north and south) were randomly selected from Xinjiang.In the second stage, one county was randomly selected from each sub-regions (Urumqi in northern Xinjiang and Luopu in southern Xinjiang).In the third stage, five communities were randomly selected from each county.In total, 1500 individuals were invited for this investigation.To ensure the samples were representative of the specified population, sample weights were used based on the results of the sixth national census of China.According to the sample weights of Luopu and Urumqi Counties, the sample sizes of the two counties were determined to be 472 and 1028, respectively.
Eligible individuals were aged over 60 years, had the ability to complete the survey, understood the investigations, cooperated with the investigators, and provided signed informed consent forms.The signature of a parent or legal guardian was required in case the participant was illiterate or incompetent.The exclusion criteria are older adults with disabilities, severe dementia, serious illnesses visual or auditory impairments.All the participants underwent physical examination and comprehensive geriatric assessment (CGA).The clinical and demographic variables were collected using a face-to-face questionnaire by trained staff.

Physical examination
Height, weight, body mass index (BMI), waist circumference, and handgrip strength were measured during the interview with the individuals wearing light indoor clothes without shoes.BMI was calculated as body weight in kg divided by height in m 2 (Bailey and Ferro-Luzzi, 1995).Handgrip strength was measured using a hand JAMAR dynamometer (JAMAR Hydraulic Hand Dynamometer, Lafayette, IN, USA), and the maximal reading of two trials was recorded (Fried et al., 2001a).Two readings were obtained from each side, and the maximum values of the right and left sides were used for the analysis.Weakness meant hand grip strength <26 kg for male and 18 kg for female.

Measures of intrinsic capacity [2]
With the process and tools in this Handbook-Guidance on personcentered assessment and pathways in primary care, trained healthcare workers can use the ICOPE screening tool to start the identification of people with losses in intrinsic capacity in a community or at home.We have provided an overview of the Intrinsic Capacity Score in Supplementary Fig. 1 (Tavassoli et al., 2022; WHO Guidelines Approved by the Guidelines Review Committee, 2017).The locomotion domain was assessed using the five times sit-to-stand test within 14 s (Hellmers et al., 2019).The psychological domain was evaluated using the following two questions: "Have you felt down, depressed, or hopeless in the past two weeks?" and "Have you felt little interest or pleasure in doing things over the preceding two weeks?"The impairment of each item was scored as 0 points.The sensory domain was assessed using selfreported hearing loss (failing to hear whispers) and visual impairments (any problem experienced with the eyes, difficulties in seeing far or reading, eye diseases, or currently undergoing medical treatment).The vitality domain was related to weight loss (>3 kg in the past 3 months, excluding deliberate weight loss) or appetite loss.Cognitive decline was recognized if they responded incorrectly to either of the two questions on orientation in time and space or if they could not recall the three words that they were asked to memorize.
The score of each domain dichotomized as 0 (normal) and 1 (impaired) was added together to an intrinsic capacity total score.If any of the assessments yields a result indicating a damaged domain, intrinsic capacity impairment is indicated and further evaluation of the individual is required (Tavassoli et al., 2022; WHO Guidelines Approved by the Guidelines Review Committee, 2017).Higher intrinsic capacity scores indicated better performance in intrinsic capacity (Ma et al., 2020).Method for evaluating Intrinsic Capacity Score -from WHO ICOPE screening tool showed in Supplementary Fig. 1.

Parameters of CGA
The parameters of CGA were collected during a standardized interview, including the patients' demographic information, such as age, gender, education level, marital status, number of chronic diseases, presence of chronic pain, history of falls, care-giving support, and living conditions.Subjective living conditions were assessed as participants living alone or not living alone, and for those not living alone, information on who the participant lived with was collected (Chen et al., 2020).The measurement data involved cognitive impairment (defined as scores <24 on the Chinese version of the Mini-Mental State Examination, MMSE (Chen et al., 2017)), mood disorder (defined by scores 2 on the 5-item Chinese Geriatric Depression Scale, GDS-5 (Hoyl et al., 1999)), medical condition (defined by the Charlson comorbidity index, CCI (Charlson et al., 1987)), polypharmacy (defined as currently using >4 drugs (Rankin et al., 2018)), malnutrition (defined by scores <12 on the Mini-Nutritional Assessment-Short Form, MNA-SF (Kaiser et al., 2009)), physical function (assessed by the Barthel index of Activities of Daily Living, ADL (Mahoney and Barthel, 1965) and the Lawton Instrumental Activities of Daily Living Scale, IADL (Graf, 2008)), as well as frailty in accordance with Fried's definition of the frailty phenotype (Fried et al., 2001b), which was evaluated based upon the presence of three or more criteria: weight loss, low physical activity, exhaustion, weakness (handgrip strength), and slowness (walking speed).Weight loss was defined as an unintentional decrease of >5 kg within one year.Low physical activity meant a weighted score of kilocalories expended per week based on each self-report activities <383 kcal/week for male and 270 kcal/week for female.Exhaustion was defined as self-reported fatigue.Slowness was defined as walking speed slower than 0.8 m/s.Frailty was defined as the presence of three or more of these criteria, prefrailty was defined as the presence of one or two of these criteria, and robust was defined as the absence of any of these criteria.

Quality control
To control for observer error, five doctors, three nurses, and two medical college students underwent a 2-day training on conducting questionnaire surveys.In this survey, qualified surveyors were asked to participate.In order to ensure the accuracy of the data, two professionals entered the information in parallel and performed statistical analyses.

Statistical analysis
Descriptive analysis was conducted to evaluate the normality of the data.Baseline characteristics, intrinsic capacity, and subdomain scores were presented as number of percentages for categorical variables and as mean (standard deviation [SD]) for continuous variables, where appropriate.Independent t-tests and chi-square tests were used to examine the differences in characteristics by sex and with or without intrinsic capacity impairment between participants included for data analysis.Spearman's correlation coefficients were calculated to assess the relationship between intrinsic capacity and differentiated observed factors.Missing data were addressed by missing value analysis.
In the binary logistic regression analysis, with or without intrinsic capacity impairment was set as the dependent variable.Model 1 was the crude model.Model 2 of the binary logistic regression analysis was adjusted for age, sex, waistline, marital status, presence of chronic pain, comorbidities and living conditions.
We used with or without intrinsic capacity impairment as a gold standard based on the WHO ICOPE screening tool (WHO Guidelines Approved by the Guidelines Review Committee, 2017).Receiver operating characteristic (ROC) curve analysis was performed to evaluate handgrip strength for detecting intrinsic capacity impairment in older adults.Statistical significance was set at p < 0.05, and all data were analyzed using Statistical product service solutions (SPSS) Statistics version 26.0 (IBM SPSS Statistics for Windows, Version 26.0.Armonk, NY: IBM Corp.).

Clinical characteristics of participants
A total of 1358 individuals completed the survey, resulting in a response rate of 90.5 % (1358/1500).We excluded 286 older adults who could not cooperate with the investigators.Therefore, the statistical analyses included data from 1072 older adults.The basic characteristics of the participants and a comparison between men and women were shown in Supplementary Table 1.The enrolled older adults included 542 women (50.6 %) and 530 men (49.4 %).Their ages ranged from 60 to 98 years, with a mean of 71.98 ± 8.19 years.The average age of men was older than that of women (p = 0.004).Of the 1072 older adults, 787 (73.4 %) were categorized as having intrinsic capacity impairment, with the rate of intrinsic capacity impairment being higher in women than in men.The mean total intrinsic capacity score for the whole cohort was 4.68 ± 1.09, and the prevalence of intrinsic capacity impairment for hearing, vision, mobility, cognition, psychological, and vitality domains were 8.6 %, 4.8 %, 39.6 %, 47.3 %, 12.0 %, and 18.8 %, respectively.

Significant differences in clinical features among older adults with and without intrinsic capacity impairment.
According to the criteria described in the Methods, older men and women were classified into two groups (with and without IC impairment), and their characteristics were indicated in Table 1.Participants with intrinsic capacity impairment were older and more likely to have chronic diseases, weaker handgrip strength, lower education level, and chronic pain compared to the participants without impairment, as shown in Table 1.

Correlations of intrinsic capacity score with age and handgrip strength
The correlations of intrinsic capacity score with age and handgrip strength were presented in Fig. 1. intrinsic capacity score was significantly negatively correlated with age (r = − 0.19, p < 0.0001), whereas it was significantly positively correlated handgrip strength for both men (r = 0.43, p < 0.0001) and women (r = 0.37, p < 0.0001).

ROC curves for handgrip strength for detecting intrinsic capacity impairment in older adults
ROC curves were constructed to estimate the sensitivity and specificity of handgrip strength for the detection of all older adults with or without intrinsic capacity impairment (Fig. 2).The area under the curves (AUCs) of the handgrip strength in older men and women with intrinsic capacity impairment were 0.73 (p < 0.0001) and 0.75 (p < 0.0001).The handgrip strength cut-off points were 28.5 kg (60-69 years), 25.8 kg (70-79 years), and 24.5 kg (≥80 years) for men and 20.8 kg (60-69 years), 19.9 kg (70-79 years), and 16.2 kg (≥80 years) for women, after categorizing older adults as having intrinsic capacity impairment or no intrinsic capacity impairment (Table 3).

Discussion
This study reported a high prevalence of intrinsic capacity impairment (73.4 %) in community-dwelling older adults in Xinjiang, and it was relatively higher than that reported in previous studies in other regions of China (Ma et al., 2020).This indicates the urgency of community-level support to older adults in Xinjiang.We have recognized as well that the rate of prevalence of deficits in the mobility and cognition domains were pretty high in this study.The possible reasons for this observation include the following.1) The difference in the prevalence rate is related to the differences in lifestyle, geographical environment and education levels of residents in different regions.2) The age of the participants is higher compared with those in previous reports.This observation was in accordance with the intrinsic capacity model showing that individuals' capacities declined with aging (Giudici et al., 2019).Our results suggested that participants with intrinsic capacity impairment were more likely to have a worse quality of life, such as more comorbidities, chronic pain and weaker handgrip strength.This is in line with previous studies showing that intrinsic capacity can effectively predict adverse outcomes in older community-dwelling adults (Liu et al., 2021;Zhao et al., 2021).A study from Brazil observed significant sex differences for the intrinsic capacity construct (Aliberti et al., 2022).However, our study did not find any gender differences in intrinsic capacity, possibly because of insufficient sample sizes for males and females, as well as age differences between males and females.
Intriguingly, our findings suggest that intrinsic capacity score correlated well with handgrip strength and education level, after adjusting for age, sex, waistline, marital status, and living conditions.The main objective of this study was to identify some easily available and accurate indicators with high sensitivity and specificity on intrinsic capacity impairment in community-dwelling older adults in Xinjiang.Handgrip strength is an important marker of intrinsic capacity.Previous studies have shown that handgrip strength was an independent predictor of disability, frailty, morbidity, and mortality (Syddall et al., 2003).Notes: Data are presented as mean ± SD, n (%).BMI body mass index.The relationship between handgrip strength and health-related outcomes have identified handgrip strength as the most important biomarker of aging and health (Bohannon, 2019).Additionally, previous studies showed that weak handgrip strength has been shown to increase depression risk and malnutrition risk (Beaudart et al., 2019;Amasene et al., 2021).Handgrip strength was associated with walking speed, cognitive ability, and activities of daily living disability (Lin et al., 2021;Chou et al., 2019;Vermeulen et al., 2011).The afore mentioned results of these studies indicated that handgrip strength is likely associated with four domains of intrinsic capacity, including psychological, vitality, locomotion, and cognitive domains, in addition to the sensory domain.It appears that handgrip strength can also serve as an indicator for intrinsic capacity.Therefore, the results of this study contribute to the current literature system by presenting gender specific and age specific intrinsic capacity impairment cut-off points among older adults in Xinjiang, China.
Handgrip strength testing is a simple and effective tool to identify decreased intrinsic capacity.Some studies have confirmed the correlation between handgrip strength and intrinsic capacity, and others have demonstrated that the handgrip strength cut-off points vary among countries and may reflect differences in stature, body size (Koopman et al., 2015), race, ethnicity (Thorpe et al., 2016), nutrition, diet, health behavior, and environmental situations that contribute to social determinants of health (Robinson et al., 2018;Sadana et al., 2016).This study is the first epidemiological survey of intrinsic capacity and handgrip strength in Xinjiang with a large sample size owing to the multi-stage random sampling strategy used in this study.We were able to obtain a representative sample population and uniform data coverage across continental Xinjiang.Compared with other regions in China, Xinjiang has a unique geographical and cultural environment.The older adults in Xinjiang also have a specific dietary culture, mainly consisting of carbohydrates and meat.The handgrip strength cut-off points may differ from those in other regions in China.The handgrip strength cut-off points reported in the present study are useful for determining the older adults that may benefit from lifestyle modifications to preserve muscle strength and reduce the odds of physical and mental limitations (Ramírez-Vélez et al., 2019).Based on our research data, for adults over 60 years old, the handgrip strength test should be conducted before    (Lu et al., 2023).Through this simple handgrip strength test, the risk of intrinsic capacity damage can be predicted, and early intervention can be achieved to delay the development of intrinsic capacity damage.Our results may inform intervention strategies aiming to increase muscle strength and promote healthy aging.In community medical service stations, a simple and convenient handgrip strength test can be conducted on older adults to determine the risk of intrinsic capacity damage using cut-off value.For older adults at risk of intrinsic capacity damage, a comprehensive assessment of intrinsic capacity can be conducted, and corresponding health guidance can be provided, including protein nutrition intake, appropriate activity guidance, and the need for family and social support systems.Some older adults have problems with oral frailty, which leads to malnutrition, frailty, and weakened handgrip strength and to some extent affects intrinsic capacity.These adverse outcomes may be estimated through simple handgrip strength testing.This may be the most valuable application of this study, as the handgrip test serves as a direct and convenient predictive tool for older adults in Xinjiang, China.
Our study has some notable limitations.First, we are not sure of the temporal sequence of the events in a cross-sectional study because the weak muscle strength and adverse events are assessed at the same time.
A further longitudinal study is needed to distinguish between determinants and impacts, which limited the causal interpretation.Longitudinal data are needed to directly assess the directional link between functional phenotype and intrinsic capacity and to test the validity of the cut-off points in predicting negative health outcomes, such as mobility, disability, and mortality in later life.Second, several measures, such as falls, history of chronic disease, and chronic pain, were self-reported by participants; therefore, different types of response biases may have been introduced.
Despite these limitations, our study has several strengths.To the best of our knowledge, this is the first epidemiological survey of intrinsic capacity and handgrip strength in Xinjiang with a large sample size owing to the multi-stage random sampling strategy used in this study, we were able to obtain a representative sample population and uniform data coverage across continental Xinjiang.Consequently, these cut-off points for handgrip strength in community-dwelling older adults in Xinjiang may serve as an early indicator of the developing of intrinsic capacity impairment and suggest that this is an easy, convenient, and cost-effective test that can help identify people who may benefit from early intervention to prevent or delay the development of intrinsic capacity impairment.

Conclusions
Handgrip strength can be used as a convenient tool for evaluating intrinsic capacity.Weak handgrip strength and low education level were associated with intrinsic capacity impairment in community-dwelling older adults in Xinjiang.Using the cut-off points of handgrip strength for different age groups and genders, older adults with impaired intrinsic capacity can be identified, which may reduce the occurrence of adverse outcomes.In future, we would intend to perform a cohort study to better understand the causal interpretation between intrinsic capacity impairment and physical function.

Ethics approval and consent to participate
This study involves human participants and was approved by Ethics Committee of People's Hospital of Xinjiang Uygur Autonomous Region (reference number: KY2021110801).Participants gave informed consent to participate in the study before taking part.In cases where a participant was unable to sign the informed consent form personally due to limitations in behavioural capacity or other reasons, the informed consent form was signed by their guardian or authorised representative.Participants' records were anonymised and de-identified prior to analysis.

Fig. 1 .
Fig. 1.Correlation between intrinsic capacity with age and handgrip strength.Spearman correlation coefficients were calculated between intrinsic capacity score and (A) age, (B) handgrip strength for male and (C) handgrip strength for female.

Fig. 2 .
Fig. 2. ROC curves for handgrip strength for detecting intrinsic capacity impairment in older adults.(A) ROC curves of handgrip strength to distinguish differences in all men with intrinsic capacity impairment.(B) ROC curves of handgrip strength to distinguish differences in all women with intrinsic capacity impairment.ROC area under the curve of the receiver operating characteristic.

Table 1
Characteristics of participants with or without intrinsic capacity impairment (N = 1072).

Table 2
Logistic regression for associated variables with intrinsic capacity score in 1072 participants.
a Model1: crude model.b Model 2: adjusted for age, sex, waistline, marital status, presence of chronic pain, comorbidities and living conditions.

Table 3
Weak handgrip strength cut point values by sex and age group.Using the handgrip strength cut-off points of different age groups and genders, older adults with weaker handgrip strength can be screened and identified, and their nutritional status, psychology, cognition, exercise ability, hearing and vision should be further evaluated.Specific intervention measures can be provided on the basis of the evaluation results.Handgrip strength cannot replace the screening tools recommended by ICOPE, but can serve as a tool for predicting intrinsic capacity damage.The different ways of measuring the intrinsic capacity domain of vitality in Wan-Hsuan Lu et al.'s study confirmed that handgrip strength provide clear targets for subsequent intervention to enhance intrinsic capacity