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Association of handgrip strength asymmetry and weakness with functional disability among middle-aged and older adults in China

Quhong Song*, Xiaoyu Shu*, Yuxiao Li*, Yanli Zhao , Jirong Yue

Department of Geriatrics and National Clinical Research Center for Geriatrics, West China Hospital, Sichuan University, Chengdu, Sichuan, China
* Joint first authorship.

DOI: 10.7189/jogh.14.04047

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Abstract

Background

Little is known about the association of handgrip strength (HGS) asymmetry with functional disability in China. We aimed to examine the individual and combined association of HGS asymmetry and weakness with functional disability among middle-aged and older Chinese adults.

Methods

We included participants aged ≥45 years from two waves of the China Health and Retirement Longitudinal Study (2011 and 2015). HGS weakness was defined as the maximal HGS<28 kg for men and <18 kg for women. HGS asymmetry was measured by dividing the maximal nondominant HGS (kg) by the maximal dominant HGS (kg), with the value <0.90 or >1.10 considered as asymmetry. Functional disability was assessed by activities of daily living (ADL) and instrumental activities of daily living (IADL) and was defined as encountering difficulty in completing one or more ADL/IADL tasks. The logistic regression models were used to explore the association between HGS measures and functional disability.

Results

11 950 (mean age 59.2 ± 9.6 years, 47.9% males) and 7540 (mean age 57.5 ± 8.6 years, 50.1% males) participants were included in the cross-sectional and prospective study, respectively. HGS asymmetry and weakness, individually or simultaneously, were associated with an increased prevalence of functional disability. During the four-year follow-up, 1822 (24.2%) participants had incident functional disability. The separate exposure to HGS asymmetry (odds ratio (OR) = 1.18; 95% confidence interval (CI) = 1.05–1.32) or weakness (OR = 1.59; 95% CI = 1.30–1.95) was independently associated with functional disability. For combined associations, those with both weakness and asymmetry showed the greatest risk of new-onset functional disability (OR = 1.91; 95% CI = 1.45–2.52).

Conclusions

HGS asymmetry and weakness were associated with a higher risk of functional disability. Assessing HGS asymmetry together with weakness may help to better identify those at risk of functional disability to enable early interventions.

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Functional disability, characterised by the impaired ability to perform activities required for independent living, affects around 1.3 billion people worldwide (16% of the global population) [1]. It is common among older adults, with an estimated 34.4% of the world’s population aged 60 years and above experiencing disabilities [1]. This number will continuously increase as the population ages [1]. Preserving the functional capacity that enables well-being in later life is the key to healthy aging and has become a top priority for promoting public health [2]. Functional disability can cause undesirable outcomes like depression [3], falls [4], cognitive impairment [5], hospitalisation [6], mortality [7], exerting heavy burdens on individuals, families, and society. Fortunately, functional disability is preventable and intervenable [8], and a better understanding of its underlying risk factors is vital to designing effective interventions to delay functional loss and associated negative consequences.

Adequate muscle strength is fundamental to maintaining physical functioning, and deficits in muscle function strongly predict disability [9,10]. Handgrip strength (HGS) is the simplest method for assessing muscle function in clinical practice, which can be easily measured with a handgrip dynamometer [11]. It has been reported that HGS weakness, as assessed by maximal HGS, was associated with functional limitations [10] and increased risk of other poor health outcomes (e.g. chronic morbidities, frailty, premature mortality) [12]. However, the maximal HGS alone cannot fully assess muscle function, as it exclusively involves grip force in one hand while disregarding hand dominance and hand differences [12]. The human body exhibits laterality, with a natural difference in strength between hands [13,14]. HGS asymmetry, featured by a large difference between bilateral grip strength, has recently been identified as another dimension of muscle impairment [15] and has important prognostic values [16,17]. Emerging evidence suggests that HGS asymmetry and weakness may have synergistic effects on health [1821]. Analysing those two indicators simultaneously may provide a better understanding of how different aspects of muscle function influence health.

With respect to functional health, although some literature has reported the association of HGS asymmetry and weakness with functional disability [15,2123], only a few have assessed their joint relationship with functional status [15,21]. In addition, previous studies focused primarily on Western countries, with limited evidence from Asian countries. Given the ethnic and geographical variations in anthropometric measures [24], whether and to what degree the relationship of HGS asymmetry and weakness with functional disability can be applied to non-Western populations remains to be elucidated. China hosts the largest older population in the world and is aging faster than many other countries [2,25]. In 2020, there were 264 million Chinese aged 60 years and over (18.7% of the total population) [26], and this population is estimated to reach 479 million (35.1%) by 2050 [27]. In parallel, it is projected that the number of disabled and semi-disabled elderly will increase from 48 million in 2020 to 121 million in 2050 [28]. With China’s population aging, functional disability not only threatens the quality of life for millions of people, but also brings significant social, economic, and health care burdens given the growing demand for long-term care and medical services [2,28]. It is therefore of particular practical importance to identify relevant modifiable risk factors of disability in Chinese settings.

In the present study, we conducted the cross-sectional and longitudinal analysis to explore the individual and combined association of HGS asymmetry and weakness with functional disability among middle-aged and older Chinese adults, by using the nationally representative data from the China Health and Retirement Longitudinal Study (CHARLS). The main purpose was to evaluate the role of incorporating HGS asymmetry assessment on disability risk, and the findings may provide insights into early identification, prevention, and intervention of functional disability. We hypothesised that individuals with both HGS asymmetry and weakness will have a higher risk of functional disability.

METHODS

Study population

This study was a secondary data analysis based on the CHARLS, which is a nationally representative prospective survey of Chinese community-dwelling adults aged 45 years and older. A detailed description of CHARLS has been previously published [29]. Briefly, a total of 17 708 participants in 10 257 households were recruited from 150 counties or districts and 450 villages within 28 provinces in China between June 2011 and March 2012 (wave 1). Subsequent follow-ups were conducted biennially, with the first follow-up survey in 2013 (wave 2), the second in 2015 (wave 3), and the third in 2018 (wave 4). The CHARLS data sets are publicly available at http://charls.pku.edu.cn/en. This study followed the Strengthening the Reporting of Observational Studies in Epidemiology (STROBE) reporting guideline [30].

In the current study, we used two waves of CHARLS data (2011 and 2015). Eligible participants were those aged ≥45 years. We excluded subjects if they had: (1) missing values on age; (2) no information on hand dominance, or with two hands equally dominant; (3) no data on HGS; and (4) missing data on baseline functional status. The study was divided into two parts: (1) In the cross-sectional analysis, we eliminated 5758 participants following the above-predefined exclusion criteria, leaving 11 950 participants for the cross-sectional analysis. (2) In the longitudinal analysis, we further excluded 3271 subjects with baseline disability in 2011, and 1139 individuals with missing information on functional status in 2015, which resulted in 7540 eligible participants. The detailed flowchart of participants’ selection process was displayed in Figure 1.

Figure 1.  Flowchart of the participants’ selection. ADL – activities of daily living, IADL – instrumental activities of daily living

Handgrip strength weakness and asymmetry

HGS (kg) was measured by a mechanical dynamometer (YuejianTM WL-1000, Nantong, China), which has been proven to have satisfactory test-retest reliability [17]. After reporting hand dominance, participants performed the test in a standing position with their elbow flexed at 90° and held the dynamometer as hard as possible. For those who cannot stand unaided, HGS can be measured in a sitting position. Each participant was tested twice for each hand. If the subject was unable to perform the task on either hand (i.e. the greatest HGS value in one hand equals zero), the HGS was treated as missing. The maximum value of all four readings was used to evaluate HGS weakness. According to the Asian Work Group for Sarcopenia 2019 consensus [31], HGS weakness was defined as the maximal HGS of <28 kg in men and <18 kg in women.

HGS asymmetry was assessed by the HGS ratio, which was determined by dividing the maximal HGS of the nondominant hand (kg) by that of the dominant hand (kg) [20,21]. Consistent with prior literature [13], the 10% rule, which suggests that HGS is generally 10% stronger in the dominant hand compared with the nondominant hand, was employed to define HGS asymmetry. Accordingly, participants with an HGS ratio <0.90 or >1.10 were considered to have HGS asymmetry.

Based on HGS weakness and asymmetry categories, we further divided participants into four groups: (1) normal and symmetric HGS, (2) asymmetry only, (3) weakness only, and (4) weakness and asymmetry.

Assessment of functional status

The primary outcome was functional disability, and the secondary outcome was functional dependency. Functional disability was measured by activities of daily living (ADL) and instrumental activities of daily living (IADL). ADL includes six activities: eating, dressing, bathing, toileting, getting in or out of bed, and controlling urination and defecation [32,33]. IADL consists of five activities: shopping, cooking, doing housework, taking medications, and managing money [32,33]. Each item in ADL and IADL contains four answers: ‘don’t have any difficulty’, ‘have difficulty but can still do it’, ‘have difficulty and need help’, and ‘cannot do it’, which were assigned scores from 0 to 3, respectively [33]. Those with difficulty in one or more ADL/IADL items were classified as having functional disability [32,33]. We also calculated the continuous scores of functional disability (scores 0-33), ADL disability (scores 0-18), and IADL disability (scores 0-15), with higher scores indicating poor function [33].

Functional dependency was determined by the previously reported interval-of-need method [34], which is considered to be a more informative measure of disability burden that can reflect the potential need for personal and family care, supervision, and medical-related services. We divided participants into four categories based on the frequency with which they need care: high dependency (requires 24-hour care), medium dependency (requires help at regular times daily), low dependency (requires help less than daily), or independent (don’t need care) [34,35]. In line with prior studies [35,36], we constructed the interval-of-need categories according to the need for help with ADL and IADL activities (Table S1 in the Online Supplementary Document).

Covariates

The following baseline variables were included as potential covariates: age (years), sex, marital status (married/partnered, unmarried/others), educational level (illiterate, primary school, middle or high school, college or above), residence (urban, rural), household income per capita (Chinese yuan (CNY¥)), occupation (agricultural work, non-agricultural work, retired, unemployed or never work), social activities (no, yes), smoking status (never, past, or current), drinking status (never, ≤1 time/mo, >1 time/mo), multimorbidity (the presence of 0, 1, and ≥2 chronic diseases), visual problems (no, yes), hearing problems (no, yes), depression symptoms, cognitive function, and body mass index (BMI).

In this study, social activities were defined as the respondent’s engagement in any of the following activities: interacting with friends; playing mahjong, chess, cards, or going to a community club; going to dance, exercise, practice Qigong in parks or other places; taking part in a community-related organisation; doing voluntary or charity work; and attending an educational or training course. Multimorbidity was assessed based on the presence of 14 chronic conditions: hypertension, diabetes, heart problems, stroke, dyslipidemia, cancer, chronic lung disease, digestive disease, liver disease, kidney disease, arthritis, emotional and mental problems, memory-related disease, and asthma. Depression symptoms were measured by the 10-item Center for Epidemiologic Studies Depression Scale, yielding a total score of 30 [37]. Cognitive function was evaluated by episodic memory, the Telephone Interview of Cognitive Status (TICS-10), and figure drawing, totaling a score of 21 [38]. BMI was calculated as weight divided by the square of height (kg/m2) and was classified into four groups: underweight <18.5, normal 18.5–23.9, overweight 24.0–27.9, and obese ≥28.0 kg/m2.

Statistical analysis

Continuous variables were described as mean with standard deviation (SD) or median with interquartile range (IQR), and categorical variables were presented as frequency with percentages. For comparison among different groups, χ2 or Fisher exact test was used for categorical variables; whereas the t test, Mann-Whitney U test, analysis of variance, or Kruskal-Wallis H test was used for continuous variables, as appropriate. Missing covariates for participants (55.7% (6662/11950)) and 54.2% (4088/7540) in the cross-sectional and prospective analysis, respectively) were assumed to be randomly missing and were imputed using the chained equations method with 10 replications via the ‘mi estimate’ command in Stata statistical software version 15.0.

The binary logistic regression models were used to assess the cross-sectional and longitudinal association of HGS status with functional disability, and the multinomial logistic regressions were employed to examine the associations of HGS status with functional dependency (the independent group as reference). The results were reported as odds ratio (OR) and 95% confidence interval (CI). Relations of the exposures with functional outcomes were first explored by the separate exposure of HGS asymmetry and weakness. Then, the models were re-run using the composite measure derived from the two exposures. Three models were fitted: (1) model 1: unadjusted; (2) model 2: age and sex-adjusted; (3) model 3: further adjusted for marital status, educational level, residence, household income, occupation, social activities, smoking, drinking, multimorbidity, visual problems, hearing problems, depression score, cognitive function, and BMI. In the prospective analysis, follow-up time was also adjusted in model 3.

Given that age and sex may affect the association between HGS status and functional disability [21,39], subgroup analyses were performed to explore the possible heterogeneous effects of age (<60/≥60 years) and sex. In addition, as HGS difference between hands may be influenced by hand dominance [14,40], which may potentially bias the association of HGS measures with functional outcomes [21], additional stratified analysis by hand dominance (right-handed/left-handed) was further conducted. The potential interactions were evaluated by including a multiplicative interaction term in the model. The results were visualised by forest plots. Three sensitivity analyses were conducted to test the robustness of our findings: (1) we repeated the analyses using the complete-case data sets (5288 and 3452 participants in the cross-sectional and longitudinal analyses, respectively) to evaluate the potential effect of multiple imputations; (2) as HGS between hands may vary across individuals [14], to reduce asymmetry misclassifications, we also defined HGS asymmetry using 20 and 30% cut-points and re-ran the models. Specifically, asymmetry was defined as HGS ratio <0.80 or >1.20 (20%), or HGS ratio <0.70 or >1.30 (30%) [19,22,23]; (3) we reanalysed the data treating the outcomes as continuous disability scores, using linear regression models, to assess the robustness of the relationship between HGS status and functional disability.

All analyses were performed with Stata 15.0 (StataCorp, College Station, TX, USA), and a two-sided P < 0.05 was considered statistically significant.

RESULTS

Baseline characteristics

Table 1 presented the baseline characteristics of the study population in the cross-sectional analysis. The mean age of the 11 950 participants was 59.2 ± 9.6 years, and 5729 (47.9%) were males. Of these subjects, the prevalence of HGS weakness and asymmetry was 10.5% (1256/11 950) and 41.6% (4974/11 950), respectively. Compared with individuals without weakness or asymmetry, those with weakness or asymmetry were more likely to be older, unmarried, less educated, and had higher comorbidity burden, higher depression score, and lower cognitive score (all P < 0.001, Table 1). Baseline characteristics by the combined HGS weakness and asymmetry categories were provided in Table S2 in the Online Supplementary Document. Meanwhile, Table S3–S4 in the Online Supplementary Document also showed the characteristics of 7540 participants without baseline functional disability (mean age 57.5 ± 8.6 years, 50.1% men) in the longitudinal study.

Table 1.  Baseline characteristics of 11 950 participants by HGS status in the cross-sectional analysis

BMI – body mass index, CNY¥ – Chinese yuan, HGS – handgrip strength, IQR – interquartile range, SD – standard deviation

*Missing data: 107 for BMI, 4290 for household income, 163 for occupation, 126 for social activities, 1 for smoking, 630 for drinking, 270 for multimorbidity, 3 for visual problems, 7 for hearing problems, 174 for depression score, and 2862 for cognitive function.

Cross-sectional associations of HGS status with functional outcomes

Among the 11 950 participants, 3271 (27.4%) had functional disability. The prevalence of functional disability was significantly higher in those with HGS weakness or asymmetry (non-weakness vs. weakness = 24.7 vs. 50.0%, symmetry vs. asymmetry = 25.2 vs. 30.5%, Figure 2, panel A). After adjustment for covariates, HGS weakness was independently associated with functional disability (OR = 1.47; 95% CI = 1.27–1.68), including ADL disability (OR = 1.50; 95% CI = 1.29–1.75) and IADL disability (OR = 1.53; 95% CI = 1.32–1.76) (Figure 2, panel A). HGS asymmetry was also significantly associated with functional disability (OR = 1.11; 95% CI = 1.02–1.22), ADL disability (OR = 1.14; 95% CI = 1.02–1.27), but not IADL disability (OR = 1.09; 95% CI = 0.99–1.20). When comparing with those with normal and symmetric HGS, participants combined with weakness and asymmetry had the greatest odds for functional disability (OR = 1.60; 95% CI = 1.33–1.93), ADL disability (OR = 1.65; 95% CI = 1.35–2.02), and IADL disability (OR = 1.67; 95% CI = 1.38–2.02). The cross-sectional associations between HGS measures and functional disability were unchanged in the complete data sets (Table S5 in the Online Supplementary Document). Similar results were noted when HGS asymmetry was defined by the 20 and 30% rule (Table S6 in the Online Supplementary Document). Analyses treating the outcome measures as continuous variables found that participants with weakness and asymmetry together scored significantly higher in functional disability (Table S7 in the Online Supplementary Document).

Figure 2.  Cross-sectional associations of HGS status with functional outcomes. Panel A. Functional disability. Panel B. functional dependency. Adjusted for age, sex, marital status, educational level, residence, household income, occupation, social activities, smoking, drinking, multimorbidity, visual and hearing problems, depression score, cognitive function, and BMI. *P < 0.001. †P < 0.01. ‡P < 0.05. ADL – activities of daily living, CI – confidence interval, HGS – handgrip strength, IADL – instrumental activities of daily living, OR – odds ratio

The associations between HGS status and functional dependency were displayed in Figure 2, panel B. The presence of either weakness (OR = 1.59; 95% CI = 1.35–1.87) or asymmetry (OR = 1.17; 95% CI = 1.04–1.31) was associated with an increased prevalence of high dependency. Relative to participants with normal and symmetric HGS, those with both weakness and asymmetry were more likely to suffer from functional dependency, including low dependency (OR = 1.42; 95% CI = 1.05–1.92), medium dependency (OR = 1.41; 95% CI = 1.03–1.93), and high dependency (OR = 1.77; 95% CI = 1.42–2.20). The complete case analysis confirmed the weakness and asymmetry in association with high functional dependency (Table S8 in the Online Supplementary Document). Analyses using different asymmetry cutoffs yielded similar relationships between HGS status and functional dependency (Table S9 in the Online Supplementary Document).

Longitudinal associations of HGS status with functional outcomes

During the four-year follow-up (average follow-up time 47.7 months), 1822 (24.2%) participants developed functional disability. Compared with individuals with normal HGS, participants with HGS weakness were more likely to experience new-onset functional disability (OR = 1.59; 95% CI = 1.30–1.95), including ADL disability (OR = 1.49; 95% CI = 1.19–1.86) and IADL disability (OR = 1.50; 95% CI = 1.21–1.86) (Table 2). Subjects with HGS asymmetry also had higher risk of functional disability (OR = 1.18; 95% CI = 1.05–1.32), ADL disability (OR = 1.17; 95% CI = 1.02–1.34), and IADL disability (OR = 1.18; 95% CI = 1.04–1.35) than those with HGS symmetry. In comparison with those with normal and symmetric HGS, respondents combined with weakness and asymmetry had the greatest risk of incident functional disability (OR = 1.91; 95% CI = 1.45–2.52), followed by those with weakness only (OR = 1.47; 95% CI = 1.10–1.96) and those with asymmetry only (OR = 1.15; 95% CI = 1.02–1.29). Participants with both weakness and asymmetry also had the highest risk of ADL disability (OR = 1.98; 95% CI = 1.48–2.65) and IADL disability (OR = 1.76; 95% CI = 1.32–2.35). The relationships were not significantly changed among the subpopulations of 3452 subjects with complete data (Table S10 in the Online Supplementary Document). The results remained similar with the HGS ratio at 20% (Table S11 in the Online Supplementary Document). When the HGS ratio at 30%, weakness and asymmetry together predicted ADL disability (OR = 2.28; 95% CI = 1.23–4.23), but not IADL disability (OR = 1.23; 95% CI = 0.64–2.34). Linear models revealed that both weakness and asymmetry were associated with higher disability scores (Table S12 in the Online Supplementary Document).

Table 2.  Odds ratio (95% CI) for the longitudinal association of HGS status with functional disability

ADL – activities of daily living, BMI – body mass index, CI – confidence interval, HGS – handgrip strength, IADL – instrumental activities of daily living

Model 1: crude model; Model 2: adjusted for age and sex; Model 3: adjusted as model 2 plus marital status, educational level, residence, household income, occupation, social activities, smoking, drinking, multimorbidity, visual and hearing problems, depression score, cognitive function, BMI, and follow-up time.

*P < 0.001.

P < 0.01.

P < 0.05.

For functional dependency, we found that exposure to weakness (OR = 1.67; 95% CI = 1.32–2.11) or asymmetry (OR = 1.20; 95% CI = 1.04–1.38) was significantly associated with high dependency (Table 3). The risk of high dependency further increased if participants combined with weakness and asymmetry (OR = 2.17; 95% CI = 1.59–2.97). Similar results were observed by analyses with complete data sets (Table S13 in the Online Supplementary Document) and analyses using different asymmetry cutoffs (Table S14 in the Online Supplementary Document).

Table 3.  Multinominal logistic regression for the longitudinal association of HGS status with functional dependency

CI – confidence interval, HGS – handgrip strength, OR – odds ratio, Ref – reference

*Adjusted for age, sex, marital status, educational level, residence, household income, occupation, social activities, smoking, drinking, multimorbidity, visual and hearing problems, depression score, cognitive function, BMI, and follow-up time.

P < 0.001.

P < 0.01.

§P < 0.05.

Subgroup analyses

Figure S1 in the Online Supplementary Document presented the results of subgroup analyses. The associations of weakness and asymmetry with incident functional disability were not changed by age, sex, and hand dominance (all P for interaction >0.05). Similarly, subgroup analyses revealed that age, sex, and hand dominance did not significantly modify the relationships between HGS status and functional dependency (all P for interaction >0.05, Figure S2 in the Online Supplementary Document).

DISCUSSION

The present study found that HGS asymmetry and weakness were independently associated with functional disability and functional dependency among middle-aged and older Chinese adults. HGS asymmetry and weakness affected functional health additively, with participants with both weakness and asymmetry having the greatest risk of functional disability and high dependency.

Our results were compatible with previous studies reporting that declines in HGS predicted ADL/IADL disability and loss of independence [9,10,23]. Several explanations may account for this finding. First, HGS is a marker of physical activity, which itself holds important functions [11]. Decreased HGS and hand dexterity may directly affect the function of the upper limbs, impairing the ability to complete self-care activities (e.g. eating, dressing, cooking, shopping) [9,41]. Besides, lower HGS was also related to poor physical performance in the lower limbs, such as slow gait speed and mobility impairment [11,12,42], which may further exacerbate functional decline. Second, HGS weakness may reflect reduced neurological function or brain health [43], though it is primarily regarded as age-related deficits in the musculoskeletal system [43]. The measurement of HGS requires complex coordination movements that are heavily regulated by the neural systems [43]. It has been reported that higher HGS was associated with larger brain volumes in areas relevant to executive and memory function [44]. Adults with reduced HGS may experience an accelerated decline in neurocognitive function [19,20] and have a higher risk of future stroke [45]. The dysfunction of the nervous system may reduce the coordination of various tasks, such as difficulty in getting things, taking more time to finish tasks, and asymmetric motor performance [17,46], limiting the capacity to execute daily living activities and causing the resultant disability. Third, HGS weakness may place older adults at greater risk for metabolic dysfunction and chronic morbidities (e.g. insulin resistance, diabetes, and cardiovascular disease) [12,42]. The presence and accumulation of these chronic diseases may potentiate the disabling process [47].

Consistent with prior studies from Aging Americans [2123], we found that Chinese adults with HGS asymmetry had an elevated risk of functional disability. Though our results suggest that HGS weakness is more robustly related to functional disability, HGS asymmetry may pose similar health consequences that aggravate the disability risk. Humans prefer to use their dominant hands in daily activities [48], and the overreliance on the dominant hand while underuse of the nondominant hand may exacerbate strength imbalance. Other factors such as acute and chronic injuries may also affect hand usage and strength, causing asymmetry in HGS. A large difference in bilateral HGS may represent asymmetric motor function, which may factor into physical decline and functional limitations [22,23]. Indeed, previous studies have found that the presence of HGS asymmetry was related to poorer standing balance and timed-up-and-go performance [49,50], and could predict future limitations in activities like transferring and toileting [22]. Moreover, HGS asymmetry may indicate an imbalance in brain hemisphere activation or impaired neural system functioning [20,22,48]. Growing evidence has suggested that HGS asymmetry would increase the risk of neurodegenerative disorders [17], motoric cognitive risk syndrome [19], and cognitive impairment [20]. The cognitive vulnerability may further exacerbate the functional loss [51], and prior studies have demonstrated that individuals with HGS asymmetry had greater odds for limitations in tasks that require higher neuropsychological functioning (e.g. managing money and using maps) [23]. Our results may be supported by these findings. However, the mechanisms underlying the relationship of HGS asymmetry and weakness with functional disability are not completely understood and await further investigation.

The combination of HGS asymmetry and weakness showed a stronger association with functional disability than either of them alone in our study. Although the additive effects of HGS asymmetry and weakness on health outcomes (e.g. cognitive function [20], morbidity accumulation [18], and mortality [52]) have been reported in recent studies, to our knowledge, only two studies have examined their joint association with functional disability [15,21]. A cross-sectional study found that older Americans with HGS asymmetry and weakness had greater odds for limitations in ADL and IADL activities [15]. Similarly, a longitudinal cohort from the Health and Retirement Study revealed that the presence of both HGS asymmetry and weakness was more strongly related to future ADL disability [21]. These findings collectively suggest that functional decline may be accelerated in those with concurrent HGS asymmetry and weakness. Our study supports and complements the existing literature, addressing the gap in previous research which was limited by the lack of epidemiological studies on this topic in developing regions like China.

Our findings have important clinical implications. China is currently experiencing rapid population aging accompanied by a rising burden of functional impairment, which often contributes to an increased risk for disability, reduced quality of life, and socioeconomic burden [2]. Understanding the determinants of functional disability, especially in middle age and old age, is imperative to develop effective countermeasures and guide appropriate public health initiatives. Our study suggests that the presence of HGS asymmetry and weakness may potentiate functional decline. HGS asymmetry, a simple and quick measure, should be evaluated in clinical and research settings as an addition to HGS measurement protocols. The combined assessment of HGS asymmetry with weakness may help to better identify at-risk populations for functional disability. Interventions to improve muscle strength and correct strength asymmetry (e.g. exercise training programmes, nutrition therapy, task-oriented motor learning and related bilateral and unilateral therapeutic physical activities) [53,54] may prevent or delay functional disability and improve quality of life for middle-aged and older adults.

The present study has several advantages. First, this is the first study to examine the individual and combined effects of HGS asymmetry and weakness on functional disability in the Chinese population based on the cross-sectional and prospective analysis. Second, we employed a nationally representative longitudinal survey, and the large sample size made our results reliable. Third, functional status was measured not only by binary disability variables but also by continuous functional scores. Besides, the disability burden was further evaluated through the level of dependency reflected in the interval of care needs, which may provide a clearer indication of the intensity of care required than usual disability measures.

Limitations

Some limitations must be noted. First, we excluded ambidextrous participants and those lacking HGS data on either hand, limiting the generalisability of our results to the general middle-aged and older Chinese population. Second, selection bias may be introduced, as we eliminated participants without hand dominance or HGS data and those who had missing functional status during the two waves. Individuals who cannot complete the HGS test and those who lost to follow-up or died after their baseline interview may have experienced an accelerated decline in their strength and functional ability. The exclusion of these participants may underestimate the actual association between HGS measures and functional disability. Caution thus should be taken when interpreting and extrapolating our findings. Further well-designed, large-sample studies are warranted to verify our results. Third, self-reported measures (e.g. ADL/IADL and hand dominance) may cause potential recall bias, even though this method has been widely used in population-based studies [17,21,32,33]. Fourthly, HGS differences between hands may vary among individuals [14]. Although we defined HGS asymmetry by three different rules (i.e. 10, 20, and 30%), future studies are needed to create a robust HGS asymmetry cut-off point. Fifthly, regarding drinking status, as data on the quantity of alcohol consumption was unavailable in CHARLS, we were unable to assess the potential effect of drinking amount on functional disability, which needs further research. Lastly, despite that we have adjusted for multiple potential variables, residual confounding from unmeasured factors may still exist, for example, dietary intake and other time-varying confounding. More research is needed to validate our results and confirm the clinical applicability of HGS asymmetry.

CONCLUSIONS

HGS asymmetry and weakness were associated with higher risks of functional disability and functional dependency among middle-aged and older Chinese adults. Our findings extend the knowledge regarding associations between HGS measures and functional health, and suggest that assessment of HGS asymmetry together with the maximal HGS may help identify individuals at risk of functional disability. Interventions of HGS asymmetry and weakness may prevent the disabling process.

Additional material

Online Supplementary Document

Acknowledgements

We thank all participants and staff for their great contributions. We also sincerely appreciate the China Health and Retirement Longitudinal Study team for providing data.

Ethics statement: This study conformed to the ethical guidelines of the Declaration of Helsinki. The CHARLS was approved by the Ethics Review Committee of Peking University, Beijing, China (IRB00001052-11015). Written informed consent was obtained from all participants.

Data availability: The datasets used and/or analysed during the current study are available from the website of China Health and Retirement Longitudinal Study at http://charls.pku.edu.cn/en.

[1] Funding: This study was supported by grants from the National Clinical Research Center for Geriatrics, West China Hospital, Sichuan University (Z2023LC006), the Chinese National Science & Technology Pillar Program (2020YFC2009004), Sichuan Science and Technology Program (2022YFS0295, 2022YFG0205), 1.3.5 project for disciplines of excellence, West China Hospital, Sichuan University (ZYJC21005), Health Research of Cadres in Sichuan province (SCR2022-101), and Project of Chengdu Science and Technology Bureau (2022-YF05-01799-SN). The funders had no role in the study design, data collection, data analyses, data interpretation, or writing the manuscript.

[2] Authorship contributions: JRY and QHS conceptualised and designed the study. QHS and XYS cleaned, analysed, and interpreted the data. YXL checked the statistical methods and analysis results. QHS drafted the manuscript. XYS, YXL, and YLZ reviewed and edited the manuscript. JRY provided critical revisions to the manuscript. JRY and QHS contributed to the funding acquisition. All authors had full access to all the data and accepted the responsibility to submit the manuscript for publication. All authors read and approved the final version of the manuscript.

[3] Disclosure of interest: The authors completed the ICMJE Disclosure of Interest Form (available upon request from the corresponding author) and disclose no relevant interests.

references

[1World Health Organization. Global report on health equity for persons with disabilities. 2022. Available: https://www.who.int/publications/i/item/9789240063600. Accessed: 27 July 2023.

[2X Chen, J Giles, Y Yao, W Yip, Q Meng, and L Berkman. The path to healthy ageing in China: a Peking University-Lancet Commission. Lancet. 2022;400:1967-2006. DOI: 10.1016/S0140-6736(22)01546-X. [PMID:36423650]

[3F Tian, H Yang, and J Pan. Association between functional disability and long-term trajectories of depressive symptoms: Evidence from the China Health and Retirement Longitudinal Study. J Affect Disord. 2022;310:10-6. DOI: 10.1016/j.jad.2022.05.001. [PMID:35525506]

[4L Shao, Y Shi, XY Xie, Z Wang, ZA Wang, and JE Zhang. Incidence and Risk Factors of Falls Among Older People in Nursing Homes: Systematic Review and Meta-Analysis. J Am Med Dir Assoc. 2023;24:1708-17. DOI: 10.1016/j.jamda.2023.06.002. [PMID:37433427]

[5J Zheng, J Liu, and R An. Functional limitation and cognitive impairment among 80+ year old Chinese. Australas J Ageing. 2016;35:266-72. DOI: 10.1111/ajag.12341. [PMID:27320413]

[6TV Nguyen, HT Dang, MJ Burns, HH Dao, and TN Nguyen. Impairment in activities of daily living and readmission in older patients with heart failure: a cohort study. BMJ Open. 2021;11:e044416. DOI: 10.1136/bmjopen-2020-044416. [PMID:33619200]

[7Z Hu, B Zheng, AC Kaminga, F Zhou, and H Xu. Association Between Functional Limitations and Incident Cardiovascular Diseases and All-Cause Mortality Among the Middle-Aged and Older Adults in China: A Population-Based Prospective Cohort Study. Front Public Health. 2022;10:751985. DOI: 10.3389/fpubh.2022.751985. [PMID:35223720]

[8SL Szanton, RJ Thorpe, C Boyd, EK Tanner, B Leff, and E Agree. Community aging in place, advancing better living for elders: a bio-behavioral-environmental intervention to improve function and health-related quality of life in disabled older adults. J Am Geriatr Soc. 2011;59:2314-20. DOI: 10.1111/j.1532-5415.2011.03698.x. [PMID:22091738]

[9ME den Ouden, MJ Schuurmans, JS Brand, IE Arts, S Mueller-Schotte, and YT van der Schouw. Physical functioning is related to both an impaired physical ability and ADL disability: a ten year follow-up study in middle-aged and older persons. Maturitas. 2013;74:89-94. DOI: 10.1016/j.maturitas.2012.10.011. [PMID:23159191]

[10R McGrath, SG Robinson-Lane, MD Peterson, RR Bailey, and BM Vincent. Muscle Strength and Functional Limitations: Preserving Function in Older Mexican Americans. J Am Med Dir Assoc. 2018;19:391-8. DOI: 10.1016/j.jamda.2017.12.011. [PMID:29371128]

[11RW Bohannon. Muscle strength: clinical and prognostic value of hand-grip dynamometry. Curr Opin Clin Nutr Metab Care. 2015;18:465-70. DOI: 10.1097/MCO.0000000000000202. [PMID:26147527]

[12R McGrath, N Johnson, L Klawitter, S Mahoney, K Trautman, and C Carlson. What are the association patterns between handgrip strength and adverse health conditions? A topical review. SAGE Open Med. 2020;8:2050312120910358. DOI: 10.1177/2050312120910358. [PMID:32166029]

[13CA Armstrong and JA Oldham. A comparison of dominant and non-dominant hand strengths. J Hand Surg [Br]. 1999;24:421-5. DOI: 10.1054/JHSB.1999.0236. [PMID:10473148]

[14P Petersen, M Petrick, H Connor, and D Conklin. Grip strength and hand dominance: challenging the 10% rule. Am J Occup Ther. 1989;43:444-7. DOI: 10.5014/ajot.43.7.444. [PMID:2750859]

[15K Collins, N Johnson, L Klawitter, R Waldera, S Stastny, and WJ Kraemer. Handgrip Strength Asymmetry and Weakness are Differentially Associated with Functional Limitations in Older Americans. Int J Environ Res Public Health. 2020;17:3231 DOI: 10.3390/ijerph17093231. [PMID:32384713]

[16LA Klawitter, KS Collins, D Ringhofer, BK Christensen, and R McGrath. The Association Between Handgrip Strength Asymmetry Severity and Future Morbidity Accumulation: Results from the Health and Retirement Study. Int J Exerc Sci. 2022;15:1133-41. [PMID:35991351]

[17Z Chen, M Ho, and PH Chau. Handgrip strength asymmetry is associated with the risk of neurodegenerative disorders among Chinese older adults. J Cachexia Sarcopenia Muscle. 2022;13:1013-23. DOI: 10.1002/jcsm.12933. [PMID:35178892]

[18L Klawitter, BM Vincent, BJ Choi, J Smith, KD Hammer, and DA Jurivich. Handgrip Strength Asymmetry and Weakness Are Associated With Future Morbidity Accumulation in Americans. J Strength Cond Res. 2022;36:106-12. DOI: 10.1519/JSC.0000000000004166. [PMID:34941610]

[19S Jia, W Zhao, M Ge, L Zhou, X Sun, and Y Zhao. Association of Handgrip Strength Weakness and Asymmetry With Incidence of Motoric Cognitive Risk Syndrome in the China Health and Retirement Longitudinal Study. Neurology. 2023;100:e2342-9. DOI: 10.1212/WNL.0000000000207308. [PMID:37076310]

[20R McGrath, PM Cawthon, M Cesari, S Al Snih, and BC Clark. Handgrip Strength Asymmetry and Weakness Are Associated with Lower Cognitive Function: A Panel Study. J Am Geriatr Soc. 2020;68:2051-8. DOI: 10.1111/jgs.16556. [PMID:32473060]

[21R McGrath, BM Vincent, DA Jurivich, KJ Hackney, GR Tomkinson, and LJ Dahl. Handgrip Strength Asymmetry and Weakness Together Are Associated With Functional Disability in Aging Americans. J Gerontol A Biol Sci Med Sci. 2021;76:291-6. DOI: 10.1093/gerona/glaa100. [PMID:32319511]

[22SJ Mahoney, KJ Hackney, DA Jurivich, LJ Dahl, C Johnson, and R McGrath. Handgrip Strength Asymmetry Is Associated With Limitations in Individual Basic Self-Care Tasks. J Appl Gerontol. 2022;41:450-4. DOI: 10.1177/0733464820982409. [PMID:33356740]

[23K Parker, Y Rhee, GR Tomkinson, BM Vincent, ML O’Connor, and R McGrath. Handgrip Weakness and Asymmetry Independently Predict the Development of New Activity Limitations: Results from Analyses of Longitudinal Data from the US Health and Retirement Study. J Am Med Dir Assoc. 2021;22:821-826 e1. DOI: 10.1016/j.jamda.2020.11.006. [PMID:33290729]

[24J Woo, H Arai, TP Ng, AA Sayer, M Wong, and H Syddall. Ethnic and geographic variations in muscle mass, muscle strength and physical performance measures. Eur Geriatr Med. 2014;5:155-64. DOI: 10.1016/j.eurger.2014.04.003

[25World Health Organization. China country assessment report on ageing and health. 2015. Available: https://www.who.int/publications/i/item/9789241509312. Accessed: 1 August 2023.

[26National Bureau of Statistics of China. Communiqué of the Seventh National Population Census (No. 5). 2021. Available: https://www.stats.gov.cn/english/PressRelease/202105/t20210510_1817190.html. Accessed: 17 December 2023.

[27United Nations. Population Division. World Population Ageing. 2017. Available: https://www.un.org/en/development/desa/population/publications/pdf/ageing/WPA2017_Highlights.pdf. Accessed: 1 August 2023.

[28Y Ge, L Wang, W Feng, B Zhang, S Liu, and Y Ke. The Challenge and Strategy Selection of Healthy Aging in China. Journal of Management World. 2020;36:86-96.

[29Y Zhao, Y Hu, JP Smith, J Strauss, and G Yang. Cohort profile: the China Health and Retirement Longitudinal Study (CHARLS). Int J Epidemiol. 2014;43:61-8. DOI: 10.1093/ije/dys203. [PMID:23243115]

[30E von Elm, DG Altman, M Egger, SJ Pocock, PC Gotzsche, and JP Vandenbroucke. The Strengthening the Reporting of Observational Studies in Epidemiology (STROBE) statement: guidelines for reporting observational studies. Epidemiology. 2007;18:800-4. DOI: 10.1097/EDE.0b013e3181577654. [PMID:18049194]

[31LK Chen, J Woo, P Assantachai, TW Auyeung, MY Chou, and K Iijima. Asian Working Group for Sarcopenia: 2019 Consensus Update on Sarcopenia Diagnosis and Treatment. J Am Med Dir Assoc. 2020;21:300-307 e2. DOI: 10.1016/j.jamda.2019.12.012. [PMID:32033882]

[32L Guo, L An, F Luo, and B Yu. Social isolation, loneliness and functional disability in Chinese older women and men: a longitudinal study. Age Ageing. 2021;50:1222-8. DOI: 10.1093/ageing/afaa271. [PMID:33352582]

[33J Wang, Q Wang, XY Hou, S Chen, Z Guo, and W Du. Spousal Concordance in the Development of Functional Limitations Among Married Adults in China. JAMA Netw Open. 2021;4:e2125577. DOI: 10.1001/jamanetworkopen.2021.25577. [PMID:34581797]

[34B Isaacs and Y Neville. The needs of old people. The ‘interval’ as a method of measurement. Br J Prev Soc Med. 1976;30:79-85. DOI: 10.1136/jech.30.2.79. [PMID:953380]

[35A Kingston, A Comas-Herrera, and C Jagger. project M. Forecasting the care needs of the older population in England over the next 20 years: estimates from the Population Ageing and Care Simulation (PACSim) modelling study. Lancet Public Health. 2018;3:e447-55. DOI: 10.1016/S2468-2667(18)30118-X. [PMID:30174210]

[36X Lu, Y Yao, and Y Jin. Digital exclusion and functional dependence in older people: Findings from five longitudinal cohort studies. EClinicalMedicine. 2022;54:101708. DOI: 10.1016/j.eclinm.2022.101708. [PMID:36353265]

[37H Chen and AC Mui. Factorial validity of the Center for Epidemiologic Studies Depression Scale short form in older population in China. Int Psychogeriatr. 2014;26:49-57. DOI: 10.1017/S1041610213001701. [PMID:24125553]

[38H Xu, Z Zhang, L Li, and J Liu. Early life exposure to China’s 1959-61 famine and midlife cognition. Int J Epidemiol. 2018;47:109-20. DOI: 10.1093/ije/dyx222. [PMID:29126190]

[39CM Germain, E Vasquez, JA Batsis, and DR McQuoid. Sex, race and age differences in muscle strength and limitations in community dwelling older adults: Data from the Health and Retirement Survey (HRS). Arch Gerontol Geriatr. 2016;65:98-103. DOI: 10.1016/j.archger.2016.03.007. [PMID:27017414]

[40NA Incel, E Ceceli, PB Durukan, HR Erdem, and ZR Yorgancioglu. Grip strength: effect of hand dominance. Singapore Med J. 2002;43:234-7. [PMID:12188074]

[41R McGrath, KM Erlandson, BM Vincent, KJ Hackney, SD Herrmann, and BC Clark. Decreased Handgrip Strength is Associated With Impairments in Each Autonomous Living Task for Aging Adults in the United States. J Frailty Aging. 2019;8:141-5. [PMID:31237315]

[42RP McGrath, WJ Kraemer, SA Snih, and MD Peterson. Handgrip Strength and Health in Aging Adults. Sports Med. 2018;48:1993-2000. DOI: 10.1007/s40279-018-0952-y. [PMID:29943230]

[43RG Carson. Get a grip: individual variations in grip strength are a marker of brain health. Neurobiol Aging. 2018;71:189-222. DOI: 10.1016/j.neurobiolaging.2018.07.023. [PMID:30172220]

[44S Meysami, CA Raji, RM Glatt, ES Popa, AS Ganapathi, and T Bookheimer. Handgrip Strength Is Related to Hippocampal and Lobar Brain Volumes in a Cohort of Cognitively Impaired Older Adults with Confirmed Amyloid Burden. J Alzheimers Dis. 2023;91:999-1006. DOI: 10.3233/JAD-220886. [PMID:36530088]

[45G Liu, Y Xue, S Wang, Y Zhang, and Q Geng. Association between hand grip strength and stroke in China: a prospective cohort study. Aging (Albany NY). 2021;13:8204-13. DOI: 10.18632/aging.202630. [PMID:33686964]

[46E Carmeli, H Patish, and R Coleman. The aging hand. J Gerontol A Biol Sci Med Sci. 2003;58:146-52. DOI: 10.1093/gerona/58.2.M146. [PMID:12586852]

[47J Zhou, MY Wei, J Zhang, H Liu, and C Wu. Association of multimorbidity patterns with incident disability and recovery of independence among middle-aged and older adults. Age Ageing. 2022;51:afac177. DOI: 10.1093/ageing/afac177. [PMID:35930720]

[48M Wallden. Stimulus and response. J Bodyw Mov Ther. 2011;15:525-7. [PMID:21943627]

[49KK Chen, SY Lee, BWJ Pang, LK Lau, KA Jabbar, and WT Seah. Associations of low handgrip strength and hand laterality with cognitive function and functional mobility – the Yishun Study. BMC Geriatr. 2022;22:677 DOI: 10.1186/s12877-022-03363-2. [PMID:35974301]

[50R McGrath, JJ Lang, FB Ortega, JP Chaput, K Zhang, and J Smith. Handgrip strength asymmetry is associated with slow gait speed and poorer standing balance in older Americans. Arch Gerontol Geriatr. 2022;102:104716. DOI: 10.1016/j.archger.2022.104716. [PMID:35569287]

[51K Jekel, M Damian, C Wattmo, L Hausner, R Bullock, and PJ Connelly. Mild cognitive impairment and deficits in instrumental activities of daily living: a systematic review. Alzheimers Res Ther. 2015;7:17 DOI: 10.1186/s13195-015-0099-0. [PMID:25815063]

[52R McGrath, GR Tomkinson, DP LaRoche, BM Vincent, CW Bond, and KJ Hackney. Handgrip Strength Asymmetry and Weakness May Accelerate Time to Mortality in Aging Americans. J Am Med Dir Assoc. 2020;21:2003-2007 e1. DOI: 10.1016/j.jamda.2020.04.030. [PMID:32611522]

[53R McGrath, GR Tomkinson, BC Clark, PM Cawthon, M Cesari, and S Al Snih. Assessing Additional Characteristics of Muscle Function With Digital Handgrip Dynamometry and Accelerometry: Framework for a Novel Handgrip Strength Protocol. J Am Med Dir Assoc. 2021;22:2313-8. DOI: 10.1016/j.jamda.2021.05.033. [PMID:34166628]

[54E Woytowicz, J Whitall, and KP Westlake. Age-related changes in bilateral upper extremity coordination. Curr Geriatr Rep. 2016;5:191-9. DOI: 10.1007/s13670-016-0184-7. [PMID:27917365]

Correspondence to:
Jirong Yue
Department of Geriatrics and National Clinical Research Center for Geriatrics, West China Hospital, Sichuan University
No. 37, Guo Xue Xiang, Chengdu, Sichuan
China
[email protected]