The most important function of the hand may be the ability to grip.1 A person with impaired grip secondary to weakness may have difficulty completing common activities of daily living that involve carrying, lifting, and manipulating objects.1 Measuring grip strength with a hand-grip dynamometer is simple, portable, affordable, and reliable.2–6 Grip strength has been reported to be predictive of disability and mortality, as well as a surrogate measurement of overall muscle strength.2–6
One in 4 adults younger than 65 years and almost 3 in 4 adults aged 65 years and older have multiple chronic health conditions, also known as multimorbidity.7,8 Americans with multiple chronic conditions now comprise more than 25% of the population.7 As the population ages in the coming decades, the percentage of adults with multimorbidity is expected to increase.7,8 In the United States, 85% of health care dollars are spent on people with chronic conditions.7 Multiple chronic health conditions negatively affect quality of life, contributing to declines in functioning and the inability to remain living in the community.9 Despite the prevalence and impact of multimorbidity, adults with multiple chronic conditions are commonly excluded from research.10
Utilization of the hands, including the ability to grip, is required to function effortlessly and independently.1 The current literature provides evidence on the impact of single chronic diseases on grip strength without consideration for multimorbidity.11,12 Single chronic conditions such as coronary heart disease, stroke, chronic obstructive pulmonary disease, arthritis, and diabetes mellitus have been found to be associated with decreases in muscle strength, while the presence of hypertension has been associated with increased grip strength.11 A negative relationship has been reported between grip strength and multimorbidity, as measured by the number of diseases.13,14 In a cross-sectional study of adults aged 50 years and older living in China, decreased grip strength was reported to be significantly associated with an increased odds of having multimorbidity.15
Despite the relationship between grip strength and multimorbidity, currently a lack of grip strength values exists, which would serve as a reference point for the growing number of adults with multimorbidity. Clinically, grip strength values are used to determine the presence and extent of weakness as well as to set rehabilitative goals for a patient.16,17 Grip strength values have been published in individual studies and meta-analyses.5,6,16,18–37 Current normative data published on grip strength are available for healthy adults,16,18–30,35 as well as adults with specific disabilities,13 specific health conditions,31–34 and from different countries.6,18,22–25,27,30,35 To represent the heterogeneity of the population, samples utilized for a normative study should be random and large.17 Grip strength norms developed from other countries have been found to differ from those established in the United States.30,35 The majority of published grip strength normative studies employ a convenience sample utilizing a relatively limited number of subjects.5,17,21,24–29 Research is needed to establish grip strength values for a variety of diagnoses and age groups representative of the US older population so appropriate benchmarks can be implemented in a variety of clinical circumstances.17 Because of the increasing numbers of adults with multimorbidity and the lack of published grip strength values utilizing data collected from a large nationally representative US population, establishing grip strength values based on the presence of multimorbidity may provide guidance to health care providers who monitor and manage an aging adult's health and functional status. The purpose of this study was to describe grip strength values in adults aged 50 years and older in the United States, based on age, gender, and the number of chronic diseases using data collected from a nationally representative survey.
Data from the University of Michigan Health and Retirement Study (HRS) were obtained for analysis. The HRS is a nationally representative biennial longitudinal study of adults older than 50 years in the United States.38 The HRS is sponsored by the National Institute on Aging and conducted by the Institute for Social Research at the University of Michigan.38 The Health Sciences Institutional Review Board at the University of Michigan approved the HRS.38 The data used for the analyses are publically available and contain no personal identifiers, ensuring respondent anonymity. This study was considered exempt by the Institutional Review Boards at University of Michigan-Flint and Western Michigan University.
This study included a secondary data analysis of HRS data collected in 2008, which included a total of 17,217 subjects of which 7403 subjects were eligible for physical measurements, including grip strength. From that sample, respondents who did not provide consent or had incomplete demographics, chronic disease information, or physical measures were excluded from subsequent analyses. An unweighted sample size of 5877 respondents remained for analysis, representing 64.4 million US adults aged 50 years and older.
Variables and Their Measurement
Demographic variables of interest included age, gender (male/female), and race (white, African American, other). Based on previous publications of grip strength values, age was further divided into 4 groups for analysis purposes (50-59 years, 60-69 years, 70-79 years, and ≥80 years).4,19,20,23
A self-rating of respondents' physical health was assessed in HRS with respect to 7 chronic medical conditions. Respondents were asked whether a physician had ever told them that they had hypertension, diabetes or high blood sugar, arthritis or rheumatism, heart conditions, lung disease, cancer, or stroke. Each chronic condition was coded as having been diagnosed (yes) or never been diagnosed (no). The 7 chronic diseases chosen for analyses were selected on the basis of prevalence, morbidity, disability, health care utilization, and availability in the HRS data set.7–9 The range of potential diseases for participants in the survey was from 0 to 7, and 4 groups were created by categorizing numbers of chronic diseases (0, 1, 2, ≥3) and used in the analysis.
The HRS trained testers collected grip strength measurements after the respondent provided consent and did not report surgery, swelling, inflammation, severe pain, or injury in both hands in the past 6 months.39 The dynamometer used in the study was a Smedley's spring-type hand dynamometer (Scandidact, Denmark). The accuracy of the Smedley's dynamometer to a known force has been shown to be high (r = 0.98) and a strong association (r = 0.83) with the JAMAR Hydraulic Hand dynamometer (Lafayette Instrument Company, Lafayette, Indiana).2 The HRS trained testers adjusted the device to fit the respondent's hand size by lining the bottom black handle of the Smedley to the metacarpophalangeal joints, while the upper edge of the stirrup was placed in the middle of the second phalanx, just above the proximal interphalangeal joints of the index and pinky fingers. Once the dynamometer was been adjusted correctly, the stirrup was locked with the metal brace on the side. Respondents were placed in the standing position with the shoulder adducted and elbow flexed to 90°. If a respondent was unable to stand while completing the test, sitting was permitted. Respondents were allowed to practice and were instructed to provide maximum effort for several seconds and then release. Measurements were taken on each hand twice, starting with the dominant hand, alternating hands between measurement trials. The average of the 2 trials was used to develop an average grip strength value for the right hand and the left hand measured in kilograms. Mean grip strength, measured in kilograms, was treated as continuous variable in subsequent analyses. All 4 grip strength measurements demonstrated high agreement (Cronbach's alpha = 0.979). In the HRS study, grip strength was reported for the right and left hands, with no reference to hand dominance since hand dominance does not appear to have a significant influence on hand grip strength measurements or have functional implications.20
To adjust for the HRS complex sampling design, including the differential probability of selection and nonresponse, all analyses were weighted and adjusted using the IBM SPSS Version 20 Complex Samples module (Armonk, New York). Standard descriptive statistics, including means, 95% confidence intervals, and frequencies were calculated for age, gender, race, and chronic disease status. Grip strength means and confidence intervals were calculated and stratified by gender (male, female), age group (50-59 years, 60-69 years, 70-79 years, and ≥80 years), and the number of chronic diseases (0, 1, 2, ≥3). The reporting of confidence intervals provides information about the range of grip strength values that should contain the population mean.17 If the confidence intervals of different groups do not cross, an assumption can be made that the populations are different.17
Table 1 provides selected characteristics of the study population weighted to be nationally representative. Stratifying the sample by gender resulted in 2442 males and 3435 females. The average age for males was 65.9 years (95% CI: 65.3-66.4) and for females was 67.3 years (95% CI: 66.9-67.8). The mean number of chronic diseases was similar for males and females at 1.9 with 31.0% (n = 874) of the males and 29.7% (n = 1078) of the females having 3 or more chronic diseases.
Table 2 provides grip strength values for the entire sample stratified by gender and age without consideration for chronic diseases. The average right/left grip strength for males ranged from 45.1/41.1 kg (males 50-59 years) to 29.0/26.5 kg (males ≥ 80 years). The average right/left grip strength for females ranged from 27.1/24.4 kg (females 50-59 years) to 17.5/15.7 kg (females ≥ 80 years). Grip strength values for both males and females, when comparing ages 50 to 59 with those aged 80 years or older, decreased by 8.9% per decade over the 4 decades represented.
Grip strength values by age and chronic disease groups are shown in Table 3 (males) and Table 4 (females). Only 3.5% of men aged 80 years or older reported having 0 chronic diseases while 15.5% of men aged 50 to 59 years reported having 3 or more chronic diseases. The average right/left grip strength for males ranged from a 46.8/42.7 kg (men 50-59 years with 0 chronic diseases) to 28.1/25.3 kg (men 80 years and older with ≥3 chronic diseases). Grip strength values decreased for males when comparing ages 50 to 59 with those aged 80 years or older within chronic disease groups, ranging from 7.3% (1 chronic disease, left grip) to 10.2% (0 chronic diseases, right grip). Grip strength values demonstrated a smaller decrease when comparing males within the same age group as compared with the number of chronic diseases ranging from 2.2% (ages 50-59 and 60-69 years, left grip) to 2.9% (age 70-79 years, left grip). Men who were 80 years or older did not demonstrate a decrease in grip strength, according to the number of chronic diseases.
Only 4.7% of women aged 80 years reported having 0 chronic diseases whereas 12.9% of women aged 50 to 59 years reported having 3 or more chronic diseases. The average right/left grip strength for women ranged from 27.5/24.9 kg (50-59 years with 0 chronic diseases) to 16.8/15.2 kg (80 years and older with 2 chronic diseases). Grip strength values for women decreased when comparing ages 50 to 59 with those aged 80 years or older within chronic disease groups, ranging from 7.5% (≥3 chronic diseases, left grip) to 9.4% (2 chronic diseases, right and left grip). Grip strength values demonstrated a smaller decrease when comparing females within the same age group as compared with the number of chronic diseases ranging from 1.8% (ages 50-59, right grip, and ages ≥80 years right and left grip) to 3.1% (age 70-79 years, left grip).
Grip strength has been reported to be a valid measure of overall muscle function and predictive of mortality and functional limitations.6 Approximately 75% of Americans older than 65 years have multimorbidity.7,8 Both age and gender have been previously listed as the strongest influencing factors on grip strength; however, a number of chronic conditions can also contribute to muscle weakness.13–15 Using data from a cross-sectional, nationally representative US study, the present study provides grip strength values based on age, gender, and the number of chronic diseases. The values presented in this study in general demonstrate that as the number of chronic diseases increases, grip strength decreases.
Grip strength in adults begins to decline at a rate of 1% per year after middle age.11 The results of this study demonstrate grip strength decreases with aging at approximately 0.9% per year without consideration for multimorbidity and ranged from 0.7% to 1.0% when multimorbidity is considered. Grip strength also demonstrated a decrease trend with the increasing number of chronic diseases. Confidence intervals in right grip strength in males and females did not cross when comparing those with 0 chronic diseases and those with 3 or more chronic diseases across the age groups of 50 to 59 years, 60 to 69 years, and 70 to 79 years. Grip strength in men older than 80 years (right/left grip = 29.0/26.5 kg) was stronger than that in women aged 50 to 59 years (right/left grip = 27.1/24.4 kg) Consistent with previous research, grip strength in the right hand for both men and women was stronger than that in the left hand.16,18,23
Challenges exist in directly comparing grip strength values secondary to differences in sampling procedures, populations, protocols, and dynamometers. Although reference values for grip strength have been published previously, the majority of studies utilized convenience sampling with a limited number of participants, which may produce inflated estimates of normative values.5,16,21,24–29 Mathiowetz et al16 demonstrated variable differences between gender and age groups as compared with the current study. Two recent meta-analyses on grip strength in older adults generally demonstrate wider confidence intervals as compared with the current study.36,37 Both meta-analyses reported lower grip strength values when compared with this study in adults matched by age and 0 chronic diseases. The results of this study, when including the entire sample and stratified by age and gender only with no consideration for multimorbidity, were comparable to the meta-analyses with values in the present study not being different by more than 5 kg for men and 3 kg for women. Grip strength has been found to differ between people living in different countries.30,35 Grip strength values developed in a population-based study in Australia were generally lower in adults older than 60 years as compared with the adults in this study with 0 chronic diseases; however, when including the entire sample without consideration for multimorbidity, no more than a difference of 2 kg was found between age and gender.23 Norms developed in Canada were greater in males (range, 4-7 kg) as compared with males in the current study; however, the females in Canada demonstrated greater variability when compared with US females (ranging from American females being 3 kg weaker to being 3 kg stronger based on age group).19 Neither of these studies reported the presence or absence of chronic diseases in the sample.19,23 As published elsewhere, grip strength values based from an American sample were larger than that collected from one of Asian descent.35 Based on the results of these studies, grip strength values without any consideration for multimorbidity among age matched American adults, Australians, and Canadians are similar.
The JAMAR hand dynamometer has been utilized frequently in studies publishing grip strength; however, different models of dynamometers (eg, Smedley's, Baseline Hydraulic, Grippit) have been used in research to develop grip strength norms.4,24,27 Grip strength values developed on different types of instruments are not meant to be interchangeable.40 A standardized testing protocol is important for reliability and to compare results across normative studies; however, wide ranges of protocols have been utilized for grip strength testing.41 A recent proposal has called for the standardization of grip strength testing across epidemiological studies and expands on the standards promoted by the American Society of Hand Therapists.41 The proposed Southampton protocol recommends utilization of the Jamar with 3 measurements completed while the respondent is seated.42 Three primary differences exist between the proposed Southampton and HRS protocol and are as follows: the use of the Smedley, the respondent standing (if able) during testing, and 2 measurements completed on each hand.39,41 The Smedley's dynamometer has been found to have a strong association with the JAMAR (r = 0.83); however, the Jamar has been found to yield higher grip strength values.2,40 Standing during hand grip strength testing has been shown to produce higher strength values than when sitting.42 The mean of 2 measurements of grip strength has been found to have acceptable test-retest reliability (ICC2,1 = 0.96).43
Because of its clinical utility and predictive abilities, the measurement of grip strength has been promoted to be included in the physical screening of older adults.6 Providing grip strength values for clinicians allows a measurement beyond single disease to track an adult's physical performance over time. If a patient begins to fall below what is considered appropriate for their age and gender, as well as the number of chronic diseases, a clinician should consider intervening with a physical activity and/or exercise program. An increase in physical activity has been shown to increase strength, promote function, and manage the effects of chronic diseases.44 Patients are commonly aware of single disease assessments that allow them to track their health status (eg, blood glucose levels). Aging adults may consider the possibility of self-monitoring their grip strength and track changes over time.45 Objectively quantifying grip strength, an overall measure of muscle function, may provide a trigger for older adults to engage in a strengthening exercise program.45
This study is not without limitations. The current study employed a cross-sectional analysis and does not imply causality of decreased grip strength due to the presence of self-reported chronic diseases. The state of disease management and specific medications for each of the respondents was unknown. By stratifying the data by age, gender, and number of chronic diseases, there was a wide range of respondents in each category. The sample of respondents ranged from women aged 60 to 69 years with 2 chronic diseases (n = 368) to men older than 80 years with 0 chronic diseases (n = 15).
A key strength of this study is the use of HRS data. The HRS is a nationally representative survey and includes self-report information on chronic diseases as well as physical measures collected utilizing standardized methods and trained testers. The agreement between the self-report of a diagnosis and confirmed evidence of diagnosis has been found to be excellent for diabetes mellitus (kappa = 0.92-0.93), cancer (kappa = 0.72-0.90), and stroke (kappa = 0.81-0.85) and good to fair for angina (kappa = 0.73-0.57), congestive heart failure (kappa = 0.48), and myocardial infarction (kappa = 0.47-0.70) in 2 separate studies.46,47 The development of grip strength values utilizing a nationally representative data set improves its generalizability to the population. Stratifying the data by gender, age, and the number of chronic diseases provided a novel and simplistic method in developing grip strength values. Considering the prevalence of multiple chronic diseases in Americans, the grip strength values provided offer a different, yet important standard that clinicians and researchers can implement in practice. Since the HRS is completed every 2 years, future research could examine the longitudinal changes that occur with grip strength and the presence of multimorbidity over time. Further research could also be completed to investigate the potential combination of most prevalent combinations of multimorbidities and the impact on grip strength as well as the utilization of grip strength cutoff values to predict disability in adults with multimorbidity. Further investigation of the barriers, outcomes, and utilization of grip strength values into the management of patients with multimorbidity may assist in increasing the acceptance of grip strength into in clinical practice.
The most prevalent chronic condition of aging Americans is multimorbidity.7,8 Multimorbidity is associated with decreased strength and disability.9 Grip strength values have commonly been developed on healthy adults from a convenience sample.5,16,21,24–29 The grip strength values based on age, gender, and the number of chronic diseases described in this study can be compared to evaluate performance of older adults who commonly have a history of multiple chronic conditions. Data provided for the study were from a nationally representative sample, improving its generalizability to a growing American population with multimorbidity that requires health care services. Clinicians should consider incorporating grip strength into a comprehensive physical assessment and consider prescribing exercise or referring a patient for rehabilitation services if there are declines in hand grip strength that fall below anticipated values.
This article was completed in partial fulfillment of Dr. Amy M. Yorke's pursuit of a PhD in Interdisciplinary Health Sciences at Western Michigan University.
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