Disability in old age can severely compromise quality of life. Research indicates that decreased muscle strength may lead to disability and functional limitations. Could handgrip strength serve as an easily measured and valid predictor of disability in old age? Researchers used data from the Honolulu Heart Program and the Honolulu-Asia Aging Study to see if grip strength predicted ability to perform activities of daily life. Subjects included Japanese-American men aged 45-68 years at baseline between 1965 and 1968. Grip strength was measured between 1965 and 1970 using a dynamometer. Handgrip strength is easily measured in a doctor's office. Over an average follow-up period of 25 years, hand grip strength did not predict mortality. However, low handgrip strength did predict various aspects of difficulty in performing daily tasks (such as lifting 10 lbs, dressing, and bathing), as well as functional limitations (walking speed of less than 0.4 mph, inability to rise unassisted from a chair). Thus, handgrip strength can be used to easily evaluate the potential for late-life disability.
Purpose in life
Purpose in life predicts certain positive health behaviors and biological processes that may protect against declining physical function. Researchers at Harvard investigated whether higher purpose in life among older adults predicted lower risk of developing weak grip strength and slow walking speed over time. Longitudinal cohort data from the Health and Retirement Study, a nationally representative study of US adults older than 50 years, were collected in 2006 and again in 2010. Researchers evaluated grip strength using spring-type hand dynamometers and walking speed with subjects walking 8 feet at their normal pace. Data from 4,486 adults had grip scores at baseline that indicated adequate function, while data from 1,461 adults had walking scores that indicated adequate function at baseline. After controlling for sociodemographic factors, each standard deviation increase in purpose was significantly associated with a 13 percent lower risk of developing weak grip strength and a 14 percent decreased risk of developing slow walking speed after four years. Thus, a sense of purpose in life may help maintain physical function in older adults.
Grip strength as a screening tool
Greater physical strength predicts reduced risk of mortality in longitudinal studies. Would varying levels of cardiorespiratory fitness and grip strength moderate the link between physical activity and mortality? Researchers in the UK used data from 498,135 participants in the UK Biobank to answer this question. Cardiorespiratory fitness was measured with a cycle ergometer, while grip strength was measured with a hand-held dynamometer. After a median follow-up of 5 years and after adjusting for a host of confounders, higher levels of physical activity, grip strength, and cardiorespiratory fitness predicted lower risk of mortality. Of more interest, the increase in risk of both mortality and cardiovascular disease was highest in the lowest one-third of both cardiorespiratory fitness and grip strength compared to the highest. This finding has clinical significance, because it suggests that patients with a ‘low-fitness profile’ (meaning low physical activity and either low cardiorespiratory fitness or weak grip strength) would derive the greatest longevity and cardiovascular benefits from physical activity interventions. Alas, cardiorespiratory fitness is not easily measured in normal clinical settings. But grip strength is easily and accurately measured and could be used as a screening test for low physical strength, especially for older persons.
Observational studies show inverse associations among fitness, physical activity, and cardiovascular disease. But do these associations apply to people with elevated genetic susceptibility for these diseases? Researchers at Stanford used data from 502,635 individuals from the UK Biobank to find out. Specifically, researchers used data for grip strength, objective and subjective physical activity, cardiorespiratory fitness, cardiovascular events, and all-cause mortality. Individuals were grouped in thirds for comparison. The mean period of follow-up was 6 years. Grip strength, physical activity, and cardiorespiratory fitness were inversely associated with incident cardiovascular events (coronary heart disease and atrial fibrillation). Higher grip strength and cardiorespiratory fitness were associated with lower risk of incident coronary heart disease and atrial fibrillation in each genetic risk score group. High levels of cardiorespiratory fitness predicted a 49 percent lower risk for coronary heart disease and 60 percent lower risk for atrial fibrillation among individuals at high genetic risk for these diseases. Thus, low grip strength and fitness predicted lower risk of incident cardiovascular diseases for people with or without elevated genetic risk for these diseases.
You might think that greater muscle strength would help older people function better in the world. But would greater physical strength predict longer life? An international team of researchers conducted a systematic review and meta-analysis of 38 longitudinal studies with nearly 2 million participants to find out. The included studies primarily used handgrip strength as the measure of physical strength. Some studies used leg extension ability as the strength measure. After accounting for confounding factors and compared to lower levels of hand grip strength, higher levels predicted a significant 31 percent decline in mortality risk over an average follow-up of 12 years. Women showed even greater mortality risk reduction (40 percent) than men (31 percent). Compared to lower levels of leg extension strength, higher levels predicted a significant 14 percent decline in mortality risk. Doctors could easily use low hand grip strength to identify patients at increased risk of premature death and refer such patients to physical therapists for help.
Previous studies found that weak handgrip strength predicted increased risk of cognitive decline. A more recent study extended this line of research to incidence of dementia and dementia-related mortality. Researchers used data from 466,830 participants in the UK Biobank with an average age of 57 years who were followed for a median of 9 years. Hand grip strength was measured on both hands with a dynamometer. Average grip strength for both hands was grouped into quintiles of increasing strength from 46 lbs in the lowest quintile to 68 lbs in the highest quintile. Compared to participants the highest quintile, those in the lowest quintile had significant 72 and 87 percent higher risks of developing dementia or dying from dementia during follow-up. These results were independent of walking pace, sleep patterns, and smoking, among other factors. For each 11 lb. decrease in grip strength, the risk of developing or dying from dementia increased by 14 and 17 percent, respectively.
What to do
Ask your primary care medical provider to measure your grip strength. You can then compare your grip strength to norms for people of your age and sex.