Should this be the 5th vital sign?

The search for low-cost, reliable biomarkers of health continues. One possibility is hand-grip strength (HGS), which some experts recommend should be a vital sign, as noted by authors writing in the Journal of Health, Population and Nutrition.^[] 

"Although the HGS has been indicated as an important and reliable biomarker of health, it is still not considered a vital sign. We believe that HGS should be a vital sign,” they wrote.

Relative vs absolute HGS

“Increasing evidence indicates sarcopenia as an important risk factor of many major and common groups of disease, such as metabolic syndrome, cardiovascular disease and cancer,” wrote authors in Diabetes Research and Clinical Practice.^[] “The non-invasive nature and relative ease of use make HGS advantageous as a screening and diagnostic tool, which has, however, mainly been studied in clinical settings on elderly populations.”

Experts suggest that absolute HGS (absHGS) better predicts overall muscle strength compared with relative HGS (relHGS), which better predicts adverse outcomes. Consequently, relHGS may be more clinically relevant (relHGS = absHGS/BMI).

In one cross-sectional study, investigators showed that relHGS was negatively correlated with metabolic syndrome and novel cardiometabolic variables—except for glucose levels, diastolic blood pressure, and apolipoprotein B—in young adults without metabolic syndrome. On the other hand, absHGS was correlated with fewer metabolic-syndrome endpoints vs relHGS.

The investigators publishing in Diabetes Research and Clinical Practice wrote: “Based on these findings, we argue that relHGS should be used in studies of early risk prediction based on its association with cardiometabolic risk markers. Whereas the use of absHGS requires due attention to the role of height.”

Relationship with long COVID

HGS is a surrogate for muscle strength and power production, with the lack of both referred to as dynapenia. Dynapenia is related to all-cause and disease-specific mortality, functional health, bone mineral density, depression, cognitive disabilities, and depression, as well as premature death in older and middle-aged individuals and young people. With regard to acute COVID-19, HGS predicts increased disease severity and longer hospital stays.

In a study published in Scientific Reports, Brazilian researchers assessed whether HGS is correlated with functional impairment at 120 days post-hospital discharge in unvaccinated patients who presented with severe COVID-19 during the early days of the pandemic.^[] They analyzed the link between HGS, respiratory function, and walked distance as measured by the 6-minute walking test (6MWT).

“This study showed that an important proportion of individuals with long COVID have decreased HGS,” the researchers said. “In addition, dynapenia was associated with worse lung function test scores and lower respiratory muscle strength, which ultimately negatively impacted the walked distance on the 6MWT after 120 days from hospitalization.”

At 120 days post-discharge, many patients with diabetes, prior smoking habits, lower BMI, older age, and those who were in need for ICU hospital admission exhibited lower grip strength. A 1% loss of lean mass equals a 3% reduction in muscle strength in elderly patients, which could compromise HGS.  

Other proposed mechanisms underlying lower HGS in long COVID patients include muscle fiber atrophy (possibly secondary to corticosteroid administration for long COVID); mitochondrial dysfunction; loss of cytochrome c oxidase activity and other alterations related to mitochondrial changes; persistence of SARS-CoV-2 reservoirs; presence of microthrombi; induction of autoantibodies; hyperreactive immune activation; reactivation of other latent viral co-infections, such as Epstein-Barr virus; and gut dysfunction/dysbiosis.

“HGS is a simple, reliable, and low-cost measurement that can be performed as a proxy for functional impairment in outpatient clinics and primary care facilities,” the Scientific Reports authors explained. “Acknowledging the importance of recognizing this condition could promptly help in patient stratification and risk prevention of patients with long COVID, which may reduce the development of comorbidities, delay the functional decline, improve the prognosis and survival of these patients, and accelerate the return to daily and work-related activities.” 

Other diseases

In addition to long COVID and metabolic syndrome, HGS is also a marker of overall strength, upper limb function, fracture susceptibility, bone mineral density, heart disease, nutritional deficiency, cognitive decline, cancer, chronic kidney disease, chronic liver disease, chronic respiratory disease, and overall quality of life. 

For instance, HGS is inversely associated with head/neck, endometrium, esophagus, gallbladder, kidney, liver, pancreas, colorectal, breast, and all-cause cancer. Higher muscle strength at the beginning of palliative chemotherapy is linked to better overall survival in older patients with advanced cancer, according to the Journal of Health, Population and Nutrition authors.

Clinical relevance

These include the following:

• Serial measurements can help track muscle strength and overall strength

• Measuring HGS in the office can help with patient engagement

• Patients can leverage serial measurements to motivate exercise and other lifestyle changes

• HGS can be used in all patients, regardless of gender or age

• HGS is cost-effective, noninvasive, and rapidly assessed with little equipment (eg, dynamometer)

Looking ahead, universal standardization of HGS may be a good idea, according to the Journal of Health, Population and Nutrition authors.

“While some have provided cut points and percentiles for muscle weakness, the development of clinically meaningful ethnic-, sex-, and age-specific categories for muscle weakness from HGS measurements, similar to thresholds for BMI, would be more informative,” they wrote.

“Standardization of HGS assessments will help to reduce internal threats to validity, develop uniformity for HGS assessments, enable comparisons of results across studies that included measures of HGS, and move the application of [hypertensive heart disease] into clinical practice," the authors concluded.