The sheer range of outcomes following infection with the severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), which causes coronavirus disease 2019 (COVID-19), is astounding. The reason for this extreme diversity in clinical manifestations is not clear. However, cardiovascular disease, obesity and diabetes, among other comorbidities, have been associated with a higher risk for severe disease.
A new preprint research paper posted to the medRxiv* server discusses the results of a study exploring the relationship between increased muscle strength and hospitalization for severe COVID-19.
Muscle strength is a marker of muscle function, a crucial component of health. As such, it is a strong predictor of many morbid conditions as well as of death from any cause. This led the investigators in the current study to postulate that they would find muscle strength to be independently and negatively correlated with hospitalization from COVID-19.
The study used data from the Survey of Health, Ageing and Retirement in Europe (SHARE), which has been collected from 2004 to 2017 on a two-yearly basis. A sample of SHARE participants answered a questionnaire between June to September 2020 as to whether they had been infected with COVID-19 and whether they had been hospitalized with the disease.
This group of adults is above 50 years of age, from 27 European countries, and have all taken part in SHARE at least once. There were 3,600 individuals in this group, with a mean age of 69 years, of which over half were female (>2,000). There were 83 hospitalizations for COVID-19, making up 2% of the group.
The use of hospitalization as a marker of COVID-19 severity may have led to an overestimation of disease severity, which could have been corrected by asking about hospitalization duration or admission to the intensive care unit. Secondly, the most recent handgrip strength measure dated two years before the start of the pandemic, and the occurrence of any disease during this gap cannot be ruled out. Such disease conditions could also have affected COVID-19 hospitalization risk.
Thirdly, SHARE participants who were actually in hospital with COVID-19 at the time of the survey were typically not part of this study, nor were patients who died of COVID-19. However, they represent the most severe form of this infection. Such exclusions could explain why the researchers did not find significant associations between already established risk factors such as cardiovascular disease, respiratory disease, and diabetes, and COVID-19 hospitalization.
Muscle strength and hospitalization risk
The investigators found that people at a higher risk of hospitalization were typically older, heavier, more likely to have cardiovascular or chronic kidney disease, and weaker muscle strength.
Older patients had 70% higher odds of hospitalization due to COVID-19, while those with obesity had twice as high odds. Other risk factors failed to show significant linkages with COVID-19 hospitalization.
However, the most recent measurement of maximal handgrip strength was closely correlated with the risk of COVID-19 hospitalization. With each one standard deviation (SD) increase in grip strength, the odds of hospitalization were reduced by ~35%.
What are the implications?
This study's findings show that physical fitness is a significant correlate of the risk for severe COVID-19 following SARS-CoV-2 infection. The measure used in this study was handgrip strength, while a history of COVID-19 hospitalization was a proxy for severe disease.
The observations showed that lower muscle strength was associated with a greater risk of severe COVID-19. This is consistent with the hypothesis that muscle strength is a marker for the severity of disease in COVID-19.
This, in turn, is due to the important role of muscle tissue in human health. Skeletal muscle is essential for the body's movement mediates proper respiratory system function, and is essential in the immune response. Weak skeletal muscle is also a risk factor for metabolic stress during severe infection.
All these relationships confer a risk of contracting SARS-CoV-2 infection as well as of severe COVID-19.
Conditions associated with muscle weakness, or sarcopenias, such as advanced age, chronic disease conditions, or cancer, have been found to increase the risk of severe COVID-19. This is also the case with respiratory function, found to be reduced in patients with sarcopenia, and also in severe COVID-19. This provides indirect support for this hypothesis.
The current study's findings are also in agreement with other recent research that indicates a close association between being physically fit and a lower risk of COVID-19 hospitalization.
The association of muscle strength with severe COVID-19 indicates the utility of handgrip strength measurements as an important factor for monitoring the disease in COVID-19 patients and in arriving at a prognosis as part of a composite score.
medRxiv publishes preliminary scientific reports that are not peer-reviewed and, therefore, should not be regarded as conclusive, guide clinical practice/health-related behavior, or treated as established information.