The risk factors of COVID-19 include not only older age, male sex, and underlying chronic conditions (i.e., obesity, cardiovascular disease, lung disease, kidney disease, diabetes, and cancer), but also lower physical fitness, as indexed by weaker muscle strength, by lower maximal exercise capacity or lower walking speed.
During the current pandemic, insufficient attention has been paid to behavioural protective factors, which may yet represent modifiable and low-cost levers to support health policies. In particular, physical activity has recently been suggested as a protective factor for severe COVID-19.
The protective effect of physical activity hypothesized in the literature may be explained by at least two pathways. First, physical activity has been associated with a greater functioning of the immune system, which may in turn decrease the odds for severe illness following respiratory tracts infections. Second, physical activity can affect underlying chronic conditions that have been identified as risk factors for COVID-19 hospitalisation. Specifically, studies showed that physical activity reduces the risk of developing several chronic conditions including cardiovascular diseases, type 2 diabetes, cancer, and obesity. Moreover, physical activity, and especially certain forms of exercise, such as resistance training, has been associated with higher physical fitness, as indexed by greater muscle strength. These effects of physical activity on chronic conditions or muscle strength, for instance, using resistance training, may indirectly reduce the risk for severe COVID-19.
The objectives of this study were to test the association between physical activity and the odds of COVID-19 hospitalisation, and to investigate whether this association is explained by established risk factors for COVID-19 hospitalisation.
The authors used the data drawn from the Survey of Health, Ageing and Retirement in Europe (SHARE), a longitudinal population-based study on European adults 50 years of age or older. COVID-19 hospitalisation was measured during the special “SHARE COVID-19” questionnaire in 2020 and used as an indicator of severe COVID-19.
Physical activity was measured across the SHARE surveys gathered between 2004 and 2017, and the most recent measure of physical activity was used in the analyses, regardless the timespan between this measure and the potential COVID-19 hospitalisation. Muscle strength was indexed by hand grip strength, which was measured using a handheld dynamometer.
Univariable and multivariable logistic regression models were used to test the association between the exposure of interest (physical activity) and the primary outcome (COVID-19 hospitalisation). Model 0 tested the unadjusted association between physical activity and odds of COVID-19 hospitalisation. Model 1 tested the associations between physical activity and odds of COVID-19 hospitalisation when adjusting for the demographic covariates (i.e., age, height, and sex). Model 2 added to Model 1 the risk factors (i.e., higher body mass index, cardiovascular disease, diabetes, cancer, chronic kidney disease, rheumatoid arthritis, respiratory disease and weak muscle strength).
The final study sample included 3139 individuals (69.3 ± 8.5 years, 1763 women), from which 266 were tested positive and 66 were hospitalised for COVID-19 (75,4 ± 10.3 years, 36 women).
Bivariable associations, computed using chi-square tests and correlation tests, showed that physical activity (p = 0.024), higher age (p < 0.001), cardiovascular disease (p = 0.044), and muscle strength (p = 0.003) were associated with COVID-19 hospitalisation.
Model 0 showed that physical activity was associated with odds of COVID-19 hospitalisation (p < 0.001 for global effect). Compared with participants who hardly ever or never engaged in physical activity, the odds of COVID-19 hospitalisation were lower for those who engaged in physical activity more than once a week (OR = 0.41, 95% CI = 0.22–0.74, p = 0.004).
Model 1 showed that physical activity remained associated with COVID-19 hospitalisation (p for global effect = 0.042). Consistent with the previous model, the odds of COVID-19 hospitalisation were lower for participants who engaged in physical activity more than once a week than participants who engaged in physical activity hardly ever or ever (OR = 0.48, 95% CI = 0.25–0.87, p = 0.020).
Model 2 showed that physical activity was no longer associated with odds of COVID-19 hospitalisation, after adjustment with the other risk factors (p = 0.569 for global effect).
The findings show that physical activity is associated with lower odds of COVID-19 hospitalisation in adults aged 50 years and older. This association was explained by muscle strength, but not by the other established risk factors for COVID-19 hospitalisation. Because of the high prevalence of physical inactivity in the general population, especially at older age and during the COVID-19 pandemic, the findings highlight the need to encourage older adults to regularly practice physical activity. Engaging in strength training may be particularly beneficial to decrease odds of COVID-19 hospitalisations.
Maltagliati S et al. (2021) Muscle strength explains the protective effect of physical activity against COVID-19 hospitalization among adults aged 50 years and older. Journal of Sports Sciences.
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