# Cardiorespiratory fitness and physical activity and risk of SARS-CoV-2 and COVID-19 hospitalization: the HUNT study

## TL;DR

Higher cardiorespiratory fitness and physical activity were linked to lower risk of hospitalization from COVID-19, but not to SARS-CoV-2 infection.

## Contribution

This study is the first to show that pre-pandemic fitness and activity levels reduce hospitalization risk from COVID-19 in a large general population.

## Key findings

- Higher estimated cardiorespiratory fitness was associated with a 46% lower risk of hospitalization due to COVID-19.
- Sufficiently active individuals had a 40% lower risk of hospitalization compared to inactive individuals.
- Fitness and activity levels did not affect the risk of SARS-CoV-2 infection.

## Abstract

Physical activity (PA) has been associated with a reduced risk of severe COVID-19 outcomes. However, the relationship between cardiorespiratory fitness (CRF) and the risk of SARS-CoV-2 infection and COVID-19 hospitalization has not been thoroughly investigated. We aimed to investigate the association of estimated CRF (eCRF) and leisure-time PA (LTPA) with risk of SARS-CoV-2 infection and COVID-19 related hospitalization in a general population of Norwegian adults.

This cohort study included 48,821 adults participating in the population based Trøndelag Health Study (the HUNT Study). Individual data on pre-pandemic (2017–2019) eCRF and LTPA were linked to COVID-19 registries from February 2020 through September 2022. eCRF was categorized into sex-and-age specific quintiles based on V̇O2peak (mL/kg/min) and LTPA was categorized based on metabolic equivalent hours per week (MET h/wk): inactive (0-3.5 MET h/wk), insufficiently active (> 3.5 to 7.5 MET h/wk), and sufficiently active (> 7.5 MET h/wk). Poisson regression was used to estimate incidence rate ratios (IRRs) and 95% confidence intervals (CIs) for the association of eCRF and LTPA with SARS-CoV-2 infection and COVID-19 hospitalization.

Age averaged 53.6 years (SD 16.8) and 53.9% were women. During 2.6 years of follow-up there were 5991 SARS-CoV-2 infections and 218 COVID-19 related hospitalizations. Fitness and LTPA categories did not associate with risk of infection. However, adults with the highest eCRF had significantly lower risk of hospitalization compared to adults with the lowest eCRF (IRR, 0.54, 95% CI, 0.34–0.86). Similarly, sufficiently active adults (> 7.5 MET h/wk) prior to the pandemic had significantly lower risk of being hospitalized compared to inactive adults (IRR, 0.60, 95% CI, 0.47–0.83).

Higher eCRF and LTPA were not associated with risk of SARS-CoV-2 infection. In contrast, adults with high eCRF and LTPA were associated with a lower risk of COVID-19 related hospitalization compared to adults with low fitness and inactive lifestyles.

The online version contains supplementary material available at 10.1186/s12879-026-12684-1.