People with lower fitness before COVID are more likely to develop long COVID, but the infection itself does not cause a significant or lasting drop in fitness, even for those with persistent symptoms.

Study: Association of Pre‐COVID Fitness With Post‐COVID Fitness and Long COVID in the Cooper Center Longitudinal Cohort Study. Image Credit: p.ill.i / Shutterstock

In a recent study in the Journal of the American Heart Association, researchers investigated the impacts of COVID-19 and long COVID on adult cardiorespiratory fitness. They leveraged the Cooper Center Longitudinal Study, comprising 4,005 individuals (26.8% women) between the ages of 20 and 74 (mean age = 51.8 yrs) and compared their CRF scores pre- and post-COVID-19. Participants were categorized by their COVID status, and statistical models were adjusted for potential confounders such as age, sex, BMI, and smoking status.

Study findings revealed that individuals who eventually developed long COVID had lower baseline CRF scores than those who did not. While COVID-19 infections were associated with a small but statistically significant greater age-related CRF decline compared to uninfected individuals, this decline was not greatly accelerated. Furthermore, long COVID status itself was not associated with a significantly greater acceleration of this decline compared to those who recovered from COVID-19 without long COVID, particularly within this cohort, which had few participants with severely disabling long COVID.

Background

Cardiorespiratory fitness (CRF), often called cardiovascular fitness or cardiorespiratory endurance, reflects an individual’s oxygen use efficiency, a proxy for overall well-being. Recent research has demonstrated how individuals’ long-term CRF trajectories can significantly alter their health, heightening the metric’s importance in lifespan.

In the aftermath of the coronavirus disease of 2019 (COVID-19) pandemic, a growing body of literature suggests that COVID may reduce survivors’ CRF. This hypothesis may extend to ‘long COVID’—the persistence or development of COVID-19-like symptoms for months or even years following infection recovery.

Unfortunately, due to the unexpectedness of the pandemic and the relative lack of pre-COVID CRF assessment records, comparisons of patients’ pre-COVID and post-infection CRF records are scarce, complicating experimental validations of these hypotheses. The long-term impacts of COVID or long COVID on CRF’s age-associated declines remain similarly unexplored.

“…whether lower CRF at baseline is a risk factor for developing long COVID or whether long COVID causes a population-level reduction in CRF remains uncertain, especially among those who experience mild acute COVID and those with milder, nondisabling long COVID.”

About the study

The present study aims to inform scientific speculation by leveraging the Cooper Center Longitudinal Study (CCLS) to evaluate the impacts of COVID status on CRF and investigate if long COVID patients experience these impacts differently from survivors who do not develop long COVID. Initiated in 1970, CCLS is a long-term prospective cohort established to research preventive medicine, cardiorespiratory fitness, and long-term health. Since participants receive routine CRF assessments, this dataset provides the rare benefit of pre- and post-COVID CRF comparisons.

CCLS participants were enrolled in the current study if they met age (20–75 yrs), CRF records (at least 1 pre- and 1 post-infection CRF assessment), and medical history (no pregnant individuals or those with chronic diseases/cancers). Participants were required to complete COVID-19-related medical history questionnaires (starting January 2021), routinely reporting their COVID-19 status and associated symptoms. Participants’ CRF assessments were conducted using exercise treadmill tests, leveraging the modified Balke protocol.

Statistical models (linear mixed effects regression models) were adjusted to account for potential confounders, primarily including age, body mass index (BMI), sex, current smoking, and facemask use during the stress test. COVID status was coded as ‘prepandemic’ (two CRF measures before 2020 and no reported COVID), ‘uninfected’ (no self-reported COVID), ‘recovered’ (self-reported COVID with symptoms ≤3 months), or ‘long COVID’ (self-reported COVID with symptoms >3 months).

Study findings

Of the 7,434 CCLS participants with CRF data spanning 2017 through 2023, 4,005 (26.8% female, mean age = 51.8 yrs) provided completed study data and were enrolled in the present investigation. White individuals represented most of the cohort (87%). COVID-19 status records revealed that 41.6% of the cohort contracted the viral infection, 1.1% of whom required hospitalization.

Persistent (long) COVID symptoms were reported by 4.8% of COVID-19 survivors, with fatigue (40%), brain fog (39%), and breathlessness (24%) being the most frequent symptoms. Participants who developed long COVID were more likely to be female, had lower self-reported physical activity at baseline (though, on average, their activity levels still met or exceeded recommended guidelines), and reported hypertension. Notably, CRF evaluations revealed that this subgroup demonstrated a mean 1 MET lower CRF at baseline compared to COVID-19 survivors who did not develop long COVID, suggesting that baseline CRF values could help predict long COVID in COVID-19 patients.

Follow-up CRF assessments revealed that while COVID-19 did result in a small but statistically significant greater decline in CRF readings in survivors compared to uninfected participants, this additional decline was minor (around 0.07–0.1 METs on average). It is important to note that all participant groups, including uninfected individuals, experienced a minor average decrease in CRF of about 0.2 METs over the study period, indicating a general age-related trend. The study concluded that COVID-19 does not greatly accelerate these underlying age-related CRF declines. Furthermore, average self-reported physical activity levels post-COVID were found to be similar to pre-COVID levels across the groups, including among those with long COVID in this particular cohort.

Conclusions

The present study investigates the impacts of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) infections on individuals’ long-term CRF, and by extension, holistic well-being. It reveals that COVID-19 causes a slight additional decline in patients’ CRF readings compared to uninfected individuals. While these CRF values in infected individuals remained lower at follow-up within the study’s timeframe, the additional impact of COVID-19 on the rate of age-associated deterioration was small and not considered greatly accelerated by the study authors. The paper suggests that longer-term follow-up is needed to determine if these differences persist or widen over time.

Notably, the study also suggests that pre-COVID fitness (CRF readings) could act as both a predictor and a risk factor of an individual’s long COVID risk, highlighting the role of frequent physical exercise in mitigating long COVID incidence. It is important to consider that the paper notes its findings, particularly regarding the impact on those with long COVID, may be influenced by the inclusion of a few participants with severely disabling long COVID and potential selection bias excluding those most affected.